Sound speed and attenuation in water-saturated granular materials at MHz frequencies

Abstract

Sound speed and attenuation measurements are reported for water-saturated granular materials (natural sand and glass beads) at frequencies of 1.0 to 1.8 MHz. Median grain diameters were 0.219 to 0.497 mm, corresponding to kd>1, i.e., the scattering regime. The measurements were made for different thicknesses of sediment resting on a reflective surface using a monostatic geometry. The attenuation estimates compare well with previously reported experimental results and to the predictions of multiple scattering theory. The sound speed estimates exhibit the negative dispersion predicted by theory, but compared to previous measurements are biased low by 100 m/s to 200 m/s. It is argued that this bias is due to microbubbles in concentrations of O(10) ppm by volume.