Abstract:
The Marine Physical Lab's Adaptive Beach Monitoring Experiment was conducted from 24 April to 14 June 1995, in and near the surf zone off the S. California coast. Other participants included NRaD/NCCOSC, NRL, ARL/PSU, and ARL/UT. The focus here is on the underwater acoustic noise field properties. Contributions of breaking surf are studied in the 1- to 400-Hz band using a 35-element subsection of a bottom hydrophone array oriented perpendicular to the coast and located 3.4-km offshore in 20-m water. A 3-week time series of endfire-beamforming results are compared to the ocean surface wave height data collected over the same period. Source tow data quantify the propagation effects of surf noise to the array site and permit inversions for bottom geoacoustic properties. The array data are supplemented by the distance dependence from shore of data from bottom-mounted sonobuoys in the 100-Hz--20-kHz band, and air acoustic data recorded just landward of the shoreline. Biologics are a substantial component of the noise field and must be accounted for in evaluating the contribution from surf. Fish sounds themselves can be used as novel sources in inversion for bottom geoacoustic properties. [Work supported by ONR, Code 32.]