Low frequency sound attenuation measurements in marine sediments

Abstract

This paper reports measurements of sound attenuation in marine sediments from two locations on the outer New Jersey continental shelf. At one site the sediment in the top 20 m is primarily sandy clay, while the other site includes a thin (3–5 m), over-lying layer of sand at the sea floor. The attenuation was inverted from close range, broadband data from light bulb implosions deployed at stations at the sites. The inversion method made use of the time-frequency dispersion information in signals received at single hydrophones. The signals were first processed by time warping to resolve the propagating modes at relatively close ranges (50–80 water depths). The inversion is carried out in two stages. The first stage inverted the sound speed and density by modeling the modal group velocities, and these estimates were used in the second stage to invert the attenuation from the modal amplitude ratios. The results provide estimates of low-frequency sound attenuation that can be compared to predictions from different models of sound propagation to assess the frequency dependence in the band from 100–500 Hz.