本論文之研究主題主要是探討聲波在波導環境中的傳播機制。在本文中，海洋為水平層化介質，沈積層為具有聲速與密度連續且緩慢變化特性的流體介質，底床為彈性體，而聲源為置於環境中任意處之單點聲源。本文所探討之聲波傳播環境，已相當近似於真實海洋環境。

Kuperman 和 Ingenito 提出一隨機且連續分佈於接近海面的無窮平面上之單點聲源在海床視為流體介質，而海洋為水平層化介質之環境的傳播機制。本論文依據此模式，並使用簡正模態法 (normal mode method) 來模擬海面產生噪聲的傳播機制。Hamilton 近年來的研究顯示，海床中的沈積層具有聲速與密度連續且緩慢變化的特性。過去處理上述海洋環境中的聲波傳播問題時，都將聲速與密度連續變化之介質分割為數個常數層。但在聲波組成特性方面，層化分割無法做詳細的說明。再者，過去所做的研究，多未考量底床之彈性體性質，亦即未考慮 P 波與 S波對於聲波傳播之影響，而這也正是本論文之研究動機所在。

在本論文的研究中，我們已經分析了海洋環境中經由底床的反射、波導中的波數譜、水層中的噪聲強度以及噪聲場的空間特性等結果。在海床反射的研究中，我們探討了沈積層中不同變化狀態對反射的影響。結果顯示了沈積層厚度與聲波長的比值參數對沈積層有重要的影響，當比值參數較小時，反射主要受底床特性的影響；反之，反射係數則相依於海床的分佈。

另一方面，文中亦分別介紹並探討了波數譜中各類型波。尤其是若頻率低到足以穿透至底床以及聲源接近海床時才可能會產生的 Scholte wave。當頻率大於數百赫茲，Scholte 模態將不存在。海床性質對於波數譜的影響主要在連續及消逝波譜區，這與反射係數的結果是一致的。水層中的噪音強度主要受模態結構與連續波譜區的影響，而 Scholte 模態則無多大影響。噪聲場的空間特性之結果包含了水平及垂直相關。隨著相關長度的增加，噪聲場的水平相關長度與噪聲源有較為相關的趨勢。但垂直相關則隨之衰減。這指出了噪聲場的相關性同時受噪聲源與波導特性的影響。

Acoustic wave fields in an ocean waveguide with a sediment layer having continuously varying density and sound speed overlying an elastic subbottom is considered in this analysis. The objective of this study is to investigate the effects of seabed acoustic properties,including the density and sound speed of sediment layer and subbottom, on the characteristics of the wave fields. This geometry offers a good environmental model which closely resembles a realistic ocean waveguide.

This noise model was first proposed by Kuperman and Ingenito in the study of surface-generated ambient noise using normal mode approach.Recent experimental data provided by Hamilton have shown that the sediment layer in the seabed experiences a transitional change in which the density and the sound speed vary continuously from one value at the top to another at the bottom of the layer.
Traditionally, in treating wave propagation in a such environment,the medium is represented by a series of layers,each of which has a uniform property within the layer.While this approximation may reasonably describe the variations of the medium as a whole,the details of the acoustic constituent may only be seen when these variations are properly accounted for.
Moreover, the subbottom is taken to be a uniform elastic medium that is capable of supporting both compressional and shear waves.

For the study of reflection from seabed, various kinds of sound speed and density profiles are employed.The wavenumber spectrum has clearly shown the various kinds wave components in the waveguide,in particular, the Scholte wave mode.The noise intensity in the water column is dominated by the modal and continuous spectrum.For the set of parameters chosen,the horizontal correlation lengths of the noise
field tend to increase as the noise sources becomes more correlated, however, the vertical correlation tends to reduce. This indicates that the coherency of the noise field is controlled both by the noise sources and waveguide
properties.

第一章 緒論
1.1 研究動機與目的
1.2 研究環境簡介
1.3 文獻回顧與先期研究
1.4 研究方法
第二章 理論模式
2.1 簡介
2.2 聲波方程式
2.3 聲波方程式的解
2.4 噪聲場的空間相關函數
2.5 噪聲強度
2.6 結語
第三章 聲波在沈積層上的反射
3.1 各層之聲波方程式的解
3.2 線性系統
3.3 結果與討論
第四章 震聲環境中海床性質對聲波傳播的影響
4.1 淺海環境中之聲波傳播
4.1.1 線性系統
4.1.2 波數譜
4.1.3 噪聲強度
4.1.4 空間相關性
4.2 層化海洋中之聲波傳播
4.2.1 線性系統
4.2.2 波數譜
4.2.3 噪聲強度
4.2.4 空間相關性
第五章 結果與討論
5.1 結論
5.2 建議

1. Liu, Jin-Yuan and Chen Fen Huang , "Effects of seabed properties on acoustic wave fields in a seismo-acoustic ocean waveguide,' it Ocean Engineering, 28(2001),1437-1459

2. Liu, Jin-Yuan and Chen Fen Huang , "Surface-Generated noise in an ocean waveguide with a transition layer of continuously varying density and sound speed,'Journal of Computational Acoustics., 7(4), 253－268, 1999.

3. Bergamann, P.G., "The wave equation in a medium with a variable index of reflection,'J. Acoust. Soc. Am., 17(4), 329－333, 1964.

4. Brekhovskikh, L.M.,Waves in Layered Media, 2nd ed., Prentice-Hall, 1980.

5. Brekhovskikh, L.M. and Y.P. Lysanov,Fundamentals of Ocean Acoustics, 2nd ed., Springer- Verlag, 1982.

6. Ewing, W.M., W.S. Jardetzky, and P. Press,Elastic Waves in Layered Media, McGraw-Hill, 1957.

7. Hamilton, H., "Geoacoustic modeling of the sea floor,'J. Acoust. Soc. Am., 68(5), 1313－1340, 1980.

8. Jensen, F.B., W.A. Kuperman, M.B. Porter, and H. Schmidt, Computational Ocean Acoustics, AIP Press, 1994.

9. Kuperman, W.A. and F. Ingenito, "Spatial correlation of surface-generated noise in a stratified ocean,'it J. Acoust. Soc. Am.,67(6), 1988－1996, 1980.

10. Robins, A.J., "Reflection of a plane acoustic waves from a layer of varying density,'J. Acoust. Soc. Am.,87(4), 1546－1552, 1990.

11. Robins, A.J., "Reflection of a plane wave from a fluid layer with continuously varying density and sound speed,' J. Acoust. Soc. Am., 89(4), Pt. 1, 1686－1696, 1991.

12. Robins, A.J., "Exact solutions of the Helmholtz equation for plane propagation in a medium with variable density and sound speed,'J. Acoust. Soc. Am., 93 (3), 1347－1352, 1993.

13. Schmidt, H. and W.A. Kuperman, "Estimation of surface noise source level from low-frequency seismoacoustic ambient noise measurement,'J. Acoust. Soc. Am.,84(6), 2153－2162, 1988.

14. Tolstoy, I. and C.S. Clay,Ocean Acoustics－Theory and Experiment in Underwater Sound, AIP, 1987.

15. Williams, A.O. and D.R. MacAyeal, "Acoustic reflection from a sea bottom with linearly increasing sound speed."J. Acoust. Soc. Am.,66(4), 1936－1841, 1979.

16. 劉金源，《水中聲學-水聲系統之基本操作原理》，國立編譯館，2001。

17. 陳耀文、許世宗、黃千芬、劉金源，“海床聲學性質對於海洋表面所產生之噪聲場的影響”，第二十二屈海洋工程研討會論文集，pp.509-516，2000。

18. 陳耀文、黃千芬、劉金源，“海洋震聲波導環境中海床性質對於聲波傳播的影響”，第三屈水下技術研討會論文集，pp.A14-A21，2001。