An analysis of the effect of atmospheric conditions on the acoustic detection of low-flying aircraft. For a given position at ground level, the problem is to determine the sound intensity resulting from a sound source of known acoustical power at specified altitude, range, and direction relative to the observer. A stratified atmosphere is assumed in which the temperature, wind velocity, and humidity are dependent on the altitude only. Specification of a refraction law for the sound ray emanating from the elevated source is followed by development of a three-dimensional ray-tracing program to determine the ground level sound intensity due to a source at an altitude of 500 ft radiating 100 kW (134 HP) of acoustical power. The analysis reveals that the detection range of an elevated source is extremely sensitive to azimuth of propagation as well as to source altitude, power, and frequency. 95 pp. Refs. (KB
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