ASA 124th Meeting New Orleans 1992 October

5pUW1. Broadband measurements of sea surface backscattering strength in the Gulf of Alaska.

Peter M. Ogden

Fred T. Erskine

Naval Res. Lab., Washington, DC 20375

Measurements of low-frequency (70--1000 Hz) sea surface backscattering strength were made in the Gulf of Alaska during February--March 1992 as part of a surface backscatter and air--sea interaction experiment. The measurements described here used explosive charges (SUS MK-59 MOD1a) as sources and a towed horizontal line array of hydrophones as receiver. The experiment objective was to measure surface backscattering strength as a function of frequency, grazing angle, and environmental conditions of the air--sea boundary. Scattering strengths were obtained during 18 tests (each of duration approximately 30 min) conducted from 24 February to 1 March for wind speeds that varied from approximately 4 to 18 m/s. The experiment uses a direct path test geometry for which the measured surface backscatter originated from surface/near-surface regions at ranges of several km or less. Surface grazing angles for these measurements varied from about 5 to 30 deg. Results are compared to earlier surface scatter measurements below 1000 Hz and are interpreted relative to concurrent air--sea boundary environmental measurements.