ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

4pUW5. Acoustic wave scattering by 3D variability of deep ocean sediments.

D. Tang

D. Li

G. V. Frisk

C. J. Sellers

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

Volumetric inhomogeneities of marine sediments, especially their horizontal changes, are of great importance in understanding bottom scattering processes, but difficult to assess. Though certain theoretical models are available, so far little is known about sediment variability experimentally. During the 1993 ARSRP experiment, bottom scattering data over a sediment pond were obtained using the Deep Towed Acoustics/Geophysics System (DTAGS) near the bottom with its receiving acoustic array configured vertically. By analyzing this data set, the following results have been found: (1) The sediment is layered, but with gentle changes horizontally. (2) Beamforming in the normal direction of multiple pings reveals that there are two irregular sublayers at depths of about 16 and 60 m beneath the seafloor. Their thicknesses are both about 15--20 m. (3) Simulations based on a simple model compare favorably with the experimental data, and the results suggest that volumetric inhomogeneities can be identified by examining the ping-to-ping correlation of the vertically reflected field. (4) The backscattered field is determined by first subtracting the coherently reflected portion of the field and then beamforming the residual portion at the desired grazing angles; the behavior of the backscattered field correlates well with the aforementioned irregular sublayers. [Work supported by ONR.]