Tank Experiment for Backscattering Measurements from Rough Bottom Interfaces

Abstract

Sound propagation in shallow water undergoes acoustic interactions with both sea surface and bottom interfaces, causing reverberation effects. Especially, in case of a downward refracting sound speed profile, the important ray paths consist of the bottom-interacting paths. There have been several efforts to investigate the physics of bottom scattering mechanisms [1-4]. In general, the high-frequency backscattering from ocean seafloor consists of scattering at the water-sediment interface and scattering caused by inhomogeneities below the sediment interface. It is important to measure the bottom roughness profile to understand the bottom scattering mechanisms. The bottom roughness spectra have been estimated using a variety of techniques, including electrical resistivity probe, sidescan sonar, stereo photography, laser line scanning, and multi-beam echo sounder.[1, 5-8] In this study, to investigate the relationship between the bottom roughness and the bottom backscattering at rough bottom condition, bottom interface roughness and 50-kHz bottom backscattering strengths were measured for two-different types of roughness, which were artificially formed on a sandy bottom in the water tank. The measured bottom backscattering strengths will be discussed in comparison with the model predictions obtained using the measured rougness spectra in this paper. of the bottom-interacting paths. There have been several efforts to investigate the physics of bottom scattering mechanisms [1-4]. In general, the high-frequency backscattering from ocean seafloor consists of scattering at the water-sediment interface and scattering caused by inhomogeneities below the sediment interface. It is important to measure the bottom roughness profile to understand the bottom scattering mechanisms. The bottom roughness spectra have been estimated using a variety of techniques, including electrical resistivity probe, sidescan sonar, stereo photography, laser line scanning, and multi-beam echo sounder.[1, 5-8] In this study, to investigate the relationship between the bottom roughness and the bottom backscattering at rough bottom condition, bottom interface roughness and 50-kHz bottom backscattering strengths were measured for two-different types of roughness, which were artificially formed on a sandy bottom in the water tank. The measured bottom backscattering strengths will be discussed in comparison with the model predictions obtained using the measured rougness spectra in this paper.