High frequency backscattering from sandy sediments: single or multiple scattering

As the sand grain size approaches the acoustic wavelength, the underwater backscattering strength increases rapidly. Laboratory measurements indicate that the shallow-grazing angle backscattering strength increases as the third power of the normalized grain diameter. In this regime, it has been shown that the attenuation of the sound in the sand increases as the fourth power of frequency and the speed of sound decreases with increasing frequency. The most likely explanation for the attenuation and speed dispersion is multiple scattering [Schwartz and Plona, J. Appl. Phys. 55 (1984) and Kimura, J. Acoust. Soc. Am. Express Lett. 129 (2011)]. Single and multiple scattering theories will be applied to the backscattering problem with the purpose of determining if it is a single or multiple scattering process. [Work supported by the Office of Naval Research, Ocean Acoustics Program.]