Inversion techniques for obtaining seabed low‐frequency reflection loss at small grazing angle in shallow water

Abstract

Low‐frequency bottom reflection loss at small grazing angles is a key parameter for sound field prediction in shallow water, but it is difficult to measure directly. For small grazing angle, the relationship between the bottom reflection loss and the grazing angle is nearly linear, − 20 log|V(θ)| = Bθ, where B ∝ Kp f(n − 1) and sound attenuation in the sediments is expressed by αp = Kp fn (dB/m⋅kHz). The bottom reflection loss parameter B in shallow water can be extracted by inversion techniques from a number of different field characteristics. In this paper, some theoretical inversion methods and extract reflection‐loss parameters (B) for different sea areas are presented. The experimental results show that the parameter B apparently increases with increasing frequency. This implies that n > 1, i.e., that the frequency dependence of the sound attenuation in the sediments could be nonlinear. The experimental results of E. C. Lo et al. [J. Acoust. Soc. Am. 74, 1833–1836 (1983)] can be explained very well by using the frequency dependence of bottom attenuation (and sound velocity) obtained by inversion of the normal mode measurements made by J. X. Zhou [J. Acoust. Soc. Am. 78, 1003–1009 (1985)].