An investigation of the ability of ground observers, unaided by optical or electronic devices, to detect visually each of six reconnaissance aircraft. Calculations are made for a variety of conditions, in altitudes, speeds, and visibilities. Among several conclusions are; (1) the probability of visual detection falls off rapidly as aircraft altitude is decreased below 2000 ft; (2) increasing speed is an effective way to reduce detectability; (3) contrast is a critical factor in determining detectability but is difficult to predict or control.
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