Quantitative estimation of seafloor backscattering strength using long-range sidescan sonar data

Abstract

In ocean water depths of a few kilometers, long-range sidescan sonar systems generate “acoustic brightness” images of seafloor swaths 10 km or more in width using energy acoustic energy returned from the sea floor by monostatic scattering. When simultaneously acquired seafloor bathymetry is available, as it is for some modern systems, the acoustic received level versus time (imagery) data from the towed sonar “fish” can be inverted to extract estimates of seafloor backscattering strength and associated seafloor grazing angle. These estimates can be made for the entire “swath” of seafloor for which imagery is usually generated. Such inversion has been performed for sidescan imagery data from a portion of the Monterey Fan off the coast of California. Published sidescan imagery for the same region [Atlas of the Exclusive Economic Zone, Western Conterminous United States (U. S. Geological Survey Miscellaneous Investigations Series 1–1792, 1986)] indicates a strongly scattering seafloor for much of the region investigated. Consistent with this, the backscattering strength values estimated from data inversion are higher than typical values from the literature in the bright image regions, though consistent with typical values over much of the local seafloor. [Work supported in part by the Geodynamics Research Inst., Texas A&M Univ.]