Acoustic penetration of a sandy shallow water sediment in the 500 to 1000 Hz band

To study the transmission of sound through the water-sediment interface in a shallow water environment, sound waves, in the 500 to 1000 Hz band, were projected in water and received by an array of hydrophones buried in the sediment, in a joint experiment conducted by the SACLANTCEN in cooperation with ARL:UT. Eight hydrophones were formed into a sparse three-dimensional array, to detect the sediment penetrating signals. The sound source was a spark source towed behind a research vessel. The sediment was a silty sand. Signals reaching the acoustic sensors were recorded on tape for off-line processing. Of the eight acoustic sensors, five were buried and three were laid on the sediment surface. The collected signals were processed to give direction and speed of the sediment penetrating waves, with particular attention to phase relationships between surficial and buried sensors. From a theoretical point of view, the medium is treated as a pore-elastic solid governed by Biot´s theory of acoustic propagation. The experimental results were compared with theoretical model predictions, and with similar measurements at the same site in the 1 to 10 kHz band. The sound field was dominated by the inwater propagating modes. Wave speeds were measured as a function of frequency. There were indications of a slow compressional wave. These results are a part of a growing database of measurements designed to support the development of underwater sound propagation models, that will be useful for defense applications, such as mine hunting, as well as commercial applications including sediment classification, acoustic profiling, and marine biology