南海北部大陸斜坡之水中音傳研究

Abstract

中國南海的大陸坡上具有非常巨大的沙丘地形，沙丘分佈於160公尺至600公尺水深處，其最大振幅可超過16公尺且波長超過350公尺，推測其形成原因為南海內波經過造成的沉積物懸浮再沉澱。南海內波為世上已知最大之海洋內波，其最大振幅可達150公尺，形成於呂宋海峽並向西前進傳遞數百公里越過深海盆地，內波才逐漸因地形變淺而消散。本研究將探討沙丘地形與水文環境改變對本海域音傳產生之影響，並與南海實驗資料比較。模擬2013年與2014年南海之音傳實驗，以實驗量測之沙丘地形與2014年6月9號當日每小時之水文資料進行模擬。使用三維拋物線方程式近似法為基礎之計算模組FOR3DW(具有水平寬角度計算能力之FOR3D計算模組)進行二維(Nx2D)與三維(3D)音傳模擬，並比較兩模擬差異進以討論三維效應。受到沙丘地形與水文環境改變的影響，此海域音傳環境較為複雜且時空變動性大。受到沙丘地形影響三維效應於特定角度上較明顯，水文環境改變亦對聲能分佈產生影響，於垂直陣列錨碇上6月9號之量測資料亦可觀察出此現象。

There are internal waves in northern South China Sea, and many large sand dunes on the upper continental slope regions. Most of sand dunes locate at the depth of 160 m to 600 m, and the largest sand dunes are observed with amplitude up to 16 m. Sand dunes and internal waves may cause 3D acoustics effects, such like focusing, defocusing and scattering phenomena. Taiwan and USA researchers worked together on Sand Dunes experiment in 2013 and 2014. In this study, the 3D PE program, FOR3DW(FOR3D with azimuthal wide-angle capability), is used to simulate Nx2D and 3D acoustic propagation in sand dunes region with internal wave. The result shows the strong spatial and temporal variability. The difference between Nx2D and 3D calculations are shown to demonstrate the 3D effects. And the result would also be compared with experiment data.