A model study of acoustic reflection from a rippled water-sand interface

Abstract

A model experiment was performed to measure acoustic reflection from a rippled sand surface using a pulse-echo system employing electrostatic transducers over the frequency range 100-350 kHz. The ripple wavelength of 1.23 cm was slightly greater than the longest acoustic wavelength and had an amplitude to wavelength ratio of 1/10. Boiling of the sand to remove entrapped air was essential before the scattering effects of the ripples could be observed. The angles of propagation of the scattered spectra are found to agree with the theoretical prediction within + 2°. The amplitudes of two orders of the scattered spectrum were measured at an incident angle of 45° and compared to the theory for the limiting condition where the ripple wavelength is very much larger than the acoustic wavelength. Agreement was excellent for the spectral reflection, but was not as good for the first order reflection.