Shallow water benthic imaging and substrate characterization using recreational-grade sidescan-sonar.

Published in Environmental Modelling and Software, 2017

In recent years, lightweight, inexpensive, vessel-mounted ‘recreational grade’ sonar systems have rapidly grown in popularity among aquatic scientists, for swath imaging of benthic substrates. To promote an ongoing ‘democratization’ of acoustical imaging of shallow water environments, methods to carry out geometric and radiometric correction and georectification of sonar echograms are presented, based on simplified models for sonar-target geometry and acoustic backscattering and attenuation in shallow water. Procedures are described for automated removal of the acoustic shadows, identification of bed- water interface for situations when the water is too turbid or turbulent for reliable depth echosound- ing, and for automated bed substrate classification based on singlebeam full-waveform analysis. These methods are encoded in an open-source and freely-available software package, which should further facilitate use of recreational-grade sidescan sonar, in a fully automated and objective manner. The sequential correction, mapping, and analysis steps are demonstrated using a data set from a shallow freshwater environment.

Recommended citation: Buscombe, D. (2017). "Shallow water benthic imaging and substrate characterization using recreational-grade sidescan-sonar." ENVIRONMENTAL MODELLING & SOFTWARE. 89, 1-18.

Automated riverbed sediment classification using low-cost sidescan sonar.

Published in Journal of Hydraulic Engineering, 2015

The use of low-cost, low-profile, and highly portable sidescan sonar is on the ascendancy for imaging shallow riverine benthic sediments. A new automated, spatially explicit, and physically-based method for calculating lengthscales of bed texture elements in sidescan echograms (a 2D plot of acoustic intensity as a function of slant range and distance) is suggested. It uses spectral analysis based on the wavelet transform of short sequences of echograms. The recursive application of the transform over small overlapping windows of the echogram provides a robust measure of lengthscales of alternating patterns of strong and weak echoes. This textural lengthscale is not a direct measure of grain size. Rather, it is a statistical representation that integrates over many attributes of bed texture, of which grain size is the most important. The technique is a physically-based means to identify regions of texture within a sidescan echogram, and could provide a basis for objective, automated riverbed sediment classification. Results are evaluated using data from two contrasting riverbed environments: those of the Colorado River in Grand Canyon, Arizona, and the West Branch of the Penobscot River, Maine

Recommended citation: Buscombe, D., Grams, P.E., and Smith, S.M.C. (2015). "Automated riverbed sediment classification using low-cost sidescan sonar." Journal of Hydraulic Engineering. 10.1061/(ASCE)HY.1943-7900.0001079, 06015019.