Scattering of acoustic waves from randomly rough surfaces

Abstract

Measurements have been made of sound scattered in the specular direction by fixed rough surfaces. The surfaces used were physical realizations of computer generated topographies which corresponded to Gaussian distributions in height to within specified limits. The RMS heights and correlation lengths of the two selected surfaces are 0.124 and 0.74 cm for the coarser surface and 0.021 and 0.305 cm for the finer surface. Each surface was milled into both brass and aluminum blocks. Measurements were made in water using 0.5‐, 1.0‐ and 2.25‐MHz transducers. Transient pulse analysis techniques were used to provide information about the scattered pulse over a wide range of frequencies. The dependence of the scattered return on incident angle, the sound speed in and density of the scattering material, the RMS height and the number of correlation lengths insonified is investigated. Comparisons are made with several theoretical models including a multiple scattering model. The scattered field is also illustrated by means of schlieren visualization.