Characterizing riverbed sediment using high-frequency acoustics 1: spectral properties of scattering

Journal of Geophysical Research F: Earth Surface
By: , and 

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Abstract

Bed-sediment classification using high-frequency hydro-acoustic instruments is challenging when sediments are spatially heterogeneous, which is often the case in rivers. The use of acoustic backscatter to classify sediments is an attractive alternative to analysis of topography because it is potentially sensitive to grain-scale roughness. Here, a new method is presented which uses high-frequency acoustic backscatter from multibeam sonar to classify heterogeneous riverbed sediments by type (sand, gravel,rock) continuously in space and at small spatial resolution. In this, the first of a pair of papers that examine the scattering signatures from a heterogeneous riverbed, methods are presented to construct spatially explicit maps of spectral properties from geo-referenced point clouds of geometrically and radiometrically corrected echoes. Backscatter power spectra are computed to produce scale and amplitude metrics that collectively characterize the length scales of stochastic measures of riverbed scattering, termed ‘stochastic geometries’. Backscatter aggregated over small spatial scales have spectra that obey a power-law. This apparently self-affine behavior could instead arise from morphological- and grain-scale roughnesses over multiple overlapping scales, or riverbed scattering being transitional between Rayleigh and geometric regimes. Relationships exist between stochastic geometries of backscatter and areas of rough and smooth sediments. However, no one parameter can uniquely characterize a particular substrate, nor definitively separate the relative contributions of roughness and acoustic impedance (hardness). Combinations of spectral quantities do, however, have the potential to delineate riverbed sediment patchiness, in a data-driven approach comparing backscatter with bed-sediment observations (which is the subject of part two of this manuscript).

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Characterizing riverbed sediment using high-frequency acoustics 1: spectral properties of scattering
Series title Journal of Geophysical Research F: Earth Surface
DOI 10.1002/2014JF003189
Volume 119
Issue 12
Year Published 2014
Language English
Publisher American Geophysical Union
Contributing office(s) Southwest Biological Science Center
Description 18 p.
First page 2674
Last page 2691
Online Only (Y/N) N
Additional Online Files (Y/N) N