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Frequency Dependence of High-frequency Bottom Reflection Loss Measurements  

박순식 (한양대학교 지구해양과학과 해양음향연구실)
윤관섭 (한양대학교 지구해양과학과 해양음향연구실)
최지웅 (한양대학교 지구해양과학과 해양음향연구실)
나정열 (한양대학교 지구해양과학과 해양음향연구실)
Publication Information
The Journal of the Acoustical Society of Korea / v.22, no.8, 2003 , pp. 652-659 More about this Journal
Abstract
High-frequency(40∼120 kHz) reflection loss measurements on the water-sandy sediment with a flat interface were conducted in a water tank for various grazing angles. The water tank(5×5×5 m) was filled with a 0.5 m-thick-flat bottom of 0.5ø-mean-grain-size sand. Reflection losses, which were experimentally obtained as a function of grazing angle and frequency, were compared with the forward loss model, APL-UW model (Mourad & Jackson, 1989). For frequencies below 60 kHz, the observed losses well agree with the reflection loss model, however, in cases for frequencies above 70 kHz, the observed losses are greater by 2∼3 dB than the model results. The model calculation, which does not fully account for the vertical scale of roughness due to grain size, produce less bottom losses compared to the observations that correspond to large roughness based on the Rayleigh parameter in the wave scattering theory. In conclusion, for the same grain-size-sediment, as frequencies increase, the grainsize becomes the scale of roughness that could be very large for the frequencies above 70 kHz. Therefore, although the sea bottom was flat, we have to consider the frequency dependence of an effect of roughness within confidential interval of grain size distribution in reflection loss model.
Keywords
Bottom reflection loss; APL-UM model; Frequency dependency; Grain size distribution; Rayleigh parameter;
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Times Cited By KSCI : 3  (Citation Analysis)
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