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THE FIVE F:ACETS OF AERIAL PHOTOGRAPHY* Donald J. Belcher, President, Donald J. Belcher & Associates, Inc., Ithaca, N. Y. ow do You look at an aerial photo­ (and no better) than some of the military H graph? And how much do You see? personnel. However, when considering the Everyone has two filters built in between problem of providing organized and com­ his eyes and his brain. One is an "interest" mercially acceptable. interpretation of filter and the other an "experience"filter. aerial photographs, we should acknowledge The interest filter cuts in first. that one man cannot interpret in every If I handed photos to five different field. ,people in this audience and asked them The operation of providing information what impressed them, I would get 3 to 5 and recommendations from aerial photog­ different evaluations. A specialist tends to raphy indudes analysis and interpretation. look at a photograph through his "special­ A nalysis means breaking the photo­ ist" filter. This invisible device cuts out graphed area down into soil, rock and other "wave lengths" that carry other types of subdivisions. This saves a specialized inter­ information to those working in different preter's valuable time and he uses his fields. For example, an engineer-specialist experience in interpreting the ground con­ might examine a photograph and not ditions in terms of his specialty. realize that the area contained an unusual . An example may' help to illustrate the stand of hardwood. But a forester, recog­ difference between an interpreter and an nizing this stand immediately, might com­ analyst: A package of aerial photographs pletely overlook a gravel deposit that was comes to an office. An analyst lays them quite evident to the engineer. out, studies the over-all objectives of the Then the experience filter cuts in and job, and proceeds to divide the area into further affects the amount of information flood plains (low elevation), terraces gained from the photographs. This says, in (inter'mediate elevation), and hills and effect, that even though definitely inter­ mountains (highest elevation in the area) . ested in some special field, the amount . The analyst then goes back to the first that you can see (or extract from the major division (flood plains) and sub­ photographs) depends upon experience. divides it on the basis of soil texture and The "interest" filters can be considered drainage conditions. He repeats this action as being in red, green, yellow or other on the intermediate area and marks spe­ colors, but the "experience" filter comes cial features that occur in this zone. The in shades of gray. The more. experience a upper area is divided into rock types, man has,. the lighter the gray becomes be­ amount of soil cover, etc. The amount of cause he has ,learned how to see more. detail in each area is dictated by the job Because of this, the field of aerial photog­ requirements. raphy can conveniently be divided into This man has analyzed the photographs five facets, or uses. And what you see and has mapped conditions that he has depends upon how you look at the photo­ inferred from the soil and rock patterns. graphs. Suppose, now, that two interpreters, spe­ Before looking closely at these five cializing in different fields, huddle with the facets, we should examine the problem analyst. One interprets the lowland in common to all of them-the people. We terms of suitability for cropland; the sec­ talk about the problems of restitution, of ond, an engineer-interpreter, works on image motion and of various forms of dis­ levee location for flood control of the same tortion, but what about distortions due to area, and on a highway location on higher human handling? ' ground. If damsites, geology, aggregates Have. you ever thought of what you or other requirements were a part of the mean when you say a "photo interpreter"? job, an engineer-geologist wouldconcen­ If you mean a jack-of-al1-trades in aerial trate on the area of hills and mountains. photography, then you have hit it as well From this typical case, important dis- * Presented at Semi-Annual Meeting of the Society, Rochester, . Y., September 24, 1953. 746 • THE FIVE FACETS OF AERIAL PHOTOGRAPHY 747 tinctions are extracted. These are: thre~ individuals, experienced in photo­ 1. An analyst may not be able to inter­ analysis (but not in Agronomy) were desig­ pret skillfully. nated as "experts." 2. Interpreters need not be, and often The first two, called X and Y were given are not, skilled analysts. stereo triplets and a stereoscope. That was 3. A man needs ground experience in all they had. They had never seen the something besides photography be­ area, had no way of knowing its exact -fore he s~ould try to interpret. location, and had no reference material. Finally, there are regional and climatic Th~ third person, called Z, mapped the characteristics that limit an interpreter­ same area, but had access to reference and an analyst (but to a much lesser de­ material. Also as a separate action, he was gree). A geologist or an engineer experi­ permitted to make a limited reconnais­ enced in .Panama will be of limited value sance of the area; he thus had the oppor­ in the arctic or in Arabia; similarly, a tunity for improving his maps. ground water man from Texas will do well The maps made by these three were in North Africa but, in the northern judged on the basis of a "100% Accuracy U.S., his rating may slip markedly simply Map" compiled by the USDA soil mappers. because he has had no experience in that The results are certainly not 'biased as re­ type of area.' gards aeri<v photography because all the Today, the analyst does not appear in ratings were made by the soil mappers, and the military picture because he is not used. most practicing soil surveyors are reluctant Military "PI" todays means recognizing to go into the use of aerial photographs installations, or vehicles, or weapons, that beyond the base map stage.* Photo map­ have military significance. Even the'n, the ping does not, and is not intended to, man that performs the recog-nition work replace all ground investigations. The com- / merely reports what he se.es. It is left to bination of skilled photo-analysis with spot the Intelligence Division Qr others to de­ checking in the field produces accurate termine the significance in terms of the maps in a minimum of time. An unsup­ combat situation. ported analysis of this type is never con­ Good qIJality analysis and interpretation sidered a complete job. do not result from a part-time occupation In the test, the data show the differ­ taken up casually. The result of a man ences in the ability of persons who had spending X years in merely looking at been called experts. That there is a #ffer­ pictures is not competence as an analyst. ence in experts is important. As a guide to competence this test should The three, X, Yand Z, were not experi­ be made: enced in' interpretation in agricultural 1. Does the man really use a stereoscope? soils, but they produced these results for 2. Has he served an apprenticeship in use in determining their qualifications as the field checking his analysis against experts. ground conditions? Parent Material-This means the origin, 3. Has he had previous experience in texture, mineralogical composition of this type of area? coarse fractions, depths of leaching, or ~f there is not a firm "yes" to all three relative acidIty; they are rated as firm, questions, the man is an amateur. very firm or compact. The ratings of X, Yand Z are shown on WHE IS A T EXPERT NOT AN EXPERT? Figure 1. The obvious answer to this facetious As a matter of interest, the two conven­ question is, "When he is not qualified." tional ground surveyors rated 97% each. 'We now have a ~ay to make a measure­ Slope Classes-(N0 instruments used; ment. ground surveys use an Abney level) The Agronomy Department at Cornell, In this test and as shown in Figure 2, Y assisted by members of the Soil Survey was twice as expert as X. Division of the United States Department When Z checked his own work in the of Agriculture, carried out tests that give field, he raised his 67% to 78%. Even so some numbers for use in making a determi­ nation. * Rourke and Austin, PHOTOGRAMMETRIC Two areas in northern New York State ENGINEERING, Vol. XVIf, pp. 738-747; Soil were selected as sites for test mapping and Survey Manual, '1951, USDA Handbook No. 18. 748 PHOTOGRAMMETRIC ENGINEERING parent materia I • f FIG. 3. Ratings o(land use capability. FIG. 1. Ratings of parent m~terial. were poor and incomplete b~cause of the this was somewhat less thari that of Y aQsence of any local basis of reference for \~ithout any field checking. the straight interpretation phase. On this Erosion Classes basis, one interpreter mapped half of the X-100%; Y-99%; Z-94% area correctly. With.the chance for field When Z visited the area, he raised his reconnaissance, Z rated 76% correctly 94% to 100%. against a low of 80% for the complete Land Use Capability ground study. As shown by Figure 3, Y was three times The preceding figures can be· analyzed as expert as X. Following a quick field 'as follows: check of his work, Z raised his 62% to First, experts (so-called) vary in their 68%. ability to map various elements. In some Areas in Complete Agreement instances, where their experience is equal, (It should be noted that this means as in Erosion Classification, they do acidity, color, and every other basis 111 equally well.

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