SCATTERED ACOUSTIC BOUNDARY WAVE GENERATED BY GRAZING-INCIDENCE AT A SLIGHTLY ROUGH RIGID SURFACE

A new theory describing sound scatter from a low roughness rigid surface [I. Tolstoy, “The scattering of spherical pulses by slightly rough surfaces” J. Acoust. Soc. Am. 66, 1135–1144 (1979)] has predicted that at near grazing incidence a boundary wave will be formed in the fluid above the surface, and that at sufficient ranges the amplitude of this scattered boundary wave will exceed that of the direct wave. A model experiment has been conducted using a point source and receiver embedded in a rough plane surface constructed of close packed rigid hemispherical bosses and the prediction of the amplitude of the boundary wave has been fully confirmed. In addition, the experiment has revealed that the coherent scattered boundary wave, which at lowest frequencies or ranges leads the incident wave by 90°, becomes more nearly in phase with the incident spherical wave as frequency or range are increased, thereby further strengthening the signal at the rough surface relative to smooth surface propagation. © 1979, American Association of Physics Teachers. All rights reserved.