Frequency dependence of high-frequency bottom reflection loss

Abstract

High-frequency (40 ~ 120 kHz) reflection loss measurements on the water-sandy sediment w Second Author: Soon Shik Park rth and Marine Sciences, Hanyang Uni Ansan , Kyunggi-do, Korea 425-791 Third Author: Jungyul Na and Marine Sciences, Hanyang Ansan , Kyunggi-do, Korea 425-791 ith 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 0.5 φ-mean-grain-size sand. Experimentally obtained reflection losses as a function of grazing angle and frequency were compared with the APL-UW forward loss model (Mourad & Jackson, 1989). For frequencies below 60 kHz, the observed losses are well agreed 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. 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 grain-size becomes the scale of roughness that could be very large for the frequencies above 70 kHz.