Sound propagation near the ground in a turbulent atmosphere

Abstract

For many geometries of sound propagation in an atmosphere, the sound-pressure field is a sum of the direct wave from the source to the receiver and that reflected from the ground. The resulting field is significantly affected by atmospheric turbulence. A theory is presented that gives an analytical formula for the mean-square sound pressure in an anisotropic turbulent atmosphere with temperature and wind velocity fluctuations. This formula contains a ‘‘turbulence’’ factor T which describes the reduction of interference maxima and minima due to atmospheric turbulence. For the important particular case of isotropic turbulence, T is expressed in terms of the coherence function of the direct wave from the source to the receiver. The turbulence factor T and the mean-square sound pressure are calculated and compared for Kolmogorov, Gaussian, and von Karman spectra of temperature and wind velocity fluctuations. Furthermore, the relative contributions to the mean-square sound pressure due to temperature and wind velocity fluctuations are compared. [This material is based upon work supported by the U.S. Army Research Office under Contract No. DAA G55-98-1-0463.]