Low-frequency 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 this type of 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 ground surface is used with one- and two-parameter impedance models, while a nonreflecting boundary condition is used to handle the upper boundary. Relative sound-pressure level calculations are performed for a number of flow resistivity values in both homogeneous and nonhomogeneous atmospheres. Comparisons to experimental data are made which suggest this modeling approach can be useful in the study of these types of propagation problems.