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

5aUW3. High-frequency bistatic scattering by sub-bottom gas bubbles.

Dezhang Chu

Dept. of Appl. Ocean Phys. and Eng., Woods Hole Oceanograph. Inst., Woods Hole, MA 02543

Kevin L. Williams

Univ. of Washington, Seattle, WA 98105

D. Tang

Woods Hole Oceanograph. Inst., Woods Hole, MA 02543

Darrell R. Jackson

Univ. of Washington, Seattle, WA 98105

The acoustic scattering by sub-bottom inhomogeneities has received increased attentions in recent years. However, most of the previous studies were restricted to monostatic or backscattering. To better understand the complicated scattering process, a bistatic scattering involving both grazing and azimuth angles dependence is desirable. As part of the Coastal Benthic Boundary Layer Special Research Program (CBBLSRP), along with a previously reported backscattering experiment, a bistatic scattering field experiment using Mobile Benthic Receiver Arrays (MBRA) operated at 40 kHz was conducted at Eckernfoerde Bay, Germany in April 1993. It has been found in previous studies that high-frequency backscattering measured is due to methane gas bubbles buried about a meter beneath the seafloor. In this paper, a bistatic scattering model is proposed as an extension of the previously developed backscattering model to account for the three-dimensional (out-of-plane) scattering effect. In the model, as in the backscattering model, gas bubbles were assumed to be oblate spheroids with varying aspect ratios. While the parameters used in the model to fit backscattering data are kept unchanged, the model prediction for the bistatic scattering is satisfactory. It is found that the scattering strength exhibits a mild azimuthal dependence and is sensitive to the scattering geometry. [Work sponsored by ONR.]