Angular dependence of acoustic backscatter from simulated anisotropic Goff–Jordan seafloor relief

Abstract

The angular dependence of 12‐kHz acoustic backscatter from simulated anisotropic centimeter‐scale bottom relief is investigated for angles of incidence between 0° and 20°. 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, kn and ks, of the 2‐D surface roughness spectrum to be O(m−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.]