近年於南海海域發現大尺度水下沙波群之存在，南海海域之沙波地形屬於大型沙波，其振幅多介於10至15公尺、波長最大超過350公尺，由於沙波尺度遠大於一般聲波波長(極低頻之聲波除外)，勢必將造成聲學傳播時強烈的反射、折射以及二維與三維的音傳效應，再加上沙波地形呈不規則分布，因此對聲波的折射與反射效果將隨空間、距離變化。當聲學系統(如聲納或聲學通訊系統)於沙波環境中運用，其效能或可用性將因地形與水文變化受到極大的挑戰，因此掌握沙波環境之音傳以及通道特性，即成為聲學系統運用中相當重要的科學議題。
本研究之目的在於研究沙波地形之音傳特性與通道特性，藉由不同方位角下所接收之聲波能量與其變動來分析沙波地形在不同時空下所造成之音傳效應與現象。為了確實掌握沙波地形之音傳特性，本團隊於2014年6月於南海進行實海域音傳實驗，以搭載聲學記錄器之錨碇串為圓心，拖曳一半徑3公里的圓形測線，藉此獲得不同方位角之聲能變化。並將實測資料與數值模擬結果進行比較，以瞭解與驗證沙波地形所造成之音傳效應。
研究成果初步顯示，從空間變化的觀點而言，沙波地形的存在確實會影響通道多路徑效應，聲波經地形多次不規則反射、折射後，使回波訊號產生嚴重擾動、干涉現象，並造成垂直方向上聲能的結構產生改變；而水文環境變動則會使聲線路徑改變，例如當水表層之水溫升高、聲速較快時，聲音會大量折射至較深層、聲速較緩慢的冷水層，並與沙波底床接觸後反射至位於深水區的水下麥克風，因此會產生聲能聚集於部份深水層之現象。
本研究成果可進一步運用於討論海底沙波地形對於音傳效應以及聲學通道所造成之影響，作為日後南海海域之聲學系統效能評估與水下通訊發展之參考。

Tremendous subaqueous sand dunes were observed on the continental slope in the northern South China Sea recently. The sand dunes (sand waves) are expected to affect 2-dimensional and 3-dimensional acoustic propagation and induce acoustic field fluctuations. The purpose of this thesisis aimed to study the effect of acoustic propagation and variations in the area of South China Sea with subaqueous sand dunes (sand waves), and will focus on the variability of transmission loss, signal-to-noise ratio, and spatial coherence. In 2014, an acoustical experiment of Intensive Observation Period was conducted, supported by both the Ministry of Science and Technology of Taiwan and Office and Naval Research of United States, to study the variations of sound propagation in this area. The source transmitted linear frequency modulating (LFM) signals at 1.5-2 kHz band, received by the vertical line array at few circles. The receive data were processed via pulse compression technique, and sound energy were calculated. This thesis demonstrates the results of dispersive arrivals and transmission loss versus different bearing angles. Experimental data and numerical prediction would be applied to study the effect of acoustic propagation, and the acoustic variability would be quantified and compared in this thesis. According to the data, the results demonstrates that the sand dunes would casued a significant impact on multipath effect, and distinct disturbance in dispersive arrivals. In addition, the distribution of sound energy in the vertical direction would be repartitioned. The results of this thesis could be applied to evaluate and predict the performance of acoustic systems and SONARs in the sea area with subaqueous sand dunes (sand waves).

論文審定書　i
誌　　謝　　ii
摘　　要　　iii
Abstract　　iv
目　　錄　　v
圖　　次　　vii
表　　次　　x
第一章 緒論 1
1.1 前言 1
1.2 研究動機與研究目的 3
1.3 文獻回顧 4
1.4 論文架構 7
第二章 南海沙波音傳實驗簡介 8
2.1 2014年南海沙波聲學實驗 9
2.1.1 南海實驗錨碇簡介 10
2.1.2 南海聲學實驗流程 13
2.2 沙波音傳實驗 16
2.3 實驗儀器介紹 18
2.3.1 垂直線陣列錨碇 (Vertical Line Array，VLA) 18
2.3.2 拖曳式聲納系統 (Towed sonar system) 25
2.4 音傳實驗訊號 29
第三章 實驗資料處理與分析 31
3.1 脈衝壓縮 (Pulse Compression) 32
3.1.1 解調 (Demodulation) 33
3.1.2 頻帶濾波 (Band-pass Filter) 35
3.1.3 相關性積分 (Auto-Correlation) 42
3.2 均方根壓 (Root-Mean-Square Pressure, RMS)與聲壓位準大小 (Sound Pressure Level, SPL) 43
3.3 聲學資料分析 45
3.3.1 實測音傳資料 46
3.3.2 脈衝響應 (Impulse Response) 48
3.3.3 聲壓位準 (Sound Pressure Level，SPL) 56
第四章 實測資料與數值模擬分析 66
4.1 聲學通道分析 66
4.1.1 相關性係數 (Correlation Coefficient) 67
4.1.2 時空變化分析 69
4.2 數值模擬分析 74
4.2.1 數值模式RAM-PE 75
4.2.2 環境參數設定 76
4.3 音傳模擬結果 78
4.3.1 實測資料與模擬結果的聲壓位準比較 78
4.3.2 沙波地形與平坦地形的聲壓位準比較 80
4.3.3 方位角225度以及315度時水層中聲能分佈之情形 83
4.3.4 不同水文參數的聲壓位準比較 87
4.4 一階統計結果分析 95
第五章 結論 100
參考文獻 103
附錄A 南海沙波聲學實驗日誌 107
附錄B 聲源校正實驗 110

[1] A. Newhall et al., Preliminary Acoustic and Oceanographic Observations from the ASIAEX 2001 South China Sea Experiment, Technical Report WHOI-2001-12, Woods Hole Oceanographic Institution, 2001.
[2] C. W. Miller, M. Stone, C.-S. Chiu, S. R. Ramp, Preliminary results from the Windy Island Soliton Experiment (WISE) Acoustics Moorings, Technical Report NPS-OC-06-OXX, Naval Postgraduate School, 2006.
[3] C. W. Miller, D. B. Reeder, M. Stone, K. Wyckoff, Preliminary results from the Non-Linear Internal Wave Initiative (NLIWI) Acoustics Cruise, Technical Report NPS-OC-07-OXX, Naval Postgraduate School, 2007.
[4] D. B. Reeder, B. B. Ma, Y. J. Yang, “Very large subaqueous sand dunes on the upper continental slope in the South China Sea generated by episodic, shoaling deep-water internal solitary waves” Mar. Geol. 279, Vol. 279, pp. 12–18.
[5] 連于穎 (2014)，南海沙波地貌之音傳效應研究，國立中山大學海下科技技應用海洋物理研究所碩士論文。
[6] L. Y. S. Chiu, D. B. Reeder, Y. Y. Chang, C. F. Chen, C. S. Chiu and J. F. Lynch, (2013) “Enhanced acoustic mode coupling resulting from an internal solitary wave approaching the shelfbreak in the South China Sea” J. Acoust. Soc. Am., Vol. 133, pp. 1306-1319.
[7] 劉孟竺，” 三維海洋音傳與海床沙丘效應之研究”，國立台灣大學工程科學及海洋工程學研究所碩士論文，2014。
[8] 盧鴻銘，” 內波與沙波環境之音傳效應研究”，國立中山大學海下科技技研究所碩士論文，2015。


[9] A.A. Shmelev, (2011) “Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves.” No. MIT/WHOI-2011-16. Massachusetts Inst. of Tech, Cambridge, Thesis, WHOI/MIT Joint Program in Applied Ocean Science and Eng.
[10] C. Sungho, K. Donhyug, (2015 November) “Bottom sand waves influence on low-frequency propagation in shallow water environment” The 36th Symposium on Ultrasonic Electronics (USE 2015) Program., Vol. 36 (2015) , Tsukaba Japan.
[11] C.W.Miller, C.S.Chiu, D.B. Reeder,Y.J. Yang, Linus Chiu, C.F. Chen, Preliminary observations from the 2014 Sand Dunes experiment, Technical Report NPS-OC-14-OXX, Naval Postgraduate School, 2014.
[12] K. V. Mackenzie, (1981) ” Nine-term equation for sound speed in the oceans” J. Acoust. Soc. Am., 70, 807-812.
[13] M. B. Porter, and H. P. Bucker, (1987) ”Gaussian beam tracing for computing ocean acoustic fields” J. Acoust. Soc. Am., Vol. 82, pp. 1349-1359.
[14] A. D. Pierce, (1965) “Extension of the method of normal modes to sound propagation in an almost-stratified medium” J. Acoust. Soc. Am., Vol. 37, pp. 19-27.
[15] R. H. Hard, and F. D. Tappert, (1973) ”Applications of split-step Fourier method to the numerical solution of nonlinear and variable coefficient wave equation” SIAM Rev., Vol. 15, pp. 423.
[16] F. R. DiNapoli, and R. L. Deavenport (1980) ”Theoretical and numerical Green’s function field solution in a plane multilayered medium” J. Acoust. Soc. Am., Vol. 67, pp. 92–105.
[17] Z. Alterman, and F. C. Karal (1968) ” Propagation of elastic waves in layered media by finite-difference methods” Bull. Seis. Soc. Am., Vol. 58, pp. 367-398.

[18] M. D. Collins, “User’s guide for RAM versions 1.0 and 1.0p”, Naval Research Laboraory
[19] L.Y.S. Chiu, and D. B. Reeder (2013) “Acoustic mode coupling due to subaqueous sand dunes in the South China Sea”, J. Acoust. Soc. Am., Vol. 134, pp. 198-204.
[20] L.Y.S. Chiu and A.Y.Y. Chang, (2014) “Normal incidence measurement in a subaqueous sand dune field in the South China Sea” J. Acoust. Soc. Am., Vol. 136, pp. 376-382.
[21] L. Y. S. Chiu, A. Y.Y. Chang , D. B. Reeder , (2015) “Resonant interaction of acoustic waves with subaqueous bedforms: Sand dunes in the South China Sea” J. Acoust. Soc. Am. 138(6)
[22] C. S. Chiu, D. B. Reeder, L.Y.S. Chiu, Y. J. Yang and C. F. Chen, (2014) “South China Sea upper-slope sand dunes acoustics experiment” J. Acoust. Soc. Am. 136, 2316
[23] C. Emerson, J. F. Lynch, P. Abbot, Member, Y. T. Lin, T. F. Duda, G. G. Gawarkiewicz, C. F. Chen, “Acoustic Propagation Uncertainty and Probabilistic Prediction of Sonar System Performance in the Southern East China Sea Continental Shelf and Shelfbreak Environments” IEEE J. Oceanic Eng., VOL. 40, NO. 4, OCTOBER 2015
[24] P. Abbot, C. Emerson “Acoustic Propagation Uncertainty in the Shallow East China Sea” IEEE J. Oceanic Eng., VOL. 31, NO. 2, APRIL 2006
[25] P. Abbot and I. Dyer, “Sonar performance predictions based on environmental variability,” in Impact of Littoral Environmental Variability on Acoustic Predictions and Sonar Performance, N. Pace and F. Jensen, Eds. Norwell, MA: Kluwer, 611-618, 2002.
[26] E. Shang and Y. Wang, (1993) “Acoustic travel time computation based on PE solution”, J. of Computational Acoustics, Vol. 1, pp. 91-100
[27] 劉金源 (2001)，水中聲學-水聲系統之基本操作原理，國立編譯館。
[28] 盧鴻銘、張元櫻、邱永盛 (2015)，內波與沙波環境之音傳效應研究，第十七屆水下技術研討會暨科技部成果發表會。
[29] 謝明謀 (2015)，內波與沙波環境之音傳效應研究，國立中山大學海下科技技研究所碩士論文。
[30] 李政恩、張元櫻、陳琪芳 (2005)，台灣東北海域主、被動聲納效能之統計分析，中華民國音響學會第十八屆學術研討會論文集。
[31] 楊政儒,”聲納效能預估之統計分析”,國立台灣大學工程科學及海洋工程研究所碩士論文,2003。
[32] 王崇武,台灣周邊海洋環境對聲波傳播之影響,海洋技術季刊,第十四卷,第四期,民93年12月。