The measurement of muddy seabed properties using ambient noise coherence

The autonomous passive acoustic lander Deep Sound was deployed five times during the Seabed Characterization Experiment and collected ambient noise data on four hydrophones, arranged in a inverted “T” shape, with three spaced in the horizontal and two in the vertical. The lander was deployed with the bottom-most phones approximately 30 cm above the seafloor, recording over an acoustic bandwidth of 5 Hz–30 kHz. Pressure time series, vertical and horizontal noise coherence (directionality), and the local temperature and conductivity were recorded continuously for periods of 9 hours. Wind-driven surface ambient noise coherence was used to estimate bulk acoustic seabed properties. An analytical Pekeris-waveguide noise model was fitted to the data in order to determine the bulk sound speed, density, and frequency dependent attenuation in the bottom fluid half-space. [Research supported by ONR.]