This discussion is limited strictly to photogeomorphic,

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not bedrock mapping, applications of airborne imagery. Two factors control the value of a particular image in a particular study--scale and type of imagery.

Small scale imagery, less than 1:40,000, is particularly useful in broad, regional studies of structural trends, regional drainage pattern analysis, and lineament mapping. The larger scale imagery is more useful in fracture trace studies, local drainage pattern and single channel feature studies, and local tonal anomaly studies. Large-scale imagery may, of course, be compiled into a mosaic.

A wide variety of image types are available today. The most commonly available are black and white photography with many possible filter combinations, black and white infrared photography, color and color infrared (false color) photography, and thermal infrared and radar imagery. These images have a large range in cost and applicability. As a tool of the photogeomorphologist, color aerial photography appears to be the most generally useful for a basic study. Black and white, and black and white infrared, photography are the least expensive and quite useful. The other types of imagery have special, and sometimes very useful, applications.

Of value in some cases is sequential imagery showing, for example, variations of vegetation throughout the year. Such time-dependent changes in terrestrial features may have significance in photogeomorphic exploration.

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