Head-wave effects on bottom reverberation and scattering strength in shallow water.

Abstract

For transmitters and receivers having wide vertical angular apertures, there are always at least two paths to and from a rough bottom scattering area: the direct water-borne path and the head-wave path. At long ranges and small grazing angles, contributions to backscatter from these two paths interfere coherently and give rise to complicated reverberent signals that are difficult, if not impossible, to interpret in terms of the conventional scattering strength concept. Numerical simulations using the full-wave two-way PE model in isovelocity shallow-water environments have been used to study reverberation due to bottom roughness when head waves are present. It has been found that backscattering from a rough fluid–fluid interface is not a local phenomenon and cannot properly be described by a cross section per unit area as a function of grazing angle. Only a wave-equation-solving model that combines propagation and scattering can yield correct results. [Work supported by ONR, Code 1125OA.]