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Dynamics of Plankton Populations in Upwelling Areas
Final Report of Skylab EREP Investigation 518
DR. KARL HEINZ SZEKIELDA College of Marine Studies University of Delaware
CMS NASA-C-1-75
D,P ^' S2^,^/E-L v y ^°^iNCioA^ ^.vriEsTiGATo,e
r--^^ = 1976 EIVEII ' 11 FACIUff r BRAWN
Project from March 19, 1973 to July 31, 1975 Under Contract No. NAS 9-13344
(E76-10207) DYNAIICS OF :LANKTON N76-18619 POPULATIONS IN UPWEILING AREAS Final Report, 19 Mar. 1973 - 21 Jul.1975 (Delaware Univ.) 239 p HC $8.00 CSCL 08A G3/43 00207s I I
p.
i
. I ^j
DYNAMICS OP PLANKTON POPULATIONS IN UPWELLING AREAS
r Number of Investigation: Skylab EREP Investigation 51$
Period Covered: March 19, 1973 -- July 21, 1975
I- Contract Number: NAS 9-13 344 Principal Investigations Lyndon B. Johnson Space Center Management Office: ii. Technical Monitor: Zack H. Byrns Principal Investigator: Dr. Kax1-Heinz Szekielda;,,^^^
r. Sponsoring Institutions College of Marine Studies University of Delaware ti.. Type of Report: Final Report
(169 nal photo g raphy may be ORIGINAL CONTAIN pur EROS Data Center chased tram; ^,O ii 10th and bakota Aver Sioax Falls, SD 571;
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-`; 1. • :{ 3
I` Table of Contents
{ ! Page
Overview
Fart 1: Skylab Investigation of the Upweliing 7 _. Off the Northwest Coast of .erica f;
Part . Il: Evaluation of Chlorophyll Measurements 33 by Differential Radiometric Remote Sensing
i-^
f^
i!
i; {
OvervLew
Skylab, with its newly-developed sensors aboard, gave. a very challenging j opportunity to investigate oceanic areas, especially regions of upwelltng,
a major source for the world's fisheries. Due to many technical problems
which had to be overcome during the space mission, much of the data necessary
to meet the original objectives of the proposed studies could not be obtained,
even with repeated coverage of ^:he test site. Fortunately, additivrtal.coverage
was obtained by HRTS-1, giving very good insight into the possible dynamics of
color gradients in the oceans.
The planned cooperation with multiship cruises could not be scheduled
simultaneously because of other priorities during the spacecraft'.s missions.
However, significant results during aircraft missions and in laboratory ex-
periments have led to a better understanding of the water mass structure re-
cognized in the Skylab data. Many failures, such as useless recordings with
the S191, led to waste of man power. On the other hand, we gained information
which never could have been acquired by conventional methods. by
Karl—Heinz Szekielda Dennis J. Suszkowski Paul. S. Tabor
z1
College of Marine Studies University of Delaware Newark, Delaware 1971.1. Table of Contents
Page
Abstract and Introduction 11
Atmospheric Conditions 12
Spectral Properties of Plankton. 13
Cape Blanc 17 l; Conclusions and Acknowledgements 20
References 21 L
Titles of Figures
Figure
1. Nimbus 5 thermal image of the NW coast of 22 j Africa taken 2 September 1973.:
2. Wavelength dependent radiance caused by 23 particulate and dissolved matter..
3. Composite of chlorophyll concentrations for 24 the months January-June.
4. Composite of chlorophyll concentrations for 25 - 1. the months July-September. 5. Ground coverage provided, by the Skylab sensors 26 . during the 4 September 1973 overpass.
5. S190B color photograph of Cape Blanc. 27
7. Green band S190A image. of Cape Blanc, 28
8. Offshore ocean color boundaries derived from 29 ERTS--1 and Skylab i 9. Histogram of thermal data and color coding for 30 S192 imagery.
'_. 10. Color-coded temperature distribution derived 31 from channel 13 of the 5192 multispecbral scanner.
,a n
} 11
ABSTRACT
The upwalling oft the NW coast of Africa in the vicinity of Cape Blanc was studied in February - March 1974 from aircraft and in September 1973 from Skylab. The aircraft study was designed to determine the effectiveness of a differential radiometer is quantifying surface chlorophyll concentrations.
Photographic images of the S190A Multispectral Camera and the 5190E Earth Ter- rain Camera from Skylab were used to study distributional patterns of suspended material and to locate ocean color boundaries. The thermal channel of the S192
Multispectral Scanner was used to map sea-surface temperature distributions off
Cape Blanc. Correlating ocean .color changes with temperature gradients is an effective method of qualitatively estimating biological productivity in the up-- welling region off . Africa.
INTRODUCTION
From a practical standpoint, phytoplankton is a very important life form in the ocean, since primary productivity can be directly related to potential production of commercial fish. In upwelling regions of the world, such as off
the northwest . coast of Africa, wind stress produces an offshore movement of surface waters which are replaced by cooler, nutrient-rich subsurface waters.
These upwelled waters are an excellent medium for the propagation of phyto-
plankton. Though upwelling regions comprise only about one-tenth of one per-
.. cent of the ocean surface,. Ryther (1969) estimates that they produce about
half of the world's fish supply.
When studying plankton over large areas of the ocean, oceanographers..
face serious logistics problems. Since it may take several days to several weeks to cover a large study area by ship, the best that can be- -hoped. is IR tt _
12
a tame-averaged picture of plankton distributions. The ship sampling program
may miss patches of plankton of significant interest and the concentrations
may be changing rapidly over time. Since barge surface aieas of the ocean
can be easily seen from space, the possibility of synoptically determining
plankton quantities and distributions ,from, earth orbit is extremely attractive.
On September 4, 1975, the Skylab spacecraft passed directly over the Cape
Blanc section of NW Africa. This report will summarize the interpretation to
date of radiometeric data derived from Skylab as it pertains to plankton dis-
tributions off the African coast.
ATMOSPHERIC CONDITIONS. j The NW coast of Africa can be effectively studied from space, since favor-
able meteorological conditions are present throughout most of the year., During.
winter in the Northern Hemisphere, a high pressure system is centered between
the Canary Islands and the Azores. In summer, this system extends further to
the north and west. Therefore, the coast of Africa experiences clear weather
during most of the year with extremely: good horizontal and vertical visibility.
The NN trade winds are responsible for the upwelli.ng conditions off the
NW African coast.. During the summer months when the Trades are located between
15°N and 35°N latitude, the principal component of the winds is northerly,
therefore giving rise to the most intense upwelling conditions. (Szekielda, 1973),
Figure 1 shows a Nimbus 5 thermal image of the NW coast of Africa taken.
September 2, 1973, two days prior to the Skylab overpass. The clear conditions
surrounding Cape Blanc indicate the influence of the offshore anticyclone and
the low-moisture NB trade winds. The band of thick clouds to the south represent:
the Intertropical Convergence Zone. i i y
13
SPECTRAL PROPERTIES OF ELANMON
Light penetration in water is affected by plankton, algae, and dissolved and suspended matter. As a result, the composition of backscattered light from the air-sea interface is determined by the nature of the constituents in the water column. In contrast to the absorption spectrum of chemically-pure chlorophyll in^solution, algae suspensions absorb and scatter light more uni- formly throughout the visible part of the electromagnetic spectrum. Because of the spectral absorption and scattering properties of plankton, its concen- tration can be estimated by measuring the spectral backscattered radiance over water.
When monitoring plankton or biomass from hie; altitudes, we must consider the fact that algae behave more like a suspension than a pure solution of chlorophyll. As a result, solar light will be scattered at the outer shell of tha plankton organisms. The absorption of incident irradiance by the cells de- peads on their outer structure and the optical density inside the cell. Varia- tion in the optical density or the configuration of the cells may change the intensity of backscattered light even if the incident solar irradiance, sun angle, and chlorophyll concentration per unit of volume remain constant.
Yentsch (1960) found that the ,red absorption band of chlorophyll has little influence on water color. This means that the signal obtained with a red band sensor would record primarily the effect of backscattered light from the organ- isms.
The intensir-y of backscattered light caused by plankton and dissolved matter from the ocean as a function of aveleagth is given in Figure 2:. Gulf
Stream water was used as a reference water assuming that the chlorophyll con- centration of less than 0.02pg-1 l ,does not change significantly the. backscattered f t
}
14
light compared to pure water. It was assumed, for the interpretation of the
different spectra, the sky conditions, sun angle, and sea state were the same
over both sites. The spectrum in Figure 2 is the difference in energy between
the spectrum obtained in near-coastal water and the spectrum recorded over the
Gulf Stream.
If both water masses had the same optical characteristics and oceanic
conditions, the energy difference in both spectra should be equal to zero.
Any differences between the two signals would thus be caused by dissolved and/
or particulate matter in the sea. If chlorophyll affected the backscattered
light by its absorption properties in the shorter wavelengths, we would expect
differences near the absorption bands of chlorophyll..
Chlorophylls have two main absorption maxima in the visible region of the
electromagnetic spectrum. The main absorption peaks for pure chlorphyll a are
.at 0.446pm and 0.663pm. However, the naturally occuriug chlorophyll a types
in plants have spectra with peaks near 0.673pm and 0.683pm. Other forms show maxima near 0.690pm and 0.710pm.
The spectrum in Figure 2 shows that the first and the second absorption
bands of chlorophyll have only a minor influence on the total backscattered
light. Strong absorption appears at about 0.72pm, but the maximum of back-
scattered light appears at 0.381im. Considering only the portion between the
second absorption band and the near-infrared, it can be seen that only a
linear decrease of backscattered light appears. This is an indication that in
addition to the absorption of light by chlorophyll, backscattered light from
the organisms themselves contributes to the total backscattered energy. Thus,
the size and concentration of particles or marine organisms seem to b e the im-
portant contributors to the changes in backscattered light intensity as measured x i I
15
in the Skylab sensors. The scattering intensity of suspended particles is
proportional to Jl_71' where a is the wavelength and n the Rayleigh value which
may vary from 4 for pure water to 0 at high turbidity. In other words, the
intensity of backscattexed light increases with particle concentration. This
shows the important influence of particles without chlorophyll on the back-
scattered light from below the sea surface. Lorenzen (1970) established a
correlation between surface chlorophyll concentrations and primary productivity
for different oceanic waters. Better correlations were found when chlorophyll
and primary productivity data from the upwelling region off the IOW coast of
Africa were compared. This suggests that a significant relationship between
the two parameters can be obtained when individual oceanic regions are studied,
thus malting surface chlorophyll measurements that much more valuable.
An often suggested algorithm of narrow band ocean color reflectances was
employed in an aircraft mission for evaluation of its effectiveness in chloro-
phyll determination and in recognition of changes in regional ocean color dis-
tributions. A ratio of the Q..443pm to the 0.525pm reflectances has been dis-
cussed by Clarke and Ewing (1974) and Duntley (1972) as having the ability to
determine chlorophyll concentration in near-surface waters from aircraft and
satellite altitudes. From these observations Arvesen et.al . (1973) developed
a differential correlation radiometric method to detect chlorophyll. Their
measurements of ratio values, using the continuous recording differential ra-
diometer, correlated well with real.-time sea--truth measurements of surface
chlorophyll. concentrations. From the results of flights over various types of
water masses. ,,a calibration of the reflectance ratio to surface chlorophyll.
Concentrations (mg/m3) was Constructed.
During February and March 1974 the differential radiometric (DR) method
was used iii. an extensive oceanographic aircraft mission as part of the JOINT-1 16
project in a one square degree region (20 9 - 210 N latitude x 17° - IS' 1-1 long-
itude) offshore of Cape Blanc. In comparison with surface chlorophyll sea-truth,
the DR method was not effective in the determination of chlorophyll off Africa.
Interferences caused by suspender: particulates of eolian origin in the surface j waters plus presumed concentrations of Gelbstoff, resulted:in an "enhanced" j apparent chlorophyll signal,. These interferences can be explained by the
following: 1) Increased backscattered radiance was caused by the high con-
E centration of high refractive index (highly reflective) eolian and wave eroded
particulates; 2) Inherent optical properties including absorption by dissolved i Gelbstoff, attenuation of radiance by sea water and particulate scattering (in-
eluding multiple scattering) produced a spectral signal that the ratio method
€ couldcuo nott differentiateti t from tha ot chlorophyll;f 3 )Selective scatteringg. b Y i phytoplankton and high non--selective scattering by the additional particulates
in multiple events produced an increased backscattered signal to the DR which
was an "enhanced" chlorophyll signature. These apparent chlorophyll signals
were investigated in laboratory studies and were found to be principally attri-.
bated to the scattering properties of both inorganic particles and algae in
suspension. s Although this color ratio did not effectively determine chlorophyll levels,
there was a strong correlation between sea surface temperature (SST) gradients
and*:ie observed ocean color ratio gradients. Higher ratios Caere coincident
with low temperatures with only a few nearshore exceptions. A significant Cor-
relation of this color ratio and total particulates from sea--truth measurements
does.exist and, in addition, increased fishing was observed to be closely associ-
ated with the SST-DR ratio gradients (Tabc-- 1975). Therefore, ocean color
i changes associated with sea-surface temperature gradients are indicative of pro-
ductive water masses off the M4 coast of Africa. 17
CAPE BLANC
The hydrography between Cape Blanc and Cape Timiris can be described by the
^s T-S diagram based on 16 stations (Allain, 1970) where data were collected be- tween 0 and 300 m. Two main formations of water masses can be recognized. The first is within the upper 300 m and can be considered a, mixture of surface water and Central South Atlantic water with values of 12 0 C and a salinity of 35.35°/oa at 300 m.
The layer between 400 m and 800 m consi s ts mainly of Central North Atlantic water with tempez g ture ,< between 12 0 C and 8°C. The influence of Antarctic In- termediate, Water is shown by water with a salinity of 35.05 0 /oo and a tempera- ture of 7°C. Upwelling in this area is limited for water types with tempera- tures between 18.5°C and 20.5 % and salinities between 35 . 8 and 35.950/oo, which show that the upwelling has its origin in the upper 100 m.
The upwelling in the vicinity of Cape Blanc is persistant throughout most of the year and is evident by the high concentrations of chlorophyll noted in
Figures 3 and 4. A survey of fish tonnages between Cape Blanc and Cape Timiris was made by Boley (1974) in July of 1973. High concentrations offish were observed west of Cape Blanc while very high tonnages were noted near Cape Timiris.
The tonnages of fish therefore, show some correlation with surface chlorophyll concentrations in this area.
During the September 4, 1973 overpass, Skylab collected radiometric data with the S190A Multispectral Camera, the S190B Earth Terrain Camels, and the S192 Multi.spectral Scanner. The ground coverage provided by these sensors is shown in Figure 5. During the subsequent Skylab 4 mission, photographs were also taken of the study area with hand--held cameras.
Figure 6 is a high resolution color photograph of the Banc d'Arguin taken with S190B Earth Terrain Camera. The scale of the photograph is approximately
*Temperature--salinity
i^ 1
z
18
1:900,00.0 in covering an area of 110 km x 110 km. There is an obvious color
gradient of blue to green from offshore to nearshora waters indicative of the
presence of suspended material and Gelbstoff. Figure 7 is the green band
S190A multispectral spectral image having a response region between 0.5um and
0.6pm. The scale of this photograph is roughly 1;2.7 million covering an
area of 157 km x 157 km. The patterns and patchiness of offshore suspended
material are evident from this photograph.
The nearshore patterns of suspended material indicate a northerly flow of
waters toward Cape Blanc. The "U-shaped" plankton patch. southwest of the Cape
indicates a southerly, drift of waters from north of the Cape. Us 4mg dynamic
topography, Fedoseev (1970) discussed the geostrophic circulation of .surface
-•- craters in the shelf region and concluded that quasi-stationary gyres are formed
in the eastern boundary of the Canary Current. The most stationary gyre south
of Cape Blanc was observed throughout the year and the offshore patterns noted
in the. Skylab images are influenced by the ,flow of the gyre.
Szeki.elda (197.4) reports that plankton patchiness varies especially with
the change of seasons. A strong gradient of chlorophyll and/or plankton off-
shore of Cape Timiri.s is connected with the converging Seater masses from the
Banc d'Arguin and has been detected in all four season. Figure 8 shows the
location of offshore ocean color boundaries as derived from ERTS--I and Skylab.
The souther?:. gradients show seasonal positions between 1972 and 1973. Besides
small--scat% fluctuations, the gradient shifts over a maximum distance of only
about 16 km. This is an indication that the offshore gradien,t`ie a fairly per-
manent feature.
The enclosed lines south of Cape Blanc, are the relative positions of the
ITU-shaped suspended material patch observed from Skylab 3 and 4. Between
i 19
September 1973 and January 1974, the patch experienced a broadening and shore- ward movement. This may be a result of a seasonal change in the circulation.
Channel 13, of the multiscanner scanner of Skylab, recorded emitted thermal radiation from the surface of the earth. For the Cape Blanc over- pass, the radiation data were converted to blackbody temperatures and a histogram was generated by the Johnson Space Center as shown in Figure 9.
Classifications were chosen and a color-coded image was produced corresponding to different temperature intervals. Figure 10 is a color--coded temperature map of the"waters off Cape Blanc. The temperatures have not been corrected for atmospheric affects, however, the relative temperature gradients can be used to locate the .origin of upwelled waters. The cold patch of water. in Figure 10 is shown to be roughly between M and 11°C. Coldest known upwelling wafer off..the African coast has.only been reported to be as low as 14 9 G. Therefore it is estimated that the calculated blackbody tempera- tures are at least 4 % to VC colder than actually present; Since the cold. patch directly corresponds to the "U--shaped" , suspended material pattern observed in the imagery, this is undoubtedly a source of upwel.led. water.
In September of 1972, Dr. Ballaster (Szekiel.da 1974) observed a strong gradient: of temperatures and fluorescence to the south*.4est of .Cape Blanc. .
The temperature distribution is shown i.n Figure I.L. The temperature gradient off Cape Blanc is located in the same area as the cold patch we observed
Lrom Skylab.
As described previously, ocean color changes associated with sea surface temperature 'gradients indicate productive wa.termasses in this region.
The Skylab spacecraft was effective in recording these gradients and it can therefore be determined that an intensive area of upwel.ling was present in 20 ri September of 1973. By correlating the observed ocean color changes with
the low temperature readings, an obvious area of productive waters was
apparent offshore of Cape Blanc.
CONCLUSIONS
The spectral properties of ti. upwel.led waters off the N14 coast of
Africa have been studied with observations derived from aircraft and Skylab.
Results of the aircraft study indicate that the two--channel, ratio approach
is ineffective in determining surface chlorophyll concentrations and should
not be used in future studies. Ocean color boundaries and temperature 1 gradients were found to be directly correlated with each other and also with
fishing effort in the upwel.l.ing region. Photographic and scanner data derived
from Skylab has been effective in locating ocean color boundaries and
mapping temperature distributions. Both can be utilized in this region to
qualitatively determine areas of biological productivity. This simple
correlation may be .applicable in future efforts toward fishery resource j
management in upwelling . areas. i
ACTNOMED MENTS I Portions of this research were sponsored by NASA under Contract No.j
NAS9-1334+. We would like to acknowledge the assistance by the University
of Washington during the J'OIN'T--I project from Vebruary through March 1974. 21
REFERENCES
Allain, C. (1970). Les conditions hydrologiques sur la bordure .Atlantique de 1'Afrique du nord--ouest. Rapp, P. v.Cons. Hxplor. tier. 159, 25.
Arvesen, J. C.., Millard, J. P. and Weaver, E. C. (1973). Remote Sensing of Chlorophyll and Temperature in Marine and Fresh Waters. Astronautica Acta. Vol. 18, 229-239.
Boley, M. T. (1974). Compte-Rendu De Da Mission Tassergal, Cap 73-11, 9 au 23 Juillet 1973. CTNECA Newsletter, Inc. Council: for the Expl. of the Sea., Charlotrenl:und Castle, Denmark, 62-67.
Clarke, G. L. and Ewing, G. C. (1974). Remote Spectroscopy of the Sea for Biological Production Studies. In Optical Aspects of Oceanography, Julva, N. G. and E. Steeman Nielsen, eds. Academic Press, New York, N.Y.' 389--412.
Duntley, S. Q. (3.972). Detection of Ocean Chlorophyll from Earth Orbit,. 4th Annual Earth Res. Program Review, Vol. IV, NOAA and NRL Programs, January 17 -21, 1972. NASA, Manned Spacecraft Center, Houston, Texas, 1-25.
Fedoseev, A. (1970). Geostrophic Circulation of Surface Waters on the Shelf of North-West Africa. Rapp. P. v.Cons Explor. Infer. 159, 32-37.
Lorenzen, C. J.. (1970). Surface chlorophyll as an index of the depth, chlorophyll content, and primary productivity of the euphotic Layer Limnol. & Oceanogr. 15, 479-480.
Ryther, J. H. (1969). Photosynthesis and Fish Production in the Sea. Science, Vol. 166, No. 3901, 72--76. Szeki.el.da, K.-H.. (1973) . Distribution Pattern of Temperature and Bio- mass in the Upwell.ing Area Along the NW Coast of Africa. ;ASP Fall Conv., Lake Buena Vista, Fla., 664-716.
Szekielda,.K.-H. (1974). Observations of Suspended Material from Space- craft Altitudes.. Deutsche Hydrographische zeitschrifo, Jahrgaat 27, 1974, Heft 4, 159--170.
Tabor, P. (1975); Evaluation of Chlorophyll.Measurements by Differential Radiometric Remote Sensing. Master's Thesis, College of Marine Studies, University of Delaware, 194 p.
Yentsch., C..S...(1960).. The Influence of Phytop^ankton. Pigments .on the. Color of Seawater. .Deep-Sea Res. 7, 1-9. I I I I
LA
22 U ,
Figure 1. Nimbus S thermal image of the NW coast of Africa taken 2 September 1973. Cape BZnnc is located within the encioiure. ^, J 23 u A m watts • cm -Z - microwl u 0 u 0 0 0 0
u D O 0 D z u C) D rn m 6) rn D rn z x t; o rnz C) -r. o c rn 3 1-4 r m rn
u ^ rn 0 m r'' 00 D Z z rn D D O m n ^0D iA rD 0
Figure 2. Wavelength dependent radiance caused by particu- late and dissolved matter. ( from Szekielda ( 1974)). Gosablanca a ti
r .1 I,-/,
nposite Odorophyll (rn9/m3) January - June
Nouakchott
I Senegal River Dakar 1 2- a River IA .// ,Oi. LI
Figure 3. Composite of chlorophyll concentrations for the months January — June. u
u J U 25
11 Lj n Casablanca d U U 0 i n O
H 1 - 5 1 U Chlorophyll Composite U (mg/m3) 'S [11 3 July - September .5
Nouakchott
o Senegal River 0
t Dakar Gambia R
eq o i o ^o t 1.J
r Figure 4. Composite of chlorophyll concentrations for the months July — September.
1 1 f I +i
26
1>f' Igo
Cap Barbas
22
Blanc
P anc 'Arqu,n ^e
C. Timiris
/ A/I /
Figure 5. Ground coverage provided by the Skylab sensors during the 4 September 1973 overpass. 1 I ;_
27
Figure 6. S190B color photograph of Cape Blanc.
REPRODUCII3II. f BRAC3IN AL PAGE 18 POUi^0 i
1 -_ t^
28
Figure 7. Green band S190A image of Cape Blanc u
RPRODUCMIT,rrY OF MI r DIUGINAI PA r ", 1,C)OP v u
J
• a {. ^.. j ^ "i i t li^40
ERTS l Gnu° 2e JUNE 73 --- 22 FEB 73 26 AUG 72 SKYLA 4 SEPT 73 ` ^►— 2 6 DEC 73 Q ^^ --- 29 JAN 74
t
Figure S. Offshore ocean color boundaries derived from ERTS-1 and Skylab. i
1I+ 30
NUMBER OF PCM COUNTS o ^
r :>Ta _y
•r
m
`t ~ ^^
= J=
r a ^ ^
r r ^
s
Figure 9. Histogram of thermal data and color coding for 5192 imagery. r u u 31 9 I I I t
Figure 10. Color-coded tempersture distribution derived from channel 13 of the S 192 multispectral scanner.
DRYIWAl 33
FART zI ;
EVALUATION OF CHLOROPHYLL MEASUREMENTS
BY DIFFERENTIAL RADIOMETRIC REMOTE SENSING
by
Paul Stephan Tabor
College of Marine Studies University of Delaware Newark, Delaware 19711 J
35
AWTI'RACT
A differential radiometric (DR) method for continuous determina-
tion of near surface chlorophyll levels from aircraft altitudes
measures intensities of two narrow wavelength bands of the spectral
reflectance from the sea. An evaluation of the effectiveness of the
DR method for measuring and surveying the regional distribution of
chlorophyll is . given..
Two aircraft oceanographic research studies in a region of
dynamic ocean color off the NIV coast of Africa are described. The
Sahara Upwelling Project (SUE) focused on a survey of apparent
chlorophyll (Chl.) and radiometric sea surface temperature (SST)
distribution in a 11,000 mi l region. Correlations of SST and Chl.
gradients were found in the longshore and offshore directions. A
constant onshore gradient of increasing Chl, as well as recognizable
structures far offshore, including isolated features, were observed
The regional development: of SST and Chl. structure was synoptically
monitored from 18-26 August, 1973, with an expendable probe
study on 21 August, Recordings of additional ocean spectral reflectance
at yellow (576 nm) and red (663 and 7.23 nm) bands nearshore show.
correlations in intensity of .response with the pR method; while
often offshore SST' and Chl. gradients do not correspond to any
feature in the reel or yellow signals.
Oceanographic research flights of the JOINT-I project are
described and interpreted with available -real-time sea truth . measure-
k Ou U^ 3 NOT ^^LMED P ^C
- ;1 36 ments. A partial description of the synoptic time-series of results is given for recognition of upwelling events; !Analyses of apparent r chlorophyll, SST and the DR ratio . value (L443/L525 ) are presented I for all flights. Gross differences Between apparent Chl. and surface measurements are observed < 20 km offshore with apparent Chl. levels an order of magnitude greater than surface sea truth. In contrast,
an inverse relationship exists offshore with sea truth an order of magnitude greater than Chl. A multi-comparison showy increasing
particulates, decreasing 50o depth, decreasing chlorophyll and 1 decreasing ratio (443 nm/525 nm) values are positively correlated
nearshore.
From preliminary interpretation of atmospheric effects on
the DR method, the solar elevation is a far greater influence than
atmospheric composition even in high eolian-load areas.
Laboratory investigations on the interference of chlorophyll_ I free particulates in suspension with algae employed multiple scattering
samples which were spectrally scanned and interpretations of increased
effective reflectance . of the suspensions were made. When a multiple
scattering situation exists the increase of photon survival in a
algae-xei'lective clay suspension causes an enhanced chlorophyll Sig-
nature to be produced. In an optically dense base water, successive
additions of an algae standard and reflective particulates were
related when sample particle counts were correlated to the change in
reflectance ratio value (L /L525 ). Successive additions of only 443 37 chlorophyll-free particles showed a similar relation of total counts to ratio change, but the relationships of algae-only and algae-clay suspensions were independent. The dissolved blue colorant and non-selective particles were predicted to behave in the same manner as Gelbstoff and reflective particulates do in high concentrations in the ocean.
From the results and interpretation of this study the DR method is evaluated not to be effective in determining concentrations
.of chlorophyll even on a relative basis due to interferences, predominately in the ocean, of additional wavelength selective optical properties and particle multiple scattering conditions. 'The DR method was effective in monitoring an ocean color parameter L443/L5251
Which had a distribution very closely identified with SST. Patterns from the recordings of these sensors were recognized and their develop- ment could be monitored in repetitive coverage. 'rhe parameter is not well defined., but is strongly correlated to near surface particulate concentrations. The 443 run and 525 nm bands are concluded to be inadequate alone as an algorithm for determination of chlorophyll by ocean color measurements. Recommendations for directions of further research on the backscattered spectral reflectance from the ocean are made. E
•
! 1. 99
TABLE OF CONTENTS
Chapter Pie
1. INTRODUCTION 45
2. OBJEurius 47
'3. BACKGROUND OF RADlom-TRIC DETERMINATION O1. CHLOROPHYLL IN THE 48 OCEAN
3.1 Optical Properties of Ocean Features 48 3.1.1 Significant Optical Processes in the Ocean 48 3.1,2 Optical Processes at the Ocean's Surface 52 3.1.3 Atmospheric Processes on Optical Signals from 55 the Ocean
3.2 Summary of 1te5carclt on 12adioanetric Determination of 59 Chlorophyll 3.2.1 Conclusions from ProvAus Investigations 59 3.2.2 The Differential Radiometer 71 i
4. FIELD STUDY M13THODS 78
4.1 The SAIIAItA 1J1 1 4VELLING EXPEDITION 78 4.10 The Experimental Instrumentation Package 80 4.1.2 Experimental Procedures and Data Collection 82 4.1.3 blight Planning 84
4.2 The JOINT--I .PROJECT 84 4.2.1 Airborne Measurements 85 4.2.2 Flight Planning 86 4.2.3 Acquisition, Format and Data Handling 88
S. RESULTS OF FIELD STUDIES 92 I
5.1 SAHARA UPWELLING.EXPEDITION . 92 5.1.1 Bata Analysis 92 5.10 Description and Interpretation of Sensor and 94 Probe Measurements
5.2 JOINT-1 PROJUC`1' I.1.1. a. Z.1 1)aw Ana: ysis 11.1 5.2.2 Description and interpretation or Sensor Measure- 1.1.2 wants and Comparison with Preliminary JOINT-1 Sep. Truth Measurements
G 6. LABORA'T'ORY iNvus'r1GATIONS ON IN'1 TERFURENCES IN RADIOMG'nuc 1.40 CIILOROP.IIYLL UUT}Ilzt~11NATION .
.
e
.--^9 40
TABLE OF CONTENT'S (continued)
Chapter Page
6.1 Reflective Spoctroscopy of High Chlorophyll Concentrations .140 and Chlorophyll-Free Particulates in Suspension 63.1 Design of the Reflection Spectrometer Experiment 140 6.1.2 Results and Interpretation 142
6.2 Coordination of Differential Radiometric ;.End. Spectro- 146 radiometric Measurements of Chlorophyll and Chlorophyll- Free Particulate Suspensions 6.2.1 Experiment Design 147 6.2.2 Results and Interpretation 149
7. EVALUAT.CON OF THE EFFECTIVENESS OF THE D IFFERENr IAL . RADIOMETER 158 FOR CHLOROPHYLL DUTL'RMINAT1ON
7.1 Comparison of Radiometric Results with Ilistorical and 158 Real-Time Sea Truth Measurements
7.2 D efinition and Discussion of the Interference Processes 164 in the Differential Radiometric Method . Developed from Field Studies and Supporting Laboratory Investigations
8. CONCLUSIONS 171
8.1 Summary of Study 171
8.2 Summary of Evaluation 175
8.3 Recommendations for Further Research on Radiometric 177 Chlorophyll Determination
9. BIBLIOGRANIY 180
10, APPENDICES 191
A. Corresponding Vertical Temperature and Light Penetration 191 Profiles from the SAHARA UPWELLING EXPEDITION
B. Anal yzed'Rad Lometric Sea Surface Temperature, Differential 203 Radiometer Ratio, and Apparent Chlorophyil.Concentration Maps from the JOINT-I Aircraft Mission
MW i
41
TITLE 01: FIGURES
PAGE
Figure
1.1 The Correlation between Chlorophyll a and Primary 46
Productivity off the NIV coast of Africa
3.1 Calibration curve of DR Ratio values to Chlorophyll 75
Concentrations
4.1 Qathymetry of the Sahara Upwolling Expedition 79
Research Area
5.1 Analyses of Apparent Chlorophyll and Sea Surface 97-98 a-d Temperature Distribution from Airborne Sensor
Measurement ,, during SUE, 18-26 August, 1973
5.2 Comparison of Continuous Recordings from Airborne 103.-107 a-e Sensors during SUE, 22 and 26 August, 1973
5.3 Coincident Light. Penetration and Temperature . Profiles. 110
of Offshore Sections, 21 August, 1973.
5.4 Specific Comparison of Values of the Reflectance Ratio 113
L443/L525 at the Airborne Differential Radiometer to
Ocean Parameters versus Offshore Distance
5.5 General Comparison of Values of the Reflectance Ratio 114
L443/L525 at the Airborne Differential Radiometer to.
Ocean Parameters versus Distance Offshore
5.6 Analyses of Apparent Chlorophyll, Reflectance Ratio Value115--126 a-f and Sea Surface Temperature Distributions during a 14 Day
Period of. the J011fr-I Project, 8-21 Murch, 1974 I f y
42
TITLE OF FIGURES (continued)
PAGE
Figure
5.7 Comparison of Apparent Chlorophyll-Surface Chlorophyll 132
Concentrations versus Offshore Distance
5.8 Relationship between the Solar Standardization Setting 135
of the Differentiol Radiometer and Incident Radiation
Intensity
5.9 Solar Standardization Settings of the Differential 138-- a-c Radiometer and Daytime Incident Radiation Curves for 139
the JOINT-I Period 7-22 March, 1974.
6.1 Reflection Spectra of a dense Algae Sample, Mixed 143
Algae-Clay Particulate Suspensions, and a Clay Suspension
6.2 Reflectance Spectra of the Standard Algae Mixture 151
and 'Three Algae Samples of Various Concentrations
6.3 Reflectance Spectra of Algae Samples and Mixed 153
Algae-Clay Suspensions
6.4 Reflectance Spectra of Algae Samples, Mixed Algae-Clay 154
Suspensions and Clay Samples
6.5 Relationships between Particle Counts and Reflectance 156
Ratio Value Change for Chlorophyll-free Particulate
Samples, and Algae-only and Algae-Clay Samples
A.l Schnnatic of Expendable Probe Operation 193
A.2 Evolution of the Signal from an Expendable Probe 194
A.3 Profiles of Light Penetration and Temperature from 195-- a-h Airborne Expendable Photometers and Airborne Expendable 202
Bathythermobraphs during SUIT, 21 August, 197.1 43 TITLE OF FIC;URES (continued)
PAGE
T' i'^ure
B.la-c Analyses of Apparent Chlorophyll, Reflectance Ratio 204-- through 13.19a-c Value and Sea Surface Temperature Distributions 238
from Aircraft Sensors during the JOINT-1 Project,
17 February, 28 March, 1974
TI'T'LES OF TABLES
Page
Table
4.1 Research Flights of the Sahara Upwe.l.ling Expedition 83-84
4.2 JOINT-I Oceanographic Research Ilia., 90-91:
5.1 Results of Airborne Expandable photometer Study, 108
August 21, 1973
6.1 The Differaitial Radiometer Laboratory Study, 150
Composition of Samples 1 I
45
1. INTRODUCTION
This study is an extension of an area of research which is
stimulated by the possibilities of using reflected signals of visible
radiation to determine phytoplankton pigment concentrations in natural
haters. The determination of color by remote methods is a very useful
parameter to monitor because of its sensitivity to many properties
in the ocean, thus giving estimates of biological chemical, and
physical construction (Ewing, 1969). Research on ocean color
reflected to an-aircraft has shown, quite satisfactorily, correlations
between spectral signals and chlorophyll concentrations in surface
waters (Strickland, 1962; Duntley, 1963 and 1972; Clarke et al.,
1970a; Arvesen at al., 1973; Mueller, 1974; and Pearcy and Keene,1974).
The practical utility of these measurements, due to the i coverage that can be gained in relatively short times has been a recognized (Yentsch, 1971), and synoptic monitoring approaches have
been initially developed (Pearcy, 1971; Pearcy, and Keene, 1974).
The strong relation between concentrations of green photo-
synthesizing pigments of phytoplankton (especially chlorophyll a)
and more tangible parameters in surface waters such as primary
production, phytuplankton standing crop and total biomass, supports
the use of the optical properties of this biochemical as a f biological index (Riley, at al., 1971). Correlations between surface
1
j3LA-ND NOT FZMW ppBC'ID TNG PAGE f
46
chlorophyll concentrations and primary productivity measurements of
a wide variety of marine waters were made by Lorenzen (1970).
Historical data from a more defined ocean area (the upwolling region
of the NW coast of Africa) shows a stricter correlation with an rZ
(correlation coefficient) range of 0.758 to 0.824 for individual
cruises. Figure 1,1 shows the regression from the March-April 1971 r CINECA-Charcot-II cruise.
2,d r
I
a, a
E±
E
CO d'
rn n
k
I
•l0 -f 110 :4 12 0 .2 ,4 .6 10 11 V log surf. 011.E (mg•m-3)
i N gure 1, 1 The Correlation Between Chlorophyll a (Chl . a) Arid
Primary Productivity ( 14 C uptake) off the NW Coast of
v Africa from 30° 38 I N to 17° 22% During March-April, 1971.
i. 47
2. OBJECTIVES
Continuous recording of measurements at two wavelengths of the reflected spectral energy as ratio values has been proposed as a method for determination of chlorophyll pigments in natural waters (Clarke et al., 1970a; Arvesen et al. ) 1973; Duntley et al., 197 11). The objectives of the present study are 'to: 1) evaluate a differential radiometric method proposed by Arvesen
(cit. loc.) for measuring chlorophyll and surveying its regional distribution by defining the limitations of its effectiveness and by identifying and investigating interferences in the method, and
2) also gain positive information on ocean feature patterns through comparisons of the reflected wavelength ratio signal with sea truth measurements.
3 i
48 F^ t
3. BACKGROUND
In attempting to expand the use of chlorophyll measurements,
radiometric methods were developed preceded by determination of optical
properties of ocean features from measurements of radiance from the
ocean.
3.1 O ptical Pro }erties of Ocean Features
As a prerequisite to the identification of ocean parameters
of interest, it is necessary to identify the spectral signature
produced by optical properties in the open ocean or varying coastal
waters.. A second, simplistic prerequisite is that the incident
radiation is of suitable wavelength (X) and intensity to produce a
detectable spectral signature.
3.1.1 Significant Optical Processes in the Oc ean
Very clear seawater has a well defined spectral signature
(Clarke and James, 1939; Hulburt, 1945; Jerlov, 1968; and Morel, 1974).
The processes of Rayleigh-like scattering in liquids (Einstein, 1910)
and absorption is responsible for a low attenuation "window" in the
400-500 nm region. [below 250 nm in the UV and above 700 run in the IR
region, the absorption increases strongly by electron transitions
and intra-intermolecular motions respectively. In addition, the
volume scattering function for pure sea water, caused by d 0 fluctuations of molecular movement, increases nearly ton fold from
600 mr. to 360 nm (proportional to a ") (Morel, 1966) . Thus increased scattering is found at the wavelength regions of least absorption.
The wavelengths of maximum reflected intensity, then,are between
460 and 480 nm in the clearest .raters.
Dissolved organic materials (especially Gelbstoff) are the greatest influence on the spectral character of sea water excluding particulate effects. These melanodines described by Ralle (1966), absorb strongly in the UV and carry over into the blue visible region.
In a region where plankton populations are continually fluctuating, the backscattered spectra of the filtered "base" water is not that of the very clearest blue sea water. The diffuse reflection coefficient at 460 nm is 2-3 times lower in biologically active regions than in the open ocean (Uuntley et al., 1974). Yentsch and Reichert (1962) observed that Gelbstoff concentration increases were proportional to decomposition of phytoplankton pigments. Uuntley et al., (1974] suggest that base water spectral characteristics for the regions of interest in remote optical studies be well defined. Jerlov (1964) presents a relationship between the total scattering function and the irradiance attenuation coefficient at 465 nm for optical class:
Lion of many ocean regions Areas of upwelling, including the NV coast of Africa, have a far greater absorbance contribution than o; ocean areas. This further indicates that spectral signatures of b waters should be defined. 50
Whereas with dissolved matter in sea water and sea water itself, absorbance predominates over scattering (excluding perhaps the
400 . 500 nm "window"), particulate scattering is two to three lames greater than absorbance by particulates. In .fact except in clear, opea ocean waters, particulate processes dominate the characterization of the optical signal (Kullenberg, 1974; Jerlov, 1974).
Backscattered light in the ocean is a process of interest for remote studies. Although the lack of reflected radiance can also aid in description of the optical properties of a region (e.g., implying a few, large,forward scattering particulates), only the backscattered portion of the light field radiance can describe features characterized by spectral signatures.. Unfortunately, much scattering and transmittance research has used meters designed to measure forward and lotia backscattering angle propogati.on (2 0 <0< 1650).
A computation of particle scattering functions observed in situ is given by Kul,lenbcrg (1974). The water mass types measured range from turbid . likes and coastal waters to the low productive Sargasso and Mediterranean Seas. The largest difference in Q e functions is in the backscattered 6irection, and this is Martially attributed to the variations in the scattering particles. This indicates, first, that
Uuntley's et al..(1974) suggestion of a . well defined base water should be extended to include the ident:ificaticn of the particulate composi- tion, especially including size distribution and.indives of.refraction associated with different fractions, that may commonly occur in regions of interest for xemote.optical studies. The use of optically
I I I I
51
effective areas (Owen, 1974) of particulates is a good example of the
type of the basic knowledge needed. Secondly, if optical signals
backseattered and reflected from the sea are going to be used for
recognition of particulate frequency or composition, a more specifically
defined interpretation of the backscattering process is needed. And
?r^ this requires experiments designed for measuring scalterance,
including the contribution of multiple events, in the 120 0 <0< 1800
1i scattering cone as well as total scattering function.
The production of the optical signal backscattered to the
atmosphere is, of course, a combination of dissolved and particulate
properties in the ocean. The integration of contributions from all
processes that are studied in situ, and using these in a radiative
transfer (Freisendorfer, 1965) calculation to describe an observed
signal is a complex problem, especially when multiple scattering
is included. Although not yet fully utilized, the Monte Carlo
computer modeling approach as described by g lass and Kattawar (1969),
and used by Gordon and Brown (1973) for computation of diffuse
reflectance may be the only practical calculation solution.
t f I
The dependence of the optical properties of pure sea water
on changes in temperature, pressure, salinity was reviewed by
Morel (1974) and is very slight. Pure sea water, then, can be
assumed nearly constant. However, the particulate and dissolved F matter in the sett are not found to be conservative in distribution,
composition or in their inherent optical properties (i.e., volume
I ^ 52 scattering function, absorption or attenuation),
Tile optical properties of phytoplankton have bee, recently described by Muoller (1974). lie considers the chlorophyll signature from wavelength dependent scattering of the phytoplankton to be a much flatter spectral response than previous measurements by Yentsch
(1960) and Shibata et al. (1954). The latter two investigators measured diffuse forward scattered light, while Mueller was concerned mainly with beam extinction and cross section scattering spectra.
Optical remote sensors with specifications such as the differential radiometer (see Section 5,2,2) receive a signal of diffuse reflectance from the ocean closer to that described by Yentsch (cit. loc,),
3.1.2 Optical Processes at the Ocean's Surface
A boundary exists between incident irradiance from the atmos- phere and backscattered irradiance from the sea itself. This boundary between the two optical media is the air-sea interface. Processes that occur at level surfaces such as refraction, reflection and transmission have been described by Jerlov (1968), In addition, the effects of wave action, whitecaps rind foam, and slicks at the optical boundary are recognized (Cox, 1958; Cox and Munk, 1956; and Cox, 1974).
The surface processes involving introduction of incident light into the sea, reintroduction of an optical signal from the sea to the atmosphere, and return of incident light to the atmosphere never having penetrated the surface are significant for the problem of detecting a backscattored signal from the ocean.
i 1 ^ ' i
53
Direct radiant and diffuse skylight incident on the ocean's
surface is partially reflected at the surface and returned to a remote
sensor. This reflection is a function of the index of refraction of the
water, the viewing angle, and the wand speed which governs the wave
slope effect (Austin, 1974a), but is independent of wavelength of the
light. The refraction of radiance passing upward through the surface
will, in effect, spread the same amount of energy into a larger solid
angle cone. The factor of decreased energy is 1/(refractive index
of water) z or 0.555. The presnel reflectance at the surface
(Jorlov, 1968) causes a loss of transmitted signal and is a function
of the angle of observation and wind speed or wave slope (Austin,
cit. loc). Wave action scatters light at the sea surface. Swells
and waves of all sizes continually refract, reflect and even focus
some light with varying distribution. The capillary waves generated
by wind forces > 7 m/s are responsible for surface reflectance that
is observed as sea glitter (Wu, 1972). Larger gravity waves are
critical in the angular reflectance that is observed outside of the
sun's specula3r point. Natural slicks at sea are often monomolecular
layers, much thinner than the wavelength of light. In these cases
slicks have negligible effect on surface reflectivity or angles of
refraction and reflection (Cox, 1974). They do however, have a wave
dampening ,effect which drastically reduces this scattering process (:wing,
1950; Garret and Bu .ltman, 1963). Therefore, observations outside
the increased ref lection at the specular point.will be free from the
scattered light of c apillary waves. Observation angles for reduced 1
54 reflected sun glint and sun glitter input to the Signal are dependent on the elevation angle and azimuth angle of the sun. Cox (1974) also shows a dependence of observed glitter on direction of the wind.
The tilde-averaged effect by sea glitter is not as important however.
Studies of reflectance at the air-sea interface as a function of observation angles (Cox, 1974, Austin, 1974a) show that parallel polarized light will have no contribution to the reflected signal at the Brewster's angle (where the angle of radiance in air 53.19)
However, observations at this angle include 1.67 times the optical path length of sensors viewing in the nadir direction and. this atmospheric
interference severely reduces the advantage gained. For optimum viewing angles to avoid sea glitter (defined as glitter radiance observed/glitter radiance max. = 0.01), Fraser (1971) has calculated that at wind speeds of 10 m/s the glitter pattern does not extend to the nadir when the solar zenith angle is } 40°.
Austin (I 974a) has developed the following equation for total
inherent radiance, N o , leaving the surface
R No r 7t^^II '1'oT r dN (3.1) where R is the diffuse water reflectance (a ratio of the irradiance propagated through the surface to the total irradiance incident at the surface), R VoT is the total incident irradiance (sun and skylight), r is the Presnol reflectance of the. surface (a function of index of refraction and incident radiant angle), and N s is the zenith radiance. I i I
55 It This equation points out that N o ha y: a component (.-`y Ufol') which is
independent of observation angle and contains the spectral signature
of the water mass, and a component (r dN5 ) which can be considered as
glint or noise to the remote sensor and is dependent on the observation
angle, The apparent signal that will be available to a sensor at
some height above the surface, N Z , can be expressed as:
NZ = No 'a + N* (312) where: No is from equation 3.1, and Ta is the transmittance of the atmosphere and is a wavelength dependent process that reduces the
signal,- N* is the radiance contribution to the path of sight by
atmospheric scattering processes.
3.1.3 Atmospheric Processes on Optical Signals from the Ocean
Atmospheric processes on signals reflected from the sea are
studied mainly to discover the applicability of detection of these
signals from orbital altitudes. The processing of insolating light
by the atmosphere must also be considered in the production of a
signal from the ocean. Depending on the altitude of flight, aircraft
measuremoiits of returning surface signals, to a varying degree, are
effected by atmospheric processes.
The most important process in the atmosphere is scattering.
Rayleigh scattering was mentionod in Section 3.1.1 Again, the
scattering coefficient is proportional to A -`' and in the visible 55 i region the exponent is-4.08 (Ramsey, 1968). Yor particles with sizes
larger than the light wavelength, Mie theory is used to predict
scattering attenuation. The attenuation coefficient for Mie scattering
is a function of the dumber, radius of the particle , and wavelength
of light. forward scattering predominates with aerosols (considered
to be Mie scatterers). Ramsey (1968) has pointed out from previous
research that'sea salt particles in the atmosphere have a very uniform
size distribution from 1-2, and exhibit a non-selective attenuation
of visible light, while the distribution of particulates which
originate from land sources (which influence coastal water measurements)
is of much more polydisperse composition and seems to show a higher
_ scattering coefficient for light in shorter A regions.
Measurements of the contribution of radiance backscattered
from the atmosphere and that returning from the sea, (avoiding specular
reflection), for a variety of turbid atmospheres and at various
altitudes (in Ramsey, 1968), show that 1) the atmospheric signal
measured at 1 km is from one-fifth to equal to the returning signal
from the sea in turbid atmospheres and at a sun elevation angle of
459 ; 2) in Rayleigh atmospheres the signal from the sea is only.
ti 10% greater in wavelength region 400-500 nm. and nearly equal at
higher wavelengths to that of the atmosphere; 3) the total radiance
signal from a turbid atmosphere is 0 40% gre itcr than that from a
Rayleigh atmosphere,
The apparent signal to a remote sensor in the atmosphere can be F
57
quantified in terms of the albodo of the surface by:
As {A) [uopt {^) C0 (^} ] (3.3)
where IQ) is the wavelength dependent radiance leaving the sea, whether
backscattered or surface rcflected,u oFt Q) is the directly transmitted solar irradiance and a function of the cosine of the solar zenith
angle, p o , and Lp (A) is a wavelength dependent diffuse incident,
component (Curran, 1972). The equation above sloes not consider
the albedo contribution from the optical bath of the atmosphere.
Curran has'calculated this contribution as a function of A (460 nm
and 540 nit) and found that increased aerosol optical depths
(defined in terms of particle number density and the volume scatter-
ing coefficient) and varying solar zenith angles have a much larger
effect than A 5 alone, Comparisons of one standard deviation in the
color ratio (540 nm/460 nm) observed at the sea surface versus one
standard deviation in the aerosol optical thickness for a variety of
optical thicknesses and solar zenith angles showed that aerosol
scatters are the dominate influence on the color ratio at
1) optical depths only slightly above clear marine atmosphere
conditions and 2) solar zenith angles > 60*.
t. A large number of albodo recordings made on a 30 m. high plat-
form above Buzzard's Bay, glass. (Layne, 1972) under various solar
elevation angles and atmospheric transmittance conditions showed
again the strong relationship of solar angle and atmospheric trans-
mittance (defined as the ratio of observed downward irradiance to
^a I I
58
irradiance at the top of the atmosphere) to albedo, except in over-
cast. (isotropic radiance distribution) instances.
From 0.9 km to 14.9 km flight altitudes, Hovi.s, et al. (1973)
found a factor of ten reduction in contrast in a 460 nm signal. It was
indicated that 1/2 of the light backscattered from the sea surface
was scattered out of the view of the sensor and that the atmospheric
addition to the radiance signal was 5 times as great at 14.9 km.
Generally the observed effects (LZ E apparent signal) ca:n.he
represented by the equation given by Austin (1974x):
L2 = (Lw Lr) 'Ca + L* (3.4)
where L11 and L are the components of radiance front the sea and
radiance reflected from the surface respectively, T is the transmit-
tance of the atmosphere and is wavelength dependent, and L* is the
scattered atmospheric light contributions and was considered only
20 % of L3.
Clarke and.Lwing (1971 and 1973) have observed the sequential.
effects of an increased atmosphere on surface ocean color. Correlations
for the atmospheric contribution were made by substracting. the change
in signal between observations at 305 m altitude and 152 m altitude
Nom the 152 m curve. The resulting surface curve approximates a
spectra of upwelling irradiance measured at 0.2 m below the surface.
T11B wavelength dependent '1'a was not considered, and ivay hav^ ^*"••'^•^^^'
the correlation of the ocean color curves.
{
l
^M I
59
In an ocean-atmosphere model by Katta.war and Humphrey (1973) the optical depth made a negligible change.in . the radiance ratio
(upward radiance/downward radiance) only at measuring altitudes below
0.1 km.
Uuntley et al. (1974) have studied the apparent orbital contrast of computed apparent spectral radiance signals available at an orbital altitude from a water mass without phytoplankton to one with 00 mg/mI distribution throughout the top 50 m from the equation
R Apparent orbital contrast (C) (3.5) = N5 where: NT is the signal from the chlorophyll containing water mass, and
NB is the signal, from the water mass void of phytoplankton. Computations were made for solar zenith angles from 24.30 - 70.6° and "clear" and
"hazy" atmospheric conditions. His results for both 560 nm and 465 nm light show that > 0.001 apparent contrast can be obtained at all angles up to 0 55° from nadir viewing, both toward and away from the sun azimuth angle, The maximum contrast (> 0.003) was with the solar zenith angle of 30.9 0 ; At solar zenith angles.> 42.0° the contrast was greatly reduced.
3.2. 0 Conclusions from Previous Investigations
A representative summary of conclusions from radiometric studies developed for determination of chlorophyll in surface waters is necessary for an idea of the state-of-the-art, success of the methods,.and the expectations and recommendations given for future 60 st"di:s.
In general, three applications have been given for use of remote sensing of chlorophyll in natural waters. Before radiometric studies, fisheries scientists had observed increased fishing of migratory species at color boundaries noticed in the sea (Blackburn,
1969; Panshin, 1971; Pearcy, 1971). Interest and research in all types of radiometric approaches in the fisheries resource area has increased with developing techniques. An example of investigations on parameters considered for remote sensing in fisheries research, including chlorophyll by ocean color analysis, is the 1971 "Symposium on Remote Sensing in Marine Biology and fisheries Resources" held at
Texas A&M University. Blackburn (1969) has concluded that if aircraft and satellite sensors can determine chlorophyll at levels of significance for a biological activity index, the adequate relationship between surface chlorophyll concentrations and fish populations may present the most efficient approach to fisheries search activities. One of the most important aspects of remote monitoring of chlorophyll distribution is the short time space in which it may be accomplished.
A dynamic condition such as upwelling, and the sequential response by the food chain, requires this capability of remote sensing to be useful, in fisheries resource. The second application of remote chlorophyll determination is in assessment of pollution and eutrophication (Arvesen ct al., 1971). The use of satellites for a routine coverage of large regions has been designated the most applicable 61 method for chlorophyll measurement (Szekielda and Curran, 1973).
If changes in chlorophyll concentrations (blooms or !tills) in a specific locale can act as a judicious monitor of discharging activities of known pollutants, documented radiometric chlorophyll measurements could act as a powerful and efficient tool. Phytoplankton in water masses are a non-conservative parameter. 'Phis presents difficulties in using chlorophyll concentrations as a label in circulation and mixing studies. However, chlorophyll changes in a single water mass may be used to observe its development over time,. and in response to other changing conditions. if remote studies by aircraft or satellite can -routinely monitor the surface temperature and the chlorophyll concentrations of a region, systems, patterns, and cycles of systems of water masses may be identified and partially interpreted. This application is the most recent suggestion for radiometric measurements of chlorophyll in natural waters
(Szeki.elda, 1972a) .
Ramsey (1968) has quite thoroughly reviewed many processes which are considered factors affecting remote measurement of ocean color and chlorophyll determination at levels of 0.2 mg /m3.
Calculations were made of the contribution to a radiance signal from the ocean by water reflectance and the atmosphere under a variety of conditions. From the data presented, specifications for a spectro- meter to determine chlorophyll concentration levels of 0.2 mg/m 3 are given. '!'his reference has been used as the background for the spectrometer employed by Clarke et al. (1970a). 62
Nearcy and Keene (1974) used differences of norwalized back-
scattered signals at blue (450-470 nm), green (520-580 nm) and
orange (580-650 run) wavelength bands with additional spectra.
{ created from 7 signal' band widths in the visible region and 1R
temperature measurements to identify changes in ocean color radiance W with distance offshore from the coast of Oregon. Relationships of
these measurements to the Columbia lover plume, upwelling and open
ocean water types were observed. The oceanic type was
characterized by strong reflectance peak observed only in the blue 3
band. The differences of blue-green intensities were largest of
any Seater types. Differences of green-orange intensities were
^- n+1/3 the blue-green differences. In addition the green-orange
difference was ver , uniform in the oceanic water type. In regions
near its mouth ,the Columbia River plume was observed to have the
lowest radiance in the blue and green, but a backscattered signal in
the yellow, orange and red as high as the blue signal in the
oceanic type (blue-green decreased) while the blue intensity was as
high as oceanic water. A decreased slope in the spectra from the
reflectance peak in the blue to yellow green was observed in this
region compared to the similar slope in oceanic waters. The region
of the plume has been identified as containing a small concentration
and smaller sizes of particulates from the river discharge than the
river mouth area. Also larger chlorophyll concentration are found
in the plume offshore. The chlorophyll concentrations are larger in
the offshore plume than in the oceanic water, but this feature can not
i 63 be observed by selective blue light attenuation by phytoplankton.
The water type designated as coastal upwelled water has spectra
that vary from maximum signal in the blue (450-470 nm) to maximum
signal in the green-yellow (550-580 nm). The average slope of the
spectra from 450 nm'to 580 nm was least of any water type, with tic
exception of the river mouth discharge. The difference in water
character between the offshore plume and the most near shore upwelling
region is the greater concentrations of physotplankton, phytoplankton
degradation products and dissolved Gelbstoff in the latter, while morn
fine clays and Gelbstoff are contained in the river plume. Pearcy, and
Keene, (1974) have combined comparisons of individual backscattered
signal bands (in this case differences in intensity) with use of
the total spectra to successfully describe these water types. The
blue-green difference Y n strong indicator of phytoplankton or,
moreover, biologically established (containing Gelbstoff in addition)
waters. Figment concentrations were not estimated however. The
difference between green and orange band reflectance is an indicator
of turbidity (lower differences with increasing turbidity) generally
irregardless of chlorophyll concentration. Comparison of color
boundaries or sharp color difference gradients and surface temperature
distribution showed a more complex structure for the ocean color
patterns than temperature. At temperature gradients, color gradients
were always observed, while color gradients were observed independent
Of temperature change.
i i 54 Mueller (1974) has used oc»an color spectra collected by
aircraft over open ocean, upwelling and Columbia River plume
regions for covariance analysis of the principle color components
contributing to the observed spectra. It was Cound that 4 principal
components were responsible for > 95% of the spectral variance. Ocean
parameters of pigment concentration (treated as an average of
chlorophyll and carotenoid pigments as a function of pigment absorp-.
Lion coefficients, vertical integrations of chlorophyll concentration
aQ Secchi depth) the volume scattering coefficient, Gelbstoff
concentration and phytoplankton size distribution were shown to create
a similar variance distribution as observed spectra when calculations
- of their optical properties hs eigenvectors in a radiative transfer
model were made. Phytoplankton was found to be the major source
of variation (76%) while similar variations by non- selective
particle scattering, Gelbstoff absorption and changing phytoplankton
size distribution could produce apparent pigment concentration changes
up to 1 mg/m 3 . This large a variation could be calculated by assuming
low concentrations of Gelbstoff and chlorophyll -free particulates
and without considering multiple scattering or the incident light
spectrum. Empirically, the weighted pigment concentration and'Secchi
depth were related to the principal components by multiple linear
regression equations with residual standard deviations of 1.6 mg /m3
and 2.6 m respectively. The parameterization of principal components
as eigenvoctors allows an accurate analysis of the ocean color.
spectra. Relating ocean color spectra to eigenstructure for uniform
analysis and future reference is worthy of consideration. This would 1 I I I I I I
65
r,
be especially so if a principal component or components could, in
some way, physically characterize a water mass type. However, as
Mueller points out, an expanded model, which requires measurement
of more optical parameters at sea., must be used to estimate Agment
concentrations or other covariance parameters from ocean color spectra.
The research by Clarke at al, (1970a and b and 1973), Duntley,
(1972), and Duntley et al. (1974) have been the most direct considera-
tions in the diffrrontial radiometric method developed and used by
Arvesen at al. (1973).
Clarke at al. (1970a and b) employed a scanning spectrometer
with a spectral range from 400 to 700 on, scan time of 1.2 seconds
and field of view of 3 0 X 0.5 0 . Normalization', incidLnt light
spectrum was accomplished by scanning a horizontal "gray card",
although this standardization could not be accomplished in flight.
The view angle of the sensor for these studies was at the Brewster's
angle. 'Phis, plus the addition of polarized filter oriented at right
angles to the major polarization axis, eliminated the large
contribution of polarized surface reflected light to the signal which
has no ocean spectral information. A problem was caused at higher
altitudes of flight Q 305 m) by increased di.ffuse.atmospheric
light to the sensor and loss of spectral detail due to the large
optical depth that the signal must transit. Differences between
spectra of differing chlorophyll regions were maintained at higher
altidudes. Spectral measurements of Buzzard's Bay, the Gulf Stream and
i!t
4 -.
I:
^ l.1 66
Sargassog Sea with surface chloro1p hyll measurements of 4 mg/m 3 ,
013 mg/m 3 and < 0.1 mg/m 3 respectively (w 2 orders of magnitude)
showed very characteristic curves. Increased :intensities at shorter
wavelengths (< 520 nm) with decreased chlorophyll concentrations
co* ponded with decreased intensities at longer wavelengths (> . 520 nm)
r causing an increasing slope in lower chlorophyll regions. The j
inflection point in all spectra was % 520 nm. The curves of various ^ I spectral character "rotated" about this wavelength which seemed
insensitive to changes in chlorophyll concentration. Thus it was
called the hinge point. The average slopes correlate well to the {
chlorophyll concentrations. Changes of phytoplankton concentrations
were considered the most important influence on the spectral measure- E
ments. Szekielda (1974), has determined the difference spectrum of
intensity of backscattered light caused by phytoplankton and dissolved
matter. Gulf Stream spectral energy was used as a reference and was
subtracted from a near coastal water energy spectrum. The resulting
spectrum represents the similar spectral variations observed by
Clarke et al. (1970a). The encouraging results of this study for
chlorophyll determination from ocean color spectral character Prompted
further investigation by Clarke and Ewing (1971 and 1973). Spectra
were obtained at altitudes from 150-000 m over Waters of the Gulf of Mexico, the Pacific near the Panama Canal and along the Mexican
Pacific coast into the Gulf of California. Multiple recordings were
made of each target region at various nadir angles (0 01 400 ) and i employed different combinations of polarizing filters. In addition,
i I ^ I
67 ship sea truth data for interpretation of spectra and expendable bath- yphotometer probes as the aircraft's own sea truth was included in the research. These data and data collected over Buzzard's Bay were interpreted for the effects on the spectral characteristics by various chlorophyll levels., and the atmosphere at various flight altitudes. . Comparison . of measurements of upwelling light spectra from 20 cm below the surface and 500, 1000 and 2000 ft. altitudes revealed the addition of a predominately blue diffuse atmospheric light. The most drastic change in the spectral character is that from 150 to 300 m. A color ratio briefly described by Clarke et al. (1970b) and fully by Clarice and Ewing (1973) was used as an index to describe the character of spectra, and was related to the spectral effects of chlorophyll concentration changes. Light extinction profiles from bathyphotemeters correlated well with the ratio of reflected radiance (540 nm/460 nm).
Increasing extinction coefficients compared to increasing color ratio values. The research area of the Gulf of Mexico to the Gulf of
California was maj.-pod by the color ratio index and surface chlorophyll. concentrations. Chlorophyll concentrations were not strictly related to the ratio. Clarice and Ewing could not discriminate color contribu- tions of silt or sediments from chlorophyll in near coastal areas where the color ratio was > 0.7. In chief problems that remained to be investigated were: to assay varied incident illumination in flight, to better estimate and reduce diffuse.atmospheric light interferences, and to identify the characterization of ocean color spectra by other materials in the sea. ^ l
68
Uuntley (1972) and vuntley et al. (1974) were concerned with
detecting chlorophyll changes at levels of 0.1 mg /m 3 which was
considered the base of significant levels for commercial fisheries
interests. However, their approach was designed for measurement from
! earth satellites. Radiative transfer calculations were made on the
chlorophyll signal available at orbital altitudes from a backlog
of data collected on optical atmospheric parameters, measurement'of
optical 'processes in the sea and measurements of varieties of phyto-
plankton cultures in the laboratory. The results presented represent
the apparent optical signal contrast when passing from biologically
poor water (Chl a < Q.1 111g /m 3 ) to higher selected chlorophyll
- concentrations. Data is presented as polar plots of the field of
view and analyzed in apparent orbital contrast isopleths for green
and blue wavelengths of returning light and at varying; solar zenith
angles. These plots indicate the areas of the field of view that
sensors must focus in to distinguish chlorophyll changes. Solar
zenith angles for best contrast were concluded to be 24 0 <0< 42 0 . _..
Although most of the . reflected visible spectrum was recommended to
differentiate chlorophyll from other 'ocean colorants", Ountley (1972)
concluded that only phyt.oplankton cause a backscattered spectra to
be increased at 560 nin, remain fixed at 523 run, and be diminished
at 450 nm although only pure laboratory cultures and biologically
poor waters in situ were treasured. Both blue and green wavelengths ^^ I from ocean spectra were concluded to be of sufficient intensity to
be detected through both clear and hazy atmospheres at earth orbit. i I I
69
Ountley et al. (1974) further developed calculations of chlorophyll signal to an earth orbit by considering vertical distribution of chlorophyll, different species composition and differences in filterad base water composition. Radiative transfer calculations of two vertical profiles of chlorophyll distribution showed that the diffuse reflectance is only related to near surface concentrations (< 5 m) and integrated chlorophyll values through the water column and spectral diffuse reflectances are ambiguously related. Intensities of back- scattered light to 1.11TS-1 satellite in a 500-600 nm channel were determined to be proportional to near surface plankton (Sickielda,
1974). Calculations by lDuntley et al. (cit. loc.) suggested that increases of sediments in suspension only increase the total diffuse backscattering coefficient and not the diffuse absorption. 'Thus the net result should be reflectance increase at all wavelengths in optically deep waters, and sediments can be distinguished from chlorophyll-bearing phytoplankton by the shapes of their respective spectra.
With the previous suggestions for chlorophyll determination by
..olor ratio, Arvesen et al. (1973) studied a correlation method, rased on differential radiometry to detect chlorophyll. The criteria he used for 443 on/525 nm wavelength selections were based on independently observed characteristics of natural phytoplankton,
Rayloigh-like seawater attenuation, and ''white" Mic scattering by larger particulates. No theoretical treatment of the process of color ratio production or atmospheric transfer was considered. The { I
70
differential radiometric method did solve some of the previous
problems described. A normalization of incident light intensity could
be accomplished simply by adjusting the incident ratio(I 443 /1 525) to unity. The difficulty in spectra analysis was removed and a
continuous color index now could be more closely compare] to continuous
airborne radiation thermometer measurements. This also allowed an
easy, real-time interpretation. The results of measurements over"
varied natural water types at an altitude of 150 m dewonstrated.the
capability of this method to estimate surface chlorophyll levels.
Iiovis et al. (1973) have continued studies using numerous
reflected ratios at 11.3 km and 0.3 km altitudes over ocean areas
off North Carolina and the Gulf Steam, San Francisco Bay, and NIV
Africa. Because satellite spectral data will be recorded as spectral
bands and not complete spectra, color ratios-to-parameters comparisons
were designed. A rapid scan spectrometer with a field of view of 3.8 X
3.8 milliradians was employed in this study. At low altitudes this
narrow target resolved surface effects of waves. The spectra at the
different altitudes were compared, and, in contrast to Clarke and
Ewing (1973), there was severly reduced contrast. A factor of 2 reduc-
tion in contrast was observed even after the elimination of skylight
from the high altitude signal. The conclusion was that this informa-
tion had been scattered out of the radiance column viewed by the spectro-
meter. Hovis et al. (cit. loc), concluded that the use of ratios could
minimize changing, broad spectral atmospheric effects by referencing i
to a spectral band that is insensitive to spectral changes in the ocean=s 1
1 s
71.
backscattered signal. Besides the 550 nm/443 on ratio used previously,
ratios of 600 nm/520 Fnn, 665 nm/520 on and 550/600 on measured
at high altitudes also showed correlations to chlorophyll measurements.
Under haze conditions the 550 llm/443 not and 665 nm/520 nm ratios best
correlated with chlorophyll concentrations. The calibration by
Arvesen (Figure 3.1) was used by Havis at al. for the NW coast of
Africa data.''Correlation of temperature changes simultaneous to
color ratio changes supported the 443 nm/525 nm ratio as an index of
chlorophyll because of the known response of phytoplankton to cold,
upwclling ,raters,
3.2.2 The Uiffecential Radiometer
The differential radiometer (DR) (Arvesen at al. 1973 and
Arvesen, 1973) is an extension of the use of wavelength ratioing for
determination of phytoplankton pigments in natural waters. In general,
the instrument is designed to measure two narrow . spectral regions
of reflected. (backscattelred) light from water bodies at aircraft
altitudes and produce a continuous signal which is a ratio of the two.
The reflected light is received in a sensor assembly through
a fiber optics bundle. The field of view of the bundle is 30°. The
bundle is then divided into four sections, each section having the
same field of view. Behind each section is a spectrally narrow
bandpass filter (AA 0 15 Fun) selected to allow transmittance of the
spectral region of interest. Radiation passing.through each
selection filter is incident on a silicon photodiode detector (UUT 500). 72
Integral with each detector, a preanTli£ier produces an output voltage J
signal proportional to the incident radiation. These signals can be
monitored directly. Two .signals are further processed to produce
the following algorithm:
Ratioed output signal = 1p (Signal of detector 112-Sig nal of detector 111) Signal of detector 112 !
volts. Similarly, the signals from the remaining two fiber optic bundle
sections are processed and can yield a second ratioed output signal.
One output signal, developed for determination of chlorophyll in
water bodies, has selected filters which transmit a 443 nm band
(detector 111) and a 525 Im band (detector 112). The second output signal
was not used in this study because no other correlations of wavelength
ratios and features effecting ocean color have been proposed at present..
The objectives of the differential radiometer's design are to
provide a high resolution, continuous, real-time, remote determination
of chlorophyll pigment concentrations in near surface waters and still
be simple to operate, The principle of this method for remote sensing
of chlorophyll is a culmination of the conclusions from previous
research outlined in Section 3.3.1 First, the specific spectral
characteristics of chlorophyll in natural water were considered.
The proportional , loss of reflected intensity in the 443 nm region is due
3 to the absorbance by increasing concentrations of chlorophyll pigments,
and the insensitivity of the reflection intensity at 525 not to changes
in clear, natural waters (Uuntley, 1972). The 443 nm intensity, then, f j r i
73
is the sample signal wavelength (A), while the S25 nm exists as a back-
ground or reference A. The interference to the sample signal (443 nm)
and the reference signal (525 nm) by suspended sediments and the molecular attenuation of sea water was, from the preliminary research at the time, considered to have an equal effect on both wavelengths.
Therefore, the algorithm would continuously compare the
intensities of the reference wavelength and the sample wavelength to normalizes! interferences. From the algorithm it can be seen that
the radiance ratio is linearly proportional to the voltage output.
A normalization of the incident light intensities (i.e., 1443/
525 " 1) at the flight altitudes can be obtained. Since the sensor 1 is a flexible fiber optic bundle, direct viewing of solar radiation can be easily accomplished. A spectrally flat diffusor is placed over the sensor to decrease the intensity and also to increase
the diffuse light to the sensor. +Adjustment of a potentiometer varieg
the sample signal output so sample and reference intensity can be
normalized. This solar zero operation can be accomplished periodically
during flight with changes in sunlight conditions and changing solar
zenith angle, Limiting skylight-sunlight intensities for instrument
use have not been well established.
The sensor is mounted at an angle of 20 0 off nadir. Also, the
mounted sensor may be rotated to any azimuth angle. The conclusions
on optimum direction of sensing for the most valuable optical signal
were followed in the design of this mounting apparatus (Duntley, 1972; 74
Duntley et al., 1974; Austin 1974a and b). A field of view of 30° also gives a specular average signal: large enough that sun glitter contribution is negligible.
The calibration of the differential radiometer (DR) ratio system in termsof chlorophyll concentration is the result of 50 measurements over water bodies of various, known concentrations. This included clear lakes, eutrophic lakes, marine water of varying chlorophyll content and an estaury. The chlorophyll concentrations ranged from
< 0.03 to > 10.0 Illg /m 3 . The airborne measurements were made at an altitude of 150 m. Arvesen (1973) shows a remarkable correlation between sea truth and DR measurements along one 700 km track southwest from San Diego. Arvesen's calibration (Figure 3.1) is also in agree- ment with a well established principal in ocean color observations.
At very low concentrations of chlorophyll small changes in concentrations correlate to large changes in the 443 nm/525 nm ratio. In water masses of higher concentrations of chlorophyll, a far greater change of concentration is needed to produce the same magnitude change in the color ratio. The DR was shown capable of detecting chlorophyll variations < 0.03 mg/m 3 . Unfortunately, the total suspended particulate distributions are not given for additional comparison. I
1 75
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6
30
10 7
.5
• 3
m - E
E 1 J I , 7
o .5
... 01
i'
.07 f - .05
I I I I I I I I -10 -R -5 -4 -2 0 2 4 SIGNAL OUTPUT (volts)
Figure 3.1 Calibration curve of DR ratio values (W IR) and proportion 1, analog Signal Output (in volts) to Chlorophyll Concentration g. units (mg/m3).
• 4 76
Additional considerations for effective use of the DR
followed in the present study are: The solar elevation ankle should
be > 20° to insure adequate backscattered signal with respect to
background radiance. The direction of view was 20° from nadir oppos-
ing (1800 ) the solar azimuth angle to reduce sun glitter reflec-
tion 'o the sensor. As the solar azimuth angle changes in respect
to the aircraft, it is then necessary to correct the azimuth viewing
angle of the radiometer. The preliminary.effective depth of measure-
ment was considered to be about one-half to one-third of the Secchi
depth (Arvesen, 1173). This limitation is more firmly defined by the it present study. Additional information on the DR is given by
Arvesen (1973).
A pre-study evaluation of the effectiveness of the color
ratioing method is difficult. A number of published aircraft ocean
color spectra with corresponding sea truth chlorophyll concentrations
(puntley, 1972; Clarke and Ewing, 1973; Mueller, 1974; and Pearcy and
Keene; 1974) allow development of a color ratio chlorophyll concen-
tration comparison. However, various altitudes of flight, chlorophyll
concentration ranges of most measurements within only two order of
magnitude, and individual analysis of the data make a cummulative
comparison impractical. Generally, from comparison of color ratios
to chlorophyll concentrations for each study individually, the scatter
is far more than that seen by Arvesen.. Also, in the calibration of
very high chlorophyll values, the larger change in the color ratio i 77
(compared to Arveson's calibration) is indicated for similar changes
in chlorophyll concentrations > 20 mg/m s This is supported by
Curran (1972) in a comparison of chlorophyll co,y entrations and the
reflected color ratio 540 nm/460 nm.
{
i
is ! ^ 1
78
4. FIELD METHODS
The NW coast of Africa has long been recognized as a region of
upwelling. Smith (1968) has given a general review of the physical
I oceanographic processes which result in this phenomena observed at
the Eastern boundaries of most oceans. Results of previous oceano-
graphic exploration have been reported by Uefant (1961), Furnestin (1959), Jones anti Folkard (1970), Jones (1972), Fedoseev (1970), and
Schemainda et al. (1972). Biological results including chlorophyll
measurements have been reported by Furnestin (1970), Lloyd (1971)
Ballestex ct al. (1972) and Margalef (1971 and 1972). Interest in
better defining this upwelling area which led to the Sahara Upwelling
Expedition and the.JOINi'-1 project originated from the recognition
of the upwelling area by the previous investigations cited.
4.1 The SAHARA UPOELL1NG EXPEDiTiON
ln'August; 1373 1 a joint project based on skylab investigations
(Szekielda, 1972b) was conducted by the University of Delaware and
NAVOCEANO. The .area of operation was along the NW coast of
Africa from Cabo Juby (28 0N, 130) in the north, to Cabo Bo j actor (260, 14 0 300) in Be south; The area of operation extended seaward
90 nautical miles to Fuerteventura. The bathymetry of this area is shown ill Figure 4.1.
The -Sahara Qpwalling ExPedit,ion (SUE) was designed as an
experimental mission with these three objectives: 1) to test from
34
79
=9 16 • 1!• 14• 12• 29•
SKYLAB UPWELLING EXPERIMENT LANZAR0TE S U AUGUST 1973 ^^ BATHYMETRY FUERTEVENTURA a` (meters)
CANARY ISLANDS
app
GRAN CANARIA CA80JUBY ^° p MOROCCO ^O IAPPROFIM nT( / - - e^01MiD^11f
0 N l 2>•• 1 21• o °° 0
hall00 0 P
C2
h
/ CA90FAL5 SOJAOOR QP f h
1 2s• 1 _ .L-- .l__ I _ _. _1_ r1.J _I 1.--- - • -^ _ J— t tc• 6' IY t^• 1^•
Figure 4.1 Bathymetry of the Sahara Upwelling Expedition research area. i
80
aircraft altitudes a suite of expeviments including expendable probes r
and experimental remote sensing instruments, 2) to evaluate the ability
and utility of this system to recognize biological and physical
patterns associated with an upwelling region, 3) to be a comparison
study'of simultaneous surface truth, aircraft, and s:iellite measure-
meets in an upwelling area to aid in interpretation and correlation
of data acquired by the remote sensors employed. i
4.1.1 The Exierimcntal Instrumentation rack g
The experimental package of the Sahara upwelling Experiment
(SUE) contained both radiomotri.c sensors for reflected visible and
emitted iR radiation, and airborne expendable probes for light
penetration and vertical temperature profiles.
The differential radiometer described in Section 3.2.2 and an
airborne thermometer were the remote sensors employed on the aircraft
missions. Continuous sea surface temperatures (SST) were recorded
with a Barnes Airborne Radiation Thermometer 14320 (ART) operating
in the atmospheric window between 9.5 - 11.5 pis. This band of infrared
radiation is emitted from approximately the top 0.02 mm of the ocean's
surface and therefore reveals only the sea surface's skin temperature
(Clarke, 1964; Wilkerson, 1966). Aircraft thermal IR measurements have
been discussed by Clarke (1967) and Saunders (1967a). The raw analog
ART data were recorded on a strip chart recorder. Continual calibration
and corrections for altitude (depth of air column) attenuation; air and
lens temperatures front a format used by NAVOCEANO (Kerling, 1973)
were applied to the raw ART signal so a corrected SST could be 81 recorded on a second two-channel recorder. The ART sensor head was mounted 50 cm above the main deck of the aircraft and 1.5 m above the aircraft skin in the viewing position normal to the sea surface plane. The normal viewing angle has minimum correction due to shortest optical depth and smallest influence by surface reflected solar energy (Saunders, 1967b). The field of view (Co N.) of the sensor was 2.2 0 . Extending this solid cone for 300 m, the operating altitude of the SUE mission, the target spot of the ART was 11.5 m in diameter.
At an average ground speed of 108 m/s and an ART response time of approximately 1.0 second, the best spacial resolution available from this instrument system was 108 mi. The target spot of the OR was 184 m in diameter with its f.o.v. of 30°.
Two expendable probes, a 300 m bathythermograph and a bathy- thermograph modified to record light penetration levels, were included in the SUE 'mission. The airborne bathythermograph (AXBT) is dropped from an aircraft and on impact at the sea surface an FM transmitter is activated by a sea battery. A carrier signal is transmitted which corresponds to a temperature measurement at the surface. Following the carrier signal, the probe falls through the water column in the same manner as a conventional expendable bathy» thermograph (XBT). The signal is transmitted to the aircraft where changes in frequency are recorded versus time and calibrated to °C. versus depth.
AXBTs were modified similarly to those used by Clarke and
^i i j
82
Ewing (1973). The airborne expendable photometer (AXIM) has
incorporated a zenith viewing photocell replacing the temperature
sensor of the Am r, The carrier signal is a mea stir ement of light
incident at the sea surface. The profile, recorded as increasing
extinction of light penetration with depth, can he calibrated to
percent incident radiation (o 1 0 ). Schematics of the expendable
probe operation and a description of signal evolution are presented in'
Appendix A. AX91's and AXI INIs were dropped seconds apart so vertical
temperature profiles could be correlated with light attenuation pro-
files. Probes were dropped on parallel flight lines which ran
approximately normal to the coast. The profiles measured on these
lines iaere analyzed as two dimensional vertical slices.
4.1,2 Ex p erimental Procedures and Data Collection
'Elie elate, time, and comments of four flights in the SUE
mission are shown in Table 4.1. Differential radiometer and narrow
band airborne radiation thermometer (ART) signals were recorded
simultaneously on a two- channel strip chart recorder. Time marks,
course changes, station marks, instrument adjustments and calibrations
were noted on the strip chart by the differential radiometer operator.
Visual observations of ocean and sea surface features, atmospheric
conditions and solar azimuth positions radioed by the pilot and front
and rear observers were noted as well. Complete weather observations
were logged every fifteen minutes during the flights. The continuous
differential radiometer and ART signals were immediately available
for interpretation of-surface gradient structure and thus, were a
{ l I
_
83
decision making input in the expendable probe experiments.
Fifty-seven Airborne Expendable Bathythermographs (A.XYTs) and
thirteen Airborne Expendable Photometers^ )AXPMs wore deployedi Y in
the SUE mission for vertical temperature and incident light penetra-
tion profiles respectively.
On August 22 and 26, additional reflected wavelength regions
were recorded from the differential radiometer's secondary channels.
The continuous reflected `intensity of yellow and reel optical
energy from wavelength regions centered at 576 nm and 663 nm respectiv-
ely was recorded for a major portion of the August 22 flight (see
Table 4.1). The 576 nm yellow band and a substitute 723 nm red band
were again recorded on August 26 for the entire six hour flight.
Table 4.1 Research flight's of the Sahara Upwclling Expedition
(SUE)
Date, 1973 Comoents (2)
For all flights: ground speed 195-205 Knots Altitude: 1000 feet (305 m)
August 18 0640-1240 I AXI'M M deployed at end of leg 5, occasional haze and clouds below air- craft, > 701 cloud coverage overhead
August 21 1139-1753 Expendable probe mission, 11 AXVMs deployed during leis 8, 6, 5, and 2; > 80% cloud coverage during 200 of flight.
August 22 . 1159-1824 Additional reflected wavelength bands recorded (576 not and 663 nm), 1 AXIN dropped at 1416 (between legs 4 and 9),
(continued)
0 k
!Jl} Ii4` f
84
Table X1.1 (colltinuad)
Date, 1973 'rime Comments (2)
August 26 1143-1723 Additional reflected wavelength bands recorded (576 11111 and 723 nm), haze to 90% overcast for 15'0 of flight.
(1) Airborne Expendable Photometer
(2) Airborne Expendable Bat hythermograph deployment is given by LaViolette (1974).
4.1.3 Flight Piann:ng
The coverage intensity and regional area chosen for the research
flights were designed to give- a synoptic monitoring of an upwelling
region large enough for comparison studies with the resolution of
satellite data. biter the morning flight of August 18, in which
research was partially hampered by cloudy and hazy conditions, the remaining flights were scheduled in the middle of the day which also allowed for use of same-day NOAH-2 satellite images for scheduling.
The average duration of the flights was 6.5 hours. The regional
area was the coastal to open ocean waters between the Canary Islands
(Gran Canaria and Fuerteventura) and the coast of Northwest Africa
from Capo Juby to South of Capo Bojador.
4.2 The Joiur-1 Plinio
The JOINT-1 project of the Coastal Upwelling Ecosystems Analysis
(CUEA) program was an intense oceanographic study of an upwelling area rr ,i 3
$5
approximately one degree square (17 0 -18 O W, 21 0 -22%) off Cap Blanc in
northwest Africa for a three month period from mid February through
mid May, 1974. JOINT-I incorporated a twin-engined aircraft from
the National Center for Atmospheric Research (NCAR) with participating
U.S. oceanographic vessels from NOAH, Woods Hole Oceanographic institute
and University of Miami.. In addition the French research vessels
Jean Charcot and CaLricone, the Spanish research vessel. Cornide de
Saavedra; and the Mauritanian research vessel Almorivide participated
in the project. Synoptic temperature coverage of the research area
was performed by the NOAA-2 satellite.
4.2.1 Airborne Measurements
The aircraft's oceanographic mission was designed as an opera-
tional survey to support research vessel activities in the vicinity
with the objectives of synoptically monitoring sea surface temperature
and phytoplankton chlorophyll pigment concentrations in near surface
waters by remote sensors. In addition, the aircraft was to study
meteorological conditions related to upwelling regimes. It was
designed that data acquired over the extended period of the air-
craft's mission be transmitted daily in a hard copy form (as analyzed
sea surface temperature (SS'f') and surface chlorophyll (C;hl.) maps)
via communication satellite to ships in the research area. The
distribution of these surface parameters could then be used to locate
upwclling events and as a decision-making input into selecting areas
for intense investigation. On the other hand, the data collected by
the differential radiometer (DR) and the radiation thermometer (PRT'-5) h ' F'
86
were supported by the sea truth obtained by the research vessels.
This data includes surface chlorophyll measurements, sea surface
temperatures, distribution of particulates and incident Light
penetration.
Specifications of , the radiation thermometer and the
twin engine Beechc:raft "Queen Air" used in JOINT-1 are described in NCAR
(1973). Pre-flight calibration was accomplished by sensor measurement
of a water bath. Periodically during the flight, the solar standardiza-
tion of the DR was accomplished (see Section 3.2.2). The mounting
of the DR sensor in the aircraft allowed manipulation of the azimuth
angle, while the viewing angle was 20 0 from nadir. The PRT-5
sensor head was mounted at nadir. The operating altitude of the air-
craft was 500 feet (150 Q. The f.o.v. of the DR is 30 0 , and at the
operating altitude the target snot of the pit is 4 92 m in diameter.
The PIZT-5 sensor's view was unobstructed by the aircraft skin. The
plexiglass window through which the DR viewed the sea surface was
identical to the observation window material through which solar
standardizations were made.
4.2.2 Plight Planning i
Two types of oceanographic flight plans were devised to give
periodic intense coverage of a small (1/2 0 longitude by 1° latitude)
area and larger (1° square) area synoptic coverage. Occasionally,
both types of flights wore flown on the same clay for comparison
purposes. Intercepts in the flight tracts were designed to give 87 cross-referencing points for aircraft instrument checks. Oceano- graphic flights as scheduled did not have More than a two day lapse between consecutive flights.
Meterologi.cal flights required a profiling of the air column
and no oceanographic data were obtained. On days when one oeoano- graphic flight was scheduled, the time of optimal sun elevation for the differential radiometer was selected. This was between 1000-
1440 lir. local time. The average duration of flights was four hours.
Whenever research vessels were in the vicinity of the flight
tract, the aircraft diverted to make several overpasses to obtain sea truth measurements. The time "on course" in these passes over the vessels was usually more than one minute. The amount of time insured
stability of differential radiometer adjustments after the
course change.
Experiences early in JOIN'-I with days of high dust loading
and its detrimental effect on the aircraft's operation became a
safety factor in scheduling flights. The dust that eventur!Ily sifted
into the instruments, especially the Inertial Navigation System and
the NCAR Aris data collection system, caused frequent inflight failures
in the later flights and finally an early conclusion to the aircraft's
mission. ss
4.2.3 Aquisiti.on Format and Data Handling
Thirty-five research flights from Feb. 17 to March 28, 1974 were accomplished. 'table 4.2 shows the date, time, and type of each flight. Raw data available immediately were the precision radiation thermometer (PRT-5) and differential radiometer traces on the two- channel strap chart recorder. These recordings were annotated with time marks, visual observations of atmospheric and sea conditions by the rear observer who operated all instrumentation, a>>d with observations of the pilot and front observer. rhis was particularly important for discrimination in the data of course changes, transition from cloud-free to clouded areas and visual observations a£ properties on the sea surface such as cloud shadows, large slick areas, slick streaks, color boundaries, col(-,r streaks, fouilt lines, and fishing vessels ('tabor, 1974). Besides the detailed strip charts, the front observer kept a log of times and positions of arriving and leaving stations anc' of features noted by him or the rear observer. The
Inertial navigation System (INS) allowed a direct, real-time readout of position, heading, distance to the next station and ground speed.
'these observations also were routinely noted with the specific obser- vations made in the front observer's log.
All oceanographic sensor data were recorded via the Aircraft
Recording Instrumentation System (Aris) data collection system on multichannel magnetic tape. This included the differential radiometer and PRT-5 data, the position data from the INS, and time. A descrip- tion of the Aris system developed at NCAR is given in NGAR (1973). 89
Digital values were recoruuu on tales at eight values per second
after computer processing. I-or oceanographic data usage at this tame,
one,second averages were considered sufficient and expediated the
processing of the twenty-six oceanographic flights, At WAR in Boulder
Colorado, the data from the computer tapes were printed on microfilm
which gave fifteen-minute plots of the different parameters versus
_._ time as well as the one second average listings of parameter values.
The best spatial resolution for the one second values at the average 1 aircraft speed of 140 knots was 'L 78 meters.
_I
_I w 90
Tablo U JOINT-1 Oceanographic Research Flights
Average Wind Direc- Flight Flight tion/ 0 Date,1974 Loyal Tina Pattern Spcuo Com. ants
1 Feb. 17 0835-1320 Small 060/40 light haze (dust) - scale: N top at 2000 feet. 2 Feb. 18 0840-1300 Small 050/10- thick haze - top scale: S 89 4000 feet 3 Feb. 19 1230-1605 Large scattered cumulus scale 4 Feb. 20 0800-1200 Small occasional clouds scale: N 5 Feb. 20 1325-1630 Small -/10-67 scale:S 6 Feb. 21 0815-1215 Modified light haze small 7 Feb. 22 0810-1140 Large -/02-68 Cloudy 8 Feb. 28 1335-1745 .Small occasional clouds, light haze-top 2000 feet 9 Mar. .4 1320-1630 Small 020/12 10 Mar. 5 0800-1130 Large 050/18 few clouds, light haze-top 3000 feet 12 Mar. 6 0800-1145 Small 353/17 scattered heavy cloud cover 13 Mar. 6 1315-1700 Small 350/15 special flight for comparison with AM 16* Mar. 8 0950-1340 Small J02/14 light haze 17* Mar. 9 0800-1200 Small 045/22 Partially cloudy 18* Mar. 9 1330-1700 Large 025/23 19 Mar. 12 0750-1035 Small 045/27 low visibility. (3-4 miles), flight cut short, no Chi. data 20 Mar. 12 1320-1640 Large 040/27 low visibility, heavy clouds and dust - tole 3500 feet 23 * Mar. 16 0740-1130 Small 035/25 1 fight fog and dust - top 600 feet- I 1115 ! : , __ .
91.
Tab 10 4.2 (continual)
Average Wind Direc- F1ight Flight tion/ 0 Date, 1974 Local 'l'a.me Pattern S Reed Comments
24 Mar. 16 1320-1450 Large 034/18 very dusty, flight cut short 29* Mar. 19 1000-1305 Small 036/21 30 Mar. 20 0745-1130 Small 045/22 frequent clouds 31 Mar. 20 1315-1630 Large 32 Aiar, 21 1005-1450 Small -/23 dust top 4500 feet 33 Mar. 28 0915-1015 Small flight cut short - no data 34 Mar. 29 1345-1720 Small 359/16 occasional cumulus, light haze top 1500 feet no computer digital data, analysas from strip charts 35 Mar. 29 0815-0915 Small scattered N-S cumulus, flight cut short
* Flights described in text. i
92
5. RESULTS OF FIELD STUDIES
5.1 SAHARA UPIVELLING EXPEDITION
5.1.1 Explanation of Data Ar,"I v,cs
Analog sea surface temperatures (SST) and differential radio-
meter (DR) voltages calibrated to chlorophyll (Chl.) values from the
calibration curve described in Section 3.2.2 and presented in Figure
3.1 were digitized in one minute averages, then plotted on flight
tracts mapped by the aircraft's navigator. The rationale of using
one minute average intervals of continuous data was: for a first
comparison with either continuous chlorophyll measurements froi vessel
or spacecraft: data, G In average values would be most useful and
convenient. The analog recordings existed as a reference if greater
resolution would be needed. The decision of which data were excluded
from analysis wao made from the written comments on the airborne
recordings and. distinctive features in the traces such as signal
spikes clue to aircraft motion and loss or increasa of normal low level
surface noise by cloud scatter processes or sun glint respectively.
Cloud contaminated regions were disregarded in DR data and excessive
sun glint, cloud cover and banking motions of the aircraft were
disregarded in both the DR and ART data. For example, the August 18
flight Was the only . morning flight of the SUE mission and the large
change in solar elevation throughout the flight and variations in
atmospheric conditions suggested some limiting conditions for the
radiometric method. The DR data before 0800 hours was rejected due to
48 i
93
insufficient solar incident light and skylight through the > 710% cloud cover. Cloud contamination beneath the aircraft caused features in the recordings which had similar appearance to actual color boundaries. Loss of the background reflection noise from constant sea state oscillations helped differentiate this interference from actual features. Clouds and cloud shadows erratically increased the ratio value of reflected light. An erratic ART signal supported the DR signal under these conditions. Analysis of the data maps involved contouring of SST in °C. and DR maps in mg/m 3 chlorophyll as per calibration curve. The final forms of these maps are presented in
Figures 5.1 a-d. The flight path, uivided into one minute intervals on the SST maps and two minute intervals an the Chl. maps, is indicated by discrete data points. The intervals of chlorophyll contour are not equal and this caution in interpretation of gradient structure should be observed. A representation more closely related to ocean color changes can be exhibited by this presentation, but again a cautious interpretation is needed.
Data received from the exper d able probes were analyzed on return to the laboratory. Amplification and normalization of the
Airborne Expendable Bathyphotometer (AXPM) recordings were needed for interpretation as light penetration. Data of the routinely used Airborne Expendable Bathythermographs (AXWI's) could be analyzed immediately. The absolute accuracy of the temperature values given in the results of the SST and AM data is not known. The relative accuracy of these measurements, clue to the intercomparisons of data I F }^ 't !
94
that were matte, is reliab)e.
5.1.2 Description and Inta retatzon of Sensor and Probe
Measurements
Results of the SAHARA U1 1WELLING EXPEDITION (SUE) include:
1) maps of the regional distributions of sea surface temperature (SST)
and apparent chlorophyll values (Chl.) that were observed in an eight
day period from 18-26 August, 1973 (Figure 5.1 a-d), 2) analyzed
continuous recordings of DR and ART signals plus reflected intensities
of yellow (576 mn) red (663 nm) and near IR (721 inn) bands which are
presented far comparison of changes in the offshore and longshore
direction (Figure 5.2 a-e), 5) simultaneous light penetration and
temperature profiles of offshore sections on 21 August for identifica-
tion of upwolling phenomena and for light penetration - surface ocean
color comparison (Figure 5.3).
In figure 5.1 a-d, DR measurements indicate increased near—
shore surface chlorophyll levels in all flights with maximum
levels ranging from > 1 mg/m 3 on August 21 and 22, to > 5 Mg/m 3 on
August 18. Also common to all flights are the longshore paralleling
contours which have differing degrees of offshore distensions, but
consistently decrease in value moving offshore. The most dramatic
changes in apparent chlorophyll levels are nearshore, but structure
can be observed offshore in all flights as well. If the results of
the four Blights are observed in time sequence, a -umhor of develop-
ments can be described and interpreted. The 18 August analysis shows I f
95
the most seaward-extending temperature structure and Chi, structure
of any date during SUE. Offshore distending isotherms indicate a
plume of colder water. from the sequential flights (21 and 22 August)
this feature appears to separate from the constant coastal
structure and move generally west by 21 August and then south by 22
August. On 18 August, the Chi. is apparently > 0.5 mg/m 3 in the position
of the plume < 19°. The Chi. analysis indicates that the plume feature
is already separated from the coastal region on 18 August. 'through
21 and 22 August, the temperature difference between the plume and the
surrounding water is lost. Any Chi, difference between the surrounding
water and this migrating plume was not identified on 21 August. On
22 August, however a > 0.5 mg/m 3 feature which corresponds to the NIV
temperature boundary is apparent south of Gran Canaria. Low Chi. and
> 21° SST are observed to the south of W orteventura. In reference
to the southerly Canary Current, this would be the leeward side of
the island. LaViolette (1974) interprets the isolated patches of
> 21 0 water (on 21 and 26 August) as surface eddies or an island wake
created by the expansion of the Canary Current south of the island
after the channelling between the African coast and Fuerteventura,
The > 21 0 feature was observed on all dates. This corresponded
to the clearest waters measured by the DR. Data from 18 August
demonstrate a very strict correlation between decreasing SST and
increasing Chl. The striking identity of location for both Chi. and
SST gradients in all areas and on all dates indicates a
significant dependence of the Chl. measurement on temperature structure.
The structure noted on the 21 August in the 0.5 mg/m 3 contour (the 96 third flight line from the south) is difficult to interpret. There is a correlation between the EST and Chl. distribution. However, these measurements were taken during observations of g lint. This would have t1:e effect of: ca p. ; the chlorophyll values to lie inaccurately high. The signal re f lected from the surface would approach the ratio obtained during the solar zero procedure. Since the actual reflected ratios from the sea in this locale were low compared to the solar zero, sun glint received by the sensor would raise the values. This would cause excessive noise in the DR analog signal if it was a significant input to the sensor. The vertical section results (figure 5.3), on the other hand, support the surface temperature gradient. On August 22, an isolated patch of < 0.2 mg'/m 3 Chl. was observed to the southwest of the structure of 21 August. This may be the development of an isolated,very clear water parcel moving in the southerly Canary Current offshore of coastal upwelling activity as indicated by the temperature and apparent Chl. gradients. The distance which this feature and the lower temperature offshore patch described above have moved in a one day period is comparable with the ti 1.5 knot speed of the Canary Current
(Fedoseev, 1970). On 21, 22 and 26 August, isolated patches of-very low Chl. were measured. just offshore of strong temperature gradients.
The only high Chl. patch was measured on 26 August. The development of the large Chl.' plume extending to south of Gran Canaria can not be interpreted due to the longer time interval between this and the previous flight. ^ ^ ^ i
/ | | \ l ^ i ^ | Y | | ^ _ ^_ - ^ ^
97
LO SEA SURFACE TEMPERATU CHLOROPHYLL (mg/m
fA Wom ^r |-FAU 60JAWA p . d ' ,`. . . 2° Jp. `~. . . L^
Figure 5,1 a-d (continued 'ooS41 - ' ^ool^scu o^ apparent^^ Chlorophy ll (Mg/M3) and Sea SurfuomTomperature ("C.) distribution on 18 ^ 31, 32, 26 August, 1973. The numbered solid lines (1-5) on the 22 and 36 August flight tract indicate the direction ond position of the continuous recordings presented in Figure 5.3 w- 5.2 m respectively.
- -^^ - Atigust 21 200 ^y^/al ^&^LLfMe Temperature
lao to 2D Al
` !
^ . Fi g ure S.1b ' ` REPRODUCILIM Y Or' THE ` ORIGINAL PAGE IS POOR
^ ` -^' ^^^^ 22 FUERTEVE TUBA - August _ Aig ust 22 Sea Surface Temperature Q Chlorophyl mg/M3 CANARY ISLANDS CAMAitY ISLANDS 20.0
19. - _ 21.0 I A GRAM 28 GRAN CAMARIA CAHARiA 1.0 2 1 Z0-
20.0 .5
" [ D C . 2 P-7
q- - - - i a
a r , 21.0 .r a LL r ..^ 3CABO FAL54 BCJADDR QP T .2 f CABQ FALSE H0 IADDR Qg 5 ° . t 1^ 6 15°! !4°1 t I a t t • i 1 i i i t 26° e -
Figure 5.1c ' f
99
In actuality, both SST and Chl. have more fine structur°
variability or meandering than is shown because the analysis can
be interpolated between flight lines. This can be exhibited when
flight lines are positioned nearer each other and thus the data
distribution concentrated. in all flights, the inshore legs runn
parallel to the coast showed small, quite frequent plumes of apparent
chlorophyll. Two other observations tend to discount these as
measurements of actual chlorophyll. The SST of these plumes was
consistently ,nigher in the plume and lower in contiguous areas. In
general, this is the converse of the results that showed decreasing
Surface temperature with increases in apparent chlorophyll. This
feature could not usually be resolved in the one minute average
analysis, but it is observed in the continuous recording of
Figure 5.2c at time 1610. Photographs of the sea surface from the
aircraft showed plumes of sediment with the frequency and size of the
features indicated by the Utz. The plumes can be interpreted a, warmer,
surf zone water heavily laden with large sediment particles flowing
offshore and surrounded by colder, Tess reflective coastal-water.
In this case, it was visually clear the DR measured particulate
load as increased chlorophyll levels. More disperse non-phytoplank-
ton particulates originating from coastal orrosion and bottom distur-
bance are suspected to partially cause the general apparent chlorophyll
increases in all near shore areas. i
f r ^
100
on August 22 and 26, in addition to the DR and AIVI' signals,
red (663 nm or 723 nm) and yellow (576 nm) channels of reflected
light were recorded. The four reproduced analog recordings of five
time intervals are presented in figure 5.2 a-e. The position of each
recording is shown on the Chl. maps of 22 and 26 August
(figures 5.1 c and d) . The incorl}oration of measkrroments at these
wavelengths was designed to help interpret the effectiveness of the
DR method by having additional wavelengths which could support
the identification of the chlorophyll by its characteristic spectral
response. All large non-selective particulates should cause increased
scattered light from a clear ocean to the sensor at all wavelengths if
they are distributed in near surface waters. If phytoplankton are
present, the blue absorption and ti 525 nm insensitivity will be j
measured as Chi. by DR. The yellow band should respond to the particle
scattering much as if phytoplankton were non-selective. The red bands
are expected to have a similar response as the yellow, with an increased
---- ^ as prod ^c^ er-dzs r t =1es_r to :11-eface^TJi"63 nM
band is close to the chlorophyll absorption maxima at tv 680 nm
1 in vivo, and may indicate high concentrations of phytoplankton near
the surface by decreased backscattered intensity at this wavelength.
With the composition of coastal water including phytoplaniton, i Gelbstoff and observed sediment particulates, the response of the
yellow and rod bands are complex to calculate. In general, the more
effective backscattering situation produced the largest response at
r these additional wavelengths. In the 5.2 figures, increasing 1 {^
101.
voltages in red and yellow bands represent increasing reflected light
intensity. Positive voltage increases indicate a proportional decrease
in the DR ratio value. The SST trace is offset ten seconds behind
the other recordings. Visual comments are presented to help identify
features. The sensors recorded generally increasing reflectance in
both wavelengths and a decreasing 443 Tim/525 nm ratio going; onshore.
The features of both reel (663 nm) far red (723 nm) and yellow (576- nm)
bands correlated well with nearshore DR features while offshore
the correlation was not this simple. In Figures 5.2 a, c and d, the
time intervals devoid of features in the red and yellow had the most
dynamic DR and temperature structure, but in Figures 5.2 b and e,
the opposite was true, 11hytoplankton are believed to be responsible
for the former optical situations. The latter cases and the nearshore
areas of simple red-yellow-Ult correlations are suggested to be obser-
vations of high concentrations of non-chlorophyll, highly reflective
suspended particulates in addition tohytoP I p lanktotn. P earcY and Keene --
(1974) have identified water mass types in the Pacific off Oregon by --- spectral variability.ariability. Thei.r comparisons of blue to green and green
to orange in oceanic water, the Columbia River plume (high is suspended
particulates) and upwelling water (spectrally varying, but dense in
phytoplankton) support the interpretation suggested here. The
offshore, separated surface rlume on 22 August (Chl. > 0.5 mg/m3)
was observed to have decreased red (663 nm) signal in this area
(data not presented) in relation to the adjacent, region. 11earcy and
Keene (cit. loc.) showed spectra obtained over upwelling water furthest TV
102
from the influence of the Columbia River plume was characterized by the largest decrease in orange reflection of any water type. Although the broad red spectral , attenuation by clear sea (,rater is usually consid- ered to mask observation of chlorophyll absorbance at specific red wavelengths, the decrease in the red intensity noticed in this example in the SUIT study and possibly in the Oregon study suggests that chlorophyll absorption in the red was apparent. The vertical temperature and light penetration profiles of 1524 hours on 21 August
(Figure A.3a in Appendix A) were located in this feature. They show a more pronounced gradient at ti 30 m, but an extinction rate change at ru 5 m. This suggests that, the measurements made the following day were of a near surface feature. Figure S.2e is presented to show that sharp boundaries were observed in the longshore direction as well as onshore. This suggests the offshore extension of upwelling at the surface into the waters of the Canary Current. Such a feature could become separated from the coastal regime and develop as did the upwelling plume to south from 18-2Z August.
Table 5.1 lists the one percent light level depth and the attenuation percentage in the first five motors recorded by the expendable photometers, and the surface chlorophyll levels indicated by the DR at the drop site. Generally, the greater one percent light depths correlate with lower apparent chlorophyll
temperature and light levels. Appendix A (Figures A.3a-h) showsthe { intensity profiles have deflections in the extinction rate toward I decreasing extinction with depth at light levels £roar 80 16 to lSa and
j }
103
O5 August 22,1573 Char Sky, Clear Sea }'(14O F
a.a
Q5 } 0.4 — rn c^ 03— -1.0 r--s I n 0
-2.0
c
w
-3,0
-40
200
w 19° rn o Q, m t~ 0 ^ 0
Figure S.2 a-e (c:ontinucd through page 63). Comparison of co nt i nuous, a.tmulttntcocls, Sea Surfacc '1'cmperaturr (clashCd line, °C.), DR ratio values, 1 113 nm/525 nm (it; volts) and reflectance sigma-is at two wclvelengths (volts arc proportional to intensity of rct leCtOd miergy) , Local time mid visual comments are incl uded. Positio ns a nd d irection of the recordings are sh own in Figure 5.1 c and 5.1 d. t t
443nm Volts r• 663nm Volh 576 nm Y+^s ors ^ 325 n m o CD O O w w o w N V
ships A
1337 Is
1356 Claor ; 4$
a Ow
1334 i
1332 Bin LE{3 5 I
0 1!!fl{l. j
i
1O5
0.5 August 22, 1973 9. 0.4 -- CEoud Free, Visible Sediments to W 02
0.5
—110
—2D 200
.2
-3.0 19 ° El E C C
ie°
-5.0 170
,^'
-6.0
fi C E p (n t` 2
Cb ca S ^ Tma
Figure 5.2c i
443 nm Y ^ 723 nm Wts 576 nm Volts • ^ Volts N 525 nm p o O a o p O N W O — tv fJ I 1 w C7 D 1325 End ? EG 5 om a
n 13 23 N t?]
1327 NIaticeable Ptonkton ; Strips C3J 0 1326 rn
1325 --t 3_ M 1324
1323
S 1'X90
5Z5 nm NN v O ^ O Fi q`o . (D CA a cn ai — ns O u, c? D N ^ C CJ
165-6 i 1 . {D r v 1655 W v
165 Sea Stay Change
1653
Cross .LEG r 1652 f=rom 3 to: i
1.08
'fable 5.1 itcsults of Airbo: ire Expendable Photometer Study August 21, 1773
DR 10 Attenuation Sm-17 ► ce Position Light 4(2) Chloro- Local Latitude Longitude Level (l) (1st phyll Time (°N) (*IV) (111) 5 meters) mg/0 Comments
1152 27 0 34' 1,10581 23 3 0.4 SIV of Gran 1155 2.7 0 27' 14051' 17 4 0.4 Canaria 1204 27 0 09' 14027' 38 7 0.5 Line 2 1215 26 0 44' 130501 19 8 1.7 1308 28 0 29' 13040' NAM 4 0.3 1309 28 0 27' 13°38' NA 12 0.3 Line 4 131.8 28 0 15' 13024' NA 5 0.9 1332 27 0 35 1 130131 .r0 12 1.5 Lane 3 1354 27 0 53' 140081 65 S 0.3 1524 27 0 01' 15024' NA 18 0.3 Line 1 1548 26 0 21 1 1,10331 NA 8 014
(1) 10 of the initial Airborne Expendable Photometer (AXIN) carrier signal
(2) Attenuation percent of initial AXI'M carrier signal
(3) Data was not available t
1.09
i at depths < 20 meters. This depth may represent the bottom of the
euphotic zone --the vertical limit of distribution of a majority of
active phytoplankton is stable water masses. Phytoplankton and the i associated chlorophyll probably caused the increased attenuation in I the indicated euphotic zone. The, two nearshore profiles on lines 2 k -- and 3 are sites of upwelling, suggested by the cold water originating
at a depth of about 300 m. The well define:! offshore euphotic
zone boundaries were not found in nearshore profiles due to upwelling
effects. PhyLopiankton and non-phytoplankton suspended material from
the coast, well distributed from the surface to depth, and causing
high rates of light attenuation are indicated as causing the high
apparent chlorophyll measurements. It must be pointed out that the
percent light intensity given by the expendable photometers (AXPM)
is calibrated with 100% being the first value measured below
.the surface after impact and stabilization of the probe or approximately
1 meter (see Appendix A). The Secchi depth observed off Cabo Bojador
(just south of the 1548 probe on line I of figure 5.3) ranged between
S to 10 meters in April-May, 1973 (Cruzado and Manriquez, 1974).
The levels of 1% light intensity recorded by all probes was consistently
deeper than 20'm. Also, the 50% light level ranged from 2.8 m to as
shallow as 1 m in similar coastal arias CJOINT-1). 'Therefore, the
percentages indicated by the AXPMs are a fraction of the actual
percent incident intensity (10),
f
f f
110
k 2z
}
s _ 10
I 78
100 2Ua 19° 21° 0
f
I 100
UNtc ^ i.1N>= 2 14° 200' 1Z° Tainp.rature ( *Cj 7'rr 4watur• ° 300
-ucAYeveHruRA AUGUST 21,1873 30 84 CANARY ISLANDS 3o 315 Figuye 5.3 Offshore sections of vertical light penetration aRAH and temperature profiles CAHARIA 3 on 21 August, 1973. Light intensity (Int.) is expressed in percentage of initial in- cident intensity; Temperature sections analysis include
l oa4 additional profiles between the two AMI j 152 2 probe drops. Positions of I 2l^ the offshore lines of the 7*Y sections are shown in the inset map. 548 y F ill
5.2 JOINT-I I'rojecL
5.2.1 Data Analysis
The immediate analysis of the aircraft oceanographic data for distribution to research vessels (see Section 4.2) used the real-time strip chart recordings of DR and PRT-5 signals. This form of the data presented one minute averaged values mapped over the coverage area. The standard temperature analysis (SST) was 0,4°C. while the apparent chlorophyll (Chl.) analysis was made in intervals which more closely represented ocean color change. The calibration or the DR ratio
(443 nm/525 nm) to Chl. units of mg/m 3 is described in Section 3.2.2 with the calibration curve presented in Figuro 3.1. At the operational aircraft speed of 140 knots, the one minute averages translate to one value per 4.4 km. In July, 1974 the.digital micro film print-out of the sensor data at 1 second averages became available.
The preliminary strip chart analog data was compared to the data recorded by the NCAR ARIS III data system (NCAR, 1973). The final farm of the aircraft sensor data given in section 5.2.Z is from analysis of the ARIS digital output. In addition, an analysis of the data was made at NCAR,. Data was presented as 15 minute, 1 value/s plots of parameter versus time. These, graphs are on microfilm and offer a detailed comparison of parameters similar to the real-time comparison that was made from the analog traces. preliminary sea truth surface chlorophyll and surface temperature values from-diract aircraft over-flights of research vessels are included on the maps presented in Section 5.2.2, and in Appendix B. Neither the SST or Chl. i 1.12 .
analyses are corrected to sea truth. At present., the data available
allow an evaluation of the effectiveness of the DR for chlorophyll.
determination. Analysis of the solar radiation data recorded at
coastal stations and on the Atlantis 11 (Figure 5.9) was
accomplished by raking; averages over one hour periods where
voltages were converted to calories-cm- 2•min-1.
5.2.2 Description and Interpretation of Sensor Measurements
and Comparison with Preliminary JOINT-1 Sea 'truth Measurements
Of the 26 oceanographic research flights of JOiur-I, six are
described and interpreted in , this study for determination of the effective-
ness of the DR and for preliminary synoptic recognition of upwelling
events. Table 5.2 presents basic information on the 26 flights
and indicates those which are described here. Sufficient sea truth
was available for specific comparison and interpretation with the
results from these dates. .A 14 day period was covered by the G flights.
The intensity of coverage varied, with 3 flights flown in a 36 Hour
period on 8-9 March, a five day lapse, then the 3 final flights
extending over 5 days (16-21 March). In an exception to this, the
results presented in Figure 5.4 and 5.5 include all applicable sea
truth data from stations made on , 21 0 20 1 N and 21° 40% latitude during the period 8-21 March. The analyzed.maps of the aircraft research are shown in figures 5.6 a to 5.6 f. The NW coast of Africa, from
Cap Blanc to Cabo Barbas, the bathymetry of the shelf and contincnta;
slope, and a distance scale are included in most maps for reference,
113
.9 Average Shelf l Break
10 C INDIVIDUAL. STATION
j PARAMETERS AT E54°^° =o E,I ° N 1 H
MI A 16
M 14 1,3^ P
`E 12
10 1 Q,
C 8 w 6 4
2 x
~x^ _ _ ^fih — x j x ' ^x r fe 60 v Cb
40 4 0 30
24 Part, Count I g
10
0 {
E 5 10 15 20 25 30 35 .40 45 50 55 60 65 70 75 80 85 90 Distance•(Krn) Offshore Figure 5.4 Specific comparison of values of the Terlectance ratio at the clli'lc^i•enti<<1 radiometer (flit.R5/]Itr is = 4^i3 ri^it IR = 525 nm) and chlorophyll concentrations integrated to the 50' surface incident light (1 0) depth _(mgJm2), particulate counts integrated over the SO w Io depth and the 5C^ n ]o depth itself at individual stat iomv . r+,*rsus of s.bo a distance,
f i 114
3 xc^
xk^c x x Average
x \ x x
Is \ x x
14 x
'E 12 DI
10 x 1.4 U X 8 .
w 6 4 E Ch
2
^ 7a ! 1 E~ m 60 \ X
x .^ 50 X"- I x 2 ^' `x^ X x Depth I I 1 a' • 20
i0 Part: Cocnt I 4 3 a
5
5 10 15 20. 25 30 35 . 40 45 `^0 . 55 60 65 70 75 8.0 85 90 3 Distance (Km) Offshore Figure 5,5 • General comparison of values of the reflectance ratio at the differential rad 1.ometer (Im 1,41 1t , -is 443 11111 lit 525 nn) and chlorophyll concentrations integrated to the 50"a- surface incident light. (1 0 ) depth (mg/111 2 ), particulate counts integrated over the 50a 1 0 depth and the 50d to depth itself versus offshore distance.
..J
Ir adw r^ r` 17-QUN ' Il rI jl ; Flt. no_ 16, Chi. CCFrA %;► March 8,1974 a rA 950-1340 I! d/
1 r I:! [! j i
1 t tt 1 i t `^ i
t` ti 1 t 08`^ • .Fs VO . 8 l
1
to ^..—
(. 1 • ti ^• - J !1 Figure 5.6 a-f (continued through page 82). a 14 day time-series analyses of ap parent chlorophyll (mgfm 3 ) , reflectance ratio value (L443/L525) r 1 t t^ WISH SS}+AitA 1 i .• } ~.^s . . . and sea surface temperature distribu- J I MARKS tions from aircraft sensors. Each is labeled with the dare, flight number and duration (in local time to the nearest 5 mix..), and sea truth (ground truth) r .' r b • 1 measurements when available. ! z•da^f ! ' ^ • s ^ ^ zroo'ra r ! SEE f ; ! r'! ! +WER
^ t f iu.o.crtxs ^ uia^av J^zf•e q ! za ^o •a j ^o _ rs '4....._?.___ va u p ua[1Sl t G?L'1iNC
t
i e
^, Od c
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127
The position of sca truth measurements is labeled with the
abbreviation of the research vessel.. (Atlantis II - All,
Occanograplibr - OCN, James M. Gilliss - Gilliss). The flight tracts
are outlined by two-minute position paints. Intervals where
meta arologic atmospheric soundings were made, and no oceanographic
data could bo collected,have position points omitted. For
reference, the southern most flight line was the initial outbound leg,
the 21° 40' flight line was also outbound. Three analyses are
presented for each .flight. The first is the differential radiometric
chlorophyll values (in mg/m 3 Chl.), determined from calibration of
the reflected ocean color ratio of intensities at a 443 nm band/525 nm
nand (the ratio is normalized to incident ratio at the aircraft alti-
tude) to previously measured surface chlorophyll values by Arvesen
at al. (1973). The calibration curve is presented in Figure 3.1. The two analyses presented together for comparison are the values of
the reflected ocean color ratio (L /L ) mentioned above, and the 443 525 radiometric sea surface temperatures (SST) obtained from the aircraft,
not corrected for atmospheric effects or adjusted to actual surface
measurements. The total set of analyzed results from the aircraft
oceanographic research, with the exceptions of those presented in
this section, are found in Appendix B. A number of the maps are of
different scale due to occasional large-scale coverage and caution
should be used when identifying the same feature on successive dates. i
128
A detailed description or the surface oceanography from
aircraft data is not atteaapted here. Generally, a maximum gradient of
apparent chlorophyll (Chi.) was in the offshore direction, The
distribution of Chi, farther offshore was of more variable structure,
The Chi. and DR analyses in Figure 5.6a show plumes distending offshore f from the generpily longshore paralleling gradients. The larger ratio
values indicate particulate-free and low productive waters. Offshore, +
approximately to the 50 m isobath, increased Chi, distribution I ; (or lower DR ratio) was associated very closely with that of warmer i SSC regions. On the shelf, two separate centers of cold water !
(14.67 at 21°45 I N and < 14.0°.at 21°200) were observed, Low Chl.
and higher DR ratio values are associated with the center to the
north, while a low apparent Chi. feature was adjacent to the southern
cold center A thermal gradient was identified at the shelf break
on 214 4S I N latitude. Here, increased apparent Chi. was
associated with an offshore boundary of upwelled water at the surface. 1 The line 21 0 30 I N latitude partitioned this feature to the north from
the low temperature well on the shelf and the high DR value associated
(althougW not precisely) with it. This fapl are . represented an
active upwelling location. The 9 March (AM) anaiysos identify March 8 I features offshore of 50 m in precisely the same positions. Inshore of !
50 m a slight southerly shift of ocean color and SST features was {
observed. From a synoptic point of view, the patterns of the gradients ^
or boundaries have meandered, but the features have remained stationary
and gradient intensities have not developed or broken down. The large 1
129
scale March 9 PM flight gives additional coverage north to 22 0 00' 11
longitude. The increased area covered is compensated by a loss of
coverage intensity. This is why the higher Chi, region observed on
21° 90 1 N at the shelf break is not resolved in the large scale flight.
A better interpretation of the extent of the warm feature north of 21'
20 1 N and west of the shelf break is the trade-off gaiAed by this large-
scale flight,Flight Number 23, on 16 March, (Fig. S.Gd) shows a .
different type of situation. The coldest . suriace water was located
at the slope shelf boundary. Both seaward and shoreward there were
up to r%,1.5* thermal gradients. Beyond the shelf on 21° 301N
a colder region was depicted. The warmest temperatures were observed
onshore but staggered between the locations where the cold coastal
upwelli.ng was noticed on 8-9 March. Whereas the highest apparent Chi.
distribution compared to the lowest- onshore temperatures on flights
of 8-9 March, on 16 March the highest apparent Chi., in levels similar
to 8-9 March, were coincident with the highest onshore temperatures. A
small area.of high DR ratio was observed at 21° 20 1 N, 17 171W.
Thus far, all DR and Chi. analyses described this feature. Coverage
on other dates also confirmed a relatively constant feature of clearer
water or less apparent Chi. at this location (see Analyses in Appendix
B). On March 16 the thermal gradient at the shelf oreak and seaward
was in a region of very uniform ocean color. On March 19 and 21
(Figures 5;6e and 5.6f) a situation existed similar to 8-9 March.
Two, and perhaps three cold areas on the 50 m isubath were observed.
The 19-21 March, coastal upwelling was occurring in an even
narrower, nearshore band than on 8-9 March. These cold features i I I
1.30 t
were associated with higher apparent Chi, values than surrounding
waters, although onshore the values continued to increase. This was
the constant, general observation of apparent Chi, distribution.
A distribution of cooler water at the shelf break coexisted with higher
Olt values. Some ocean color fronts were visually observed,
as well as radiometrically, between 21° 21 1 N and 21° 31% P * 3011V
on 21 March. A development at the shelf region located at 21 0 401N
was monitored from 19 to 21 March. A cooler water miss beyond the
slope was oriented normal to the slope on 19 March. It was also
identified in the apparent Chi. analysis (Figure 5.6e) as a shoreward
extending . plume, The southern boyMaxy of this feature can be- identified thermally and spectrally on 20 March at 21 0 30%
(see Appendix B), On 21 March more well defined offshore gradient
structures have developed. The ocean color analyses for 21 March
showed much the same orientation as 19 March and apparently no depen- dence on the thermal development
Preliminary results from investigators presented at a
JOINT-I workshop (Friday ilarbor Workshop, 074) were interpreted . for
recognition of distinct upwelling types. Three types were discussed
and dates of the development of these events were given. Briefly,..
8-9 March was in a period designated as classical, one-cell upwelling
occurring over the shelf. lG March,.was in a period of shelf break upwolling, and 19 March was transitional type including two upwelling cells, It can be seen that the aircraft results lend support to. i ill 1 i +
131
these interpretations. The next step in interpretation of upwelling
processes with the results presented ]sere should include the time
sequence of the wind data.
More important to the objectives of this study is the inter-
pretation of ocean color chlorophyll - surface chlorophyll differences.
The constant feature of onshore increasing apparent Chl. is
presented in Figure 5.7, with relationship to specific real--time
sea truth measurements available. The plot: expresses the
difference of apparent Chl., measured by the differential
radiometer (DR), and the ship measurements (ship ground truth) as a
function of distance offshore. It can be seen from the preliminary
data, that extraordinary discrepancies existed between measurements
within 0 10 km offshore. The measurements correlated better at 20 In offshore (i.e., difference approaches 0), but diverged off-
shore of 20 km in a inverse manner from that observed nearshore
(i.e., ship surface measurements > OR Chl.) The trend is clear
although the statistical significance may be questioned with the pau-
.city of comparisons - especially inshore of 20 km. For identification
of interferences in the DR method, and to give a semi--quantitative
comparison of ocean color and parameter distributi.on,.Figureg5.4
and 5.5 are presented. DR ratio values from measurements on the 210
40 1 N and 21° 20 1 N lattitude flight lines from March 8-21 are '^I plotted versus offshore distance. In addition, the integrated
chlorophyll for the 50a incident light (I o ) depth, the 50.
T depth, and t]1C integrated parti^ l ^ ammf-c d'nr MA. I rinnth nvp . 1
10.0 yN
Y = 32.86 X'" 5.0 Corrournn CLEF = -.907
I DR-SNp iii groundiuth a (nv-rrr3) -5.0 0 20 40 60 s0 Y W C OfH-cre Distance Mn) Chlorophyll (m-/m 3 ) Distance Solar Local Flight R Date DR Shia. Offshore (km) Zero DR-Shin. Time
A 17 3/9 0.6S 33.07 36.5 5.42 -2.39 0948 +9.15 1337 Q 18 3/9 9.5-31.0 1.2-1.3 4,0 4.58 * 23 3/16 0.58 3.85 42.7 6.28 -3.36 84.4 N 29 3/19 2.5 1.62 12.0 5.96 +O.SS 103E a 29 3/19 2.5 1.03 17.0 5.96 +1.47 a 8 2/20 0.44 2.7 81.6 4.25 -2.26 1337 7.52 A 30 v/20 0.2 2.0 36.5 >8.00 -1.80
Figure 5.7 Comparison of the difference bet-ween apparent chlorophyli and actual surface measurements versus offshore distance (DR - Ship ground truth). A tabulation of data for each composition is given and is identified by the symbols. f E 1.3 3
plotted versus distance offshore. The effective depth sensed by the
DR roughly corresponds to the -<. 504 I o depth, from the preliminary
data. At the stations used for comparison with the DR signal, this
depth averaged 2 m. The 50' I o effective depth was determined
by comparison of the DR response to the integrated particle counts for
100%, 50%, 300, 15% and 1-,, Io depths irrespective of actual
chlorophyll concentration. The comparison at the 50a Io level was
determined to be the best correlated with DR values. The -results of
Figure 5.4 are from specific DR-to-parameter comparisons, while
Figure 5.5 results are the general case of all measurements made at
these distances offshore. The relationship between apparent
chlorophyll diverging from actual measurements shorcwa rd
(from Figure 5.4) is supported by the general case. The relationship of
DR ratio values and apparent chlorophyll has been described as a
log-linear function (Figure 3.1), with logrithmically increasing
chlorophyll concentrations -required for a-proportional decrease in
DR value. The relationship between individual comparisons shows an
inverse correlation between reflected intensity ratio values and
actual chlorophyll concentration to that ascribed. A positive
correlation in the individual comparisons exists between the increasing
443 nm/525 nm reflected intensity and decreasing particulate counts. S It may be established from the two figures that non-phytoplankton
particulates are responsible for the measured interference and
diminishod off ctiveness of the DR. At > 70 km^offshore, the apparent
chlorophyll exhibits a positive correlation with the actual measurements. t
f
r 134
The apparent Chl. analysis in the surface maps presented in figure 5.6 i often are observed to have increased values offshore. The 50% Io I
3 depth decreases while the particulate counts remain generally constant
with a slight decrease. It is suggested that the proportion of non-
phytoplankton particles is decreasing.
The atmospheric processes that affect the differential radio-
metric method can only preliminarily described at this time.
Additional support materials including the satellite coverage
imagery, meteorologic conditions, solar radiation measurements, Solar
standardization settings (solar zeros), aircraft photographs and col-
lected eolian dust loadings must be compiled for conclusions on atmos-
pheric interferences. p eliniation of the atmospheric interference is.
of prime importance in evaluation of IR thermal detection as swell,
and the corrections that can be .introduced to the ss'r results
presented here. figure 5.8 compares the DR solar zero setting during
periods of data collection by the aircraft and the incident solar
radiation intensity measured by hemispherical pyranometers at the
coastal meteorological stations (Station G at 21 0 28 1 N, Station 4 at
21' 18' N). The plot shows a correlation between increased
radiation and lower solar zeros. The solar zero is the offset
potentiometer reading of the 443 nn signal. This offset is used to
normalize the intensities of the 443 nm and the 525 nm used as the signal
and reference wavelengths (respectively) by the DR. Lower solar zero
settings are linearly proportional to lower 443 nm/525 nm ratio values..
From this comparison it is seen that changes in the .incident solar
1 i C _ 0
C
o^ l A ti n y^ • ^ ^ 1 Ay • • • • ti 1 Ln yy X . ^•`
1 ^ • ~ 1 ti 1^
4.0 - 6.0 8.0 10.0 D.R. Solar Zero
ure 5.8' . Relati.onship between the solar standardization se`ti.ng of the differential radiometer (DR solar zero) and the incident ratiation measured two coastal pyranometers (Langleys)_ See.text for explanation of solar zero setting. i 136 radiation were apparently linearly correlated to the ratio of intensities,
I443/1525 measured with a spectrally flat diffusor placed over the.
[lit sensor and viewing the sun directly at its solar altitude.
Thus, less diffuse scattering which is related to tale decreased blue atmospheric signal was observed at higher solar radiation levels.
This selective atmospheric contribution was normalized (I443/I525 = l} 1 by the solar standardization. 'Therefore, the deviation of ratio values from 1.0 are assumed to be due only to the reflected ocean color j signal. Also, the solar elevation has a far greater. influence on daylight spectra than variations in atmospheric conditions at the same time on different days. This is recognized from Figure 5.9 a-c. Daytime pyranometer recordings from the coastal stations and from aboard the
A 11 are presented for the time period of the flights discribed.
The solar zero settings are also included and increased incident radiation was again observed to correlate to decreased solar zeros.
The radiation curves on the coast are lower in intensity than the
recordings at sea due to the eolian attenuation onshore. The
variations in incident radiation from day to day were primarily due
to atmospheric eolian loadings. The hourly irregularities observed
were due both to clouds and eolian loading fluctuations. The description
of eolian loadings collected during this period has been presented by
l,epple (1974). Tile daylight spectra were dependent on atmospheric
particulate distribution. High loadings of particulates caused increased
extinction of the ocean color signal and increased. contribution of
atmospheric light to the DR sensor. i 137
{ An interference in the infrared radiation thermometer
(observed as daily variations in .radiation SST and actual SST differences)
was suspected to be clue to changing particulate concentrations of wind
blown eolian material from the Sahara. Differences between radiation
temperature measurements from SOD feet and actual SST versus offshore
i distance with respect . to the time of measurement and the solar radia-
tion intensity From either the coastal stations (if SST measurements
were from Gillis or Oceanographer} or the Al I were investigated. From
these correlations, interpretation of the eolian interference was
attempted. It was thought that Ssrdiffercnces offshore would be
less due to the fail-out of particulates from the lower atmosphere
j .[ti SOO feet). Ilowever, no simple relationship exists between the
SST differences and either time of measurement or distance offshore.
138
I.E x DR Sutar Zero X Ltlanllall CDORIaI sla. $ Caa1101 SILL 5 1.4
I
E + ^ p
U G e 1 Q A ^ A ^ r 0 o ,
5 .4 k o 0 i o • 0 A
F ^1 I t ! O I I 3 9 12 5 a I z 6 s 12 5 9 12 5 March 7 Marsh a March 9 March IQ
Figure 5.9 a-c (continued on page 95) Solar radiation Curves during 7--22 March recorded by pyranometers at two coastal stations (positions given in text) and aboard the AII. Included are the solar zero settings of the differential radiometer.
I
_..^ 1.39
i x OR Solar Zero
.Coastal Sic. 4 C"XII01 Sta.6 i j I.a
Y
N O i NV fl E Ns .a a U i ^ r
.6 r Y l vr
4 1 --1- - I I I 0 12 5 a. lz 5 12 5 a 12 5 March 15 March 15 March 17 Mwch la ^l4 x OR Solar Ie j ^• Atlantic IC 1.6 a Coastal Sla Coastal Sic.
X
s
e 4 7Q
• 1 N^ ^, 1 E • O h I
XY
cc e I .^
1 .2 r E i
s 12 5 E 12 5 a Iz I2 March 19 mw h z0 mwch 21 metal z2 i i
140
G. LABORAT0RY INVE'S'TIGATIONS ON INTL:PFERENCL•S
IN RADIOMETRIC CHLOROPHYLL DETERMINATION
6.1 Reflective Spectroscopy of High Chlorophyll Concentrations and
Chlorophyll-free Particulate Suspensions
Field study results initiating this investigation were that
the interference of suspended, chlorophyll-free particulates in
the near coastal waters affected the radiometric measurement of phyto-
plankton chlorophyll pigments. Reflective scanning spectroscopy of
varying phytoplankton and clay suspension concentrations was . applied
to detail the sediment effects on the spectral signature of
chlorophyll. A spectral scan can deliniate the full optical contribu-
tion. of added clay particulate suspensions to a phytoplankton suspension
and allow a more concrete interpretation of the combined effects than
can the ratio of two wavelength bands from the differential radiometer.
From particle counts in the field, it is suggested that
particle multiple scattering of light must be considered in this
region. Study as to this consequence on the optical signal leaving
the sea surface has been recommended by Jerlov (1974) and by Mueller
(1974) in a similar study.
6.1.1 Design of the Reflection Spectrometer Hyper iment
For the initial investigation on the interference of suspended
particulates, a Cary 14 Reflection Spectrometer (a prism-grating, double 1.41.
monochromator) with better than 1 nm resolution was employed to measure
the reflected intensities of very dense, multiple scattering suspensions.
A phytoplankton sample was prepared by gently concentrating (via i centrifugation) 100 ml of healthy Carteria cells (obtained from
University of Delaware's Nlariculture Project) to a 5 ml volume with a
final chlorophyll a concentration of 48,600 mg/m 3 and 11 X 10 9 . cells
per liter by direct count, The concentration of the original cell
suspension was found too dilute for meaningful spectral information
to be gained. A fine potter's clay for a standard particulate suspension
i was made by airing clays and distilled water, allowing settling of
large particulates for one Hour and pipetting off the remaining
suspension. Red and grey clay standards were mixed 1:1 by volume and
contained 124 X 10 9 particulates per liter with 950 of the particles
having diameter sizes between <1 um and Slum as determined
by a Coulter Counter (Model B). For compari. , „ . e size distribu-
tion of particulates from preliminary analys_. ,i .OINI'-1 data
showed 07% of the particulates < 10 um 4 nautical miles offshore
(Castiglione, 1974a). Because there is no river input into these
coastal waters and erosion of very reflective Sahara -type material via
wave and wind action was observed in nearshore areas, detrital
material of•a higher, broad spectral extinction was not considered to
have a significant contribution to the reflected ocean signal. This
sloes not take into account phytoplankton remains that may
possibly be a significant influence in a short time period before
dispersion by mixing. 142
The incident source of the spectrometer was normal to the
sample, and the 180° reflected signal, scanned at 2.5 nidssis
referenced to the signal from a barium sulphate cell. The spectral
region from 400 nm to 800 nm was scanned. The black sample cell itself
is of nearly uniform 0.3% reflectance over the spectral range and
has dimensions of 4.5 cm diameter by 1 cm depth.
6.1.2 Results and Interpretation
i The reflection spectra resulting from this investigation are
shown in Figure 6.1. Curve A is a record of the reflectance of distilled l water (< 1 cm deep) in the black sample cell. This curve is approximately
F of uniform reflectance and thus no corrections of the following sample
curves were made. Curve B represents the reflected spectrum of a 5 ml
(T .3 cm deep), dense sus 3nsion of Carteria (4.86 X 104 Mg /m 3 Chi. a.
11 X 10 6 counts/mi.). This curve shows increased reflection in the
visible region Q 0 , 555 nm) outside of the pigment absorption bands. max The small increased reflection at 0 450 nm was also observed in a spectro-
photometric transmittance curve of the pigments extracted from Carteria.
This indicates a decreased absorbance by pigments in this isolated
wavelength region. Three reflectance minima are seen at % 428, 475
and 672 nm. and correspond to the absorption maxima that were seen in.
the pigment extraction curve. Curves C 1 and Q are repeated scans of
a suspension of sample B (5 ml algae suspension) with the addition of
1.0 m1. of the standard clay mixture (total volume = 6.0 ml,, 29 X 106
total counts/ml.) described in 6.1.1. Curve 0 is the reflection spectrum
of sample C plus 1.0 mi of the clay standard (total volume 7,0 ml.,
43 X iO G total c./my). The spectra t r
143
A. Distilled water 1.0 4 mg/m3 E B. Carteria 4.86x10 Chl.a D ClI p. Sample B plus I.OmI of clay suspension (124 x 106 counts/ml ) 1 -E D, Sample C plus I.Oml of clay suspension 0.9 E. Clay suspension ( 31 x 10 6 counts/ml)
o 0.8 w U z E
U W 07 :._ - W
w Cl
> E !a- C? 0.6 w
i
0.5
04 i
i ?._. 0.3
41 NANOMETEI
Figure 6.1 Reflection spectra of a clot
1 7 (Curve 13), mixer! aigae--c:la) r{ , (turves C1, CZ and U) and r i
1.44
of these samples appear as an enhanced signal of the chlorophyll-
containing phytoplankton in Curve B. A shift in the green reflectance
maximum can be observed (A 0 8 nm) to a longer wavelength. A small
shift towards longer wavelengths is seen for the Q 450 Q reflection
maximum as well (A 0 4 nm). The reflection minima in Curves C 1 ,C 2 and
D are also shifted from Curve B. In the blue regions, the shift in
the minima is towards shorter wavelengths (A 0 6 nm). The red
spectrum minimum, due to chlorophyll absorption, is shifted to shorter
wavelengths in Curves C 1 , C 2 and D also. More noticeable however,
is the narrowing of the minimum reflection region at w 675 nm.
With the increased addition of clay mixture, changes in the shape of
the C and D curves are noticed. This is especially the case in the shape
of the yellow-to-orange region (575 - 630 nm) where the maximum
reflectance of the clay (Curve E) appears to be contributing to
the color of the total suspension.
The effect of increased reflected radiance due to clays in
suspension with the phytoplankton can be interpreted. The phytoplankton
suspension (Sample 8) contains the dominant light absorption character-
istics contributing to the spectral, signatures in all.suspensid samples.
This is predominately due to selective absorption of chlorophylls
-which are solely responsible. for the reflection minima at 0 675 nm.
A selective attenuance is observed for the mixed clay suspension in i Curve 5. However, the dominant optical property determining the
spectral distribution in the phytoplankton--plus-clay suspensions is
the absorption by chlorophyll Backscattered light from single 1 i i
145 i scattering events is the consequence of reflection and refraction.
Refracted light acquires the spectral signal of chlorophyll through
the absorption by chloroph lls contained within phytoplankton scattering
I, layers. In a single scattering sit uation, the large flagellate
Carteria (> 10 P dia.) would have a greater reflection/refraction
proportion at backscattering angles than if additional scattering
i events occur. An the existing multiple scattering situation of sample B.
i however, the signal at backscattered ankles has optical contributions
from a very complex light field distribution. in general, the'dominant
forward propogation of refraction scattering for large biological
particles of relatively low refractive index in single scattering
situations approaches a more isotropic distribution as the number
scattering events increase (Woodward, 1964). This increases the portion
of the refracted light at backscattered angles. Sample B is approach-
ing an optical situation where further increases in the concentration
of chlorophyll-containing cells will have little effect on
the spectral distribution by scattering processes. This is due
'r A to the loss of the dominant radiance distribution by which the process
of forward scattering was able to selectively attenuate spectral contri-
butions. However, with isotropic scattering conditions, portions of
all spectral contributions by scattering are reflected to the sensor.
Also, the high, non-selective total spectral attenuance by f: phytoplankton reduces reflection of an "enhanced" chlorophyll absorp-
tion signal.
t
• r. IA6
The addition of suspended clays to sample B increases the total reflectance of the suspension. Compared to a similar addition of phy- toplankton, the reflectance is increased because the effective refractive index of the suspension is higher. The chlorophyll in suspension with the clays is being exposed to more light per volume due to increased scattering by the clays. Moreover, the selective signal scattered_. by the phytoplankton is more effectively rescattered by the clay particles than by high, broad attenuance phytoplankton. Thus, the chlorophyll signal is enhanced in the reflected signal. In sample U, again, a higher effective refractive index per volume suspension creates an increased efficient transfer of more of the specific absorption portion of the phytoplankton extinction via clay scattering, and less of the non-selective extinction by decreasing the percentage of rescattering events by phytoplankton.
Ile spectral attenuance of the clay suspension is responsible for the spectral shifts at the reflection maxima and minima from Curve B to Curves Cx, C 2 and D. The maxima will shift to regions of lower attenuation coefficients, while the minima will shift: to the high-st attenuation coefficient regions of the suspension.
6.2 Coordination'of Differential Radiometric and 51jectroradiometric
Measurements of Chlorophyll and Chlorophyll-free Particulate
Suspensions
A second laboratory inv 147
modified for airborne use from the Goddard Space blight Center's,
New York Institute for Space Studies with the NASA differential radiometer
I (6R). A comparison of the UA response to various phytoplankton and
suspended sediment concentrations . with their reflected spectra was
designed to identify interferences in the differential radiometric method
^..' in the IaboratQry.
6.2.1 Experimental Design
The spectroradiometer has 512 channels over a wavelength range
from 400-850 nm with a resolution of 0.20 nm. The experiment consisted
of a tungsten lamp as an incident source installed 0 1.5 m above a I
12 later, 20 m sleep container painted with low reflectance black paint.
The spectroradiomctor and DR were installed above the container and
focussed at the surface-at a small angle (< 20°) from nadir to avoid surface t. , glint, and to include only the sample and not the container walls
in the field of viers, of the sensors, The DR solar standardization was __i modified for use of this field instrument in the laboratory. In this i I study normalizing of the incident intensities I443/1525 a
` (see Section 3.2.2) was accomplished from the reflection of the tungsten
lamp source on a standard white disc held horizontally.at the surface
of the sample container. The standard disc also served as the reference
for the spectroradiometcr.
'tf 148
The standard suspended clay mixtures described in Section 6.1.1 were used in this study as reflective sediment load. A chlorophyll standard. (algae mixture) had a concentration of 7.93 X 10 2 mg/m 3 Chl. a.
The algae contained in'the mixture included Carteria, Phaeodactylum
Isochrysis and ether marine diatoms. The total direct count of the algae standard was 138.5 X 10 7 cells/liter. The white clay standard had 140 X 10 9 counts/liter (c/1) with 950 of the size distribution in the < 1 . 42 }gym range. The red clay standard had a total concentration of :A, X 10 9 c/1 with 95% in the < 1-60 }gym range.
The base water used in this investigation was designed to be optically dense quasi-model of clear deep sea waiver. Water soluble food dyes (McCormick, U.S. Certified) were added until a transmittance curve of the water standard (from spcctrophotometric measurements) was obtained, which was a close reproduction of the sea water transmittance curve presented by Jerlov (1968, p. 110) for clear Mediterranean Sea water. The transmittances at the 440 nm and
525 nm regions were proportional to the transmittances (in percent/ meter) given by Clarke and James (1939) for clear ocean water.
Following the incident light source standardization, ppectroradiometric spectra and OR ratios were recorded Ivor each sample.
The successive additions of standard mixture samples were kept uniformly suspended in the container by gentle stirring until the recordings were made. Measurements of a calm, clear surface with no bubbles were recorded. I I I
1.49
6.2.2 Results and Interpretation
The particle counts and .chlorophyll concentrations of samples
measured by the DR-spectroradiometer is given in Table 6.1. Samples
of the'hl-Bq were made by successive volumetric additions of the
algae (chlorophyll) standard, The C samples are volumetric additions
of clay standards to Sample B h . Sample D, is an initial addition ..
to the clear optically dense base water and the retraining D samples
are made by sequential additions. The diffuse reflectance spectra,
referenced to the standard white disc and backscattered
to the spectroradiometer, are shown for the majority of samples in
Figures 6.2, 6.3 and 6.4. The lowest reflectance is exhibited by
the deep blue base water void of particulates. The predominate
scattering of the spectral signal is forward and lost to the non-
reflectant container surfaces. Figure 6.2 reveals the increasing.
backscattered reflectance (R) with successive algae concentration.
In the visible region, at wavelengths below 650 cur, the absorption
characteristics of the blue base water are still evident. This is pointed out when the signal from the algae standard (in a 4000 ml beaker)
is compared to the samples in the dnop blue rase water (the o reflec-
tance of the algae standard curve is reduced by a factor of 0.2 for
closer comparison with the curves 13 2 -13t). The standard algae curve and
the curves arc similar at wavelengths > ti 675 nm, indicating
little .influence by dyc absorption at these wavelengths. The algae
standard sloes show lower relative reflectance at 680-690 nm than the
B curves due to greater absorption by tho denser chlorophyll suspension. i
F
Table 6.1 The Differential Radiometer Laboratory Study
Total Total Total Total Counts Chlorophylla Concentration Phytoplankton Phytoplankton San.Dl e - Description of Sample (mg/m3) (counts/1 (Cells/1) + Clays
A Optically modelled "blue" water 0 0 0 0
Bl 500 ml. standard algae mixture (S^No 35.45 0 5.81 x 10 7 S . 3-1 x 10 f B2 1000 ml. SAM 61.18 0 11.21 x 10.7 11.21 x 107 B.. 1500 ml. SAM 92.5.5 0 16.17 x 10 7 16.17 x 107 - B 2000 ml. SXNI 118.76 0 20.75 :x 107 20.75 x 107 4 7 C1 . 2000 ml. SM 118.31 52.22 x 107 20.6, x 107 72.97 x 10 E, +.50 ml. Gray Clay Standard (GCS) 0 C2 2000 ml .. S.kl l y 100 ml . GCS 117.S7 104.05 x 107 . 20.59 x 10 7 124.64 x 107 -- - - C.. 200 ? ml, SA:IN1 } 100 mi. GCS + 1171.44 143.65 x 107 20.52 x 10 7 164.24 x 107 '. 50 ml. red clay solution D 1 Clear water + 25 ml. GCS 0 50.76 x 10 7 0 50.76 x 107 D^ Clear water + 50 ml. GCS 0 61.38 x 107 0 61.38 x 107 D 3 Clear water f 100 ml. GCS 0 121.69 x 10 7 0 121.69 x 107 D Clear water + 150 m1. GCS 0 151.74 x 10' 0 181.74 x 107 J I
^—_ } 1.0 I I_ 1 I I l I
.9 51'ANDARU ALGAB MIXTURE: 793 mg/m 3 Clit.a 15.85 X 10 8 CUUNTS/LITER (C/1) SAMPLE 841 118.7 mg /m 3 CIILa 2.07 X 10 8 C/1 SAMPLE B 3 i 92.5 mg/m 3 CIIL L 1.62 X 10 8 C/1 SAMPLE B 2 ; 64..2 mg/m 3 CIILa O.S8 X 10 8 C/1— 1...: 7 l J .6 U G Std. Algae U Mixture .5 ii
0 4
.2
t _I B482 i •I B3
400 500 600 700 800 Nanometers
Figure 6.2 Reflectance Spectra of the Standard Algae. Mixture and threv Algae Samples of Various Concentrations.. Sao 'fable 6.1 ^_ for composition of samples. i 152
Comparison in the blue region (450-490 ruri) between the standard mixture
and samples B ?.-Bt, shows that properties of the blue base medium do
have an effect on the algae samples relative to the algae standard.
In this case, the relative reflectance of the samples is increased in
this region. The B curves show that on successive addition of algae
the spectral reflectance at all wavelengths is increased in this region.
They also show that on successive addition of algae the spectral
reflectance at all wavelengths is increased although not proportionally
at different wavelengths. This is caused by the wavelength dependence
.o£ the total attenuation coefficient which affects both primary and
multipl4 scattered light. Increased chlorophyll is noticed by the
changing shape of the spectral curves in the 440-550 rvn region and an
5ndentatlon in the slope between 'L 665 nm and 690 nm. Figure 6.3
presents the spectral curves of samples B 3 and By and the curves of
algae-clay suspensions. increased concentrations of particles are
again responsible for increased diffuse backscattered reflectance.
Spectra of samples C 1 -C 2 appear brighter and are described by the same
interpretation of the optical situation given in Section 6.1.2. Spectra
of B, C and D samples are presented in Figure 6.4. The most noticeable
differences in spectral signature are observed between U curves of
chlorophyll-free particulate samples and algae-clay and algae-only
suspensions. Decreased relative reflectance in the 410-450 nm ranges
increased R in 500 - 'u 570 nm region and the decreased R at u 675 nm
due to chlorophyll-containing algae are best discerned from comparison
of curves of samples Da and Cz which had quite similar particle , f
SAMPLE BW 92.5 mg/m' C11La 1.62 X 10 6 COUNTS/LITER SAMPLE 13 4 ; 118.7 mg/m l CIILa. .2.07 X 1QBC/1 SAMPLE C 1 i 118.3 mg/m 3 CHLa 7.30 X 10 6 C/1 — SAMPLE Cy; 117.8 mg/m 3 CIILa 12.0 X 10 6 C/1 — SAMPLE C 3 ; 117.4 mg/m i CH La. 16.42 X 10 6 C/1—
cs G
Q) N^ QI
- Q N
C
iI
' I f
3 1 i t i 400 500 600 700 800 Nanometers
l WWO 6.3 Re rlectunce Spectra of lllgao S. mpIcs and Mixed Al !le. Cl n R"spanslons. Su p Tnhln 6.1 for composition of samples
E I I
{
1.54
1.0
.9
.8
^7
0
(D .6 cac U )a .5 o^
400 500 600 700 800 Nonometers
1-xgure 6.4 Reflectance Spcctrn of Algae SampI s, Mixed Algae-Clay Suspensions and Clay Samples. See Table 6.1 for Composition of samples.
• 3 i
155
.concentrations. Unlike the low refractive index of the flagellate
algae suspension studied in Section 6.1, the algae standard in this
study was predominately diatoms with higher indices of refraction
resulting in greatai effective scattering. The results presented
in 6.5 are the correlations of measured DR ratio value of each sample
with the particulate count of each sample. The solid.data points k represent the extreme of the ratio value for each sample with the open
circles representing the mode average value. Thu range in ratio suggests
that the suspensions are not stable or uniformly homogeneous. The
averaging of a number of spectroradiometer spectra recorded at
32 scans per second has reduced this instability of , the spectra
presented for each.suspens,ion. Two results from this figure are the
most significant: 1) The properties of the algae-only and algae-clay
suspensions created spectral response that are related to the ratio
value The spectral reflectance of the chlorophylls-free L443/L525. clay suspensions are not related to the spectral response of B and C
samples. 2) With increased particle counts the L443/L525
value decreased. The empirical relationships and correlation
coefficients , for both related samples sets.are shown in figure 60.
It is , predicted from this figure that the possibility exists for very f l .. high concentrations of particles that have non-selective reflectance
,E in the sea to have ratio values which would indicate high
apparent chlorophyll concentrations by the differential radiometric t j' method. Also, it can be predicted that water masses in the sea will
show a enhanced chlorophyll signal faith the OR method when they are i
i,
,
E f i 1 i
1
156
p 180 D4 A. OPTICALLY DENSE "ALUO' 15AITR Ii i : A+ S()0 ml . STANDARD AI.c^At:, ^flxTUlil: (sAe1) C3 160 13 2 :A+IUUO mI, SAM 13 3 :A+1500 rnl.SAM B4 :A+2000 in I. SARI C 1 : B4+SO nil. GREY CLAY 140 STANDARD CGCS) C2: fiq+l()o nil.. (3CS C 3 :C z+SU ml . ftf'D CLAY STANDARD o C2 o 120 D3 x Line 8 L Y;: 749 x 1026 X-20.58 100 r2=-0.984 cn U4 m 80
cl a 6.0 ' D2 Line A _... Y= 5.09 x 1033 X-26.77 40 f r?- - 0.987
DI B 20 0 • B3 o ,B2 • o 81
17 1.6 1.5
DR Ratio (14-4-3/1525)_ ..
MgUre 6.5 Relationships between Particle Co unts and Itef]ectauce Ra tio Value ChCinge for Chlorophyll free Particulate Samples, and Algae only and Algae:-Clay samples. See Table 6.1 for composition of samples
I
r li f n" _
157
I composed of phytoplankton and more reflective, chlorophyll,-free
particulates in concentrations high enough for multiple scattering
events to occur. The enhanced chlorophyll signal will be proportional
E to the total particulate counts. However,, if the reflectance spectra L` of these water masses are observed, the intensity of total backscattered
reflectance is_a simple method to identify regions of.chlorophyll-._
containing particulate composition from those of chlorophyll-free
particulate composition. Even from their spectral signature, chlorophyll-
{ free parrticulates added to algae suspensions appear undifferentiable
from algae-only suspensions under the conditions of this investigation z LJ and perhaps also in natural waters.
i in addition to the results on chlorophyll enhancing by
inarticulate scattering, the use of the blue modelled water allowed an
" interpretation of the combined effect of particulates all y dissolved
compounds with specific optical characteristics of which Golbstof£
is an example. It can be seen from the D samples that the addition of
clay suspension standard caused reflectance of a brighter blue..
r. The probability of photon backscattered reflectance to the sensor
X, can be expressed as the ratio of total effective scattering
coefficient to total effective attenuation coefficient Q = b/c).
Specifically, the backscattered signal with the s2ectral characteristics
of the dissolved Celli Sound will be increased.
y
U 158
7. EVALUATION OF EFFECTIVENESS OP THE 01P ER1,NrIAL
11AUlOME-TER FOR CHLOROPHYLL UETE-101INA'I'1ON
7.1 Com parison of Radiometric Measurements with Historical Data
and !teal-Time Sea 'Truth
Velasquez and Cruzado (1979) reported results of surface chlorophyll
and surface temperature distribution from the SAHARA-I expedition of
July, 1971. The 6-8,July cruise tract from 2491 0 N, 14.29°19 and 26.09 0N,
14.76 * W corresponded to the Sti ll coverage area from 18-26 August. The
-- chlorophyll gradient structuro'onshore tends to confirm the DR effective-
ness of chlorophyll survey. The surface values are comparable
with tho ocean color chlorophyll calibration. The surface temperature -
chlorophyll relationship described in Section 5.1.2 is supported here
as well. Many radiation temperature-apparent chlorophyll patterns were
observed to be, essentially, reconstructed in these surface results.
A consistently colder and apparently more productive region at the coast
between 26 0 20'N observed in during the Sahara Upwelling Expedition
(SUE) was substantiated by the Sahara-F results. Cruzado (1874)
reported the continuous underway fluorometric and surface temperature
distribution of the same cruise from the method described by
Ballester et al. (1972). Results were presented as parameters versus
offshore distance and one tract, coincident with the onshore flight _-
line at the southern tip of Fuerteventura, was available for comparison,
Surface temperature values were in the same range of values as those i
1 I I ! i
3.59 recorded by the lit radiometer and their distribution closely approximated that observed on 18 August, 1973 in SUE with a ON temperature increase between 9 and 5 miles onshore. The lowest surface temperature
(< 18.5°) was located 10 miles offshore and the increasing temperature distribution seaward had a small deflection toward cooler temperatures
(ti 1.0 0 ) between 22 and 46 miles offshore.r then increases again far offshore. For chlorophyll, presented in fluorescence units, increasing fluorescence was inseparably identified with decreasing temperature nearshore (within 25 miles). In the offshore temperature pattern described, the fluorescence was observed to decrease with lower tempera- tures. In section 5.1.2, low apparent Chl. isolated patches were located just offshore of strong temperature gradients on 21-26 August and are comparable features in size and ,structure to the actual measurements.
Again far offshore, fluorescence decreases accompanied increasing surface temperatures.
For similar reasons of sea truth'comparison, Szekielda (1974) presented surface chlorophyll distribution analysis from the
August 1972 NORCAMARIAS Expedition. These more synoptic results showed
surface values > 8.0 mg/m 3 0 but the same nearshore gradient structure
and structure patterns offshore as noted in SUE were depicted here
as well.
From the available, appropriate-season historical data, the
DR method .ior determination of chlorophyll levels and surveying its
distribution was apparently quite successful. Discrepancies in surface 7.60 chlorophyll-temperature correlations between Historical data and the results of the SUE study existed only in very nearshore areas where visually sediment-laden water patches (< 3 miles across) had coinci- dent higher temperatures. The significance of accompanying chlorophyll and temperature regional discontinuities were discussed by Lorenzen
(1971). The lack of pronounced chlorophyll gradients with temperature gradients suggested a biological "aging" of the two adjacent water masses. In addition, the suite of sensor-probe experiments tested in SUE was shown to be valuable in synoptic surveys for recognition of upwclling patterns and monitoring development of these patterns in a time-series such as the 18-22 August 1973 results interpreted in Section 5.1.2
Vertical chlorophyll distribution profiles of the NORCANARIES
Expedition presented in Braun and de WE (1973) supported the interpretation of euphotic zone boundary detection in the light penetration profiles. Stations distributed coincidentally to probe sites of SUE (see 'fable 5.3) showed maximum distribution of phytoplankton above the depth of deflection in the extinction rates noticed in expendable probe profiles. A discontinuity in the comparable chlorophyll distribution profiles at depths < 50 meters would cause a similar decrease in extinction rate as shown in the
AXPM profiles at < 50 m. i I I i
161.
During the JOINT-1 project all vhlorophyll (CH.) and actual
surface chlorophyll measurements showed extraordinary differences
when compared. Nearshore (< 10 km) differences showed an order magnitude
higher apparent Chl. values than actual surface measurements. Offshore
(> 36 km) an order of magnitude more actual surface chlorophylls
was observed compared to apparent Chl. (see Figure 5.7). The DR method
clearly was not effective, even in relative chlorophyll level
determinations. No pr.clitainary sea truth chlorophyll measurements available
supported the DR method in the JOINT-1 area. The multi-comparison
of sea truth parameters vs. offshore distance (Figures 5.41 and 5.5)
indicated that total particulate counts were in part responsible for the
low DI ratio values (L443A525) which corresponded to high apparent Chl.
Only at distances > 70 km offshore were actual chlorophyll values
positively correlated to any degree with apparent Chl. It should be
pointed out again, that the relationship of apparent Chl. to DR ratio
value is log-linear (i.e., a linear decrease in DR ratio value is
proportional to a logaritlimic Chl.. increase).
High concentrations of particulates in the nearshore areas
originated from blowing sand and dust off the Sahara. A
complete study of atmospheric colian loadings collected on the Cap Blanc
coast and at sea has been presented by Lepple (1974). A size
distribution gradient by atmospheric fa11-out of those particulates is
created in the offshore direction and a particle size zonation was
considered by Castiglione (1974111) for this period of JOINT'-1. A.
vertical structure in particle frequency shown in nearshore areas
1 I I I ! I I !
t
1.62 indicated an atmospheric input or phytoplankton. Total particulates did not have a significant component of phytoplankton however, as shown by the general multi-comparison in Figure 5.5 and also in a statistical correlation by Castiglione, in which logarithmic surface particle j counts/liter vs. surface chlorophyll had a linear regression correlation r = D.S. A particle nwnber distribution offshore did not strictly ^l follow the We zonation of Castiglione or Figure 5.5 and the suggested :.i compositional change from predominately eolian to phYtoplankton is well considered. In support of a change in particulate composition, comparisons were made between to surface incident I light. (I o ) depths and integrated chlorophyll (to the 1% level) concentrations for various zones determined by diWonce offshore.
For the nearshore (out to 0 11 mi offshore) and shelf stations (out to
0 23 mi offshore) increased to (deeper ouphotic zone) correlated 1 with increased chlorophyll concentrations when compared independently 1 i by zones. For zones determined as outer shelf break and offshore,
j the chlorophyll concentrations were an increasingly more important factor in light extinction with distance offshore (i.e., increasing chlorophyll concentrations caused decreasing 1% t o depths).
These calculations were made from preliminary data available from
Leg 1 (March-April, 1974) of the JOIN'NI Project, More complete integrated chlorophyll, In depths and other productivity data was 1 presented by Huntsman and !Barber (1974) and showed that Leg I data fit the chlorophyll-light penetration relationship better than later Logs
(after April 1), although the trend was apparent for the whole
JOINT-1 period .. This situation of inverse correlation of particulates . .1 1.. __ I - - -1 -
163
to chlorophyll was a rigorous test for the DR method. The historical
data available for comparison with the results presented here tended
to point out that such large quantities of chlorophyll-free particulates
over ,the shelf may have been an anamoly. Lloyd (1971) presented photic
zone depth and surface chlorophyll (mg /13 3 ) data for May and June, 1969
for ' tions positioned on the shelf off Cap Blanc, which agreed with
the established increased light extinction with increasing chlorophyll
correlation made by Lorenzen (1972). An exception (shallow photic
zone and lower chlorophyll) was observed at 'u 11 mi. offshore. Two
stations nearshore Cap Blake studied during the CINECA-Charcot iI
study (11-13 April, 1971) also show increased chlorophyll concentrations
with increasing 1% I o . Margalef (1973) positively correlated total,
particulates to increasing chlorophyll concentrations in upwelling regions
off NW Africa during; March, 1973. Similarly, Lascartos (1974) found a
strict positive correlation, of chlorophyll a and particulate concentra-
tions and also between total concentration of particulates and organic particulates in the regions of upwelling off Cap Sim (w 31 0 30'N)
during CINEGA-Charcot III (July-August, 1972). The volume percentage
of the mineral component in the most nearshore areas derived from the
coast: K 6 mi.) was w 20%,
The particulate distributions during SUE might be concluded to
be closer to those described by the historical data, and therefore the
Utz method was actually more effective for chlorophyll determination when
the concentration of high refractive index, mineral particulates was low i 164
(an onshore limit in effectiveness still must be established). When i data from SUE are compared to these of JOINT-1, the discrepancy between
the magnitude of apparent Chl. values recorded nearshore was not r
only an effect of the inherent backscattered reflectance from
the ocean, but also an effect of altitude of data collection. It was
seen from previous work (Clarke et al., 1971; and Uuntley et al., 1974) i that investigators have recognized the increased diffuse atmospheric
light scattered into spectral signals of ocean color, The greatest
blue addition was going from 500 to 1000 feet altitudes and the color
ratio was observed to decrease 0 64 with this increased optical L5404460 path. Since the JOINT-•I aircraft operated at 500 feet while SUE flights
were at 1000 feet, the apparent Chl, signal would have appeared greater,
even over identical spectral areas, at the lower altitude.
7.2 Definition and Discussion of the Interference Processes in the
Differential Radiometric Method Developed from Field Studies and
Supporting Laboratory Investigations
With the preliminary results available from JOINT-t Leg l
(March, 1974), the predominate interference to the DR method for chloro-
phyll determination can be defined. The unusual correlations of
increasing particulates with decreasing chlorophyll concentration and
decreasing depths of 1% surface incident light (1 ) with decreasing 0 chlorophyll(mg/m2 ) nearshore and an the shelf, described in 7.1, point
out the fact that chlorophyll,-free particulates, certainly a large
percent coli.nn in origin, govern important optical properties and
l
i thereby the apparent chlorophyll signal measured by the differential ^ f
radiometer. The three-factor attenuation model presented by Lorenzen
!4 (1972) which relates light extinction to phytoplankton, Gelbstoff and
undifferentiated particulate concentrations, and which was determined
{ from a wide variety of ocean waters including upwelling areas, did
not define the relationship of light penetration-to-extinction parameters
observed from JOINT-1, Leg l results. however, this did support the
unusual, if not anomolous, compositional and, thus, optical charactoriza-
tion of this region. Recognition of the compositional change of suspended r.' materials from offshore to nearshore waters can be matte from the continuous
recorded yellow, red and near 1R reflectance signals. (Figures 5.2 a- e).
Areas of large increases in these reflected intensities and corresponding
j '! small temperature changes represented a composition of predominately
coastal, highly reflective sediments. This was substantiated by
corresponding airborne photographs and visual observations. The
comparison of the continuous red and yellow reflectance with the
OR signal and SS'T's enabled a broader based interpretation of
apparent chlorophyll and SST features. However, for these spectral
measurements to support interpretation of optical properties,. a
!' greater quantitative certainty of combined effects by these properties
on the spectral reflectance in particular optical situations is required.
This can only be accomplished by optical sea truth measurements in a
region of interest and semi-empi.ri.cal modelling of these measurements
to describe a spectral signal, The same quantification of optical
properties is required for interpretation of light penetration profiles
such as those presented in Appendix A for support in defining spectral,
1 f
I 3
166
signals. Not enough particulate frequency and area distribution data are available now to do a semi.-empirical modelling of optical properAes
from actual observatio p s to reconstruct the backscattered spectral
reflectance changes observed in JOINT-1. In addition to the information
above, the fluorescent particle distributions and morphology (which
can be then related to phytoplankton), the particulate organic carbon
distribution and some quantification of Gelbstoff concentration are
needed. There have not been any successful attempts to quantitatively
interpret backscattered signals by modelling radiative transfer
calculations of optical properties observed at sea. This is also duo
to lack of essential optical property information. Simplifying models
^- have been presented for estimation of particulate Mie scattering properties
(Gordon and Brown, 1972) which consider an average refractive index
without absorption and compared well with observed scattering
functions in the Sargasso Sea. Maul and Gordon (1973) also attempted
to interpret qualitative changes in spectral reflectance in relationship
to ERTS-1 (Earth Resources Technology Satellite) spectral sensor signals.
The simplifying assumptions only consider wavelengths > 500 nm
anu A effect of particulate concentration variability. This model
is not rigorous enough to interpret the observed variability of
numerous optical properties.
It was not apparent from the field studies if only sediment
suspensions would cause the high apparent Chl. values, or if phytoplankton-
sediment mixtures were required. Gelbstoff and particulates have
been previously recognized as producing a signal nearly indistinguishable i
iS I
F ^^ 161'
1 from chlorophyll by airborne spectral measurements in coastal areas
(Clarke and Ewing, 1973) and from radiative transfer
calculations (Maul and Gordon, 1973). A conclusion from Chapter 6 i 5 ' is that Highly reflective suspended material, which are only to a small
degree solective,.causes a measurement of significant enhancement of the
chlorophyll present in suspended mixtures. It is suggested that situa-
tions of multiple scattering in chlorophyll-clay suspensions were
observed by the changes in spectral structure. The non-phytoplankton
material in the Nld African coastal waters is composed of highly
reflective material, because of the input from the Sahara. Similar
highly reflective suspensions of clays were used in the laboratory to
investigate the interference by spectral comparison of phytoplankton-
clay mixtures. In laboratory investigations, changes in the shapes
of the spectral curves were noticeable on successive additions of clays
to algae suspensions. In Section 6.1, the most concentrated particulate
sample (represented by Curve U in Figure 6.1) exhibits the contribution
of the selective optical properties of the clays. .A partial differentia-
tion of sediment interference from chlorophyll, signature in natural
waters could be accomplished if the concentrations and distribution with
depth of chlorophyll--free particulates and the entire diffuse reflectance
spectra were available. But the reflectance ratio from two -avclengths
can not differentiate the interference. In Section 6.1, two
processes were defined in multiple scattering suspensions of phytoplankton
and non-selective absorbing particulate that were applicable to explain
the DR measurements off NW coast of Africa. first, the field distribution
i ^s
3i I
1
1.68
of radiant light is changed by the fact that more isotropic back-
scattered light is "chlorophyll enhanced" because the proportion of
refraction/reflection scattering; is larger than in single particle
scattering situations (the refraction contribution containing the
signature of chlorophyll absorption). Secondly, by increasing; the E chlorophyll-free particulate concentration and thereby the effective
"white" scattering of the suspension,an "enhanced" chlorophyll
signature was produced by two means: 1) a greater number of 'white"
scattering events exposed the algae to more light which was
effected by chlorophyll absorbance. 2) The processed signal scattered
by the algae, having predominately the signature of pigment absorption,
~ was rescattered and eventually reflected.with a diminished probability
of additional scattering events involving the high, broad spectral
attenuance of phytoplankton.
lf , intermixed phytoplankton and chlorophyll-free suspended
sediments were found in a near surface distribscion in
concentrations large enough to consider muiciple scattering; processes,
the effects seen in the laboratory investigations could well be observed
in the ocean. The lowest chlorophyll concentration (in the areas of
highest particulate frequencies) still was > 1.0 mgr/ma which can be
considered a large enough fraction of phytoplankton/total particulates
for chlorophyll.--lieu particulate - phytoplankton multiple scattering;.
events and thereby an enhanced chlorophyll signal. Perhaps more i f
1.69
significant to the production of the high apparent Chl. signal are the
interactions of Gelbstokf and particulate optical properties. These
interactions could be explained from the laboratory
investigation in Section 6,2 when chlorophyll-free particulate concen- t'. trations are high. The general conclusion from observations in
Chapter 5 . and Chapter 6 investigations is that, besides chlorophyll,-
the 525 nm and-443 nm wavelengths bands are not equally affected
optical properties in multiple scattering samples or in nature where
inherent properties process the incident radiance and the diffuse
reflectance is an apparent signal which may not be unique to any one t^ optical situation. i'
Sea surface effects could be identified in the analog
recordings (see Chapter 5) as an interference to the
effectiveness of the OR method. The 30° field of view, variable
azimuth angle control and 20 0 from nadir viewing angle reduced any
glitter or specular glint addition to the'sonsor.
The atmospheric interference on the signal backscattered to the
airborne sensor can not be adequately considered at present.
Additional available data plus historical measurements of
solar radiation attenuance by pyrano:deters and sun photometers such
as those made during BOMEX (Carlson et al., 1973) can be used to define
this interference in DR methol.oby, Briefly, the ]laze and dust
frequent during JOINT-1 was considered to follow Mie theor y; thus strong
forward scattering and low diffuse atmospheric (Rayleigh) scattering
should cause the incident radiance spectrum to more closely approximate
the solar spectrum than if the sky were clear and free of co] 1.70
In these situations the :increased aerosol scattering would reduce the
fraction of parallel beam solar radiation and, in turn, reduce the
intensity and frequency of specular reflectance from the ocean's surface.
Jerlov (1974) has reported the effect of solar elevation on a i color index, nm just below the surface and at various depths l'450nm/L520 of the wafer column in differing water masses (see Section 8.3) . ills
results showed that with sun elevation < 15 1 , the blue skylight 1 significantly increased the value of the color index in a uWar water
mass at depths, while a considerably lower index in turbid water was
less effected at all depths by the high percentage skylight with the sun
near the horizon. The greatest effect in color change in the latter case was the attenuation by the water mass. In clear water, therefore,
diffuse atmospheric light, predominately blue, contributes to the
spectral character of ocean color at periods of lower solar radiation.
The solar standardization procedure could be used to measure a
defined limit of diffuse light. The solar zero was effective in normalizing the atmospheric selectivity of the reflected ratio L443/L525 from the ocean as described in Section 5.2.2 Qualitatively, a limiting
condition for OR effectiveness even with solar standardization was when
haze in the atmosphere obscured the outline of the sun. This was
determined by observations of discrepancies in apparent Chl. values
when cross-points on flight tracts were crossed at low (< 10) solar
elevation angles and then again at hillier Q 30°) solar positions.
i f 1 JJ^, d k ^ I ^
171
8. CQNCLUSiONS
8.1 Summary of Study
A differential radiometric (DR) method for continuous
determination of near surface chlorophyll levels at aircraft altitudes
continu6usly measured two narrow wavelength bands of the spectral
reflectance from the sea as a ratio value. A wavelength Highly influenc-
ed by phytoplankton attenuance (443 am) has been correlated to change
in chlorophyll concentration from aircraft measurements. A second
wavelength (525 nm) was selected for an intensity-normalizing
reference signal because of its insensitivity to changes in chlorophyll
concentrations and the additional preliminary assumptions that optical
properties of parameters other than phytoplankton do not effect the
value of the reflectance ratio A chlorophyll calibration L443/L525. from the values of the spectral reflectance ratio was accomplished
from aircraft and corresponding surface chlorophyll measurements in a
variety of natural waters. Advantages of this method include real--time
interpretation, airborne solar standardization and continuous recording;
capability.
In this study an evaluation of the effectiveness of the DR
method for mensuring and.surv.cying the regional di stribution of chloro-
phyll was made by defining limitations of successful use and by
identifying and investigating interferences in the method. 1.72
Two aircraft oceanographic Cesearch studies in a region of dynamic ocean color as a partial function of upwclling o££ the NW coast of Africa are described. A regional survey was accomplished and allowed identification. of interferences in chlorophyll determination.
The SAIIAM UPIVELLING EXP1:U1Tl0iV (swo was an experimental study designed. as a survey of surface waters with known optical,_ variability clue to high phytoplankton concentration in response to upwclling (Szekielda, 1973). Goals of this preliminary study were to
establish the effectiveness of using a differential radiometer (DR) and an airborne radiation thermometer (AIU) for simultaneous recording of surface parameters and synoptic analysis of a coastal region over a period of time. Expendable probe data and visual observations
supported the interpretation of the system's effectiveness. The DR method for chlorophyll determination was preliminarily evaluated. The conclusion is that the method was effective in measuring changing
apparent chlorophyll levels in the experimental conditions with
support for visual observations of noticeable plankton strips (Figure
5.2) and a nearly constant dependence of apparent chlorophyll change
with temperature (see surface maps of Figure 5.2). In addition - to the
evaluation, a valuable collection of oceanographic data was obtained,
the results of which were preliminarily interpreted in Section 5.1.2. it
A full interpretation of the oceanographic processes identifiable by
the data was not an objective of this study, but is a study that can
now be made with Fiore significance clue to this prior evaluation.
However, quantitative evaluation of chlorophyll determination was # ^ s
1.73
not considered, nor the quantitative evaluation of what parameters.
were actually measured by the DR.
Six of 26 oceanographic research flights of the JOINT-I
project are described and interpreted with preliminary available
real-time sea truth measurements for defining the DR method's
limitations and identifying interferences in its effectiveness in the
square operations area (20-220, by 17-18°N) off Cap Blanc.
In addition, a partial description of the synoptic time-series of
results is given for recognition of upwelling events. Analyses of
apparent- ocean color chlorophyll, ssr and the DR ratio value i Q443 /L525 are presented for all flights. As in SUE, a maximum
gradient of Chi. in the offshore direction was located in the
nearshore areas. Besides this constant nearshore gradient, Chi.
distribution farthor offshore had a more variable structure. There
was a close identification between SST and Chi. gradients although
at times it was an inverse relationship. Comparison of Chi. and
1 surface chlorophyll levels raised immediate concern about the DR
measurements. Gross differences between apparent Chi. and surface
measurements were observed < 20 km offshore with apparent Chi, levels
an order of magnitude greater than surface sea truth. An inverse i relationship existent offshore with sea truth an order of magnitude
greater than Chi. To identify the interferences in the DR method,
a multi.--comparison of ocean color ratio value (DR ratio value), chlorophyll t :. concentrations and total particulate counts (both integrated to the
50% t o depth) to distance offshore was made which shaved increasing
particulates, decreasing 500 1 0 depth and ratio values positively correlated
nearshore. Expected decreasing ratio with increasing; 174
Chl. was observed to be the inverse. A positive correlation of Chl. and
DR ratio was observed > 70 km offshore. The effective depth of measurement was not determined for all varieties of optical water masses, but was about 50' I or < 2 motors for this study as o — determined by correlation of the integration of particulate counts to various incident light penetration depths with the effects on DR response.
Sufficient data were collected for interpretation of atmospheric effects on the DR method and IR therinal measurements. When these support materials become available, complete conclusions can be made.
From preliminary interpretation of atmospheric effects oil DR method, the solar elevation was a far greater influence than atmospheric composition even in high eolian-load areas.
Two laboratory investigations oil interferences of chlorophyll- free particulates in suspension with algae employed multiple scattering samples which were spectrally scanned. interpretations were made of increased effective reflectance of the itu.pensions. When a multiple scattering situation exists the increased photon survival to the back- scattered signal in the algae-reflective clay suspensions
causes an enhanced chlorophyll signature to be produced. In optically dense (blue) base floater, successive additions of an algae standard
and clay particulates were related when sample particle cnnntS were correlated to change in reflectance ratio value (L443/L525).
Successive additions of only chlorophyll-free particles showed a similar relation of total counts and ratio change, lout, was not related i
175 to the algae-only and algae-clay mired suspensions. The dissolved blue colorant and particles were also predicted to behave in the same manner as Gelbstoff and reflective particulates in high oceanic concen- trations. It was concluded from this prediction that optical situations could exist when Gelbstoft and particulates could be undiff eren- tiable from chlorophyll even with analysis of reflectance spectra,
$,2 Summary of Evaluation
From the results and interpretation of this study the Olt method was evaluated not to be effective in determining concentrations of chlorophyll even on a relative basis due to interferences, predominately in the ocean, of additional wavelength selective optical properties and particle multiple scattering conditions. The DR method was effective in monitoring an ocean color parameter, b443A. 25' which had a distribution closely identified to SST, The parameter was not well defined but was strongly correlated to near surface particulate numbers. The 443 nm and 525 nm wavelength bands are concluded to be inadequate alone in an algorithm for determination of chlorophyll by ocean color measurements.
An increased apparent Chi. gradient, which was not due to actual increased chlorophyll especially within 20 km offshore of the NW African coast correlated far better with the distribution of total particulates. The gradient was a constant feature in the two fields studies. The DR method did distinguish features offshore that were known or suggested to be actual chlorophyll from historical data I
176
and real--time sea truth. The atmospheric interference beyond that
which could be normalized by the solar standardization procedure,
was minor compared to the interferences of processes in the ocean.
With the availability of support material, a full definition of the
atmospheric interference can be made,
Without measurement throughout the visible spectrum or at least
additional wavelengths that distinguish pre-quantified sediment: influences
in spectral reflectance, the two wavelength DR method in this
study is limited in effective use for chlorophyll measurements. To
be effective, the attenuation.of the incident light signal must be
entirely due to phytoplankton. In addition, the cell concentra-
tion must be low enough that only single scattering occurs. Suh
conditions are not the case in near coastal regions. In tact,
in productive areas, the detrital and other suspended materials may
exceed the amount of phytoplankton (as in .JOINT-1). Detailed study on multiple scattering processes and the influence on optical properties
is desperately needed. This process has been disregarded in light
attenuation and transmission studies in the sea because the small path-
length of mater measured. The laboratory results of this study have
shown that spectral reflectance maxima and minima are shifted to represent the effective scattering and attenuation coefficients of the particular optical situation. Very narrow multiple spectral bands or the entire spectrum are needed to recognize this shift. However, in nature it may be impossible to recognize spectral shift effects due to 177 illdefined optical properties. A .fact that must be recognized is; the more of the spectrum recorded, the better the ability to interpret it for identification of processes that created the spectral signal.
Ratios of wavelength bands, on the other hand; 1) facilitate data reduction and presontation and 2) allow continuous rec-rding from which small ocean color structures, sea state and atmospheric effects can be discerned and simultaneously compared with continuous .-ea surface radiation temperatures.
Although the evaluation of effectiveness of the Dlt method fr,^ its specific purpose was not encouraging, the synoptic coverage aL)proach for support in oceanographic research of dynamic regions may be evaluated as important in the recognition of large-scale, time-sequence patterns developments as demonstrated by the results of the Sahara
Upwelling Bxpedition and JOINT-1.
8,3 Recommendations for further Research on Radiometric Chlorophyll
Determination
Chapter 3 points out basic considerations for effective radiometric chlorophyll determination and will not be repeated here. The following list of recommendations were concluded from this study: 1.78
1) The total reflected intensity 011 the sea surface should be measured along with the reflected intensity and spectra of the atmosphere obtained by ground-based, upward oriented sensors for normalization of the atmospheric effect and determination of the backscattered reflect- ance for recognition of multiple scattering optical situations.
2) Detailed studies on multiple scattering processes and the influence on optical properties aredesperately needed. This process has been disregarded in light attenuation and transmission studies in the sea because the small pattt-length of water measured by the instrumentation allows this simplification.
3) Two other basic evaluations are needed to allow significant determinations to be made frojn the vast airborne data collections from JOINT-1 and SUH: the atmospheric processes and the effectiveness of lit thermal measurements. They are seen to be compli- mentary.
4) A reconsideration of the evaluation should be made when all
JOINT-1 support data becomes available including semi-empirical modelling of optical properties to the DR measured spectral reflectance.
5) The great difficulty of "fitting" reflectance spectra and inherent optical properties (discussed in Section 7.2) for an interpretation of dissolved and particulate composition of water masses may never prove a satisfactory course of action although the Monte Carlo technique may prove an exception to this (Gordon and Brown, 1173). One alternative is recognizing in ocean color signal as a parameter itself, for example, the relationship of the lilt ratio values can be compared much more easily to apparent optical properties. For example, Jerlov
J r i
1 1.
179
(1974) showed inverse relationships between color index values defined
as the ratio:
L(180°)4 45nm r T L(180 ) (8.1) 520nm
and the depth of 30% incident blue light and loo surface irradiance
of quanta (350-700 nm). Bressette (1974) has also shown that
green and yellow-reel backscattered reflectance to an aircraft
was 'inversely proportional to the Secchi depth in Chesapeake Bay. In
these cases a color index was used to optically classify water
masses and in an area where there is a limited range of variability.
G) The ultimate application of a differential radiometric correlation
method such as the one described in this study is routine coverage of
oceanic regions of interest and importance by earth satellites so
development of hydrographic parameters, recognized by semi-
conservative ocean color parameters, can be synoptically monitored.
It is recommended that further studies consider satellite application
in their design.
7) With all the radiometric sensing of Chl. work to date, it must
be realized that: the correlation between any remotely measurable optical
signature of chlorophyll in the ocean, whether entire spectra or
color ratios, is far from established. It is recommended then, that
ground truth correlations always be included for radiometric
determination of chlorophyll.
1 1
-1
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191
APPUND1X A
Corresponding Vertical Temperature and Light Penetration Profiles
From the SAHARA llP{ ELLING EXPEDITION
The analyzed profiles of the near-simultaneous recordings of air-
borne expendable bathythermographs. (AXsrs) and photometers . (AXPMs) for-
21 August, 1973 are presented in this section. 'These results,'pius
additional temperature profiles were used in the comparison of the
vertical-plane sections presented in Figure 5.3, The profiles can be
identified with the positions in Figure 5.3 by tho time labels.
Figure A.1 is a schematic of the expendable probe operation after
deployment from the research aircraft. During the dro p the probe is
stabilized by a rotochute. On impact at the sea surface the stabilizing
apparatus is released and the antenna emerges. After activation of a
sea battery the sensor probes begins its descent with signal from the
probe assembly transmitted via a single cable. The probe, with its r
zenith viewing photocell descends at a rate of 1.5 m/s for a maximum
cable length of 300 m. It is observed from the position of the probe
and-buoy at time of probe release that the initial recording of light
incident on the detoctor is that at a depth of 1 m. Figure A.2 describes
the evolution of the signal by the probe. The photocell converts incident
downward irradiance to a resistance via the prob e; electronics. This
signal is carried by the cable to the surface and changing resistance
will cause .a change of frequency produced by an audio oscillator. The
resulting audio frequency modulates a VHF transmitter and the signal i f
192
is received in the aircraft and either recorded directly on tale
(much as an R1 radio broadcast), o r the frequency is converted and
recorded as an analog; signal for real-time interpretation. Further
details on the conversion of the expendable probes from bathythermo-
graphs to photometers are described in a University of Delaware
C.M.S. technical report. No absolute calibration of frequency.to
light intensity was accomplished in this experimental study.
The profiles of AXPMs and AXBTs are presented in Figure A.3 a-h
with light intensity expressed as o I n , where n = depth of initial
probe recording, and temperature as a function of depth in meters
respectively. j
193 Drop Impact Roiachuie Retaining ring Rotochute Anienna Release Plate ^© ----Lanyard OF Antenna Retaining Spring Lanyard Retainer
F ^ ^^ rf
Stabilizing and antenna Erection Probe Descent
_-- - Antenna
Cable uncoils from probe '^^ /Ejector Springs
Probe Assembly Li Backup Place ^---- Bottom Plate
Figure A.1 -Schematic of Expendable Probe Operation
f
I I
Modified AXBT's Photocell
Probe V. H. F. Modulator Electronics i ansmitter
Data Acquisition
Frequency V.H.F Stripchart to Q.C. Receiver Converter Recorder
Tape 90 M 80 70 N 60— O e4 40 co 34 N w L;.yht Intensity Gv N Nv N 1 9 8 .^ 7 ^6. ^- m Temperature ^- .^ r w3 Ln s a _. 2— U f- a ^v rua ^ 0_. l 21 August 1973 a$ 07— 0.6— time 1524 hours n It a3 N
02 O
40 60 80 100 120 140 160 980 200 220 240 260 28:1 zoo DEPTH ( M ) Figure A.3 a-h Profiles of Light penetration and Temperature from Airborne Expendable Photometers and Airborne Expendable Eathythermographs during SUE, 21 August, 1973
i i
e p
QM 40 Nco MtD ZC Light Intensi#y
10 cq T
D^ Temperature H F 3 M —
CL 2 a ca W..:E ni N Q 21 August I973 4 a time 1548 hours
^r
o C. 021— 0 ---
0 80 70 60 50 40— 30
20
t 4 s Temperature
w r x x V wr- c z Light Intensity x z w
21 August 1973 0.7 time 1204 hours 0 03_
CM
20 40 60 80 100 120 140 160 180 200 220 240 280 280 300 OEPTH ( M ) Figure A.3c
r
1
•r so N M
2 {.0 4 30- N
N 2d wN
10 9— 0 N 7 S
_. 1-j 4 m z Temperature x X—Or h 2 S a N 0 w— b Light Intensity i 09 co as 07 21 August 1973 Qfi 0 time 1215 hours 0.4- 4
Q3
0.2 0 N 1 20 40 60 80 I00 120 140 160 180 200 220 240 260 280 30 DEPTH ( M ) Figurs A.3d so d 9
70 N 60 rq 0
NCD .n N 20 cu N N 9 O B tv r. 7 0 6 T ^- v Y r 4— wz^ z Temperature to 3 .r a w ^- 2
C2 w Light Intensity 0,9 Os 21 August 1,973 0.7 Q'6 O time 1354 hours
04 c 0.3 N 02 0
' 20 40 50 BO IOU ILU i4V Inv usv cvv ccv c-tv -cvv COW auv DEPTH (Ml
Figure A.3e
t
1 T to 80 70 so
+40 3
z0 ^. rt N N 9 o 7$" cV 6— .^U A } N rhn s Temperature x 4 ^-LO ^ 3 ^ x ^^ z 2 a U ^ N
Q
o.a 21 August 1973 0.7 Q6 Light Intensity time 1331 hours 0.s V W N
0.2 0 N i 20 40 60 80 100 MO 140 160 180 200 220 240 260 280 301 DEPTH (M)) Figure A,3f T M
Q M Light Intensity
N
.,. 9 U 7 a ^ 6 w wt a Temperature t— ^.- i wa n G ca 3 w J }- r"
7
p 21 August 1973 0.7 p time 1 1309 hours r E 1308 hours
Figure A.3g i 9 ^ ran so 70 so c 40 30 04 2fl IT N CV N 9 8 O 7 ^ t 6 co U Y- N a^ 4 tw ,a Q x er — N w 3 z aYa ^2 aN v w- J ^- O 0.9 v 0.8 07' 06—v 0a 04 ^. 0.3 N 02 O 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 DEPTH (M) Fi gure A.3h 203 Ai3PI'IsND1X Analyzed RadiomcL• ric Sea-Surface Temperature, Differential Radiometer Ratio and Apparent Ocean Color Chlorophyll Concentration Maps from the ` JOINT-I Oceanographic Aircraft Mission This section presents the analyzed data of the JOINT-I flights with the exception of six flights appearing in the text 'o£ this paper (Section 5.2.2). Bach figure number includes three analyses of the same flight. The first is ocean color chlorophyll concentr: tion (mg/m3) followed on the next page by differential radiometer (DR) ratio values at the left and sea surface temperature (SST) in °C. on the right. The flight tracks are shown by two ininute position points on each map. Tile approach to the analysis of the data is given in Section 5.2.1. A representative description of these 3 analyses for -' .G flights is given in Section 5.2.2 'Fable 4.2 gives additional y . basic information of each flight. -- - These results are included with those of the text for a report of the complete time-series of tlie.JOINI-I oceanographic aircraft mission. 1 i t 1 ! 1 . 7 1 3dw !r nrfl,, r- 1 I Fix 17, {974 f^i i s B '9 FIt. tw. I; Chl.;r I^ r 1 t w_ca ' 6 3•'` f . a Pr+T^ 835-13 0.• ^r^ ^1 4 \ !y / ^ 1 j 1 i rr ! I , I i { • 11 Il L 1 1+ j ^ Y ' T r ^t 1 . ^ ^ 11 ^` \ 1 ^ ^^^ ` S S r I, j ^' MO SRO PI o tt t t - • • ' f^• hr + %0 !i v. ^ a rcr ..^ i t t + ^ 1 ! f•► r ,f r z OWN Nil W ,x 1 f i rrr y uTA1A Mary B.1 a--c "r^.. agh 5:18 a-c i f ^ ^ ^ 11 ^^^ J Analyses of .Apparent Chloroph; ll, Reflectance Ratio ^, value.. and Sea Surface Temperature Distributions from i 1 t.o r • ^ I 1 . t -Aircra5t Sensors during the JOINT-I Project, S it ^r 17 February, to 28 March, 1974. zroa^ ^ i rf 1. ^ e^E l V;,- t i i r i4.53 4 m3ow i , irdC+r' 11 !dW! z od+^ ! ' ^4 Feb. 17,1974 / ^' ! I / Asa Febnxx y 17,1974 /AM/, r / JfI II -!F t Flt no. [,'DR ^/l a&^ Fli na. i 835^/i3 / l' ^ ^" •4 :,' R^ ^ , ^ ^ ^ ^ ^ ^ ^/ a^ "TAror+A 834-1320 ^^ ^r, « ^. ,a^ Sea Sarface,Terrq, rai'jrd 1 ! ,'` mac ^' 4TA` ^` .l %,% s t l l^ J f / Ga0 Cffi9ER9 - i r $ J ! C.=80 f.r•10 F ^ f/r r ! 8 ^ ^ ^ r r / ^ ^ o ^^ 7 q CD t t S t r f i ! .r u' 2,•^k 2l•3C`+ J, { ;` 2t-^pk ti • `. _ ` y 'rte ^ S ! !! Yf + - 1^T'. `/ ^ i ti . r , •'r l •! -cPAN"St! SAHARA j I L ,A:Sr1 RNA R=._._y I 34.53 ♦ 1 346 J ^ 1 MgUFt1 rAL.4 C^ l t i • . J ! MAURIT:A % j ^ 'ti /L4 ^i try" i k L2 / ,r 1 t 1 ^ y^j g r^ >> 1 1 : ,!! l ?T00•H ` l! O BX E J ME 1 ' I / !f aj f i I , 1 t et l i ! J LEMER 1 ^ ^ / J ! ` / J ^ ^ear I / cuaaco / - IjSt'y -0 ^ 2t^^T7lY •O l ]O !O { JiJ ]^] b , 20^1os a0 l ]D ^50 ^ ^^ _ 9., HC is ^v uo.x7iA -' G BL'JiC _ - y IJ a W uAtlu 3 CA a - rI^,SF1 J.^rr '4i+[ryYS1.++^:C! ^ f irlodw F ^rmv 1j r j^ FE18.8. 1974 Bu.so Fft no. 2, Clt,84013p J^ I J !^ M=c t /IIJ / I } ^^ 22vak _ zroc. 1 ^y L L^ /^J r^ 18 g 8 to Mao ca--en r; - --zo zv i i 4r 2^ ^^ t ♦\ I 0 ^^ .; • I, L .. r I i / t IL ^ I ' ^ I I I ♦ •I ^rschr / ^ ^ ^ t • ,^ ♦ ^ ^-zs^afr 1 y - s r ^ / rI51! 1 ! . ^ Lt2 ^ f 1 ^ 1; . 1! ^ 1 l .L^ I t J Figure B.2a-c ^ 2°'S)0 H LEVRER _ Ir Feb. 18, 074 ii i Flt no. 2, DR, 840-1`300 f tr i i Fetruery 18J974 AM ; 1 fI ^ ] ^ ^^ noa[ / fI, f ; Flight m 2 840-1300 I. _ // I - a! PJry7A GO-= r ^[++ ,^ [+ T S o Mace empprI^JI , U "TA OGRJ. . f' I/^ II / // I K.4E r 1 ! zzroax gook i—^ y 1 t _ .. _ _ . / z 1 1 ^l ^ r 1 l 6 1 ^% t {tiI ] \ ^ ` E ^A tt s ^i n c:^o c^eEea e; 1 1 =80 costa ^ , $ r r- 1348 °s s48. e Ila ,` r ^ ` 1 a f 1 14 ^ti^43 L ^ 1 ^ t ` ^ ^'^ •1^ 1 to t.^I • T 1461 l;l ^ . 1 ^ f r l .^_ s 2."3c17 ------`^^ 1 2 r 1 1 r--'132' ^ .1 f •' .1 - ^ 1 t ^ t • 1 ^ , 1 1 ^ t f l SPAMS4 SAHARA t ^M.et G7Iti7A 1 t t 1 1 NISL'RIT^Ltill1 i t ^^ dRl' i I t i l 1 ^^ } ^ r 1 1 ^ ^ ^i jF ^^^• r .. I e AM r` k8A: • f , L.EVRM ! i II / t//• f• i 111 LEvP ER } ! ^ -^• I ! 1 nowau ii 1 i O^ts•i a / in so- -+a I• se_ y ] x7.7 b / xo- I•n " 7o ao es m s 20` ri = .0 artRA C-P -ELA.NG 3 r ty a n I. AOI.>7U .y Ce7^+.NC. , ^S i zr ^ I 0Ila z,- 15.2 14.8 14B 1 1^a14B • • 158 • • Cy G•ri••r• • ON - • •^^ii L^Aws li^t^ J • • J1 J J f • f Fttna3 Ko !4.4152 t FWxuary l9P74 3, OR (PM)1230-I605 974 Sea Surfocs Temperature 605 r,-w tz- NW l 1 O--Ek-E 3ai STA H 17• v 1T A ' 17!3O^r !^ T f J7.0(7W ! • 144 I • • ' • • r 11r^20, 974 ; ME {,2 s raa ^13CU13t^ 20,1974 TAM^t E ^ BAR I' ! y Flt no.4, 1.0 ^ 2 11 . / ^, r OR 80.0-1200 ^ ;^• ROO.E Y -: ^Pq ! 'RIX2£ c "TA GCRM • ^:` p PSIRTA c bCl ^ ` Sexa St ce'^e ^^a ^^.ru^ 1/¢^,, ROOUC' I Rowe 1 ^ !f ^^^ . !jr fEc2 ^ 2Z ^tl^7 i ^ ^ ' ^ 1 22' ?2ro4N ! +r ! +/ 1}. 1 l i \ / %% `tip 1 1s ^ ^, r^^^_` • I f \ i i .r ^: $ ^r rf .• o r o t f ,rr ^fR `^ ^'^ / r ^^ 142 / ^^ ^^• f j N F^ / r f z^. ! l 15 1 iO r t2 It`.• !ir % .... ! SR=SH S H.ARA ^ ! t ♦ t 1 1 S^Av19-1 Sr.F+A RG, i . ! hML,FTSTA!•iA MC,MNT/sst' s. N ! / 144 - 144 r i, l r f f 11 \j gi rf r^ j s i t r i12 j ! 1 ^ r . ! ! /' rr r 1 p D^ E /_ aue j s Or 1 ( ! rEVMM l.EV4^3 ' j T 1 / r J j + ' r r ^„ra, AKXv>-ecv 1 ti ! j / sterns r ^ eua^oa 1 j 1 ,o^-.^recs :.vauo . - .^tTS v ! - S6 ao +o eo ea i . ozs.s w / z: as ,> sa w' i La uum a za n >a p CAP BLANC m zs a: LAmm i C.:P BLANC . :Q,avrsru'ss rs ' ^+UTsGc.lnLS i MV j !/ i7.0Cw Feh 20.1974 f csea ll^; Flt. no, 5. Chi.; 1325-1630 ROOX // 1 t G- W^TA CCf6^l CRAPOC ti i r; r t 22ooN l i^ ^,`t r ►^ ^^ i4 `1y' $ ^ t ^^ I •- u g p 3 f crag cameo ^, I^ f f 1 . O P -^ /; r y • ra 5 i ^f / ^g , I ! I I f f ; 1 \ x^ 7 N. pr — r t a •sow . /^._^ / ^ ! •^^ fit' ^ I . ^ ^ 1 i - - ! ^^ J NAURTANA ^P 1 r :^ i I tll^ ^ { ! i ^^ g ^ • ^yair ^A— • . ^ I` 7 f of Figure B. Sa-c ! ^ Jr 4^-r^ ^ ^ ' ^•oa'sa r {^ ;^, ! r ,. .f . 1 iEu ^ l i I ^ ^^ : ! r^wn^aau r t ^^ I p9.30ETF . . .1. 1.5 ' ff 20 S R r , t aow 1 I r trodx ! ` [ :oYr '.I I ! lT'nUX i i Feb_ 2R 1974 l r /I ri i^ II i Felxl xy 2019741 i 1325-16,50 J/ f^. Flight no.5; 1325-1630 CCLIC !rr f ; Fit no.5, DR; ROCUE R1 ^r ^0 Rwracaak cvw ,^ ^rll^ f^ Sea Surface Temraiur, a uuwt I I ! / / rwf.^c Q 3 ^ / J rt t l^JJ 1 i f i E I I f i^ l J/ + If/r ! r i rl' I! r I 22's70 ?2'CON r ti tti^, r ILt u ti 1, 1 `^• ^^:5_ r = g144 8 o 1-0f = r: a0 ct i5ERV f4$ • C:BO CCRSEM N V^ fir.I ^;, ^^ r - Fl • w •- 136 , J { 1E '' ^ ! } i 11 t ^ 1 ^t _t r r —^ ^ • r 7 ^ ^ ^ ^! 1 t Jr iI '. •{, 1 t aati G=am=^_ '' %^ r •~^ r rfos^A v ^ 1/ r ti 5 ^ ^.^-1 r • J ^ •- - 1 ^ y.f I 1 ^ r ^^ ^ ^ t •/ . I / . 2rC Vu ; zl^lCtf 6 R I r ! r BAiE e^ I r 14 .r r r 1 l 1 $^ / • 1 /f`• .J . •` IEVRFR lFVR£Ft 1i " 52t p{54 j !f ap.tslau • i1 1 1 I ^pr^trzn^• 'f C^^T2_^ ]o _ aea^ w { ^zlas .p r zb. ab ^ +a eb eR { ^, ^ T ar V u T u ucttA. y Cp ELA.vC a o n e a sz ua^u Ci• I3[2f C _ . rr+mW u..,a-.^«, I7^^!!w Lrr4aare.n 1 ._Ci-44L I r t 1 i i Jr.r. s.rMIL f 4 6 .B L4 3 5 cy. c..f:w. r N 2^ i1 .F 2r Fit mG,Chl RE 21,1974 3 5 815-1215 I x^Y i7• I t 1!r Fe njcry 21,1974 i I ^^ Flit nab 815-121 19' „^ Sea Surface Tervratore °' s ,^T"`°^` rf //' / t i 22roCN 1 / ^ 22'OCN- r ^^ `` t ! t\`^ ` `1 t g S _ 1 141 coo C4" CWbovr+ I _ ---- '^, fIr $V 146 142, 7 l 1 ^ ! 1 UM I . ^ r !4 tt ^qp . i J M4MFA'VA r t ti i IL 1 1 ^^ !1 Fit na.6; DR ' ^r2a .^ ^ J r A r - J Fels 21,1974 . 815-1215 .c ^ / • 1 l ^ J1 zm.H 132 r aaE cu LEVFUR ! E / ourA= .1D / 23-S ! I xo^ ao 1 i 1 f 216 2 3 10 t ^f 11 i ..^ 1 CVo lorbas ^i^j /! 7 r 1 1 • ^- / Cato Gorlaw* ^ l 1 r r t • i 1r 3 htbw ! t / 6^/ 1/ 5 7 9 t ,4^ • ,S 1.0 2 Fil. no. 7, Chi. Feb. 22, 1974 610-1140 la a w t7• r gure 11.7a oil W-4 POOj-j i ^ 1 i ,-. f• i jJii , t 219 1 . Ground Truth C qrl .arse SST = 1675. °C 22ON CMo c•r6M«ro 16.4 16B 16.4.. a s• 172 17.6 + .• _..._ ^ . • ^ FiwrfM^la 172 • . ! cap • • • / 3, ! 16.8 164 152- • • F1t,no.8 • ^• No t 1 fpm? 1335 -! -(45 16.8 • Sea Surface Temperature leew figure B.8c t . 31W !r `I iz•Pdw i 1` M=h4.I974 Gi&0 Flt nag, Chl.;1320-163,0 /r r 1 I ^f eoae a+ xrn caw o ► i f ,, 1 e r a^. , 1 I I It i ` \^, ^^^ - .t l {^ ,l.0 3 5 'r A] __'. 1 r ON `., 1 .l r y i SPt-VSH SAHARA r:T ^^ -^^i ^\ I r s ! h AURTANA 1 I I $ .6 ^, • rr ,8 I r^ ' I Figure B.9a—c ^ f' ^' ^ .tar r z-^ r a ^nx ^ i r ^ I I ^ arue !k i^ UVRM r I 1 / c`rr'''° ^^27+7 b ^ 7o 10 +a 3tl s0 n LAO=X GP8i1JiL ' '^i.urrx°^^cea xa 3 / t1 r March 4,1974 : ^^ ^f ri Ma ^a^ rch 4,,1974 PM i ^^'^ Flt. no. 9 DR; 1320-1636 ^ !! 1 1 I ! •. 1. r /I ! r Fight no. 9, i320-IFr O ! f r ww PUNTA taw i r I ! onm PUNTA, r orA Sea Surface Te WefotLT% ,,, ° + a /; l r 1 ^ ^ r i' r I S / r/ /^ i 1 lI/ I E 1 / r ^^ ^ r r^^r ! f j 1 ! - 22'DO?7 ! ^ ^' tiCV ' F x •rte— 2Z•^C,^r ; \ L1 \ \ 1\ t I t ^ t^^ !1T 1 1.6 L4 ^^1 121 Q .9 .64 3^ •^ 7 P ^ ^ ^^ a tl+ C= - i aaa coo I ! 1 r t L6 l fi ^t. 1 Gass N E1 i'- '. } pct i•.. rr / i ^ - 4 i , s . i ^' • i •1 i + ^ ^ ' ( l ^^ ^Z i l l — f i 21•-04 1 ♦ ` ^^ E • ^ . ^ll'.^ 5!,i=^,:; F • ~ r • •` SF;w`M.^ S :^YFt^ ^.. i^ MAURTAEv14 f VALRTANIA .. c l r- E / !: i i / ! t _ 1 tt 1 152 1 S , 2:'OG(N 21'00'N1.2cc6Ti ^^5 ^,. _ 2r"OON• BATE r E ! / B A!EE y !f ! f /i t 1G0 • + 1 r/ 1 r // 1 ewwa Mrae ! j !f 1 f h«x^almw 7e •^ 90 sp - •'•' / iv _ ^o^__e_o 7:x!•3 a / :^ is Y xr 4. \ xs as tsuvu } CAP BL NC u ma as u^rlcu y :"?B1st+C ' "^uttrxxui[s m Y . ^ p- . w r7• i!7 W s ,. 1 V 4-11! 2Y. QQ wmv P W" 411— 1 _V1 an y 1]. i 0464 e Do-"& t to 4'6 •^ 3 1.6 14 1 It _ - C^a C^ririira t CA" Cedw-w. ^•ti f 1.6 1 tv _ayr'Ji srY-^ •llJf 3.0" sm6wc 1.8 m witmw Ir • t ^ tt L. Il l %% !i ` ^ 11 1 • 1f 21° . r Fil-no. fD, Chf. March 5,W4 10, DR 800-1130 5, 1974 130 5f - 1T• - ure B.10 afb Cope iai•t 1 16.B 16.4 160 156 15.6 22ON s t • f ^ C•N C •rM•ir• • • • • r 1144 48 • 56 • • ^^a^i+h S•i►.c^ ^ ^ • t I^•rrf ta^ia — — — • • f 3 ^ \^ 0 r 15.2 ♦ s / r YN • 1 Flt. no. 10 16.0 • '• k1bod Ma1r-h 5)974 1 (am) 80 0 - 1130 Sea Surface Temperature 1e • w 1.7• ' ^ ^yJ ^ 1 ^ ^^ 17'OCfi^l f ^ /i it March 6, {974 i ' ^^ Fit. no 12, Chl. 800 )145 >:C%Gk r f e ' r r u-ooH ^1 ^ ^ ^^ f r ► i ti 1 , ti ^^^ ^^^ ; ► i t I ^t rt 6 8^ 5 =0 CtRDF—M t « ^ r^ •^ ^ ^ f`, `^ rte '`L f 5 t 9C ^ >'^ t .1 ^ / I r I; ' t ti '. I i lir ' I t Figure B.11a-c ^^ ti^ r ^ ' 1 r J sa^ LEVRER i s f i r f ' o,z^:e b f t ^^ •a ^ ^o w 1 r t7•t7t7w 1 II 17, col /! t ^w I^ r i . Ir aYw % l " SBA fit ! Nkrci^ 6,1374 AM `„ March 6 1374 ( i ifl i t / / ► Flight no.12 , 800-111 Fit. no. 12, DR 800,445 m i^NTALOiG f^^ ! J!^ 1 S S[3rface Temp2rafua ':o° ` —`` A ROME O I i/ i / r Ground Truth I SAI- s -i 16.137 \ r r / J f / f rr l ^ j /{ r r !!jr / / 2Z—.C+ a^ON ^`YOTM \ \ l 12 42] 1.4 1 6 2 ; \ 1148 . • ►11 1 Ln r ij z.^:N• + ' r . ^ ' { 2rsoh^^3L'rr r '• f ' [48 144 r 152 r r 141 ( ^^ t ( `' SP;.\TS4G _P1 Spy*`S}t _^• —..., ; t, { I _. r , . t. .. ' •t J "VAt^r*ITA SO / iV' RITA.N:A i 7 •144^ ^ ` t • 8 I ^ r A ^ • I ^ ^ ' i 4 r ^• r^ { ^ i r L6^ t, t t / r t ! ^ ! trt " " • I ^ ! / iI Z"oCalr f ^ ^ ^'^ ^•ddrf ! eaip r10 6AX ff L4 ! t I i^ f tEV sEFVUIIR r s i ! n^uxxreou _- rr ^ ! t 1 r ^ - i f r _ ^ f euswa r i !/ t°r`cTres' f r r xi ors f 1 a t^.a a / :: so s: 1 1is+s v / :o ^a .^ fCAP ^o ea S ^.41iGxM ;a M W - ucwu j CAPO4ANG ^ _ `° J "^w +^w .,.Y , u ,• 3a LAW '^iusnrlc° i , I 17, 3C j! ' Ix=ocw i ' !r ^ I I s^ses % Fit: no. I5, Chi. ^^ J "TA oo-m o J March 6,1974 ^ 1 i DRAKAE 1315-1700 ^ecw i r All J _ WOCIM `_ ,^ t 1 `^ 4 ro e 1.01 3 t \ t • S q ^! rAM, C^ER4 t,t lot t r W I } t ^r ' . • ^^ 1 ^ '^1.ti^51-!SCd-'BRA 'r l i ^i.^ y 1. . t ! f Figure B.12a-c r i t 2"00'N 1r 7 I BATE r ! r I^' ! a f .! 1 J ^ ^ ^wuan.as^ 1 j ! /, spa 1 1 cws+m orra +a a 7 se an .e .^ ti a m zs b uwC}tt r =P &—Pic ^^CUrt7c^tetCe r Ir 3 17-DOW t7• 'p w 11I I 17•oaw % I4 ca A"O BAR I !t ii March 6,1974 Phil ^rC ♦1 i rr + 1 Fit. no, 13, DR / 1r 1r >,} Flight no. 13.-,13-15 —1 760 1 ' anu //'r ,r+,++ 1 March 6,1974 ^^ e0 c— Sea Su Terface m^turg ♦+: ♦^ 1315-1700 tr a r + ,. ^ cc7r L ,} } % \ ,+ t ,sc ^ :ice ,so 1 \ 1^ 13 12 iLO i6e1 a ^^^, ^ `\ 37S d o ^` ^ r 1 - ,fib .' r =0 CORD .' ^ ^,. 3 I cao ca^E:eo ^ F \ t ^,. 1 + t ` i2r3C - I f • . , ii2 r 1 N'^ LFdTA%A • t r ^,,r ` • . r i ^ I • t 1 r ♦ ti ! i t 1f '^ g ^ r f 1 t I f /^ 1 ♦ Z"OpN+ ^•oClt 1 ^oo^l ♦ 1 BE EE rr j EXE t 1 j i i Ou t 1 1 / 11 1 LEVIER LEVRER NO aaa t 1 ^ ^ ! I .^s+.^ecv 1 ^vdcsSaO n^i,s , / ^ ^^in .e 1 ae t^ } 1).a,4, ^/ ?^t .a ae W' ti^ y^ t7 W LtCU[M C.•?P....ANG ^.j K+U7rJLirLL] `3 i, t F I zdw 17 OC'N 1j it, Mach l2J974 am' /^ Baas /^ I ! r t Flight no- G. 750°1035 , / .1OK W ; ; Sea Surface Terrpoaiare,,, ""'"` • WAKE O % Ground Truth / j Oce Mgrj[t}hgr 11 16,4'C 124 2)14,2-C F . 9l _ ..-3116.2 _Tctr '^ j ► ^. t7RJI^ 148 {44\ 4 -1$81.._ 2 ' S e = ti / ^• 148 `J I n E ^ 1 ^^ ^i^ N Co I r t • ' n 2E 2t°3GH ; .. ^.,.,?a 1 it > > ... 14P- ;: f ^ f t g r i 1 I it F j # r Figure B.13c t f r / / BA!£ l ; 1 !' ^ ^ L£S^IRER Ci+6+70 71K1f+ET^ t . - 7i7.s ,U / .s ' en cA 4;^ e. ,o a :s b M LAPARA S r PELXM "I 2 3 71- + ._....1. 22° I r CaN Cerfee.r n j IS N tx.+ Z6 »a Fit no. 20 ^' ► March 12,I974 1320-1640 Figure B.I4a-c Chi. I Ground Truth tSST) QB is SST = 17.2° •s I we Oftr► Oceannar_gphU 16.2° L1 LDg .Q ...... n^• 1 22 22 1.0 c.r. zK...r• w ' 1.0 0 ^• 1 1 14.8 • • 144 ' • • ^ S`rwi 51hre l r • ^'. • . 1 it i • i 14.0 • 1 t• Fltno.20 4.0R.4 h3Sw K8 I Flt. no.20 March 12,1974 ; 1320-1640 Sea Surface Temperature March, 12,1974 1320-1640 DR I i W F-^ Figure B.15 a-c I ee«fl,. I wad•s I 22 Gab 0 '^' Cyr Csrfe.re ► » 1.2 1.3 l • . I.1 N 4I68 w 172 N 16.8 t7.2 80 1 f r. 16. • t • 1' rr P-In Flt. no. 24 '• Flt no. 24 1 3h1!:,rch 16,1974 pm 1320-1450 March 16,1974 Sea Ssrface Ternperature 1320-1450 DR N W W Figure B.16a-c 9 l 3 t .• 3dAr mww 1 20 - 11 f ' 17-WW fill Flight rLo...O,D.R. 1 i CAED • 11 1 1 r I March 20, 974 AM /' XS J 1 r March 20,19T4 l ROME r' Flight no.30; 745-IC30r ,,, fI1/% 745'1IBO FL TAC pJNTA GgTA ` J Sea Surface Tempe duu re °` o It % f srLIXtE .^ ! l^ 1 D Ground Truth 1/ I O I 1 1 ^ , / ^ A11pntISIL 16.9°C ; Vi i;/ // j 1 5 I ., I 1 1 I I i r i )oH ^^oy 1 I r i . _ / 22'oat } ,y \ . yy y,y 1 yy ! ♦ ^ 0 1t t 1 LC\ 1.0 y ly y ♦ `` 168 N 4 164169= n^^yilg l\^ 168 • .°.° $ • • , 8 8 • r • [ . CS*D CMERa \e • . - ' C:3^ C^-'..E'RB N ♦ ♦ y io W f7P • 1 t ZIMN .J i k7 t • • j 1 MAURITA ^ 1 1^I ^ •r f ` • I j 10 /^ l^ rl l }. ^I Iy { ^ ^J 1 `t ! t 1 i` 1 ! ' 1 F-^ 8 i ^ eP 1 • ,a• . i r j 7 I^ 1 • ^ f 1 / t t ^ tt ^a6N ^/ 1 2"OON 4N i 1 . r ! l ` 9AIE 'f `^^ 1 J 60.E ! EU LEVRO J r tZVP^ t ^ r /l 543 b / za sb [_ !o - ^! d%j jA-mx7A 1 UP BLANC uy 7] ]7 RJICSRA C:r' E3L.l H.^. ^• a sa __ 20 a ]] ' 1fallrl[Jl. 4lF3 `D e .. ,,b a f ` /Croe Bar" it .6 •g t 2 3 Jr^1 • \ t ^` 17 ^ r ^ r 2K Flt. nn. 31 ^' ^I ►ar r March .20,1974 Fi.;ure B.17a-c 1315- 1630 Chi. t i f 1.2 1 0 .9 .8 17.2l6^ 22 • 22• J6 n !.I • • n CC" C«i.nr• C+r• corl,w • 172 r •^ • W • CON a !.2 1.2 .^. 1.2 !04 164 160 J* sw,r..a . • w.rrr.in r 14B [ 27° [ 2i° ' 1 1 4. 164 arm. Flt no. 31 [• k3.r. Flt. no. 31 , M,crch 20,1974 March 20,1974 (Pm) 1315-1630 1315-1530 Sea Surface Temperature DR. T ^.ti 17• trx :z• _ _ • ^ r 7 ^^ II f i March 28,1974; ; Ha afl,°s Fit na 34,Ch1. {anol6t r 1345-1720 'rCHCO "r. cam. GROOE \ I// f / ! Z^bO?l I f / ^p}F 1 ! ^ ^1 4 B1D 5 CAM CQIS^ f r ^ ! iv • . L`^ ..^ i 1 f^ .i .t \ ♦ I t'! II w v - \. t r ^ [ i, ^.. ^ -, I Imo► ! r t ^~ ^ t { / I ^ ^Ah=Srl fI ',t ^r •}`r ".'L - r1j 1 ! h'4:Lk'iITCd+ Figure B.18a HNE Ca 1 T ' I /^ ^r LEVRER 1 I 1 ' I Nnuo^a, I wabo ' 1 1 ^ sao•cs^es 23.5 2a !P 4 q 10 -2 a 20 a » L4W3TA i CAP O—Q C U=.ALjLCs i 1 17- 3JW MchWr 28,1974 PM^ s Flight na 34; 1345-),-/20 o nr+ra cuaa I j Sea JIr IOG2 Tefll^3i`0 e Ground Truth .I 16.05'c 1 lE'LB 1 y 16616,8 17D 1 Z f ^^,^^ i \fc ! 17. 0 '^ r {^ ^ GEs. i re f ^ tv t,J R2 GAD S^ 1r • 1 ^ j I zr30k ^ 2r^oN 170 I ^ j ^ •/• ^^ ^ ^ L ^^t s t11..2 V Figure B.18c ' ^' I troo'r1 i e I I Iss Eli E S LEVRM f r I /^ t 1 , ^ x, c.Cr^s I r-^o .i3.3 d / to !^ ^7 !e N s J v 23 » LA OLM 1 CAF D.RHC M1v KW71rJ4. 1 r