Attenuation in fine-grained sediments for New England Mudpatch in 25–5000 Hz band

Abstract

A subject of considerable importance in littoral ocean environments is the frequency dependence of sediment attenuation for various classes of sediments. The well-known frequency exponent value of 1.8 for sandy sediments was the subject of numerous research studies. For mud-like or mixed sediments, for which there is a scarcity of experimental data, values for the frequency exponent are not well established. Previously, the sound speed structure of a surface mud layer in the New England Seabed Characterization experimental area was estimated with inversion and Bayesian methods. The inversions utilized MK-64 SUS explosive sources in a 25-275 Hz band placed on concentric circles of 2, 4, and 6.5 km radii in the latitude-longitude plane. The area was previously surveyed with CHIRP sonar allowing for multiple sediment layer horizons to be constrained for layer thicknesses by measured two-way travel times. In this analysis, a larger bandwidth (25-5000 Hz) of the SUS, the Combustive Sound Source (CSS), and tonals from towed sources at multiple frequencies allow for the development of posterior probability distributions that contain the statistics of the frequency dependence of sediment attenuation up to about 5 kHz. [Work supported by ONR]A subject of considerable importance in littoral ocean environments is the frequency dependence of sediment attenuation for various classes of sediments. The well-known frequency exponent value of 1.8 for sandy sediments was the subject of numerous research studies. For mud-like or mixed sediments, for which there is a scarcity of experimental data, values for the frequency exponent are not well established. Previously, the sound speed structure of a surface mud layer in the New England Seabed Characterization experimental area was estimated with inversion and Bayesian methods. The inversions utilized MK-64 SUS explosive sources in a 25-275 Hz band placed on concentric circles of 2, 4, and 6.5 km radii in the latitude-longitude plane. The area was previously surveyed with CHIRP sonar allowing for multiple sediment layer horizons to be constrained for layer thicknesses by measured two-way travel times. In this analysis, a larger bandwidth (25-5000 Hz) of the SUS, the Combustive Sound Source (CSS), and tona...