| Summary: | 碩士 === 國立中山大學 === 海下技術研究所 === 94 === Sound propagation can be greatly affected by seabed, especially in shallow water, therefore by understanding the geoacoustic parameters of sea bottom can help to improve the performance of sonar systems. In this study, ship noise collected by the vertical line array (VLA) in South China Sea experiment of the Asian Seas International Acoustics Experiment (ASIAEX SCS) in 2001 was used as a sound source to invert the geoacoustic parameters. The nearest horizontal distance between VLA and the passing ship was estimated by beamforming the receiving sounds on the array, and this distance was used in the sound propagation modal. In the modal, two layers structure were assumed for the bottom, so the sound speed (C1) and density (ρ1) of sediment layer, sound speed (C2 ) and density (ρ2) of subbottom layer, and total absorption coefficient (α) need to be inverted. Matched field processing is used to solve this inverse problem, and computing the minimum cost function between the measured and modeled sound field, the best matched bottom parameters are C1＝1600 m/s、C2＝1650 m/s、ρ1=1.6 g/cm3、ρ2=2.1 g/cm3、α=0.6 dB/λ. These results were compared with chirp sonar survey in this area, and the agreement is satisfactory.
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