Study of Underwater Acoustic Transmission Loss Variation in Taiwan South-West and North-East Regions

本研究利用實測之音傳損耗量測數據，及以實地測量或海洋數值模式模擬之水文場之音傳損耗模擬，探討臺灣東北及西南海域之水文變化，如冷渦漩及內潮期間音傳損耗之變動性。並藉由海洋數值模式之水文模擬結果進行音傳損耗模擬，比較只在聲源處使用單一聲速剖面，即聲速剖面不隨距離而變(Range-independent)；或沿著模擬測線，隨距離改變使用多個聲速剖面(Range-dependent)，兩種聲速剖面給定方式對臺灣東北及西南海域內潮期間的音傳損耗結果所產生的差異，以了解不同時間及空間對水文場完整度之需求。 本論文分為臺灣西南海域及東北海域兩區域進行討論，臺灣西南海域討論主題為民國96年於臺灣西南海域所進行的音傳損耗實驗數據，利用此結果進行西南海域音傳損耗變動性的討論，並使用三維斜壓潮汐模式所得之水文場模擬結果，進行使用單一聲速剖面或使用多個聲速剖面的音傳損耗模擬比較。其結果顯示距聲源10公里外，只使用單一聲速剖面之音傳模擬會產生較大的誤差；10公里之內差值小於1分貝。 在臺灣東北海域則分別使用三維斜壓潮汐模式及三維海洋環流模式所得之水文場模擬結果，討論內潮及冷渦漩發生期間的音傳損耗變化情形。結果顯示內潮期間表面聲道的產生與否，對本區音傳損耗有很大的影響。冷渦漩期間之音傳損耗模擬則顯示，音傳損耗在聲速剖面等聲速線傾斜處，有冷渦漩出現時期音傳損耗提高1至6分貝。另外春季冷渦漩在深水區對音傳損耗有較大影響力，夏季則在淺水區影響較大。在水文場的完整度的討論上，也就是使用單一聲速剖面或使用多聲速剖面進行音傳損耗模擬的比較顯示，東北海域內潮期間兩者在淺水區的音傳損耗模擬差異較大。冷渦漩為一水團，考慮對音傳損耗的影響為水團整體，單一聲速剖面勢必無法表現，故不討論單一聲速剖面或使用多聲速剖面進行音傳損耗模擬的比較。The purpose of this thesis is to study the variation of transmission loss in Taiwan’s South-West and North-East Regions during the occurrence of internal tide and eddies. Both the experimental data and simulation using temperature profile from ocean model are used for the study. In addition, the study used the result of ocean model as transmission loss simulation input, to compare the result of Range-independent and Range-dependent transmission loss simulation, and to understand the need of a complete ocean background during internal tide period. This thesis studied South-West and North-East Regions in Taiwan respectively. In the South-West Regions, the transmission loss experiment data analysis shows the variation of the transmission loss. We also used the results of three-dimensional tide model as inputs to compare the Range-independent and Range-dependent transmission loss simulation. The results showed that using single sound speed profile at source produced errors at simulation range large that 10 km. In North-East Region, this thesis studied how internal tide and eddies period affected transmission loss individually. The ocean backgrounds data of internal tide and eddies are from three-dimensional tide model and DUPOM (Duo Grid Pacific Ocean Model). The results of transmission loss simulation during internal tide period showed that the surface duct was an important factor affecting the transmission loss. The comparison of Range-independent and Range-dependent transmission loss simulation showed that the effect was higher in shallow water. The transmission loss simulation in eddies periods showed that the changes of transmission loss occurred where the iso-sound-speed-contours were inclined. Compare with the no-eddies period in winter, the occurrence of eddies raised the transmission loss up 1 to 6 dB. The effect was higher in deep water in spring and higher in shallow water in summer.致謝 I文摘要 IIBSTRACT III目錄 VI格目錄 X一章 緒論 1.1 前言 1.2 研究動機與目的 2.3 台灣周邊海洋環境簡介 4.3.1 西南海域 5.3.2 東北海域 8.4 參考文獻 10.5 研究方法 12.6 論文架構 16.7 主要成果 16二章 環境對音傳損耗之特性影響 18.1 水文環境對音傳損耗性質之影響 18.1.1 內潮對音傳損耗之影響 18.1.2 冷渦漩對音傳損耗之影響 21.2 底質對音傳損耗性質之影響 27三章 臺灣西南海域音傳損耗實驗 30.1 實驗介紹 30.1.1實驗目標 30.1.2音傳損耗實驗規劃 30.2 實驗結果與討論 32.3 應用海洋數值模式環境場計算音傳損耗 39四章 臺灣東北海域內潮音傳損耗變動性算例 47. 1 實地量測水文 48. 2 應用三維斜壓潮汐模式環境場計算音傳損耗 55五章 臺灣東北海域冷渦漩音傳損耗變動性算例 74.1 冷渦漩水文場 75.2 春季冷渦漩算例 78.3 夏季冷渦漩算例 88六章 結論與未來研究方向 99考文獻 10