Space Photography in Geologic Exploration

Abstract

Space photography provides a perspective of the terrain not possible from aircraft-flying heights. The chief advantage of this photography is the increased amount of coverage made possible. Tens to hundreds of thousands of square kilometers of the earth's surface can be imaged in a single photograph, revealing gross structural features which may not be apparent in larger scale photography, as well as the spatial relations between widely separated features, such as the relation of major lineaments to folding and volcanism. Mosaics of thousands of conventional aerial photographs would be required to achieve a somewhat similar perspective. Considerably more geologic information is recorded on photos of arid or semi-arid regions than on those of humid or temperate regions where soil and vegetation mask much of the underlying lithology and structure. Moreover, the wide coverage, which is the chief advantage of space photography, is possible only at the expense of lower ground resolution. Lithologic units are mappable only if they form extensive outcrops and contrast sharply with adjacent units. Hence, space photography should be considered a supplement to, rather than a substitute for, aerial photography. Although space photography does not provide the geologic detail necessary for a complete understanding of areal geology, this may be an advantage during the initial stages of exploration planning. Hyperaltitude photography draws attention to the broad aspects of the regional geology; the overview afforded from space facilitates the elimination of unpromising areas and the focusing on promising areas for more detailed aircraft and ground survey.