Low-frequency single interaction acoustic scatter from the sea surface using short pulses

Abstract

During February/March 1992 a comprehensive low-frequency (<1000 Hz) and low-grazing angle (<30 deg) acoustic sea surface scatter and air/sea interaction experiment was conducted in the Gulf of Alaska. For comparison with acoustic models, measurements were made of air/sea boundary descriptions such as near-surface bubble characteristics, wind speed, wave height, whitecap coverage, volume scatterers (fish), wind stress, etc. A variety of waveforms of short duration (<500 ms) were scattered from a surface path simultaneously isonified by three collinear vertical towed source arrays at frequencies around 250, 400, and 1000 Hz. Surface-scattered energy was received on a horizontal line array towed by the source ship. During the measurement wind speeds from 4 to 19 m/s and rms wave heights from 0.9 to 2.3 m occurred associated with sea states 2 to 6. Surface grazing angles of 4 to 32 deg and horizontal bistatic angles of 15 to 82 deg were observed. Scattering strength analysis includes frequency, grazing angle, waveform, and wind speed dependence as well as correlation with air/sea boundary descriptors. Current scattering strength model predictions utilizing the appropriate measured environmental parameters will be compared to measured data.