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

Abstract

Analysis of the spectral content of long-range reverberation yields two observations. First, there is a remarkably similar scale, O(0.1) m, between three diverse continental shelf regions. This is surprising given the complexity and diversity of geologic processes. Second, 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. Neither the feature nor mechanism is known at this time.

Acoustic Wave Dispersion and Scattering in Complex Marine Sediment Structures

“…In the long term, the theoretical relationships developed for volume scattering will improve our understanding of the marine benthic environment: what kind of scatterers are important, are they best described by a discrete or a continuum approach? In the shorter term, the results are important for reexamining recent volume scattering analyses [3] in several continental shelf environments. While the analysis in [3] assumed that the heterogeneities were described by a continuum with an outer scale of 0.1 m, the current research will link those results to a discrete scatterer hypothesis.…”

“…In the shorter term, the results are important for reexamining recent volume scattering analyses [3] in several continental shelf environments. While the analysis in [3] assumed that the heterogeneities were described by a continuum with an outer scale of 0.1 m, the current research will link those results to a discrete scatterer hypothesis. The importance of this is that the outer scale controls the frequency dependence of scattering and reverberation of active sonar systems.…”

Discrimination between discrete and continuum scattering from the sub-seafloor

“…5 in Ref. 7 shows that from 200 to 3000 Hz, the measurements can be explained by a single set of volume scattering parameters, with clear low-frequency (200-800 Hz) and high-frequency (1400-3000 Hz) scattering regimes.…”

Seabed roughness parameters from joint backscatter and reflection inversion at the Malta Plateau

“…The use of direct techniques (e.g., stereoscopic photography, laser imaging) to measure seafloor roughness over small scales 1,2 and long-range reverberation methods to infer roughness over large scales have been carried out. 3 However, the characterization of seafloor roughness on the mesoscale (patch size of order 10 2 m with sensitivity to seabed fluctuations in the vertical and horizontal of order 10 À1 m) requires attention. This paper applies transdimensional (trans-D) Bayesian inversion to measured backscatter and reflection data to estimate mesoscale interface roughness parameters and geoacoustic profiles together with a fully nonlinear uncertainty analysis.…”