Low‐frequency, long‐range sound propagation modeling over a locally reacting boundary with the parabolic approximation

Abstract

There is substantial interest in the analytical and numerical modeling of low‐frequency, long‐range atmospheric acoustic propagation. Ray‐based models, because of their frequency limitations, do not always give an adequate prediction of quantities such as sound pressure or intensity levels. However, the parabolic approximation method, widely used in ocean acoustics, and often more accurate than ray models for frequencies of interest, can be applied to acoustic propagation in the atmosphere. Modifications of an existing implicit finite‐difference implementation for computing solutions to the parabolic approximation are discussed. A locally reacting boundary is used together with a one‐parameter (the flow resistivity) ground impedance model. Intensity calculations are performed for a number of flow resistivity values in both quiescent and windy atmospheric sound channels. Variations in the value of this parameter are shown to have substantial effects on the spatial variation of the acoustic signal. [Work supported by NASA.]