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

4pUW2. Shallow water bottom scattering strength at low frequencies.

Peter G. Cable

BBN Systems and Technol., Union Station, New London, CT 06320-6147

Mike Steele

James O'Connor

BBN Systems and Technol., Arlington, VA 22209

Determinations of acoustic scattering strength for sand bottoms have been made at several shallow water sites under downward refracting sound propagation conditions in the frequency band 50 Hz to 1 kHz. The measurements have been made using explosive sources detonated at mid-water depth and received on two collocated, bottom-mounted hydrophone line arrays, with one array in vertical and the other in horizontal orientation. The major focus of this work has been the variation of scattering strength with frequency and with bottom grazing angle. For the scattering strength measurements, the presence of multipaths in shallow water prevents a direct path scattering geometry from being used at low frequencies and, consequently, scattering strength must be extracted from the full reverberation field. Two techniques for obtaining scattering strength integrated over grazing angle and for using the vertical array to examine the angular dependence of the scattering strength will be described. The results will be compared with other determinations of scattering strength for shallow water sand bottoms and will be discussed in terms of the role of scattering from structure within the bottom sediment.