ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

5aUW14. Effects of shear elasticity on high-frequency bottom scattering.

Anatoliy N. Ivakin

Andreev Acoust. Inst., Shvernika 4, Moscow 117036, Russia

Darrell R. Jackson

College of Ocean and Fishery Sciences, Univ. of Washington, Seattle, WA 98105

It is known that marine sediments can support both compressional and shear waves. However, published work on scattering from irregular elastic media has not examined the influence of shear on seabed scattering in detail. Here, a perturbation model for high-frequency sound scattering from an irregular elastic bottom is considered. The seabed is assumed homogeneous on the average and two kinds of irregularities are assumed to cause scattering: roughness of the water--seabed interface and volume inhomogeneities of the sediment mass density and the velocities of compressional and shear waves. The first-order small perturbation approximation is used to obtain expressions for the scattering amplitude and average intensity of the scattered field. The angular dependence of the backscattering strength is calculated for different types of sediments and the influence of shear elasticity is examined by comparison with the case of a fluid bottom. Shear effects on both roughness and volume scattering are found to be rather strong (up to 5--7 dB) for dense sandy sediments at near-critical and subcritical grazing angles. The difference between the angular dependencies of roughness and volume scattering is examined and features of interest for remote acoustic characterization of seabeds are noted. [Work supported by ONR.]