1pUW4. A shallow-water experiment for estimating bottom geoacoustic properties at a site off Numazu.

Session: Monday Afternoon, December 2

Time: 2:40


Author: Keiichi Ohkawa
Location: Tech. Res. and Development Inst., Japan Defense Agency, Yokosuka, 239 Japan
Author: Toshinao Tukimori
Location: Tech. Res. and Development Inst., Japan Defense Agency, Yokosuka, 239 Japan
Author: Hiroyoshi Nakajima
Location: Tech. Res. and Development Inst., Japan Defense Agency, Yokosuka, 239 Japan
Author: Kazuhiko Ohta
Location: Tech. Res. and Development Inst., Japan Defense Agency, Yokosuka, 239 Japan
Author: Itaru Morishita
Location: Oki Electric Industry Co., Ltd., Tokyo, 108 Japan
Author: Tsuneo Ishiwata
Location: Oki Electric Industry Co., Ltd., Tokyo, 108 Japan
Author: Shunji Ozaki
Location: Oki Electric Industry Co., Ltd., Tokyo, 108 Japan

Abstract:

An experiment to estimate bottom geoacoustic properties was conducted in the coastal area of Gulf Suruga off Numazu in August 1995. The measurements were made at a 70-m-depth site using a vertical line array of 12 receivers spaced at 5-m intervals. A cw source output at 55 Hz with 167 dB re: 1 (mu)Pa source level was towed at a constant depth over 3 km in horizontal range along the coast. Acoustic fields measured by a synthetic array at each channel were processed with a Hankel transform, whose output wave-number spectrum provided several peaks corresponding to mode eigenvalues. The position of each peak, however, varies slightly depending on the channel; this variation is considered to be caused by the range dependence of the waveguide and/or by mutual interaction of adjacent mode spectrum due to the finite aperture. Applying an inversion method to the observed mode eigenvalues, bottom geoacoustic parameters (sound speed, attenuation, and density) were estimated under several assumptions. Propagation loss calculated with use of the estimated parameters was found to be in good agreement with the observed one.


ASA 132nd meeting - Hawaii, December 1996