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

4pUW6. Backscattering data analysis using multiple constraint beamforming.

D. Li

D. Tang

G. V. Frisk

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

Using a vertical receiving array to measure bottom backscattering is clearly advantageous over the single receiver configuration. In the single receiver case, one uses arrival time information and the assumption that the scatterers are on the seafloor to obtain backscattering strength as a function of grazing angle; a vertical array, on the other hand, can be steered in various desired directions without invoking the aforementioned assumption. However, sediment stratification causes reflections in the normal direction, which are generally much stronger than the scattered signals at oblique angles. If one uses conventional beamforming, the reflected signals in the normal direction may therefore contaminate the signals received at oblique angles through sidelobe leakage. Therefore a multiple constraint beamforming technique is applied which substantially reduces the sidelobe level in the normal direction and enables one to measure backscattering strength at oblique angles. This technique is employed in the analysis of a deep ocean backscattering data set, and it is found that sediment inhomogeneities rather than seafloor roughness are the primary cause of backscattering. [Work supported by ONR.]