A comparison of the passive infrared reconnaissance performance of the mercury-doped germanium (Ge:Hg) detector, operating in the 8 to 13 micron atmospheric window, and the indium antimonide (InSb) detector, using the 3 to 5 micron window. The Ge:Hg signal-to-noise ratio is superior by a factor of 2.5 at close range to 8.4 through a mile of hot, humid atmosphere with targets at ambient temperature. It remains superior through useful atmospheric path lengths for targets up to 530 degrees K. This extra value is often lost because of the limited number of shades of gray available on photographic film. Some of the unused S/N is typically traded for increased resolution in detecting small warm targets, at the cost of lowered display of terrain background features. For good terrain registration and maximum detection of point targets, simultaneous use of high- and low-resolution detectors is suggested. 16 pp. Refs.
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