JAMES C. HAMMACK Defense Mapping Agency Hydrographc Center Washington, DC 20390
Landsat Goes to Sea
Landsat MSS film imagery was used to evaluate and revise the positions of islands, banks, and reefs on the nautical chart of the Chagos Archipelago in the Indian Ocean.
INTRODUCTION moon and several planets, fully 70 percent of IOLOGISTS TELL US that man's ancestors the earth's surface remains shrouded in mys B emerged from the sea. Economists tell tery beneath the oceans. Major technology us that man must now turn again to the sea. development effOIts are being oriented to The world's economy is becoming more and wards exploring and exploiting the earth's
ABSTRACT: Current and proposed technological advances in naviga tion technology and the remote sensing of oceanic parameters will require nautical charts more accurate than many ofthe charts that are in use today. This is of serious concern to the international hy drographic community since existing hydrographic survey resources are too limited to perform the detailed surveys required to produce the type and volume ofcharts that will be required in the 1980's. The Defense Mapping Agency, which has a statutory responsibility to provide charts for civil maritime use in addition to its defense obli gations, has been investigating a new charting tool that may provide a partial solution to this dilemma. NASA's Landsat returns data from its Multispectral Scanner (MSS) that can be used to evaluate and update medium- and small-scale nautical charts. The MSS green band data can be used to probe clear oceanic waters to those depths required for safe navigation by most ships. The data also may be used to plan hydrographic surveys of reef and shoal areas so that limited survey resources can be exploited to their fullest. Existing charts can be evaluated for accuracy and currency of hazardous, near surface features, thus permitting the hydrographic survey re sources that are now stretched thin to be most effectively used where they are most needed: to define the safe shipping routes. A recent test project, performed at the Defense Mapping Agency Hydrog raphic Center, has demonstrated the feasibility of using MSS film imagery to evaluate and revise the positions of islands, banks, and reefs on a nautical chart. Additional research is being funded to investigate the practicality of using, and to optimize the digital water depth determination capabilities of, the MSS data as demonstrated in the 1975 joint NASAICousteau Ocean Bathymetry Experiment. Such techniques then could be more effectively applied to the chart production. more dependent on the oceans; for food, for last frontier. In the United States these minerals, for energy, and for transportation. marine studies are supported by the Marine Yet, at a time when cameras and sensors Resources and Engineering Development aboard National Aeronautics and Space Ad Act of 1966 (Public Law 89-454, June 17, ministration's (NASA) interplantetary probes 1966). The policy of the United States as have mapped the surface features of the stated herein is "to develop, encourage, and
PHOTOGRAMMETRIC ENGINEERING AND REMOTE SENSING, 683 Vol. 43, No.6, June 1977, pp. 683-691. 684 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1977 maintain a coordinated, comprehensive, and has been collected than during the rest of long range national program in marine sci man's recorded history. However, a recent ence for the benefit of mankind to assist in appraisal by the International Hydrographic protection of health and property, en Bureau estimates that only about 16 percent hancement of commerce, transportation, of the oceans has sufficiently adequate and national security, rehabilitation of our soundings to determine sea floor topog commercial fisheries, and increase utiliza raphy. Another 22 percent of the oceans has tion of these and other resources." data sufficient only for the determination of the major sea floor features and the remain HYDROGRAPHIC SURVEYING HISTORY ing 62 percent of the ocean area has data that is too sparse for determining sea floor Although man has been venturing over the topography2. In fact, one French expert, oceans for thousands of years, it was only within the last 50 years that advances in Captain L. Oudet, Ret., has stated "that any chart based on surveys before 1970 carries technology enabled him to make more de with it a risk that the surveyors may have tailed observation of features hidden in the missed some dangerous wreck or other obs depths beyond the limits of his natural tacle to navigation"3. senses. Until the invention of the echo sounder, knowledge ofthe sea bottom topog raphy was primarily limited to that informa tion which could be gleaned by lowering a CHANGING REQUIREMENTS rod or a weighted line over the side ofa boat until it touched bottom, or until it reached its Until recently, in spite ofthe limitations of length. In the latter case, a no bottom sound the survey data, most charts available have ing was recorded in the survey data. Such been satisfactory for conventional ships in sounding methods have been documented areas where safe routes have been estab as early as 1422 B.C. when they were de lished. Unfortunately, however, these sea picted on the wall of the tomb of Menna, an lanes do not always follow the most direct routes3. Additionally, some conventional Egyptian scribe1 . Actually, this simple pro cedure could be said to be the first fonn of passages such as the Strait ofMalacca are too remote sensing. The sounding line con shallow for the new deep draft vessels (some tinued to be used to determine depth during of which require clearances of nearly 30 the extensive worldwide surveys underta meters). Consequently, they must seek out ken by the major sea powers during the longer, less well surveyed, but deeper routes nineteenth and early twentieth centuries. to their destinations. A number of other fac Despite the phenomonal efforts of these tors are contributing to the opening of new early hydrographers, they were able to trade routes for vessels of all sizes. The in examine in detail only a fraction of the creasing production and export of natural re oceans' 360 million square kilometers. The sources from the developing nations, par majority of these surveys were dedicated to ~icularly those in the southern hemisphere, ensuring safe passage for vessels with less IS resulting in increased shipping through than ten meters draft. The relative ac areas with outdated or inadequate surveys. A curacies of many of these early surveys in large majority of these developing nations areas near land features was often astounding, have not yet established hydrographic ser 2 especially considering that their primary vices • Present technology trends will result tools were leadline, sextant, and chronome in even more drastic changes to shipping ter. On the other hand, the absolute accuracy patterns during the 1980's. The proposed of these surveys and the relative accuracy of NAVSTAR Global Positioning System will any surveys made out of sight of land were provide mariners with continuous, precise limited by the ability ofthe hydrographer to positional information anywhere in the obtain adequate celestial fixes which at best world. Environmental monitoring satellites could only define his position to within sev will be providing worldwide weather condi eral kilometers. The fact that they were often tions, ice patterns, sea state, and ocean cur unaware of currents that carried them off rent data. Maritime communication satellites course also degraded the results. will make this type of information available to the mariner in near real time. With the inflated fuel costs projected for the next dec DATA SHORTFALLS ade, more navigators will plot their course Since the widespread use of precision to minimize distance traveled while taking sonar equipment in the early 1950's, more advantage of all favorable winds and cur information about sea bottom topography rents. LANDSAT GOES TO SEA 685
ATIONAL AND INTERNATIONAL PRIORITIES NASNCoUSTEAU OCEAN BATHYMETRY Thus, the requirement to acquire accurate EXPERIMENT and adequate hydrographic surveys over With such inadequacies in surveying re large areas of the world's oceans demands sources in mind, NASA and the Cousteau immediate attention. However, hydro Society conducted ajoint Ocean Bathymetry graphic survey resources are quite limited Experiment during August and September, and tend to be expensive. Both national and 1975. The goal of the experiment was.to de international interest is being taken in this termine the capability and feasibility of de problem. In April 1970, the President's mes termining water depths from special high sage to the Congress4, prepared by the a gain data collected by the Multispectral tional Council on Marine Resources and En Scanners (MSS) aboard the two Landsat gineering Development, stated: (formerly ERTS) satellites currently in orbit. Previous studies with both aircraft and stan "More efficient sea transportation vitally dard MSS data from Landsat-l had dem depends upon portfolios of accurate nautical onsh'ated the general techniques of remote charts and publications for the open ocean as bathymetry from multispectral scanner 7 well as coastal ports and waterways ... Inter data. •s The NASA/Cousteau Ocean national, oceanic, legal, and political ques Bathymetry Experiment did prove the feasi tions often require facts available only from bility of satellite bathymetry. In the Berry precise maps and accurate marine data ifthey Island test area, depths as deep as 22 meters are to be answered."-Chapter IX, Page 115; (10% rms accuracy) were measured from the "The seemingly simple activities of chart ing the ocean and predicting its future actions satellite data and verified by the ground are in fact the most massive and intractable truth team on the Calypso9. Landsat also re problems which now face marine scientists. vealed shoals that were later determined by At our present rate of progress, mapping the the Calypso to be at a depth of40 meters. In topography of the ocean bottom will involve the less clear waters off the Florida coast, hundreds ofship-years ofwork ... Faced with Landsat data were used to map shoals as tasks of this magnitude, the United States deep as 10 meters9 . Additional research and clearly must take two steps: First, delineate comparison of Landsat high-gain data with what parts of the sea are the prime interest aircraft acquired data and recent charts indi and therefore to be given priority attention; and second, increase the speed and efficiency cated that depths could be deduced without knowledge of the measured optical proper of survey operations."-Chapter IX, Page 1o 127-8. ties of the waters in the area investigated . This capability could be very important when studying remote areas. Internationally, 47 nations are cooperating in hydrographic surveying and charting under the authority of the International DMAHC EVALUATION Hydrographic Organization (IHO) which Within the United States, the Defense was established in 1921 as the International Mapping Agency (DMA) through its Hy Hydrographic Bureau. By means of confer drographic Center (DMAHC) carries out ences, publications, and correspondence, statutory responsibilities to provide "accu the IHO has developed international accu rate and inexpensive nautical charts" and racy standards for hydrographic surveys5 and other marine navigation data "for the use of an international series of small-scale charts, all vessels of the United States and of and is encouraging the exchange of hydro navigators generally" for all areas outside ll graphic data among nations as well as coor U.S. territorial waters . Following the pre dinating joint multinational surveying ef sentation of the initial results of the NASN forts. In spite of international cooperation Cousteau experiment, a comparison was and even allowing increased survey effi made between worldwide Secchi disc data12 ciency from improved technology, much of and the areas most deficient in adequate the ocean will still lack adequate hydro bathymetry13. It was found that many of graphic surveys during the 1980's. (As a basic those areas lacking adequate survey data example, a recent British Hydrographic have water as clear as or clearer than that in Study Group concluded that 284 ship-years the Berry Islands test area. Thus, in Feb of work will be required to bring their ter ruary 1976 the Defense Mapping Agency re ritorial waters up to modern standards and quested NASA to provide special Landsat that their foreign areas of responsibility high-gain MSS data over three tests areas would require an additional 300 ship-years where forthcoming survey efforts would be of effortS.) able to provide ground/sea truth for evalua- 686 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1977 tions. The goal was to test the practicality of capabilities of the Landsat film imagery14. 15, using Landsat MSS data for chart evaluation 16 to the evaluation and the correction of the and preparation as well as to appraise their horizontal positions of features on a use as a survey planning tool. Pending re medium-scale nautical chart. Film images at ceipt of data from the special tasking, a re 1:1,000,000 scale were obtained for the search contract was initiated with the En Chagos scenes and the chart of the area was vironmental Research Institute of Michigan reduced to the same scale in order to com to convert digital MSS data from two previ pare features. ously acquired high-gain images of the When the imaged island features were reg Bahamas to a form that could be used in chart istered to the charted island features, sig production or survey planning. The results of nificant variations were immediately appar this endeavor will be available laterthis year. ent. There was a major reef or bank where the chart showed safe, deep water and some CHART REVISION banks appeared to be out ofposition by more At the conclusion of the data acquisition than 15 kilometers relative to the nearest period, only partially cloud-free imagery had land. Next, the existence and permanency of been received over the Bahamas test area; the features imaged on Landsat was con the Virgin Island test site had been com firmed by cross comparison of scenes ac pletely cloud covered; but 80 percent quired on two different days. At this point, cloud-free imagery had been obtained over priority evaluation was switched to the the third test area, the Chagos Archipelago Chagos area from the Bahamas. The Director in the Indian Ocean. It was the initial evalu of the DMA Hydrographic Center directed ation of the Chagos imagery acquired in that radio warnings be sent to mariners and March and April that resulted in a profitable that a new chart edition be prepared by the side application beyond the original test de first ofSeptember 1976 by using the Landsat sign. The film imagery acquired on March images to adjust the horizontal positions of 29, 1976 revealed a major reef 8 kilometers the islands, banks, and reefs. Geodetic con long as well as a number of other varia trol was plotted and a new mosaic of the tions that were not portrayed on the existing Landsat photography was prepared at the chart of the Archipelago. (U.S. Chart No. original chart scale. An initial determination 61610, Second Ed., February 21, 1976, of the positions of the most hazardous un 1:363,230). This discovery resulted in an ap charted reefedges was made and on June 18, plication of the proven cartographic 1976, a radio warning was broadcast to ships
FM DHARC WASHINGTON DC
TO AIG 9280
MIDEASTFOR-RHCFMKK
UNCLAS
HYDROPAC / '7.s- /76 (61). INDIAN OCEAN, CHAGOS ARCHIPELAGO. CHART 61610.
1. DANGEROUS SHOAL EXTENDS BETWEEN 04-51S 04-56S AND 72-36E 72-38E.
2. GANGES BANK IS LOCATED 8 MILES WESTWARD OF CHARTED POSITION 07-22S 71-06E.
3. PITT BANK 07-005 71-14E EXTENDS 4 MILES FURTHER NORTHWESTWARD k~D 6 MILES
FURTHER SOUTHEASTWARD THAN CHARTED.
FIG. 1. Radio message to mariners warning of hazards revealed by Landsat. LANDSAT GOES TO SEA 687
at sea (HYDROPAC 1175/76(61), Figure 1). adequate worldwide hydrographic survey These same data were included in Notice to data. The use of Landsat high-gain MSS im Mariners #28, dated July 10, 1976. Addi agery for bathymetric application was tested tional refinements were made to the data in the joint NASA/Cousteau Ocean and Notice to Mariners #29, dated July 17, Bathymetry Experiment. This joint venture 1976, carried a more detailed description of proved the feasibility of detecting and map the dangerous new reef and corrected reef ping shoals in clear water to depths equal to positions. Work was completed on the third or greater than those required for most sur edition of ChaIt 61610 and it went to press face shipping. Although its limited resolu on August 28, 1976. The horizontal positions tion cannot identify small navigational of islands, banks, and reefs portrayed on the hazards, in many areas it can provide data new edition were derived from the Landsat that are, in some cases, orders of magnitude MSS imagery acquired in March and April better than the existing surveys. With this and which had been adjusted to geodetic upgraded information, adequate ship sur control. The present effort used only film veys need be planned only for those ex imagery to derive the positioning data for panses that offer a potentially safe route for subsurface as well as surface features. Even shipping. This will result in optimal use of though water depths for the newly discov the limited and expensive hydrographic sur ered reefs could not be determined from veying resources. Even though several years the film, the fact that they could be seen on of research and development will probably the film indicated that they represented a be required before satisfactory algorithms navigational hazard. can be developed that will permit opera Such an approach leaves a major problem tional bathymetric analysis of the MSS digi to be resolved: namely, how to use the old tal data, the revision of the Chagos sounding data in areas where the imagery Archipelago chart demonstrated a valuable showed changes in the alignment or posi use ofthe film imagery: shoal features can be tions of reef features. The only detailed sur found and positioned with respect to known vey of the entire archipelago had been con surface features. The very fact that a shoal or ducted by the Indian Navy in 1837. Typi reef appears on the images indicates that it cally, survey accuracy in this time period presents a hazard to navigation. Thus, the was limited by navigational capabilities. The Landsat high-gain imagery currently repre data were reasonably accurate in and around sents a useful tool that can be used to pro islands (as confirmed in several places in vide improved realtive horizontal informa Chagos area by the Landsat imagery). How tion about remote islands and reefs. It also ever, in the more remote areas, out ofsight of exhibits a great potential in the digital mode land, there were problems in obtaining a for supporting international hydrographic good navigational fix as well as with omis surveying and charting efforts, thereby in sions in the sounding data, as when the track creasing the efficiency of limited hydro lines pass on either side of a reef. (These graphic surveying resources and making the cases were demonstrated by the Landsat im seas safer for the international maritime agery revealing positioning errors ofup to 18 community. kilometers and by the discovery of new shoals or reefs as shown in Figures 2 and 3.) For the present chart revision, a number of REFERENCES soundings were removed (Figures 4-7). 1. Deacon, G. E. R., Ed. Seas, Maps, and However in the future, digital depth analysis Man-An Atlas-History of Man's Explora of the MSS data as in the joint NASAl tion of the Deep. London: Crescent Books, Cousteau experiment should permit correla 1962. tion and adjustment ofold soundings to their 2. Kapoor, D. C. "International Cooperation in true positions. In this present work, how Hydrography." International Hydrographic Review, Vol. LUI (2). Monaco: July 1976. ever, many soundings had to be deleted for the sake of safety. 3. Oudet, L. "The Value of a autical Chart." International Hydrographic Review, Vol. SUMMARY L(l). Monaco: January 1973. 4. Marine Science Affairs, Selecting Priority National and international concern is Programs, Annual Report of the President to being expressed over the growing need to the Congress on Marine Resources and En improve the quantity, currency, and accu gineering Development, Chapter IX, April racy of worldwide hydrographic survey data 1970. to assure navigational safety. Thousands of 5. I.H.O. Special Publication 44. Monaco: ship-years will be required to acquire January 1968. 72 C 30 IE 72°30'E ":""". 10 km I '0 -:.~ I L 10 km _, 90 Os 65 a. OJ ~'\..... 00 €rI ... g, \-0 00 1 ~"" .. ,~~!) $0 13/. 11 \ '2 ""E("' S'" 10 6 \ ..90 ::11 \ 14 .) I.-a ,0; , 24 20 "~:\.--~[-_. 21 60 ':11 11: ... 6 fs Il I Ito " 6 \ Co,ol "'1 45 183 to 11 .."'s (0(.1 lila 18, ,,"I • 6,its '- 3- 11 "'tl //6 22 9~ -:;j-- 42 ~{ 00 40 CAJTlON NO t t§ "?" ::t: 45 ...../ 23 .~ ·-'13 II m\ o 22 r :;:i--.f ~2R oil; S PEA K S 11 ". ..../7 • " i ,:::.' \ SPEAKERS !fo 40 40 d ;"0' /6 '5\ 'a '2 l'::~ 11 o 22 20 4s ~I 22 ","- B.4NK" 13:. j Col 20 ~""'-...Q 40 11 ". Sf ~ 6s ~ , .:o(~ BAN K 16, 42 14, . \ ~,. ~ 22 ,,<: II ...; \ 23 • tOO -' -.:'" .:'11 39 ~ . ) 23 6) 80 S:;>nd '9 11.: / 4S : 6 2' 16, trl \ 2' '9 Rodl(.t>d land ..'". / Newly discovered o-J 14l. 42 14, " /8 . 28 ..... ~~. / Colvocoresses Reef ::0 ,lib 20 'O" ..oJ.. " '00 ~* 5 S I (') 23 a 15 .. ?'""~~:.-t.io 0 - to_~\_13 u"" trl ---~~~::;:;":, :~>~f" 0 a 'a • . vl~ 5 S , to .. Z i 8 o \ a & • • ~ ~ 6\\ • ;9' 11 ll: Formerly charted Z 20 ,. i," ,ISo ,',)',,£, q,"1,,,,""'1,~ .. 1. "'",., ',d. 1,."'" 11.: . ," reef boundary 1361 trl 2' ..J 90 ,f> ••"- I. ~'
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343,
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FIG. 4. Portion of Chart 61610, 2nd ed., February 21, 1976, showing southeast portion of Great Chagos Bank.
50 73 CAUTION NO 2 77 73 70 73 77 79 90 33 31 B. 75 73 77 39 16, 29 64 64/ IB, 185 Rody 33~6'j 16, 29 2B 39 37 22 33 2B 46 29 29 64 31 50 26 IB, -_ ...... 55 24 '0,", 22 brohn co.ol 33 37 29 29 ~: 31 , . 26 51 31 37 "'/CAUT ON NO 29 31 29 31 31 "'" . ;-.:/'\'-J'\"rt;6/+f Formerly ch ;rted reef bounda y
10 km 2203
12B 627 , 1198
1185 n030'E
FIG. 5. Portion of Chart 61610, 3rd ed., August 28, 1976, showing revised reef boundaries. Many sound ings have been deleted and Caution No.2 warns against trusting validity of soundings within this reef. .00 .81 O'J '0 ~ 1218 o ~ , I \ 1218 /1 '/ 42 12 23 ~ "C / ::r: - I 46 24 !locb / I o '.-". -. 1220 ..., 22 "0 6" / 44 i~!!!.... 7'-" ,roo . ." / 3' o 24 20 6~ ··f~. 8" I o /; 16 20 . 100 28 37 20 I ~ 100/ IS . ~ I " 17 7 .... ~~ .., 170S I 7'S ill 37 So~~~!.~ a::: 7~ I( I i/ 20 H"q ."" brolo:M cor.I " ---,'" 200--- - 44 33 a::: 24 /8 17 &.... ·'···,.1.. 31 3\ l"=1 17 ~ '- ..., PIT T BANK 35 PIT T BAN K.. .3"" \ 33 28 \ ::t' '8 15 I ' 3\ 35 I (5 17 •• .2 31 31 Sand ~...~~ 17 17 urtJ 28 l"=1 I \ -'gl 170 12 Z " \ 35 ~I Ito .• 4 0 \ CAUTION NO 2 o .to 1 '1 37 \8, 52 '0 '0 , 20 C 90 2'5 31 Ii: l"=1 150 17 \ 33 '8 20 ;' l"=1 10) \ ~I 13 ~j ::t' I. 29 I 2to .• I 52 31 o liO 17 , 8,o~~ (f>',f 17 )"" corol 31 ~ ,so ""'- I 10 km I "- ,to ill 33 '8 " ::t' .4 " 26 l"=1 "" 10km a::: '0 Ito ...... - ...,o Its /' ...... - -- Formerly charted l"=1 ree f boundary en 1~5 l"=1 Z IJ'O '/ 238 en '00 (\ • .;0 5 ~ 11 •• ...... -\0\80 38 ,s" ';"'"'' lO_ Ganges Bank now charted 52 J.6 .: 8 8 \Ga1lges 150 S 18 km westward .0 \.., 9 12 \Bank 2>4 2>2 ", ",S S s ''"'..... "';;'0"/,1 65 S +----- 3€6 """'CD .00 ioo PO -.l ts r~~~Wi (~'}) -.l 150 ~ 295 :70 '"' 6 "8 21 710 30'E 10"0 , 71 0 30'E
ISO 275 130
FIG. 6. Portion of Chart 61610, 2nd ed., February 21, 1976, showing FIG. 7. Portion of Chart 61610, 3rd ed., August 28, 1976, showing Pitt and Ganges Banks. revisions resulting from Landsat imagery. LA DSAT GOES TO SEA 691
6. Haslam, D. W., Rear Admiral, O.B.E., Oceans' 76 Symposium, Washington, D.C., F.R.I.GS., "Report by the Hydrographer ofthe September 1976. Navy." N.P. 130. Taunton, England; 1975. II. Title 10, U.S. Code 70A Statute 456, para 7. Brown, W. L., F. C. Polcyn, A. N. Sellman, graphs 7391-7394. and S. R. Stewart. "Water-Depth Measure 12. Frederick, M. A. "An Atlas of Secchi Disc ment by Wave Refraction and Multispectral Transparency Measurements and Forel-Ule Techniques." Report No. 31650-31T. Ann Ar Color Codes for the Oceans of the World." bor, Michigan; Willow Run Laboratories, Au U.S. Naval Postgraduate School Thesis, Mon gust 1971. terey, Caldifornia, September 1970. 8. Polcyn, F. C., and D. Lyzenga. "Updating 13. U.S. Chart No. 5103, First Ed., July 1974. Coastal and Navigational Charts using 14. Colvocoresses, A. P. "Evaluation of the Car ERTS-I Data." Paper M4, Third ERTS Sym tographic Application of ERTS-I Imagery." posium, December 1973. The American Cartographer, Vol. 2, No. I, 9. Polcyn, F. C. "Final Report on NASAl April 1975, p. 5. Cousteau Ocean Bathymetry Experiment 15. Fleming, E. A. "Positioning Off-Shore Fea Remote Bathymetry Using High Gain Land tures With the Aid of Landsat Imagery." Ad sat Dta," NASA-CR-ERIM-1l8500-I-F, May 1976. vance copy published as USGS EROS Carto graphic memorandum No. 35, April 26, 1976. 10. Middleton, E. M., J. L. Barker, "Hydrographic 16. Conversations behveen the author and NASA Charting From Landsat Satellite; A Compari Goddard Spacecraft Center System En son With Aircraft Imagery." Presented at gineers, Summer 1976.
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