Evidence for a common scale O(0.1) m controlling seabed scattering and reverberation in shallow water regions

Abstract

Long-range reverberation spectral analysis yields two observations. Firstly, there is a remarkably similar scale, O(0.1)m, between 3 diverse continental shelf regions. This is surprising given general understanding of the complexity and diversity of geologic processes. Secondly, there is strong evidence that the scale is associated with heterogeneities within the sediment. Thus sediment volume scattering, not interface scattering, controls long-range reverberation from a few hundred Hertz to several kiloHertz. This is also unexpected given that at long-ranges the vertical grazing angles are less than the critical angle, and hence the penetration of the acoustic field into the sub-bottom is expected to be modest. The consistency of the scale, O(0.1)m, suggests an underlying feature or mechanism that is consistent across many ostensibly diverse geological settings. The most likely mechanism is scattering from mollusks. [Work supported by ONR Ocean Acoustics]