A long‐range outdoor sound propagation model based on an analytical determination of the acoustical ray paths

Abstract

For short‐range sound propagation problems, the acoustic energy reaches a remote receiver via a straight direct ray and a ground‐reflected ray and the total pressure at the receiver can be precisely computed considering the geometrical spreading, the atmospheric absorption, and the ground effect [Piercy et al., J. Acoust. Soc. Am. 61. 1403 (1977)]. For long‐range sound propagation problems, additional effects have to be considered: mainly, the refraction due to temperature and wind gradients that curve the rays and the turbulence that destroys the coherence between the rays. To evaluate the effect of refraction, a constant linear sound‐speed gradient is assumed. This assumption allows an analytical determination of the curved rays and it also permits the determination of additional reflected rays that may appear in the presence of positive gradients, or of the position of the shadow zone in the presence of negative gradients. The total sound pressure at the receiver is computed by summing up the contribution from all the rays existing between the source and the receiver and, if the receiver is in the shadow zone, the diffraction solution of Berry is used [A. Berry and G. A. Daigle, J. Acoust. Soc. Am. 83, 2042–2058 (1988)]. The comparisons between theoretical and experimental results show the accuracy of the proposed model.