本研究在於探討海床的層化特性對於海表面噪音經由波導傳播之後所產生之環境噪音場的影響。本研究引用 Kuperman 與Ingenito 於 1980 年提出一有關海洋環境噪音模擬的簡化模式，作為環境噪音模擬的基礎。該模式將海面的噪音源用一接近海面的連續單極聲源 (continuous monopoles) 來表示，而海床的部分乃以一有限厚度的均勻沈積層表示，並經由理論的推導，建構一環境噪音強度與空間分佈特性之運算公式。本研究另一方面引用 Robins(1990、1991、1993) 探討聲波自各種聲速與密度變化組合的沈積層上反射問題之研究成果。 Robins 之環境模式，乃將沈積層聲速的變化分別以常數分佈、k^2線性分佈及反平方分佈表示，並求得上述三個模式之聲波方程式的解析解。研究結果顯示，海床的層化性質對於反射場有重要的影響，因此，海床地聲性質也應會對低頻環境噪音造成影響，此乃本研究之動機。

在 Robins 建構的地聲性質中，有關密度呈廣義型指數分佈的變化、聲速呈反平方分佈的變化之模式，不僅與 Hamilton 實際調查結果相近，且能以數學式描述其分佈特性。因此，吾人將利用 Robins 的研究結果，結合 Kuperman 與 Ingenito 所發展的噪音模式，進一步模擬實際海洋環境噪音場的特性。本研究與過去研究不同處，乃是建立一更符合實際海洋環境的模式來探討海床層化性質對於海洋環境噪音的影響。在本研究中，我們將採用沈積層密度為廣義型指數分佈、聲速為反平方分佈的模式，利用不同的聲波頻率、沈積層密度與聲速變化、水層厚度、海床厚度等相關參數，來模擬及分析海洋環境噪音場，探討沈積層的地聲性質對於環境噪音強度及空間關連函數的影響。

在本論文的研究結果中發現，可藉由波數譜圖瞭解整個海洋環境中聲場傳播的機制。另外從噪音強度分佈結果，得知當頻率增高時，則噪音強度隨深度的平均變化，越呈現不均勻的分佈，此乃因為在高頻的情況下，聲源項越為重要的緣故。再者，從噪音場空間關連性來看，隨著頻率的增加，關連長度增大，且包含著曲線之包絡線 (envelop) 遞減變率 (roll-off rate) 越快。而沈積層厚度的改變及不同聲速變化的曲率，對於水平相關函數包絡線的遞減變率也會造成影響，但是總體而言，對於相關長度的影響不大，大約仍維持在半個波長左右。此外，聲場的垂直相關性並不太受到參數變化的影響。

Surface-generalized ambient noise in a shallow ocean waveguide with a sediment layer possessing a specific class of density and sound speed distributions capable of describing a realistic seabed environment is considered in this analysis. This class of non-uniform sediment layer has the density and sound speed distributions varying with respect to depth as a genearlized-exponential and an inverse-square function, respectively. The study invokes a formulation developed by Kuperman and Ingenito for surface noise generation, in conjunction with the analytical solutions for the Helmholtz equation corresponding to the sediment layer, to arrive at an analytical expression convenient for numerical implementation. The intensity and spatial correlation of the noise sound field are analyzed with respect to the variations of the system parameters, including frequency, sediment layer thickness, sound speed gradient, with emphasis on the effects of sediment properties on the ambient noise field. The results have demonstrated that the intensity of the noise field is relatively sensitive to the variations of the paramters, while the spatial correlation is not, suggesting that the energy distribution, rather than the spatial structure, of the noise field is susceptible to the environmental variation.

第一章 緒論
1.1 研究主題與動機
1.2 文獻回顧
1.3 研究方法
1.3 論文範疇
第二章 理論模式
2.1 簡介
2.2 聲波方程式
2.2.1 均勻介質
2.2.2 非均勻介質
2.3 聲波方程式之解
2.3.1 均勻介質
2.3.2 非均勻介質
2.4 噪音產生模式
2.3.1 空間關連性
2.3.2 噪音強度
2.5 結語
第三章 數值模擬
3.1 各層之聲波方程式的解
3.2 邊界條件
3.3 線性系統
3.4 運算方式
3.5 結語
第四章 結果與討論
4.1 波數譜
4.1.1 頻率對於波數譜的影響
4.1.2 沈積層厚度對波數譜的影響
4.1.3 聲速曲率變化對波數譜的影響
4.2 噪音強度分佈
4.1.1 頻率對噪音強度分佈之影響
4.1.2 沈積層厚度對噪音強度分佈之影響
4.1.3 聲速曲率變化對噪音強度分佈之影響
4.3 空間關連性
4.3.1 水平相關性
4.3.2 垂直相關性
4.4 其他因素對噪音場的影響
第五章 結論與建議
5.1 結論
5.2 建議

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