Comparison of acoustic backscattering from a sand and a mud bottom in the South Yellow Sea of China

Abstract

Acoustic bottom scattering is the main source of reverberation background in the shallow water environment. Backscattering characteristics of a sand and a mud bottom in the South Yellow Sea of China were compared. The backscattering strength in the grazing angel range of 20°–70° over a wide band (6–24 kHz) was measured employing an omnidirectional projector and an omnidirectional hydrophone. For the sand site, the backscattering strength enhances with the increase of grazing angle and has a high variation rate at large grazing angles (60°–70°). For the mud site, it decreases with the grazing angle in the range of 50°–70°. A comparison of the data at different frequencies reveals that the backscattering strength in general slightly rises at the sand site, while it somewhat declines at the mud site, with the increase of frequency. A fitting curve of Lambert's law against the backscattering strength indicates that the measured data depart from Lambert's law at large grazing angles. Fitted results of a scattering model based on that of Jackson et al. to the backscattering strength suggest that seafloor roughness scattering is the main scattering mechanism at low frequency (<10 kHz) for the two sites, while volume scattering from sediment heterogeneity is dominant at high frequency and large grazing angles for the mud site.