Acoustic Propagation in Gassy Sediments
Conference proceedings 5-9 Sep 2000
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOSCIENCES DIV
Pagination or Media Count:
Gas bubbles are ubiquitous in organic-rich, muddy sediments of coastal waters and shallow adjacent seas Judd and Hovland, 1992 Richardson and Davis, 1998. Depths and horizontal distributions of these gas-charged sediments are usually determined from seismic profiling. The presence of gas bubbles often impedes acoustic characterization of sediments below the gas horizon and terms such as acoustic masking or blanking, acoustic turbidity, bright spots, wipeouts, and pulldowns are used to characterize these gas- charged sediments. Acoustic turbidity also produces anomalously high acoustic backscattering from the seafloor Lyons et al., 1996 Tang, 1996 degrading the effectiveness of high-frequency sonar. Models of acoustic- bubble interactions in fine-grained sediments developed by Anderson and Hampton 1980 have been corroborated by laboratory Gardner, 2000 and field Wilkens and Richardson, 1998 Lyons et al., 1996 Tang, 1996, Anderson et al., 1998 experiments. In this paper, we model the effects of bubble volume, bubble size and bubble distribution on sound speed and attenuation in the well-characterized sediments of Eckernforde Bay, Baltic Sea and from experiments recently conducted in Cape Lookout Bight, North Carolina. These two areas constitute the best known and most studied area of gassy sediment in the world Richardson and Davis, 1998 Martens et al., 1998 thus providing the ideal settings for such comparisons.