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Studies indicate that the Kelsh stereoplotter is capable of locating subtle surface anomalies using high-altitude photos and ground control.
Petroleum explorationists in the early 1950s used the Kelsh plotter to map in detail known geologic surface structures in order to determine the amount of structural closure and fault throws. In the early 1960s, with the advent of high-altitude photographic coverage over much of the United States, a new role developed for the plotter. The large, 40-sq-mi/print, lateral stereoscopic coverage allows a much wider look at large areas, and thus a new system of geologic reconnaissance mapping with extremely accurate results. Tip and tilt, inherent in all aerial photographs, can be removed. An enlargement factor of 5, together with vertical ground controls for each stereo pair, makes possible dip-magnitude readings of 1/2 degree and accurate structural elevation work. Using the Kelsh plotter to evaluate larger geologic provinces, many previously undiscovered subtle nosings, faulted noses, and independent surface closures become apparent. Cross-section work and measurement of the thickness of formations also may be accomplished. A newly developed system of polarized light makes possible the use of color aerial photographs with the same accuracy as conventional black and white prints.
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