V. Premus D. Alexandrou
Dept. of Elec. Eng., Duke Univ., Box 90291, Durham, NC 27708-0291
The angular dependence of 12-kHz acoustic backscatter from simulated anisotropic centimeter-scale bottom relief is investigated for angles of incidence between 0(degrees) and 20(degrees). Numerical simulations of backscattering strength as a function of elevation and azimuth are obtained by merging the Kirchhoff approximation with realizations of seafloor topography derived from the Goff--Jordan surface model. The surface model has been theoretically extrapolated to the small-scale roughness regime by connecting the spatial sampling interval with the incident acoustic wavelength and defining the characteristic wave numbers, k[sub n] and k[sub s], of the 2-D surface roughness spectrum to be O(m[sup -1]). The viability of extending the Goff--Jordan model to centimeter-scale relief is supported by the recent observation of power-law spectra within the spatial frequency range of 0.01 to 1.0 cycles/cm [D. R. Jackson and K. B. Briggs, J. Acoust. Soc. Am. 92, 962--977 (1992)]. The results demonstrate that backscattering strength can be very sensitive to azimuthal variation in surface correlation properties. It is also observed that the spectral roll-off parameter has an important impact on the minimum degree of anisotropy that can be identified by the backscattered acoustic signature. [Work supported by ONR through Contract No. N00014-93-I-0049.]