Abstract:

Sound scattering from the seabed can be generally attributed to two major mechanisms connected with seabed roughness and volume inhomogeneities. Each of these two mechanisms in turn can contain different components. For unconsolidated (fluid) sediments, volume inhomogeneities are due to spatial fluctuations of two different parameters, the density and compressibility, or the density and compressional wave speed, with respect to their mean values. For elastic bottoms, one more fluctuating parameter, shear wave speed, is to be considered. The roughness component can be attributed to the water--sediment interface and to various internal interfaces in the seabed medium as well. In this paper, the effects of cross correlations between the roughness of different interfaces and between the volume fluctuations of different parameters, as well as possible volume--roughness correlations, are examined using a first-order perturbation model. Expressions for the bottom scattering cross section involve corresponding cross-correlation and cross-spectral matrices of seabed medium perturbations. Frequency-angular dependencies of the scattering strength in monostatic and bistatic cases are analyzed for various types of seabed stratification and correlated irregularities. Comparisons are presented for the cases of strongly correlated, anticorrelated, and partially correlated perturbations. Examples are given where the cross-correlation effects are important and should be taken into account in development of methods for