Scattering of sound by atmospheric turbulence

Abstract

A computer simulation of the effect of small scale turbulence on atmospheric sound propagation over a complex impedance boundary is developed. The atmosphere is broken up into spherically symmetric eddies characterized by a Gaussian profile. Single scatter is assumed and a closed form of the first Born approximation for scattering is obtained, giving each eddie's contribution to the total fluctuation of the sound pressure at a receiver downrange. The numerical simulation was accomplished with the concept of a “realization,” or snapshot of the turbulent medium. Each eddie's scatter contribution was added up for a particular configuration of eddies, giving that realization's total sound pressure fluctuation. The eddies were then given a random change in their coordinates. The total sound pressure was calculated for this realization, and the process repeated. A complex impedance boundary was added and the predictions of the standard deviations of the amplitude fluctuations, amplitude probability distributions, and structure functions were then tested against experimental data. Good agreement was found whenever the average intensity of the fluctuations was well above the background noise level. [Work supported by U. S. Army Construction Engineering Research Laboratory.]