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

2aUW4. On the dependence of bottom scatter on frequency, grazing angle, and azimuth.

Tokuo Yamamoto

Appl. Marine Phys. Div., RSMAS, Univ. of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149

The bottom scatter data from many different shallow and deep water sites by Jackson and Briggs (1992), Ogden and Erskine (1993), Hines and Barry (1992), and others show wide varieties of dependencies on frequency, grazing angle, and azimuth. Model predictions so far have not been satisfactory. For example, Mourad and Jackson (1993) suggested that the frequency dependence of bottom backscatter is due to the vertical velocity gradient. However, unrealistic velocity gradients were needed to predict the backscatter increasing with frequency. The high resolution crosswell tomography and cores of seafloor sediments show that the three-dimensional (3-D) spectra of velocity and density fluctuations within the sediments are anisotropic and dipping [Yamamoto, J. Acoust. Soc. Am. (to be published)]. It will be shown in this paper that the various dependencies of bottom backscatter on frequency, grazing angle, and azimuth observed in the data are results of the 3-D spectra of density and velocity fluctuations in sediments based on a volume scattering theory by Yamamoto [J. Acoust. Soc. Am. (in press)]. [Work supported by ONR.]