ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2aUW13. Effects of ship trim and dynamic attitude on the relative noise level measured by a hull-mounted multibeam bathymetric sonar.

C. de Moustier

Marine Physical Lab., Scripps Inst. of Oceanogr., La Jolla, CA 92093-0205

Acoustic data recorded in various sea conditions with the hull-mounted multibeam swath bathymetry system SeaBeam 2000 aboard R. V. MELVILLE have been analyzed to quantify the relationship between the ship's attitude and the relative noise levels observable in the data. The data consist of concurrent time series of echo magnitude and direction of arrival for each transmission cycle, and of the three attitude components roll, pitch, and heave. Although higher noise levels are usually associated with pitch, in these data heave has the greatest impact on noise level, presumably because of bubble syphoning from the areated surface layer. In addition, a slight change in the trim of the ship from horizontal to bow up results in an average relative noise increase of about 12 dB. [Research supported by ONR.]