Color Aerial Photography

the photography of terrain from the air for the purpose of reproducing the terrain’s landscapes or individual features in their natural colors. The information content of aerial photographs and the possibility of interpreting such photographs are enhanced because the color differences in the terrain are captured on color aerial photographs.

Color aerial photography may be carried out by taking pictures with multilayer aerial film simultaneously in the blue, green, and red regions of the visible portion of the electromagnetic spectrum (see). It may also be performed by using three separate aerial films and later combining the monochromatic images obtained during processing to produce a full-color image. The second method makes it possible to obtain the most accurate differentiated color reproduction of features but, on the whole, is more complicated and expensive than the first method at the present time. Aerial photography in transformed colors, which is called multiband aerial photography, is sometimes regarded as a type of color aerial photography.

Multilayer negative and reversal aerial films are used for color aerial photography (seePHOTOGRAPHY). Color negative aerial film is intended for the large-scale production of prints and makes it possible to photograph under a fairly wide range of conditions, since the color reproduction in the film may be adjusted during processing. The colors of the dyes for each layer of the aerial film are the complementary colors with respect to the region of the layer’s spectral sensitivity. The use of reversal, or false-color, aerial film makes it possible to obtain directly a positive image of the terrain; in addition, the natural color contrasts are captured somewhat better. At the same time, color aerial photographs may be taken with such film only under strictly limited conditions and are intended for direct use in the interpretation of original aerial photographs or for making a few positive prints from individual frames.

Color aerial photographs are taken with the same aerial cameras (except for superwide-angle cameras) and from the same altitudes as are black-and-white aerial photographs in plan and in perspective. To improve the image properties of color photographs, aerial cameras are equipped with lenses characterized by reduced chromatic aberration and with lens shades for decreasing the scattering of light during the photography. As a rule, the development of color aerial films is automated. Prints are made on paper or positive film or, for high-precision measurements, on glass plates. Semiautomatic electronic copying devices are used to print the photographs. Both color prints and black-and-white prints (as intermediate materials) are made for cartography based on color aerial photographs. Conventional instruments for photo interpretation (mainly stereoscopes or topographic plotters), as well as stereophotogrammetric instruments, are used in the study of landscapes or individual terrain features on the basis of color aerial photographs and in the compilation of various kinds of maps from such photographs.

Color photography from the air was first performed in 1936 in both the USSR and Canada. In both countries, motion-picture cameras were used rather than aerial cameras. In the USSR, the photography was carried out by the Leningrad Division of the Central Scientific Research Institute of Geodesy, Aerial Photography, and Cartography. Color aerial photography proper was first used for scientific and economic purposes immediately after World War II. By the late 1950’s, it had been used extensively.

Color aerial photography is effective in the general geographic study of the earth (especially studies of seasonal changes in the earth’s appearance), in the geological mapping of outcrop areas, in the management of coniferous and deciduous forests, in making inventories of tree stands damaged by industrial pollution or harmful insects, in the compilation of soil maps of croplands, in surveys of planted fields, and in the study of continental shelves, especially with respect to topography, shallow-water bottom types and vegetation, water pollution, and ice conditions. Color aerial photography is also employed in the planning of urban reconstruction, in socioeconomic and archaeological research, and in topographic surveys of densely populated regions. In surveys from spacecraft, color photography is used as a new means of studying the earth’s surface and phenomena that occur on the surface.