TRANSFORMATION OF BLACK AND WHITE RADAR-MAP TO FULL-COLOR 651

experimen ts will lead, and whether the re­sults will have practical application, we donot know. \Ve believe that colored radarshows great promise, especially to the mili­tary, but the potentialities of such a systemare only vaguely understood.

Time and work are needed to produce theanswers to the questions raised by these ex­periments. Before successful culmination of

the problem can be realized, a concerted ef­fort will be required to investigate the photo­graphic, electronic, and psychological aspectsinvolved. Our experiments have given us buta glimpse of the impact a multi-color systemwill have on a radar-observer and his reac­tions. \Ve are confident that such a systemis the next step in the evolutionary ladder ofdetection and surveillance.

Elements of Photographic InterpretationCommon to Several Sensors

CH A RLES E. OLSON, JR. *

ABSTRACT: Interpretation of radar and infrared photography involves the samebasic elements utilized in the interpretation of visual photography. Regardlessof origin or display represented, a photograph is nothing more nor less than agraphic record of energy intensity. While it is customary to think of the energysource in the range of visible, or infrared. light, other portions of the spectrumshould not be buried in an aura of mystery. When a photograph is accepted asa graphic record of energy intensity, it is logical to extend the interpretationprinciples developed with visual photography to the records produced withother sensors.

T ODAY, and every day, photographic inter­pretation exerts a tremendous influence

on almost every individual in society. Every­one is bombarded by increasing numbers ofphotographs. Newspapers, magazines, bill­boards, and television all offer photographs tolook at, and from each of these photographscertain impressions or ideas are gained. Theseimpressions are actually photographic inter­pretations. Such interpretations may be con­scious or unconscious, accurate or inaccurate,complete or partial, but interpretation is anessential part of the process through whichinformation is obtained from the photograph.

To place photographic interpretation inproper perspective, it is helpful to begin at thevery dawn of civilization. One of the firststeps in the growth of civilization must havebeen the development of communication.Until man could communicate his ideas anddesires to other men, the concert of actionnecessary to form tribes and to create govern­ments could not have taken place. People

may argue about the order in which commu­nication media developeet, but all agree thatdrawings came early. Man's first drawingsmay have been finger markings in the dirtwhich approximated the shape of things thathe had seen. \Vhen some indication of size, orscale, was added, his drawings became moremeaningful. Color and indications of fur,hide, or texture have been found in earlydrawings of the cave man indicating that theimportance of these qualities was recognizedat an early date.

As man and man's civilization was ad­vanced, his ability to communicate was im­proved. Languages became more expressiveand drawings more detailed. Such things asshading and shadows, repetition of patterns,and combinations of related features wereadded. Despite these improvements man'sgraphics were not good enough. Man wanteda complete picture of what he had seen, andhe kept searching for some way to recordwhat his eye actually saw.

* Assistant Prof. of Forestry and Executive Secretary, Committee on Aerial Photography, Univ. ofIllinois, Urbana, Ill.

EDITOR'S NOTE: Presented at the Society's 26th Annual Meeting, Hotel Shoreham, Washington,D. c., March 23-26, 1960. This paper was part of the Symposium on Photo Interpretation.

652 PHOTOGRAMMETRIC ENGINEERING

The search for better graphic records led tothe photographic process. Cameras and theirgraphic records have come a long way sinceDaguerre produced his first photo-sensi ti veplate in 1839, but the search for better cam­eras, better pictures, better graphic recordsgoes on. Today use is made of invisible formsof energy to produce graphic records withspecial qualities; X-ray, radar, and infraredphotographs have proved extremely useful.However, the mechanics involved in obtain­ing photographic images frequently causelosing sight of the basic situation that broughtthese sensors into existence. Man's search forbetter graphic records produced photography,and any photograph, regardless of origin orthe type of images displayed, is nothing morenor less than a graphic record; it records theintensity of energy received at the focal­plane. I t is customary to think of the energysource as visible, or possibly infrared, light.If discussion is confined to this energy spec­trum, most photographic interpreters will beon reasonably familiar ground.

Interpretation of photographic records oflight intensity requires either a conscious oran unconscious consideration of several spe­cific properties of the images contained in thephotographs. Every photographic interpretercan name several properties of photographicimages which he considers important, andsome interpreters would include items whichare not strictly characteristics of photo­graphic images; spatial relationships are im­portant, too. The author's list includes ninebasic elements.

1. Shape. The shape of some objects is sodistinctive that their images may be iden­tified solely from this criterion. The PentagonBuilding near Washington, D. c., is a classicexample of the role of shape in interpretation.

2. Size. In many cases length, width,height, area, or volume are essential to accu­rate and complete interpretation. The volumeof wood which could be cut from the stand inFigure 1 is dependent upon tree-size, standdensity, and size (or area) of the stand.

3. Tone. Different objects reflect differentamounts and wavelengths of light. These dif­ferences are recorded as tonal, or color, varia­tions. The stand of mixed hardwoods shownin Figure 1 was photographed in late Octoberat the peak of the fall color change. Speciesdifferences are obvious.

4. Shadow. Shadows can help or hinder theinterpreter; shadows reveal invisible silhou­ettes but hide some detail. The shadows inFigure 2 provide information on the size andshape of this building which is not apparent

.FIG. 1. Panchromatic-minus blue photograph ofmIxed harc\wood stand at the peak of the fall colorchange. LIghtest toned tree crowns are sugarma~le; dark-toned crowns are generally oak(Ul11versity of Illinois photograph.) .

from the image of the building alone. Thesesame shadows obscure the detail in the lawnand sidewalk areas in front of the building.

5..P~ttern. Pattern, or repetition, is char­actenstlc of many man-made objects and ofsome natural features. The land-use patterns~own in Figu:e 3 is typical of areas of deep,w1l1d-bI0\~n sods. Orchards and strip croppingare partIcularly conspicuous because ofpattern.

6. Texture. The visual impression of rough­ness or smoothness created by some images isoften a valuable clue in interpretation. Tree­size is often interpreted on the basis of appar­ent texture. Smooth, velvety textures areco~monly associated with young saplings,whde rougher, cobbled textures usually indi­cate older trees of sawtimber size.

7. Sit~. The location of objects with respectto terra1l1 features or other objects is oftenhelpful. The open pond and the flatness of thearea of dark-toned vegetation in Figure 4

FIG. 2. The shadow of this building shows thesteeple .more clea.rly t.han doc.s the image of thesteeple Itself. (Umverslty of IllInois photograph.)

PHOTOGRAPHIC INTERPRETATION COMMON TO SEVERAL SENSORS 653

FIG. 3. Land-use pattern on loess in CalhouIlCounty, Illinois. (U.S.D.A. photograph.)

. FIG. 4. Northern white cedar-balsam fir swampIn Leelanau County, Michigan. (University ofIllinois photograph.)

both indicate a coniferous swamp. In thisarea of Michigan, northern white cedar andbalsam fir are the two predominant swampconifers. The stand shown here is actually amixture of both species.

8. A ssociation. Some objects are so com-

FIG. 5. :Thermal power plant at the University of. Illinois. (University of Illinois photograph.)...~

monly associated with other objects that oneindicate§C or confirms the other. In Figure 5the two tall smokestacks, large building, coalpiles, conveyors, and cooling towers are ob­viously related. This combination and ar­rangement of features identifies the installa­tion as a thermal power plant.

9. Resolution. Resolution depends on manythings but it always places a practical limit oninterpretation. Some objects are too small, orotherwise lacking, to form a distinct image onthe photograph. The lake in Figure 6 showssome interesting tonal patterns, but the exactlocation of the shore-line is not visible alongmuch of the boundary of the lake. The shore­line failed to resolve because of insufficienttonal contrast between adjacent land andwater surfaces. Boundary contrast or edgegradient is a factor in resolution (1).

Notice that seven items on this list arequalities that man developed in his earlydrawings. The last three items are importantto interpretation because they tend to inte­grate or set limits on the others. Conscious orunconscious consideration of one or more ofthese basic elements is involved in everyphotographic interpretation. Integration ofseveral elements strengthens any interpreta­tion and contributes to the "convergence ofevidence" frame of mind so aptly describedby Colwell (2). Association, in particular, isclosely related to the "convergence of evi­dence" concept.

A list of important considerations in photo­graphic interpretation, similar to that above,is familiar to most photographic interpreters.The ease with which these same basic ele­men ts of photographic interpretation can beapplied successfully to radarscope and infra­red photographs is not as widely recognized.Radar and infrared sensing systems have beendeveloped largely to meet military require-

FIG. 6. Shallow water revealed by tonal contrast;although exact shoreline is not resolved; I.,eelanauCounty, Michigan. (Univ~rsity qf Wi,nQis ,ph0tO,'::Jgraph.)

654 PHOTOGRAMMETRIC ENGINEERING

Paducah, Kentucky

Metropolis, Illinois

FIG. 7. Simulated radarscope photograph with the radar located several thousand feet above theconfluence of the Ohio and Cumberland rivers. (University of Illinois photograph.)

ments, and much of the information concern­ing these sensors is "classified" and notreadily available. The aura of mystery whichpopularly surrounds all classified informationhas led many people to believe that radar andinfrared photography are radically differentfrom visual photography and are the dirtscratchings of prehistoric man. Many peoplefeel that it takes a "radar expert" or an "in­frared expert" to interpret photography fromthese two classes of sensors. It is the author'sconsidered opinion that this is not the case.

The development of orthochromatic, pan­chromatic, and infrared sensi tive photo­graphic films involved changes in spectralsensitivity, but these changes have been ac­cepted as natural improvements of graphicrecording techniques. Several forms of colorphotography have been accepted just as nat­urally. The development of radarscope andthermal photographic systems should be ac­cepted in the same manner, since the changefrom one part of the energy spectrum to an­other influences the nature of the graphicrecords produced, but does not alter the basicelements considered in interpreting them. Asimulated radarscope photograph of the Pa-

ducah, Kentucky, area (Figure 7) can be usedto illustrate this. In this simulation the shapeof the Ohio River as it winds past Paducah,Kentucky, and Metropolis, Illinois, is evi­dent. The relative size of the bright spots, orradar returns, from Metropolis and Paducahsuggests that Paducah is several times thesize of Metropolis. Population figures confirmthis, for Paducah numbers over 40,000 per­sons, while Metropolis claims less than 10,000persons.

Both the shape and size of the dark, or "no­show," area at the southeast edge of the sim­ulation agree nicely with the general mapoutline of Kentucky Lake. This lake and theOhio River can be identified because of tonalcontrast. The radar returns from the landareas bordering these bodies of water providethe distinct land-water contrast characteristicof many radarscope photographs. Anotherarea of distinct tonal contrast can be seenapproximately 12 miles northeast of the ra­dar. A lake might produce this appearance,but there is no lake at this location. This tonalcontrast represents an abrupt change inground elevation, where an area of rollinghills gives way to the low flood plain of a trib-

PHOTOGRAPHIC INTERPRETATION COMMON TO SEVERAL SENSORS 655

Cent ralPork

U.N.

8uildlng

8atteryPark

FIG. 8. Infrared (thermal) photograph of Man­hattan Island. (Photograph by HRB-Singer, Inc.,for the U. S. Air Force.)

utary of the Ohio River. Here the no-showarea results from lack of illumination of theground at the base of the hills. In other words,the no-show area is in the shadow of the hills.Radar shadows are common and quite sig­nificant in mountainous areas.

Pattern is seen in the radar returns fromhighways and railroads in several parts of thesimulation. The roads themselves seldom pro­duce a visible return, but the buildings,

bridges, embankments, and vehicles on theroads produce patterns of returns that formlinear traces along the transportation routes.Many man-made features produce distinctradar return patterns as do the parallel ridgesof the Appalachian and several other moun­tain chains.

Texture is present in radarscope presenta­tions, but it is particularly difficult to simu­late. Texture is produced by roughness ofland surfaces, by waves on ""ater, and byother fea tures \\"i th irregular or in terru ptedsurfaces.

Site is important in interpreting radar re­turns from many features, and the shadowarea noted earlier is a good example. Inter­pretation of radar returns from bridges anddams involves site considerations, as radarreturns in the no-show areas caused by bodiesof water are not apt to be houses or cities. InFigure 7 returns from bridges or dams appearat seven points. The bright linear return atthe near edge of Ken tucky Lake represen tsKentucky Dam. Lakes and dams of this sizeusually have power plants associated withthem, and Kentucky Lake is no exception.The pO\\'er plan t can be seen as the small,blockish return at the east end of the dam,clearly indica ti ng that associ a tions betweenseveral features are important in radarscopephoto interpretation.

The fact that the radar return from theKentucky Dam power plant merges with thereturn from the da m is a function of twothings: First, the distance between the damand power plant; and second, the resolutionpotential of the radar. The lack of a distinctno-show area from the surface of the Cumber­land River is another example of resolutioneffects. Note that the trace of the Cumber­land River is frequently shown by radar re­turns from the far bank even where the no­show area of the water surface fails to resolve.

Although this simulation was preparedspecifically for this paper and represents noparticular radar system, it does have many ofthe characteristics of long pulse-length, widebeam-width radars. Short pulse-length andnarrow beam-width radar systems are in ex­istence and produce radarscope presentationsremarkedly similar to some visual aerialphotography.

A graphic record of infrared radiationsfrom Manhattan Island obtained at 11 p.m.on January 9, 1958 is reproduced in Figure8. This record was produced by HRB-Singer,Inc., Science Park, Pennsylvania, for theU. S. Air Force and was obtained with aninfrared or thermal, sensing system. If this

656 PHOTOGRAMMETRIC ENGINEERING

graphic record is considered in terms of shape,size, tone, shadow, pattern, texture, si te, as­sociation, and resolution, the interpretationof many infrared images becomes quite sim­ple.

The shape, size, and tOlle of the dark areaa t the sou th end of Manhattan Island permi tlocating Battery Park. The Brooklyn andManhattan bridges connecting Manhattanwith Long Island are clearly visible due totonal contrast. Size, shape, pattern, site, andassociation all have some bearing on this in­terpretation. A minor amount of map com­parison would supply enough information onpattern and association to permit interpreta­tion of the images representing City Hall,China Town, and Canal Street approach tothe Holland tunnel. Farther north CentralPark provides a distinctive pattern. CentralPark and Broadway Avenue provide suffi­cient association to identify the bright imagesfrom the Times Square area. The dark arearepresenting the United Nations Headquar­ters is also apparent.

Throughout this paper the principles thatmake radar and far infrared sensing systemswork have been completely ignored. Despitethis it has been possible to demonstrate acertain degree of interpretive success withboth sensors through the application of nine

basic elements found to be important in inter­preting visual photographs. \\Then these nineelements are coupled to a basic understandingof a sensing system and its graphic records,interpretations can be greatly improved.However, such improvements result, pri­marily, from a better understanding of whatcauses the graphic record to show shape, size,tone, shadow, pattern, and texture. Integra­tion of these characteristics wi th si te, associa­tion, and resolution considerations signifi­cantly strengthens interpretation. Regardlessof how, or where, interpretation begins, con­scious or unconscious consideration of thesenine basic elements is essential to effectiveinterpretation of graphic records from manysensing systems. These nine basic elements­shape, size, tone, shadow, pattern, texture,site, association, and resolution-are elementsof photographic interpretation common toseveral sensors.

REFEREKCES

(1) Fox, R. F. "Visual Discrimination as a Func­tion of Stimulus Size, Shape, and Edge Gradi­ent." Boston University Technical Note No. 132,August 1957.

(2) Colwell, R. 1\. "A Systematic Analysis of SomeFactors Affecting Photographic Interpreta­tion." PHOTOGRAMMETRIC ENGINEERING, Vo!.XX: 433-454, June 1954.

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