FIG. I. A black-and-white reproduction of 1: 10,OOO-scale color photograph of \rake Island. The trans­parencies were cut from the roll of film and inserted between glass for measurement with a Zeiss C-8Stereoplanigraph.

EDMliND L. GEARY*

U. S. Naval Oceanographic OfficeWashington, D. C.

Coastal HydrographyColor aerial photos, as well as photos from

satellites, will aid in charting the world's coasts.

I1\TRODUCTlO\,

T HE OeTE\' QUOTED Chinese prO\'erb,"One picture is worth more than 10,000

words," is an understatement of fact whenaerial photographs are brought into their trueperspective for the purpose of charti ng coastalhydrography. \Yhen military operations andother emergencies dictate their need for arapid method of verifying the exact location

* Presented at the Annual Convention of theAmerican Society of Photogrammetry, \rashing­ton, D. c., l\larch 1967 under the title "Use ofAerial Photograph\' for Coastal Hydrography."

44

of an island or even its exact shape in connec­tion with its accessibility, a picture is noton Iy worth 10,000 words-i t may also beworth 10 times 10,000 dollars. This fact be­comes obvious when one takes into accountthe manpower, equipment, and planning thatmust be considered before a survey ship isdetailed to any area to gather hydrographicdata.

Aerial photographs, of course, have manyuses. The true extent of their value dependson the user. In the field of hydrography, theuse of aerial photographs extends from plan··ning for oceanographic and hydrographic

COASTAL HYDROGRAPHY 45

survey operations to determining waterdepths down to as much as 60 feet, dependingon water transparency and bottom contrast.\\'ith these applications in mind, let us reviewwhat U. S. Naval Oceanographic Office per­sonnel are presently doin!.!; with aerial photog­raphy and what is hoped for in the future.

AERIAL PHOTOGRAPHS AID

HYDROGRAPHIC SURVEYS

The principal objective of hydrographicsurveys is to obtain information on waterareas and adjacent coastal regions for use as

photographs can guide and assist the hydrog­rapher, especially in difficult shallow waterareas. Such photographs gi\'e him an o\'erallview of the bottom and, therefore. guide hisoperations and assist hi m to develop details.It was also pointed out that these photo­graphs could be used to indicate near-shoreareas requiring further investigation or moreintensive sun'eys to reveal hidden obstruc­tions as well as for water depth information. 2

U. S. Navy survey ships used color photos forthese purposes in the Pacific during WorldViar II.

A BSTRACT: A erial photographs have many uses, and the extent of their valuedepends on the user. In the field of hydrography, the use of aerial photographyextends from planning for oceanographic survey operations to determiningwater depths down to a maximum of 60 feet if water transparency and bollomcontrast permit. With these applications in mind, a review is made of actualand potential utilization of aerial photography by the U.S. Naval Oceano­gr(~phic Office. Color aerial photographs, as well as satellite-taken photography,will play an importanl role in the development of more rapid and comprehensivemethods of charling coastal hydrography. A proposed projecl to obtain and testcolor aerial photography of an underwater test range in the Ftorida Keys sllOutdprot1e invaluable in developing Ihese methods.

source material in the compilation or revisionof nautical charts, sailing directions. andother nautical publications of value to themariner. The results of the surveys are alsoused for planning harbor improvements andseaplane anchorages for studies of siltingand erosion and oceanographic features, andfor military defense projects.!

In planning for such surveys, one of thefirst steps usually taken is to prepare anuncontrolled mosaic from the latest availableaerial photographs. \!\lork sheets or planningcharts can be prepared showing the locationof principal landmarks; general configurationsof coast lines, locations of landing beachesand possible camp sites; probable sites for theerection of signals to mark the various sta­tions; and possible tide gage stations installa­tions. More important, the isolated reefs,rocks, and shoals which are visible on thephotographs can be located and placed on thework sheets, which greatly facilitates the fieldsurvey party's sounding development of theseafloor profile.

COASTAL HYDROGRAPHY FRO~I

COLOR PHOTOGRAPHS

Experiments conducted with color aerialphotography by the U. S. Coast and GeodeticSurvey in recent years indicate that color

The Oceanographic Office is now attempt­ing to establish that color aerial photographsare an effective and economical means ofacquiring data on water depths. A test O\'era portion of \rake Island was made in 1964by u tilizi ng selected 1: 10,000 scale colortransparencies (Figure 1) which were cut fromthe roll of film and oriented in a first-orderinstrument (Zeiss C-8 Stereoplanigraph) by

46 PHOTOGRAMMETRIC E GINEERI G

TABLE I. RESULTS OF DEPTH READII'GS INSTEREO :\IODELS \\TfH COLOR TRAI'SPAREI'CIES

inserti ng the transparencies between platesof clear optical glass. The transparencies wereorien ted to the same con trol that governedthe construction of the hydrographic surveysheet and the sounding compilation for thearea, Stereo-photogramllletric depth readingswere made at the locations of the surveysoundings over an area of water depthsranging from 0-18 feet. Studies of data sho\\'nin Table 1 reveal that: (1) the summary ofpoints concluded a mean square error of ± 1.3feet; (2) se\'enty-fi\'e percent of all points

a, Model 3 @ 492 points25 points10 points

b, Model 4 @; j

166 poinls46 points

6 points2 points

No. of points read: 127were within 1 foot\I'ere within 2 feet\I'ere \I'ithin 3 feet

No, of points read: 220were \I,ithin 1 footwere within 2 feetwere within 3 feet\\'ere within -1- feet

recorded from the photography were within+ 1.0 foot of the survey depths; and (3),ninety-five percent of all points read werewithin ± 2 feet of the surveyed depth.

Figure 2 is a portion of the stereo modelreadout. A comparison with the field soundingdata (Figure 3) illustrates the accuracy thatwas obtained, Using six-inch focal lengthphotography taken at 5,000 feet, the maxi­mum accuracy obtainable with the stereo­planigraph proved to be approximately ± 1.0foot.

Although the Wake Island test is encourag­ing as a whole, there is still some doubt as tothe accuracy of the depths recorded, bothvertically and horizontally. This is largelydue to the fact that the photographs weretaken with cameras with lenses uncorrectedfor taking colored photography. Also, therewas insufficient information on true depth inthe test area.

PHOTOGRAPHY FOR CHART REVISION

Aerial photographs and photogrammetrictechniques play an important part in nautical

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FIG. 3. Field soundings for comparison with the same area shown in Figure 2.

chart revision by reveali ng changes in ports,port facilities, and coastal areas. For example,a few years ago a portion of H.G. Chart 26-D,showing part of the Bahamas. looked likeFigure 4. Wi th the aid of aerial photographs(Figure 5) and photogrammetric techniques,the chart was revised to show shapes andlocations of all islands and features as shO\\'nin Figure 6. By placing Figure 6 over Figure 4,the errors in the earlier chart become moreobvious. The detail of Figure 6 is from a por­tion of the first edition (11 February 1963)of H.G. Chart 5954, which replaced theseventh edition (June 1943) H.G. Chart 26-D.

The use of space photography for verifyingor revising coastal hydrographic detail is afuture possibility. If the photographs arealso taken in color, more information be­cOmes visible to the photo-interpreter andthe photogram metrist. Figure 7 shO'iVS thedetail of H.G. Chart 6029 superimposed overa Gemini- V photograph. The two atolls areobviously incorrectly depicted on the chart,despite the fact that the chart was compiledfrom a 1927 Japanese survey. Until recently

FIG. 4. I LO. Chart 26-D showing partof the Bahamas.

48 I'HOTOGRAMMETRIC E 'GINEERING

FIG. 5. Photographic mosaic of a portion of theChart shown in Figure 4.

there was no way, other than a costly shipand land survey operation, by which theinformation on this chart could be verified orcorrected.

Figure 7 shows an enlargemen t of oneframe of the original film taken on the Gemini­V space flight in August 1965. Of the photo­graphs taken, only a few were useable forrevision of charted detail, due mostly to thenon-cartographic type camera and to thepresence of scattered clouds. Another reasonmay be that techniques for spacecraft orienta­tion and photography were still in the experi­men tal stages.

PLANNED DEVELOPMENT

Recently the U. S. Naval OceanographicOffice Research and Development Depart­ment initiated a project to obtain colorphotography over a test range in the FloridaKeys. I t is proposed to have a Ii array ofunderwater targets submerged at each 10­foot depth down to 60 feet. All targets in thearray can be exposed on one photographtaken from a flying height of 5,000 feet. Theflight lines will originate over land and con­tinue in a direction between two exposedreefs. A color target, 100 feet square, will beplaced on land and exposed as each flight linebegins. At the shoreline, another target will

be placed to indicate the water-line (which isoften inconspicuous on color photography).The purpose of the large land target is toprovide a comparison between the color onthe ground target and the submerged targetsmade of the same materials as the groundtarget. In order to indicate the water surfaceand provide reference points for orienting thestereoscopic photos, dye markers of aluminumpowder will be placed so that two will appearapproximately opposite the center of eachphotograph.

Concurrently with the photographic expo­sures, time and "ground truth," consistingof water temperature, salinity, current, andlight intensity data will be recorded. Thisinformation will later be correlated to theinformation recorded on the photographs todetermine the relationship between depthsand color tones; the changes that occur fromday to day, or even from hour to hour, asthe sun angle changes; and how the wateraffects the apparen t color characteristics ofthe submerged targets compared to the landtarget.

The depths of the targets will be known,and the depths of other natural featuresprominent on the color photographs will bedetermined. Photographs exposed at altitudesof 2,000, 5,000, 10,000, 20,000, and 30,000feet will be compared. Selected stereoscopicpairs will be oriented in photogrammetric

FIG. 6. Revised chart for comparison with Figure 4.

CUAST,\L IIYDRUGRAPHY 49

instruments and depths read to compare withthe true depths pre\'iously recorded. Fromthe information obtained the following canbe determined:

• Accuracy of stereo-depth determination frOI11color photography.

• Correlation of photo tOiles with depths andother physical characteristics of the water.

• Extent of the ligh t filtering effect of water 011color at different altitudes,

PHOTOGRAPHIC EQUIP~IENT

Realizing the potential of color photog­raphy for charti ng hydrography, early lastyear the U. S. Naval Oceanographic Officestarted procuremen t of color photographicprocessing equipment. Also, automated colorfilm processing equipment has been obtainedby several other Naval organizations. Oneweak link in the chain still remains; thecameras being used by the photographicsquadrons to obtain cartographic colorphotography are not adapted to obtainoptimum color photography. However, thisdeficiency may be overcome if a new colorcon'ected camem, the KC-6A now underdevelop men t for another photo system,should become a standard camera in the NayyPhotographic Squadrons, The KC-4 camera

and the "'ild RC-8 camcras will be used inobtaining color photographs o\'er the pro­posed test rangc,

Color aerial photography for mapping pur­poses requires a precision cartographic map­ping camera with the highest quality wide­angle color-corrccted lens and also a relativeaperture of f5.6 or larger. The Jens must alsoprovide good and even illumination over theentire focal plane. If not, the star filter oranti-\'ignetting filter used to eliminate the"hot spot" at the center of the photographywill be so dense that there \I'ill be too littlelight for good exposure of the film. In colorphotography, the filter must also cut out theultra-yiolet and part of the blue light,

OTHER FACTORS

Assul1li ng that eq ui pmcn t reqlliremen tsare met, other factors such as water trans­parency, bottom contrast, tide conditions,and sun spots remain as \·ariables. Of allsuch factors affecting quality and useabilityof color aerial photography, water transpar­ency is the least known. Sun spots andtide, on the other hand, can be predictcd fromkno\l'n data. Therefore, in the final analysis,the ability to determinc ,,'ater depth willbecome primarily dependent on water trans,

Rt"l>l.l.\l' \1'01.1.

FIG. 7. Detail of 1-1.0. Chart 6029 superimposed over CC11Iini- V space photograph.

50 PHOTOGRAMMETRIC ENGINEERI NG

parency and bottom con trast. vVater trans­parency will vary from 8 to 10 feet in Alaskato 60 and eyen 70 feet over a clean coralbottom as in certain parts of the Caribbean.3

CONCLUS!OK

Color photography will provide a means formore rapid acquisition of depth informationfor ncar-shore areas, and the informationobtained on the previously mentioned testwill be il1\'aluable in developing this method.Continuing use of aerial photographs, par­ticularly satellite photography, can providerapid acquisition of data over remote areasof special significance. The use of satellitephotography can vary from chart revision tothe study of disasters caused ei ther by manor nature. Its applications are unlimited.Future developments will dictate to whatextent this type of photography will be used.Until then, conyentional aerial photographswill have to provide all the necessary infor­mation.

LITERATURE CITED

1. 1-1. O. Pub. No.-9, 1958 Edition, Chapter XLI.2. Swanson, I.. \\". Photogrammetric Surveys for

Nautical Charting Use of Color and InfraredPhotography. Photogra1l1111etric Engineering. 26:137-.1 I. 1960.

3. Smith, John 1'. Color A New Dimension inPhotography. Photogra'll1111etric Engineering.Nov. 1963.

BIBLIOGUAPHY

Manual of Photographic Interpretation, Chapter 2Appendix C "The Procurement of Aerial Pho­tography of Undenvater Objects"-An analysisof the problems by Russian Scientists.

Theurer, C. Color and Infrared Experimental Pho­tography for Coastal Mapping. Photogram111etricEngineering. 25(4) pp. 565-569. 1959.

Tewinkel, G. C. Water Depths from Aerial Photo­graphs. Photogrammetric Engineering. Nov. 1963,pp. 1037-1042. July 1964, p. 647.

:\~ aruyasu, Taskakazu and Nishio, lVl ontomitsn.Experimental Studies on Color Aerial Photo­graphs in Japan. Photogralll1l1etria. 18: 87-106.1961-62.

Ottosom, L. Comparative Tests of the Accuracy ofPanchromatic, Infrared and Color Pictures fromthe Air for Photogrammetric Purposes. A'r­chives, Intern. Congress for Photogrammetry.Stockholm. 1959.

Tarkington, R. G. and Sorem, A. L. Color andFalse Color Films for Aerial Photography. Pho­togra1ll1l1etric Engineering. 29: 88-95, 1963.

Swanson, L. \Y. Aerial Photography and Photo­grammetry in the Coast and Geodetic Survey.A rchives, International Society of Photogram­metry at Lisbon, Portugal-1964.

Meijer, Groeneveld W. O. J. Formula for Conver­sion of Stereoscopically Observed ApparentDepth of Water to True Depth, Numerical Ex­amples and Discussion. Photogra111metric Engi­neering, Nov. 1964. pp. 1037-10.15.

Seiwel, H. R. Oceanographic Factors in Under­water Depth Determination by Aerial Photog­raph y. Photogram1l1etric Engineering, March1949, pp. 171-177.

Badgley, P. D. and Vest, \Y. L. Orbital RemoteSensing and Natural Resources, Photogrammet­ric Engineering, Sept. 1966, pp. 780-790.

Forum

Dear Sirs:

Enclosed is my check to cover the follow­ing: annual dues, Selected Papers on RemoteSensing, and sih-er pin.

Since my return from Vietnam, I have nodifficulties with neither receipt of the maga­zine nor any other correspondence.

Personally, I would like to see more articlesreference the interpretation of photography.Like possibly several others, I am new to thefield and my mathematics is also not up tothe level required for a fuller understandingof some of the more rarified items of interest.

I am indeed amazed at the sophistication

of much computerized equipment and amsure that it all serves a most useful purpose;however, without personnel highly trainedto permit the utmost use of the equipment,it would seem somewhat superfluous. I gatherthe impression that the highly sophisticatedequipment might possibly interfere with viewof the woods due to the obstruction of thetree line.

I do, however, thoroughly enjoy and findvery interesting the articles that I am tech­nically able to understand.

- William S. BarkerKnightstown, Indiana