Acoustic Propagation Effect due to Subaqueous Sand Dunes in the South China Sea

• Main Authors: Yu-ying Lien, 連于穎
• Other Authors: Linus Y.S. Chiu
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/18642124162561986139

碩士 === 國立中山大學 === 海下科技暨應用海洋物理研究所 === 103 === To study the characteristics of sand dunes in the South China Sea (SCS) and its effects on sound propagation, the pilot experiment of the Acoustic Sand Dune Experiment was carried on in May 2012, used a multi-beam echo sounder collecting the topographic data. The intensive observation phase of the Sand Dune Acoustic Experiment in May 2013 is planed based on the resluts of the pilot experiment, which achieve finer measurement: multi-beam echo sounder. The characteristics of sand dunes can be obtained by comparing the results of 2012 and 2013. Furthermore, the acoustic experiment was conducted in 2013; the acoustic recorders were deployed at the center and the source was towed with a 5 km radius circle to obtain the energy fluctuation under different sand dunes structure. This data was used to discuss the impact on multipath effect and energy distribution caused by sand dunes. Moreover, two numerical models: BELLHOP and RAM-PE were applied to model the propagation effects in sand dune field. The results shows that sand dunes on the upper continental slope in SCS were extended in the northeast-southwest direction; and most of its amplitude are less than 10 m, only few were observed over 20 m. From the survey results of this two years, we can see the amount of variation was small and from experiment data and numerical modeling, we can see that the sand dunes will have significant impact on multipath effect, ans also cause a great loss near sea surface. In addition, without considering the sand dunes, when the terrain change from upslope to downslope, signal energy will concentrate on the surface layer of water. This research can be used as a reference for future experiments, and be further applied to discuss the acoustic communication performance caused by the sand dunes.