| Abstract |
Tremendous subaqueous sand dunes were observed on the continental slope in the northern South China Sea recently. The sand dunes (sand waves) are expected to affect 2-dimensional and 3-dimensional acoustic propagation and induce acoustic field fluctuations. The purpose of this thesisis aimed to study the effect of acoustic propagation and variations in the area of South China Sea with subaqueous sand dunes (sand waves), and will focus on the variability of transmission loss, signal-to-noise ratio, and spatial coherence. In 2014, an acoustical experiment of Intensive Observation Period was conducted, supported by both the Ministry of Science and Technology of Taiwan and Office and Naval Research of United States, to study the variations of sound propagation in this area. The source transmitted linear frequency modulating (LFM) signals at 1.5-2 kHz band, received by the vertical line array at few circles. The receive data were processed via pulse compression technique, and sound energy were calculated. This thesis demonstrates the results of dispersive arrivals and transmission loss versus different bearing angles. Experimental data and numerical prediction would be applied to study the effect of acoustic propagation, and the acoustic variability would be quantified and compared in this thesis. According to the data, the results demonstrates that the sand dunes would casued a significant impact on multipath effect, and distinct disturbance in dispersive arrivals. In addition, the distribution of sound energy in the vertical direction would be repartitioned. The results of this thesis could be applied to evaluate and predict the performance of acoustic systems and SONARs in the sea area with subaqueous sand dunes (sand waves). |
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