ASA 125th Meeting Ottawa 1993 May

2aUW3. Measurements of the spectral characteristics of low-frequency, low-grazing-angle surface reverberation.

Roger C. Gauss

Naval Res. Lab., Washington, DC 20375-5350

Joseph M. Fialkowski

Planning Systems, Inc., McLean, VA 22102

Direct-path measurements of low-frequency (200--1000 Hz) and low-grazing-angle (<10 deg) acoustic surface scattering were made in the Gulf of Alaska in April of 1990 and in March of 1992. Short-duration (0.6--2.4 s) cw and PRN waveforms were used to quantify the spectral character of surface/near-surface reverberation as a function of frequency and environmental conditions. Measures include spreading and peak-Doppler-shift statistics versus azimuth. Results over the range of wind speeds (10--35 kns) have revealed a dominant zero-Doppler component and a weaker-than-expected dependence of spread on both sea conditions (wind speed and relative direction of the seas) and frequency. The results are consistent with sub-surface bubbles as the primary mechanism for surface reverberation when white caps are present, and give insight as to the nature of the bubble clouds that could give rise to the observed acoustic scattering.