Mid-to-High Frequency Bottom Loss in the East China Sea
WASHINGTON UNIV SEATTLE APPLIED PHYSICS LAB
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Bottom loss measurements made in the East China Sea in 2001 as part of the Asian Sea International Acoustics Experiment as a function of frequency 2-20 kHz and seabed grazing angle 15 deg-24 deg are presented. The measurements are interpreted as estimates of the modulus of the plane wave reflection coefficient, and data are compared to predictions using a reflection coefficient model, based on a two-layered sediment for which sound speed in the surficial sediment layer is allowed to vary as a linear kappa2 profile, where kappa is acoustic wave number. The region below this layer is modeled as a half-space with constant density and sound speed. The reflection coefficient model is driven by eight geoacoustic parameters. This parameter set produced model curves that agreed reasonably well with observations of bottom loss over the entire frequency range. Since this data set does not provide detailed information about sediment structure for depths beyond about 3 m, the geoacoustic parameter set is more properly viewed as description of the sediment layer and sediments in the underlying 2 m. Similarly, a self-consistent construction of a geoacoustic model for the East China Sea should necessarily amalgamate the mid to high frequency results given here with results obtained at lower frequencies.