Adaptive Beach Monitoring

The long-term goal of the Marine Physical Laboratory's Adaptive Beach Monitoring (ABM) program is to determine the capabilities of small on-shore and off-shore seismoacoustic arrays along with directional wave and current sensors to provide the amphibious force commander with a covert monitoring capability of shore-based as well as near-shore enemy forces, near-shore current and wave dynamics, and beach surf conditions. The science objectives of the ABM program are to understand the source mechanisms of naturally occurring (e.g., breaking surf and biological) and manmade (e.g., land vehicle) seismoacoustic sounds in the near-shore region, the coupling of the seismic and acoustic fields in the earth and atmosphere into the ocean acoustic field, and the propagation characteristics of these sounds within the water column. The engineering objectives are to design signal processing structures, along with arrays of appropriate sensor types, to detect, track, and classify sounds of interest (e.g., breaking surf and land vehicle sounds) in the near-surf-zone environment. The approach in the ABM program has been to plan, conduct, and analyze the data from two science-oriented experiments in the nearshore region at the Camp Pendleton Marine Base along the Southern California coast. In these nearshore experiments, a large variety of seismoacoustic and environmental data acquisition systems have been deployed. The seismoacoustic systems measured simultaneously the offshore underwater seismoacoustic field, the land seismic field, and the air acoustic field across the 0.05 Hz to 20 kHz band. The ancillary environmental information that were collected included basic weather data, water temperature and salinity, ocean bottom bathymetry, bottom sediment samples for grain size measurements and subbottom profiling, directional ocean surface wave spectra, tide activity, videotapes of surf activity, and ocean currents.