1pAO10. Ambient noise measurements in the acoustic beach monitoring experiment.

Session: Monday Afternoon & Evening, May 13

Time: 4:00

Author: W. K. Melville
Author: G. B. Deane
Author: R. M. Shear
Author: E. Terrill
Author: C. L. Epifanio
Location: Scripps Inst. of Oceanogr., U.C.S.D., La Jolla, CA 92093-0213


During the spring of 1994 (April--June) the Marine Physical Laboratory/SIO conducted the acoustic beach monitoring (ABM) pilot experiment at Camp Pendelton, CA. One component of the experiment was concerned with measurement of ambient noise up to 40 kHz, at distances up to several kilometers offshore. An array of three modified SSQ 57B sonobuoys were moored at distances from 1.5 to 3.5 km offshore. The surf zone was instrumented with pressure gauges and a current meter, and a comprehensive meteorological station was set up on the beach. A directional microphone on the beach was used to monitor the surf noise. Supporting oceanographic and meteorological data was available from the SIO coastal data information program. Near-shore acoustic spectra are characterized by two broad peaks in the ranges of 100--500 Hz and 1--7 kHz, respectively. The higher frequency peak rapidly attenuates offshore, while the lower frequency peak is essentially unattenuated over ranges of several kilometers. In contrast to deep water, the correlation of surf zone ambient noise with the local wind is poor since the shoaling waves may be dominated by swell from distant storms. Short term averages of acoustic power correlate very well with the amplitude modulation (groupiness) of the incident waves. [Work supported by ONR.]

from ASA 131st Meeting, Indianapolis, May 1996