The accuracy of perturbation theory for acoustic penetration of sediment due to interface roughness.

Abstract

Lowest‐order perturbation theory (PT) is usually considered valid for modeling scattering from rough surfaces with a small roughness. In particular, for PT to be accurate near the specular direction, it is required that kh≪1, where k is the acoustic wave number and h is the rms surface height. In the case of an acoustic wave incident on the seafloor, a rough interface will scatter sound back into the water and also into the sediment; such scattering into the sediment will occur even when the incident grazing angle is below the critical angle. Here, the accuracy of PT for acoustic penetration through a rough water/sediment interface with a power‐law roughness spectrum is examined using exact integral equation results for the 2D problem. It is found that PT remains accurate for kh up to and well beyond unity, when the incident grazing angle is either above or below the critical angle. The reason for this surprising result will be discussed. [Work supported by ONR.]