Measurement and analysis of sound speed dispersion during SAX04 : final report for Office of Naval Research award N000140310883 / John C. Osler, Paul C. Hines ; prepared for US Office of Naval Research. : D68-7/338-2010E-PDF

"Sharing the same experimental apparatus, two complementary techniques were developed to measure the frequency-dependent speed of sound in marine sediments during the SAX04 sea-trial. The first technique enabled direct time-of-flight measurements of acoustic wave speed along all three Cartesian axes. The second technique determined the acoustic wave speed based on the arrival angle of pulses generated in the water column and refracted upon entry into the seabed. None of the results could be modeled or explained when the seabed was parameterized as a sand half-space. However, both techniques suggested the presence of a thin muddy layer, 0.05–0.2 m thick within the top 1 m of the sediment. For the arrival angle technique, the layer explains the complicated frequency- and geometry-dependent results; unfortunately, the interference from the layer dominated the arrival angle behavior to the extent that sound speed dispersion could not be determined unambiguously. For the time-of-flight technique, the acoustic wave speed was found to be dispersive in the frequency regime from 0.6 to 20 kHz with the normalized wave speed increasing from approximately 1.05 to 1.13. However, the layer caused the measured sound speeds to be lower than what a simplified poro-elastic model would predict, unless one accounts for the higher porosity material present within the buried layer"--Abstract, page i.

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