Low-grazing-angle monostatic acoustic reverberation from rough seafloors

Abstract

The objective of this research is to interpret matched-filtered, beamformed monostatic acoustic reverberation data acquired when the seafloor is insonified by a bandlimited, low-grazing-angle acoustic pulse. This paper addresses the hypothesis that observed backscatter signals are produced by a combination of seafloor (interface) and subseafloor (volume) scattering from structure having variations at scale lengths comparable to the wavelength of the insonifying acoustic field. Numerical modeling, using a finite-difference solution to the elastic wave equation, is performed to quantitatively predict the monostatic acoustic reverberation signals from rough seafloor, with and without subseafloor volume heterogeneity. Wavelength-scale seafloor roughness and subseafloor volume heterogeneity are defined using stochastic distributions with Gaussian autocorrelations. Modeling results show that scattering from rough, basaltic bottoms is dominated by interface scattering. Subseafloor volume heterogeneity is shown to be capable of producing scattered signals comparable to rough seafloor scattering when the bottom is smooth and/or has a low velocity.