Frequency and angular dependence of bottom scattering strength in shallow water with a sandy seabed

Abstract

The bottom scattering strength at low frequencies and small grazing angles is difficult to directly measure in shallow water. It is generally derived from mid- and long-range reverberation measurements. Reliable estimation of the bottom scattering strength from shallow-water reverberation requires a correct reverberation model, quality reverberation data, and an appropriate seabed geo-acoustic model that controls two-way sound propagation. In this paper, an effective Biot model for sand-silt bottoms, derived from low-frequency field measurements at 18 locations in different coastal zones around the world is used [J. X. Zhou and X. Z. Zhang, J. Acoust. Soc. Am. 117, 2494 (2005) and 119, 3447 (2006)]. A simple closed form expression for the reverberation in shallow isovelocity water [J. X. Zhou, Acta Acustica 5(2), 86–99(1980) in Chinese] as well as the normal-mode expression for the reverberation in shallow water with an arbitrary sound speed profile are used to derive the bottom scattering strength. The bottom scattering strength as a function of frequency and angle, derived from broadband reverberation data, will be reported and discussed. [Work supported by ONR.]