Subcritical penetration of sandy sediments due to interface roughness.

Abstract

Seafloor roughness can cause acoustic energy to propagate into sediments for ‘‘subcritical’’ incident grazing angles, that is, grazing angles smaller than the critical angle determined by the compressional wave speed. Such effects must be considered in interpreting experimental data on sound penetration into sediments. The sediment is modeled as a fluid supporting only compressional waves and a twofold theoretical approach is used. First, an exact integral equation is solved numerically to obtain the penetrating field in two dimensions. Physical insights are abstracted from these results which are also used to show that perturbation theory is valid for problems of interest. Using perturbation theory, a numerically tractable three-dimensional model is compared to some of the experimental data of Chotiros and colleagues [N. P. Chotiros, J. Acoust. Soc. Am. 97, 199–214 (1995)]. The model and data match well subject to plausible assumptions about roughness statistics. [Work supported by ONR.]