The effect of roughness on acoustic penetration of the seafloor as given by a fluid–fluid perturbation model and comparison with recent sediment penetration experiments

Abstract

Recent experimental results [F. E. Boyle and N. P. Chotiros, 2615–2619 (1992)] reveal acoustic penetration from water into sandy sediments at grazing angles below the compressional critical angle in relation to the mean surface. These authors interpret the results to indicate the excitation of a biot slow wave in the sediment. An additional mechanism for subcritical penetration will be discussed, based on assuming a small level of roughness at the water–sediment interface. Computer simulations of these experiments using theoretical calculations based on Rayleigh–Rice perturbation theory for 2‐D surfaces reproduce experimental results, indicating that the acoustic penetration of the surface may be due to scattering (diffraction) from low levels of roughness. The accuracy of perturbation theory for the level of roughness being considered is verified using comparisons with exact calculations in the special case of 1‐D surfaces. [Work supported by ONR.]