tl, Keproduced Copy OF
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FFNo 672 Aug STATES UNlTEB Interagency Report DEPARTMENT OF THE INTERIOR NASA- 113 GEOLOGICAL SU RVEY September 1968...e WASHINGTON. D.C. 20242
Mr. Robert Porter Acting Program Chief, ). I Earth Resources Survey 5 (~Aensi Code SAR - NASA Headquarters ii 3 E Washington, D.C. 20546 (NASA CR OR TMX OR AD NUMB$RJ (CATEOORYJ
Dear Bob:
Transmitted herewith is one copy of:
INTERAGENCY REPORT NASA-113
GEOLOGIC EVALUATION OF THERMAL INFRARED IMAGERY,
CALIENTE AND TEMBLOR RANGES, SOUTHERN CALIFORNIA*
Edward W. Wolfe**
Sincerely yours,
William A. Fischer Research Coordinator EROS Program
WNork performed under NASA Contract No. Vd-12589 and Task No. 160-75- W.S. Geological Survey, Flagstaff, Arizona UNITED STATES
DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY
INTERAGENCY REPORT NASA-113
GEOLOGIC EVALUATION OF THERMAL INFRARED IMAGERY,
CALIENTE AND TEMBLOR RANGES, SOUTHERN CALIFORNIA*
by
Edward W. Wolfe5Y-X
September 1968
Prepared by the Geological Survey for the National Aeronautics and Space Administration (NASA)
*Work performed under NASA Contract No. bV212589 and Task No. 160-75-01-44-10 W.S. Geological Survey, Flagstaff, Arizona FOREXORD
The infrared imagery (8-13 micron) and photography described in this report were acquired by the NASA Convair 240 on blission 8 in June 1965.
Ground data acquisition, conducted during May and October 1967, was aimed at determining the reasons for anomalous conditions revealed on the imagery; this study was part of the Geologic Applications Program Task entitled Ground Truth Investigations - NASA No. 160-75,01-44-10. Page
ILLUSTRATIONS Figure I - Index map showing major physiographic features and approximate locations of areas described and illustrated in this report. Figure 2 - Generalized geologic map of study area. Figue 3a - Pre-damn infrared image - Caliente Range and Carrizo Plain. Figure 3b - ?re-dam infrared image - Carrizo Plain, Elkhorn Plain, and Temblor Range.
Figure 3c - Pre-dam infrared image - Temblor Range, Figure 4a - Post-sunrise infrared inage - Caliente Range and Carrizo ?lain. Figure 4b - Post-sunrise infrared image - Carrizo Plain, Elkhorn Plain, and Temblor RaEge. Figure 4c - Post-sunrise infrared Wge - Temblor Range. Figure 5 - Snall sca.le asrial photograch of Tem5lor Range southwest of Fellom. ILLUSTRATIONS (CONTINIJED)
Figure 6 - Radiation temperatures measured by Barnes IT-3 radiometer at locality 13, Temblor Rmge, May 22-24, 1967. Figure 7 - he-dawn infrared image'of part of Carrizo Plain east of Soda Lake. Figure 8 - he-dawn infrared image near southeast end of Carrizo Plain. 1
Geologic E va lza t icy. G f T'ner~naI Tiif rare6 Ir.age zj-,
Caliente and Temblor Raiiges, Soukhern California
by
U.S. Geological Srtrvey
365 Middlefield Rozd, Mcnlo Park, Calif. -
ABSTRACT.
Therm1 infrared (8 to 13 micron) imgery vas obtainsd in the Caiiente
and Temblor Ranges and Carrizo Plafn, southern California, in. the pre-
dawn and post- sunrise hours of June 18, 1965 s Field observations ; measuse-
nents of moisture 2nd specific gravity of the regolith, and radiatioa
tenperaturzs; and cozparison with geologic naps and aerial photograpts lead
to the following conclusions:
(1) Th2 specific gravities of surficial materlals (iisually nnt
be&rocl! influence tonal densities in the pre-dam imagery.
(2) GeologEc interpretation of tonal density patterns is coz;licatei
by tcpggrsptic, atmospheric, and vegetative effects 3n pi-e-dan ra3iiztion.
(3) Geologic featnres sach as outcrop patterns and somo- faults ~x-2
The sexicivity of the system to microclimztic acomalies may be val;l~Ble
in aidll.;g recognition of some geologic sub t Le ---_. expression, 2 (5) Post-sunrise iniagery is dmina'ied by he pi-eferencial wzrrning
of slopes exposed to the early morning sun and resembles low sun angle
photographs.
Introductiori
Thermal infrared imgery, recording radiation from 8 to 13 microns
in wevelength, vas flow by NASA on JULEIS, 1955 in the Carrizo Plain
of southern California. A line approsimtely normal to the regfonal
geologic structure tias selected for detailed analysis and is shoi\rn in
Yigtire I. Localities at which supplemental observations were made are
Figure 1 near here
also shown in figure 1. A preliminary report on imagery from the Carrizo
Plain was made by Vallate and Moxham (1966, 1967). A published geologic
map by Vedder and Repenning (1955) was extensively used in the Caliente
Range, and unpublished mzps by both T. I?. Dibblee and J. G. Vedder were
used to evaluate the imagery in the Temblor Range.
Figure 2 is a genEralized geologic map of the area in :ihich imagsry
Figure 2 near here
-- .
was studied in detail. The stratigraphic nonenclature used on the map
and in this report is that of Dibblee (19G2). Fi 3 In the image area the Caliente and Temblor Rafiges are underlain by
steeply dipping clastic rocks of late Tertiary age. In addition, 3 basalt
flows occur within the Caliente Range sequence. The Caliente and Temblor
Ranges in the imzge area are largely mantled by soil or debris derived
from the underlying strata, and extensive outcrcps of bare bedrock are C. rare.
Imagery
The infrared images (figures 3 and 4) are line-scan displays of the i Figures 3, 4, and 5 near here
areal distri3ution of radiation intensities in the 8 to 13 microiiwave-
length band. Areas of intense radiation are relatively Light in tone;
those of relatively weak radiation are dark in tone in the images. r' Radiation intensity varies directly with emissivity and with the fourth
power of absolute surface temperature. Curvature near the image margins
is a distortion inherent in the scanning technique.
Figure 3 is an image made shortly before dawn (0506-0510 PDT) so
that the effects of differential solar heating related to slope orienta-
tion'are minimized. Figure 4 is an image made shortly after sunrise
--- (0635-0638). In this image surfaces warmed by the sun appear relatively
bright much as they would in early morning photographs. Figure 5, an
aerial photograph of the northeastern part of the imaged strip, was taken
from about 35,000 feet on a midswmer day. Figure 3a. he-dawn infrared image - Caliente Range and Carrizo Plain. See Figure 1 for location. Figure 4a. Post-sunrise inI"r3sed image - Caliecte 3xge ad Cazrizo Plain. See Figure 1 for locatfcr,
Figure L+b. Post-sunrise infrared image - Car~izo?lain,
=horn Plain, and Temblor Xange. See Figye I
..- -.,-e I ?i,nure 3c6 Pre-dawn infrared i.;..age - Texblor Xulge, . See ?ig~re1 for locatim. Figure 4c. Post-sunrise infrared image - Texblor --gee See Figure 1 for location. strike ridges on orhich bare sandstone beds arid basnlt flows are exposed.
Pebbly testure is chapparal.
(2) White line coincides with sharp break in slope at the outer edge of a terrace mantled by old alluvium.
(3) Flat to slightly concave remnants oE an old alluviated surface appear dark as do portions of nearby streain canyons.
(4) White line coincides with strike ridge on which the uppermost of three basaLt flows forms a bold outcrop of bare rocI;.
(5) Some strike ridge as 2, but here, where the white line is in- distinct, the basalt is rnan'iled by soil 2nd rubble.
(G) White line corresponds to bare outcrop of hai-d, li ght-colored mudstone to sandy mudstone. Adjacent bcdi-oclc i!ic?ntl.i-!cl by soil.
(7) Dark band corresponds to thc! outcr~pof the QuaLal Formation, (8) Small dark patches c9rrespcF.d to outcro?s cr' reGdlsh-bmvn
expandiilg clay In hhralcs Forixst.ic;n. The bcrci3ring rna~erfzlsgivir,g
brighter tones are sandy soils developed on th2 ?IorE;ies FDrnation and
deposits of sarziy and gravelly allu-riu~that veneer all but the $.mall
areas represented 3y the dark spots.
(9) Low hill underlain by claystone, sandstme, am? 'conglomrate of
the Mcrzles Formation;'boundeS by broad alluviated areas. In. post-sunrhe
- imagery the hill is more distinctly outlined because of preferential heating
of slopes exposed to the sun.
(10) Small hill, a few feet high, relztively bright, lies within a
'dark region that corresponds approximately with the lovest part of the
Carrizo Plain in the image area.. Inages show agricultural fieid patterns
Hnc? fan pattsrns vhere 'intermittent streams deboiteh onto +he broad
alb.wi.nted Carrizo Plain. Beczusc the Carrizo Plzin is nearly flat, there t. is a&ost no preferential solar heatlng, and the post-suniise image c13seaiy
resenbles the pre-davm imap.
(11) Dark spots represect accumulations of tum5leweeb against a
fence at the northeast edge of the Carrizo Plain.
- (12) Nortt:.rest- trending trench alogg recently activc? trace of San
Andreas farrLt. Well drained grrlly boitons, includins t'rn, trench along
the fault and the fine gullies forning a filigret-pattern CR low ridze -- . southwest of the Eeilltr, appear jright, 6 (14) Bittematez Creek Shale in contact to northeast witi very coarse conglomerate of the Santa Margarita Fornation. Coa@oner&te and alluvial apron that bounds it on the sou$hh.iiest are bright and contrast sharply with darkly imaged Bitterwater Creek Shale, Note that in aerial photograph the contact between Santa Margarita conglomerate and alluvium is readily apparent.
(15) Outcrops of downfolded Bitterwater Creek Shale dark; bright in aerial photograph. Geologic map (figure 2) portrays distribution
of sandstone and shale mapped together as Bitterwater Creek Shale. linagery and aerial photograph, on the other hand, display shale facies in sharp contrast to surrounding rocks whether they be Santa Margarita Formation, a sandstone facies of &e Bitterwater Creek, &r the alluvium of the Eurhorn Plain.
(16) Sharp radiation contact coincides with a fault separating
Monterey Shale to the northeast from Santa Margarita conglomerate and
a sandstone mapped With the Bitterwater Creek Shale. The conglomerate and the Bitterwater Creek sandstone, inseparable in the imagery as well
as in the aerial. photograph, contrast sharply with the Monterey Shale, which is dark in the pre-&wn image and light in the aerial photograph. (17) Broad dark band occurs in an area underlain by Monterey Snale,
shale and sandstone of the Temblor or Vaqueros Fo-mtion, and a sandstone
unit a%the base or' the Santa bhrgarita Formation. Within tine band, shale is the pedon6nan-t Litholow.
(18) Contact beween Nonterey Shzle (dark in image, light in aerial
photogrqh) and overlying Santa Yar=l,rita Formation (ligit in inrage,
dark in aerial photograph). 7 (l?) Radiatiozl boundary at northwestern limit of con~?cn~r~tefacies
(light in image) of the Smtz FIargarica Forrnatioil rjithiii the iiliage area.
Farther northmst within the icage area tt;e Sants Xsrgn:i ta Fosix~tioil
consists predoninzntly of friable sandstone (dark In insge) -.;ith rare
granitic or natamorphic bouMers. Conglomerate .facies darker in aerial
photograph than sandstone facies.
(20) Sharp radiation boirndarjr coincides with crest cf Tsdlor Rairge.
-1nmttdiately northeast of the rmge crest Santa Xargarita conglomerate,
!Nedia Shale, and the Temblor or Vaqueros Formations all appear bright.
Most of the slope for about a miie and a half northeast of the rmge
crest in. the imege area is underlain by grass-covered Monterey Shalo,
colluvium th2t appears relatively bright.
(21) Dark band coincides with prominent, ste2pJ scuthwest-facing slope* nearly devoid of vegetation. It Is underlain iil part by diatomlte nappe8 by Dibblee as Reef Ridge Formation (fLgure 2) and In part by
Monterey %ale.
(22) Sharp radiation contact between Xsef Ridgz diatcrcits (d2rk in
image, bright in serial photograph) and ovsrlying Sants Pfargarits ccogIoracrat2
('oright in imge, Sark in aerial photogrzpii) .
(23) Small dark spots coincide with wiadovs in srivel colluvium, 8 Intensity or' pre-dam infrared radiation in the Temjlor Rang2 is
apparently related in part to slope orientation. Borth-facing slopes
tend to be relatively bright; south-facing slopes tend Lo be dark in the
pre-dam imagery (fipre 3). "lie largest topographic feature showing
this tendency is the crest of the Temhlor Range. Near locality 20 a well -_ define2 radiative bourtdary seyarates similar lithologic types at the range
crest. The northeast flank of the range is relatively bright, the southtrrcst
'flank relatively dark. A few other examples of this tendency, denoted by
letters in figures 3, 4, and 5, are listed below:
a. steep north-northeast-facing hill in liionterey Shale bright in
* pre-dawn imagery (figure 3); stidkingly warned by early morning
sun (figure 4).
b. hill underlain by basal sandstone of Santa tfargarita Formation
dark on south side, bright on north side in figure 3.
c. gullied area just southwest of range crest, southeast-facing
slopes dark.
d. three small ridge crests on northeast flank of range; all dark
on south side and bright on north side in pre-dawn image.
e. steep northeast-facing canyon walls with5n dark bad at Locality
21 brighter than nearby southliest- €acing slopes; a11 ~ndeyleiii
by diatomaceous Xonteray Shale. 9 Ground measurements
In an attemyt to find systematic relationships between ground con- ditions and tonal densities in the pre-dawn infrared hge, raciiation temperature, specific gravity, and moisture data were collected late in May 1967. According to Weather Bureau records, no rain fell in the area in Way or June prior to IR flight on June 18, 1965. Rainfall in April 1965 was approximately 2 inches both east of the area at Pnaricopa and west of the area at Cuyama. In April 1967, 1.85 inches of rain fell at Maricopa and 2.82 inches fell at Cuyama.. During &fay 1967, 0.02 inches fell at both Cuyama and Wicopa approximately two weeks before the ground data were collected. In spite of the slightly wetter weather in the spring of 1967, the ground in hte May in 'the area, of figures 3, 4, and 5 seemed thoroughly dry and grass cover was brawn. over a period of h;a days and thrse nrgiits frm N2-y 22 to 25 at t:jo 3ii-
ferent sites near coqtacts bet:..reer. Bitterwater Creek Shale and alLuviu.il
(locality 13). Infrared radiation; the quartit:. maastired by the radlorc-.t*r--I
varies as e:nissivity and a’s the foctrtil power of Zhe absalute teinperature. 4 w = &5T t? = total radiatior. per unit area (8-13 m5crcn radlatior,
in this case)
e = emissivity
0. . T.= absolute temperature ( K) cr = a constant
Emissivity of an object is the ratio of its emittance (radizct energy
ernittd per unit area) to the emittance of a perfect ridiatat- (blackbdy!
at: the same teiaperature. Blackbodies exist iri thecry only; real Su3sZail have emissivities smaller than 1, . The radionzter meiisuros emittaice; 5:;~ indicates a temperature scale based on an ernLssiv~q-oE 1. 32~2~s~ natuxl miterials have emissivities smaller thm 1, radis tiorr teqeretur2t are. lover than tree temperatures. Ir. th.e toapeiztuta range in vhich this study was made, a chzogo, cf .OS in euissivity €or high zmissivities prodilz-ls 0 a change of about 4 C in apparznt tem2eratare. Greater distortlci: occurs -- 11 Laboratory radiom2ter measurements of large samples of surficial material collected from Ijitterwater Creek Shale, Santa Z’iargarita congloncrste (cobbles and boulders excluded) , Morlterey Shele, Reef Ridge diatomite, Quatal Formation, 21orales Formation, and alluviurr, of the EL1:horn Plain suggest that differences in radiant: emittance are noc cause2 by emissivity -_ differences related to the compositions of .the soils. Radi.-.tior. temperatures of the samples, which stood for several weeks in a wrriizlly 0 heated room, were all within 1 C of each other, with a systernztic varie- ticn thzt was apparently ralated to position in the room rather thrin to 0 lithology. The apparent ternpsratures (near 72- F) approximate roan temperature and suggest that all of the sarqles h2d high emissivicies. 12 Figure 6 displays radiation tznpsrature data collected on typical gias s - cose r ed sandy alllrvium arid on barren soil developed on Eittemater Cree!< Shale. The same relatioii;I:iy, wich Bittemater Creck Shale appearing colder bcth day and night, was later rzpeated at a s2cond site. Radiation from alluvium with relatively sparse grass cover and frcm Bittenrater c. Creek Shale vith sparse grass cmer was in;ermediate between the extrexes of barren Eitterwa ter Creek Shale and typically grassy alluvium both day and night. Single boulders in the alluvium were slightly more radiant in the pre-dam hours than the deposits that included them, The radiometer measuremznts show that t€ie radiation patterns recorded in the iiiiager:; are reproducible and suggest that physical properties, such as specific. gravity and moisture coctent, that may have affected radiance when the images were made, were also effective in ?*lay 1967, when field observztions wcre made. ' - Figclre 6 near here 1.3 Densities and moisture contents of representztlvc surficial nsterials were determind. ' ApprosixareLy 1,000 cc of soil fro3 tile uppermost two inches were carefully collected and imwxliately veighed. Volune was determined by filling the excavation with a measured quantity of sand, and density vas computed. Noisture content was dcltc?rmined by cor,i?arlng 0 the sample weight after'several days cf drying ail 110 C with its veight at the time of collection. Surficial materials developed on sandy alluviun, sandstone units, and on Santa Xargarita conglonierate (co3bles and boulders excluded frcn measureaents) range in density frcm about 2.3 to 1.5 and in moisture content from 1.6 to 2.8 per cent. Surface materials representing shale units range in density from about 1.0 to 1.1, and their moistatre contents rang2 frorr. 5.3 to 8.4 ?er cent. Th= spzcifie gr,ivity of diatomita surficial debris froin the east side of the Tcablor fi;.njP (locality 18) is about 0,9. X-ray data show that much of the shde and mudstone is montmorillonitic; the high moisture coatents may re?reseni: water driven from the clay mineral structure by heating rather thzn higF accumulations of pore vater. In late May, soils irr the area of figrrres 3,.4, and 5 looked aod feli thoroughly dry. 14 Sy~lthesis Comparison of the pre-daun image, the aertal photograph, and the ground data suggest that intensity of pre-dam radiance may be relzted to specific gravity of soil, vegetative cover, reflectivity, slo?? orienta- tion, and tzicrocliatic effects as sumarizecl below. -_ Low pre-darn radiance High pre-darm radiance low specific gravity high specffic gravity (approx. 1.0) (approx. 1.3) little or no grass cover relatively thick grass cover bright ir! aerial photograph dark in aerial photograph (high reflectivity) . (low reflectivity) slope faces south slope faces rrorth ?' entrapment of cold air ... Soils developed on shale, mudstone, and diatonftt? have Low specific gravities (about 1.0) and ordinarily are dark in the pre-dam iitizge (1ocalitTes 7, 8, 13, 16, 15, 15, 17, 18, 21, 23, 24). Thz saine soils generally support little or no grass cover and reflect sunli&t relatively intensely as shown by the aerial plmtograph. IR contrast, soils devzlsped on Santa Xargarita conglomerzte, most sandstone units., ZR~sandy allcvium have higher specific Sravities (about 1.3) and tend to be btlght in the --pre-da.n image (localities 5, 14, 15, 16, 18, 22). They sxpport nore vegetatLon than :he sh21es ami reflect Less sunlight as shosa by their - darkn-?-ssin the aarial phctosraph. In dddiri-crr, south-facfrig stclpis tend to be less radiant iIz the pre-dar.,~ itit;zZ than nr-th-facing4- slo?es. :fet-.ce: the intecsity of pre-davn rat-?i~~.cefrom any- surface nay be controlled 3y several factors. Xicroc1Fm;tic EEZ~C~Srelatx? to noctu:=nal decsity stratification of atr appirzzZ2y pi~odcc2c;cIdiiior;aL Locs?. radiative anomalies that are discrrsse:! lzter. resistance of its surface t3 temperature change. Thermal inertia = K?C K = thermal cond:icFivity p = specific gravity C = specific heat Surface inaterials with high therrnzl inertia react slowly to external ternperatme c5anges and, other factors being equal, should be wilrm~rin the pre-dawn hocrs than surficia? natetials with low thema1 inertir;. Ma t e r i a 1s vit h h i gh therna 1 co ndu c t ivi t y - t r 3n s ml t hea t re12. tiv z I y easily md change in surface temperature relatively slo~ly:-n resl;onse to a change fn external temperature. Air, water, arid solid rock kicraasi in thermal conductivity approximately in the ratio 1:25:?0. Eencs dry porous material has relatively low themal conductivity'ar-d the surface tc;ir.pera- ture changes quickly in response to external tern2erature changes. Sr,aci?lc heat, a measure or' heat input necessary to produce a given tengsxture increase, is about five times 2s high for water as for air or mineral grains. Insofar as sp. inverse relation exists Setsreen syeciEtc grPvity and porosity in the surficis 1 materials of the image area, thernzl concluct:ivLty~ tilerm?L +--inertia arrd, hence, Fre-daw- rzdiance increase wlth spaciELc grzvizy. 16 In addition to the r2lations3ip previously noted between soii of lcw specific gravity and low pre-dawn rsdiance, the foLlcwing obscrvations support the correlation between specific gravity and pre-dawn radiance : (1) Outcrops of bare bedrock (localities 1, 4, 6) vith specifcc gravities inuch higher than those of: the surrounding soils ars displayed in the imagery 2s bands of high pre-davn radiance. It should be noted that a sinilar band (locality 2) apparently coincides only with a sharp break in slope. (2) As indicated by radiometer measurements in the pre-dawn hours, single boulders were slightly more radiant than the unconsolidated alluvium thzt surrounded them. (3) Tumbleweed piled along a fence at locality 11 forms a,surficial material that, because of its extremely low specific gravity and high porosity, has low therrnal inertia and appezrs dark in the pre-dam itnage. (4) Wallace and Noxham (1966, 1967) showed that unplowed fields in some other Carrizo Plain images were brig5ter in the pre-dam thm plowed fields. Plowing, by increesing the porcsity and lcwering ihe speclflc gravity of soil, lovers its thermal. inertia. 1-7 Grass cover and reflectivi~y,--Ra~ometermeasurements (figme 6) in late Y3.y shoved that Bitterwater Creek Shale at locality 13 vas less radiant than the adjacent alluvium both day and night, an unlikely situation if thermal inertia were the sole controlling influence. Perhaps vegetative cover and (or) reflectivity influence radiance in one of the following ways* (1) Figure 6 shows radiometer measure&ents on typically barren shale and on typica,lly grass alluvium, Radiant temperatures on slightly grassy shale and on alluvium with relatively thin grass cover were intermediate between the extremes shown in.figure 6. Gates (1964, p. 576) states that all plant surfaces have emissivities of 0.95 or greater andmost leaf emissivities are 0,sto 0.98. It may be that the grass-covered surfaces are slightly higher in emissivity than the barren surfaces. Under the existing conditions an increase in emissivity of O,O5 would 0 produce a radiant temperature increase of about 4 C, a temperature difference consistent With the radiometer results. photograph , absorbs less heat' theE the surrounding all~vfurnin the daytimz because of its relatively intense reflection of solq radiation. Eise- where ia the study area, scuth slopes underlaih by shale tend to be relatively barrer, and to reflect solar radiation more intensely than adjacent: areas underlain by Sandstoile, ccngloncrate, arid alluviuia. The barrer! sha1.e~; in addition to absdrbing less energy from incoining solar radiation, may cool more rapidly at night because of relatively low thermal inertia. Probably thermal inertia, vegetative cover; and reflectivity interact complexly in controlling pre-dawn radiance throughout the image area. Slope orientation.--North slopes in the Temblor Range are mere radfant in. the pre-dawn tniaga than nearby south slopes mderlafn by similar lithologies. In some places, vegetation is nore lush on north slopes than on south Ones, but the relationship is noir consistent. Untested hypotheses include the r: possibility that slightly higher- moisture content in soils on north slopes nay have caused slightly higher tiieraL irlcrtia or that atmospheric interference such as high clouds to the north at thz tima of thz flight could have Lmpedec? radiation to space froox the north slopes. 10 Kicrocl5n.ati.c effccts .--Ir, zddition to the influencFs of SiJecific gravity, vegetative cover, and slope orientation on iitiage tonal dznsities, microclimatic effects related to Local tcpographlc fegtures aiqxcerrtly influence Fre-dawn groulic! temperature and cause radiative anornaiies . Lov pre-d2v.m. radiance at localities 3 and 10 is attributed to riocturnal accum- latlor, of cold air on poorly drzlncd ground surfaces, a phenomeilorl exten- sively docunenced by Geiger (1957). The diamond-shaped dark area at locality 3 in figure 3 is a flat surface, or possibly even a shallow closed depression, partially enclosed by surrounding hills. The surface is underlain by old alfuviun, which is sandy arid closely resembles in both texture end vegetative cover other alluvial deposits that appear bright in figure 3. The suggested interpretati-on of the diamond-shaped area is that it represents an area in which cold air accurnulates preferen- \ tially at night and the surface beneath the colder air becomes slightly fl- cooler thaa nearby surfaces. A similar interpretation is sxggested at locality 10, where the dark region in the image coincides approviniately with the lowest part of the valley floor in the inege area. A s&li hili projecting through ths colder 2ir strata is slightly warmer and appears brighter in figure 3. 20 Gullies at locality 12 appear bright in pre-&xm image, and surface temperatures were no doubt warmer than on the adjacen-t; interfluves. Although they are local topographic lovs, the gullies may 'De t.~elldrained relative to air flow so that they do not permit development of the stagnation by which a thick cold air layer accumulates. The hypothesis that entrapment of cold air causes radiative andies was documented in as1 effort to test the suggestion that sorne dark anomalies ,in pre-dawn imagery represent high soil m.isture (Wallace and Moxham, ,1966; Sabins, 1967, p. 749). Two areas cited by Wallace and Moxham as places where low radiation might reflect high soil moisture content were -selected for study. Figure 7 is a pre-dawn idrared image of a site located along the ~ . Figure 7 near here San Andreas fault east of Soda Lake. The rectangular pattern is a net;Wo& of subdivision roads. A recently active trace of the San Andreas fault is bounded on the southwest by a scarp, the crest of which is bright in the hge, The ground surface to the northeast slopes toward the scarp, and the area represented by the dark band is the topographically lowest area northeast of the scarp. Tumbleweed Thich has accumulated agzinst the scarp is haged as a thin very dark band bounding the brigkt scarp on the northeast, In late &y 1967, the grass wzs green adthe soil visibly dam? in places at the foot of the scarp, Moisture measurements tn Late October 1967 showed 3 Fercent soil moisture a+ the top of the scarp and 7 percent at . the base. Radiometer readings in late Gctober showed an apparent taqera- 0 0 tura of 8 C on the scar?, crest and 5 C at the base. Pre-daI:,m air teyerature \*'tis nz3sx::ed at 1, 15, snd 31 ir.ci;es rlb~jve the grcund at tile. scc?,rp crcst, scarp base, arLd in betwcen. The data, sumzasized in Table 1, show that at. any point stratification of the air is strongly developed, ar,d that the' air becomes apyreciabljr colder as me moves rf01.m the scarp. The 10T-7 area Is 9 tsap for cold zir, which loi,?ers 0 the local ground temperature. The high radiant temperature (5 C) st the base of the scarp may ifidicate that the relatively tsll grass there projected through the coldcst air layers Cnto the overlying xarmsr air. TULE 1 near here 22 Table I Height abol=e Top of ?fiddl.e of Base of qrouitd-.inchn s scarp scarp scarp 0 0 C 3c C 31 9.5 7.5 5.5 15 9 1 4 1 7 6 1 Grousld temp. by 8 5 Table 1.--Air and grcucd tenperatlJres measured zlong San Andreas fault east of Sods Lake, October 25, 1967 - 4:30 2.m. Air teqcratures by thermometer; gr0uv.d tenpzratures are radiation tsr,-,ersZures I uieasured by Barnes IT-3 radimeter. 23 cqitier of the imzge is a flat, in port closed, all.tir~i>-lsurfact bounded on the northwest and solrtheas'i by Iov gravel hills that. zre bright in the image. Thc semi-circular bright feature overlepping the southvest flank. of the darlq trianzular erea is an 2lluvial .Ian. 1%~. flat bottom of the depzession and the surrounding hills appr extrenely dry. Phch of the depression floor is barren of grass, and there are no visible signs bf moistarc. Soil moisture measurements shot: 2 percent aoisture at the !crest of one of the gravel hills and 4 percent OE the flat surface behi. Hovever, the flat'surface is floorad by fine grained clay-ri.ch sdirneat, and the slightly highzr moisture content can probably bs sccounted for as water driven out of clay minerals by heeting. Pre-c?avn tempzrature measuc2- 8 nzents showed well developed air stratification with air temp2ratures 0 2 to 4 C lower at ground level on the flat than at %round level on the lm gravel hills. The low flat area is poorly draized relative to air flo:; and ps-mits &he accumulation of a Zhyei oE dsnse cold air. .e4 Measurements =de by A. 0. Waananen and C. T. Snyder (unpublished data) indkzte that pre-dam evaporation of water in arid regions is vanishkgly small and cast doubt on hypotheses that radiative anomalies such as that in figure 8 reflect high soil moisture content. Ekaporation from an open water surface in a 4-foot diameter evaporating pan was measured continuously for several days in lkte Jiily 1963; The pan was set on a playa surface near Coaldale, Nevada. Air temperature 5 feet above 0 0 the playa surface ranged from about 14 C at night to 38 C in the daytime. . Relative humidity, also measured at an altitude of 5 &et was extremely lar, ranging from approximately 0 in the dayt-he to 25 percent at night. Total daily evaporation averaged about 0.4 inch, but-evaporation from the open pan between midnight and 6 a.m. totued less th& 0.05 inch. surfzce in the extsremefy dry atmosphere of the X'evada playa, it seems doubtful that the' radiative anomaly of figure 8, where surface moisture content was at most a few percent, was a product of evaporative cooling. In addition, tF,e effect of high soil moisture on therzi-iaf inertia would act to inhibit nocturnal cooling, snd, in the atisence of significant evaporztive cooling, moist soils night be warniar than dry soils in the pre-dawn hours. It seems moat likely. that the radiative anomalies of figures 7 and 8 are predominantly responses to mi-croclimatic effects created by preferential accunulation of cold air. Conclusions .. Tonal densities ir. this thermal infrared imagery niay reflect in part the spp.clfic gravities of surficial materlals. Silrficial u:aterials wits relatively high spccific gravities tend to be bright in the pre-dam image. KIdweser, effects related. to atmospheric conditions, topographic setting, and vegetation may also produce marked anomalies in the imzgery. Futhermore: even in the relatively well exposed geology of tha Calieate ad Tenblor Ranges, the irrragery was Largely controlled by properties of soii - not bedrock. Lithologic inferences based on qualitative compzrisons of radiatioz from soils, 57ith the radiation complexly modified by topographic, atmospheric, 3nd vegetative effects, are difficult. - irr aerial photographs. Secausc of the potential of infrared imzgery TO display microclizatic anomalres, it might be a valuable adjunct to other typs of imagery in mapping geologic features such as recently activz faults tlia-t hav5 very subtle topographic expression. _. It h2s been suggested that anomalously weak pre-dawn radiation might indicate soil moisture concentrations related to shallow grounc! water in low areas between landslide lobes or in areas where faults might act as barriers to groundwater (Vallace 2nd Moxham, 1966, 1967 ; Sabins, 1967, p. 749). Two anoma-lies of this type were investigated ar:d niay hax c been produce? Largely, if not entirely, by density stratification of air. Post- sunrise imagery shovs the strong inf l.wmce of solar warc.ing . of surfaces exposed to the sun. Topography is the doninant control of tonal densities in the image, which resembles a LOW sun angle photograph. 27 Rc f trences qibhlee, T. Id., Ji-.? i962, "Displacemcnts ori the Szn Andreas rift zcme and relaced s truccures in Carri-zo Plain a~civicirti ty [ Califarnia ] ; -in Guidcboolc, Geolosy of Csrrizo Plains end San Andreas Fa~tit~'' --Sari Joaaui~Geol. Soc.aud im, Assor,. PetroLevci Geolcxists - SOC. -Econ. Peloontolozists and Plineralogists. Pecific Sic. (field ?~I, -1962; 3. 5-12. Gates, 3. X., 1964, "Characteristics of soil and vegetated surfaces ts reflected 2nd emictzd radiztion," S-7xposf~~aXamote Saxin& Envirsn- nte9.t. 313, Michigan Univ., A-Arbor, InfqLred Pkvsics Las., ?ro_c_., p. 573-600. ee.iger, R. E., 1957, The climate 'near the ground, 23, ed. , %r-,*arr.I 'Jciv. Press, Carnbridge, Mass., 494 pp. Sabins, F. F., Jr., 1967, "ZnfrareG imagery and geologic aspects, ts -* t PHOT"YFiETP,IC EKGiLZERIi Veddzr, J. G., and Repenning, C. A,, 1965, "Geologic map of the ooctheastez, Caliznte Range, S2n Luis Ojispo County, Califcrnia," 5.S. Ceol. Surf2-v 'of the San Andreas fault syster,, California," J.S. cleol. Sux~y