ASA 127th Meeting M.I.T. 1994 June 6-10

1pUW17. Measurements and modeling of the spectral character of low-frequency, low grazing angle surface reverberation.

Eric I. Thorsos

Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105-6698

Roger C. Gauss

Raymond J. Soukup

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

Joseph M. Fialkowski

Planning Systems, Inc., McLean, VA 22102

Measurements of low-frequency (200--1000 Hz) and low grazing angle (<10 deg) acoustic surface scattering were made in the Gulf of Alaska in February of 1992 [R. C. Gauss and J. M. Fialkowski, J. Acoust. Soc. Am. 93, 2299 (A) (1993); Gauss et al., J. Acoust. Soc. Am. 94, 1765 (A) (1993)]. Short- and long-duration waveforms were used to quantify the spectral character of surface reverberation as a function of frequency and environmental conditions. For moderate to high wind conditions, scattering from near-surface bubble clouds is expected to be the dominant scattering mechanism. This scattering process has been modeled, assuming point scatterers near the surface, representing the bubble clouds, are being convected in the orbital motion of the wave field. Measured 2-D surface wave spectra provided by J. Hanson [APL/JHU] are used to represent the wave field. This simple model is found to replicate reasonably well the spectral properties of the measurements, especially in high sea-state cases. Measurement/model comparisons will be presented. [Work supported by ONR.]