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

5aPAa11. Nonlinear acoustic scattering from trapped gas bubbles in sandy sediments.

Frank A. Boyle

Nicholas P. Chotiros

Appl. Res. Labs., Univ. of Texas, P.O. Box 8029, Austin, TX 78713-8029

A nonlinear backscattering model for trapped bubbles in sandy sediments was developed. A difference frequency scattering coefficient is computed via a technique similar to that of Ostrovsky and Sutin [Nonlinear Sound Scattering from Subsurface Bubble Layers, Natural Physical Sources of Underwater Sound, edited by B. R. Kerman, pp. 363--373 (1993)], which treats the case of bubbles surrounded by water. The Biot theory is incorporated to model the acoustics of a sandy sediment. Biot fast and slow waves are included by modeling the pore fluid as a superposition of two acoustic fluids with effective densities that differ from the pore fluids' actual density and account for its confinement within sediment pores. The principle of acoustic reciprocity is employed to develop an expression for the backscattering strength. [Work supported by ONR under management by APL/UW.]