Swath acoustic imaging of the seafloor

Abstract

Recent developments in bathymetric sidescan sonar systems and in multibeam echosounders have allowed these systems to produce coregistered bathymetry and sidescanned acoustic images of the seafloor in near real time. As a result, in addition to producing geometrically correct images with much less ambiguous information than conventional sidescanned seafloor images, the effects of the local relief and beam patterns on the magnitude of the backscattered signals can be readily compensated to bring out the angular dependence of acoustic backscatter across the swath. By isolating regions of homogeneous tonal appearance in the resulting image, a first-order assessment of the spatial variability in the composition of the bottom can be made. In such areas of the image, where the seafloor is presumably uniform in composition, the angular dependence of acoustic backscatter can be used to infer statistical terrain characteristics such as surface roughness at smaller spatial scales than obtainable with the bathymetry alone. The deterministic approach of shape-from-shading described in a companion presentation by C. Nishimura (same session) can potentially lead to greater bathymetric resolution. Examples are provided with data from multibeam and bathymetric sidescan sonar systems. [Work supported by ONR.]