Characteristics of seismoacoustic propagation in a near-shore environment

Abstract

MPL conducted the adaptive beach monitoring experiment, a near-shore, seismoacoustic experiment, over April–June 1995, at Camp Pendleton Marine Base north of San Diego, CA. Other participants included NRaD/NCCOSC, NRL, ARL/PSU, and ARL/UT. The objectives were to examine the generation and propagation of seismoacoustic energy from both signals of interest and ambient noise sources on land and in the ocean, and the signal processing structures needed to separate signals from noise. To help quantify the propagation characteristics, a series of controlled source tows was performed. Tow tracks included along-shore tows (at approximately constant depth of 20 m), upslope/downslope tows from the surf zone to 3.5 km offshore, and cross-slope runs. Four tones at 95, 145, 195, and 370 Hz were simultaneously broadcast by the source and received by two nearly orthogonal, 120-m-long, 64-element, horizontal bottom hydrophone arrays located 3.4 km offshore in 20-m water. For tows along a bottom depth contour, the acoustic field at the higher frequencies shows the classical two- or three-mode interference pattern, whereas those in the upslope/downslope and cross-slope directions are more complicated. Horizontal plane-wave beamforming techniques are used to examine the horizontal refractive effects of cross-slope propagation. [Work supported by ONR, Code 32.]