Acoustic remote sensing of seafloor roughness: Resolving ambiguous estimates of roughness spectrum parameters

Abstract

To predict or model how sound waves interact with the seafloor some parametrization of the roughness of the sediment–water interface is required. Conversely, bottom backscattered echoes contain information about the roughness of the interface, relative to the acoustic wavelength, often mixed with contributions from inhomogeneities in the sediment volume. However, inversions of seafloor roughness parameters from high-frequency (10–100 kHz) acoustic backscatter measurements often produce ambiguous results with numerous plausible parameter combinations fitting a given acoustic backscatter angular dependence curve or an echo envelope shape. Based on the data and on direct or inferred seafloor roughness measurements reported in the literature, and assuming that the relief spectrum of seafloor topography obeys a power law, it is shown that a level of inversion ambiguity can be lifted by setting the roughness spectral exponent to a value appropriate for the sediment type and by iterating on the spectral strength and the allowable amount of sediment volume backscatter. This is illustrated with examples drawn from comparisons between seafloor echo envelope models and measured acoustic backscatter data yielding interface roughness spectral parameters and rms bottom curvatures consistent with the lithology of the areas investigated. [Work supported by ONR N00014-94-1-0121.]