臺灣博碩士論文加值系統

聲波在海洋環境中具有相當好的穿透性，因此在利用聲納系統進行水下探測時，除了主要訊號之外，也接收到來自各方向的噪音，接收的雜訊也會影響著聲納效能。因此海洋環境噪音的了解，不僅是重要的學術課題，更是海軍作戰的關鍵參數。本文利用佈放於台灣西南海域之聲學儀器，所錄得的環境噪音，與此實驗區域的風速資料做比對，探討風速影響環境噪音之變化，並觀察環境噪音在時間序列上之變動，依據兩者相關性，計算其統計分佈，如平均位準、標準偏差及迴歸分析，都是分析噪音特性的重要資訊，來達到估算此海域環境噪音變動。因資料量涵蓋四季，可藉此探討其季節性變化，比較環境噪音在不同季節，與不同時間尺度的變化趨勢及差異，根據統計結果可看出，春季與夏季500與1.5k Hz受到不明高位準訊號影響，平均聲壓值比秋冬兩季來得高，500 Hz約高出約10 dB，而1.5 kHz也高出約5 dB。四季中2.4k、3.6k Hz這兩個較高頻段，整體平均位準並沒有太大差異，平均位準都在60 dB左右，且其變動也在3 dB上下，且經由不同時段分析呈現，各個月份聲壓位準的分佈發現，在3.6 kHz的聲壓位準分佈都較其他頻段集中，也觀察到聲壓位準隨著頻率增加而降低。由線性迴歸計算，可求得高風速時的環境噪音預估值，但本研究的估算聲壓值有高估之趨勢，因與風速資料分佈位置有關，資料量分佈集中於低風速位置，由統計分析中偏率來看，結果都較偏向較低的聲壓位準，所以估算值會比量測資料來的高。

Sound wave has much better transmission in ocean environment than electromagnetic waves, therefore sonar systems are widely applied in underwater investigations. However, not only the target signal is received by the sonar but also the noise from different directions. The noise will affect the performance of the sonar, so the understanding of ocean ambient is an important issue both in academic study and military applications.
The ambient noise data of this research was collected by a passive acoustic recording system deployed in the southwest sea of Taiwan, along with the information of wind velocity in the experimented area. The influence on noise level fluctuations by the variation of the wind velocity was first discussed in light of correlation analysis. The fluctuations were expressed in terms of statistic distribution, mean value, standard deviation in different time series.
As results, 500 Hz and 1.5k Hz were saturated by high levels signal from unknown sources in spring and summer, so the average sound levels were higher than in fall and winter, about 10 dB and 5 dB higher for 500 Hz and 1.5k Hz respectively. In seasonal analysis, 2.4k and 3.6k Hz have quite stable the mean levels and their standard deviations were around 3 dB. Especially, the noise level of 3.6 Hz has the least fluctuation throughout the year than any other frequencies analyzed. It was also observed that the noise level was decreased with the increase of frequency.
Calculated by linear regression, this research worked out the estimation equation for the ambient noise level at high wind speed. However, the estimated values are higher than the measured data, it is due to the distribution of wind velocity. The wind data in this study was skewed towards the lower velocity, consequently the predicted values were overestimated.

摘要
第一章 緒論 ............................................................... 1
1.1 研究背景 ............................................................ 1
1.2 海洋環境噪音...................................................... 2
1.3 風速與環境噪音.................................................. 4
1.4 研究目的與本文架構 ......................................... 8
第二章 實驗架構 ....................................................... 9
2.1 實驗地點 ............................................................. 9
2.2 儀器佈放時間 ..................................................... 10
2.3 儀器介紹 ............................................................. 11
2.4 周邊海域環境與風速資料 ................................. 12
第三章 相關理論 ....................................................... 17
3.1 訊號處理 ............................................................. 17
3.1.1 快速傅立葉轉換 .............................................. 17
3.1.2 取樣定理 .......................................................... 18
3.2 統計理論 ............................................................. 19
3.2.1 機率密度函數 .................................................. 19
3.2.2 變異數與標準偏差 .......................................... 21
3.2.3 偏率與尖率 ...................................................... 22
3.2.4 迴歸分析 .......................................................... 24
第四章 訊號處理 ....................................................... 26
4.1 噪音時頻譜 ......................................................... 26
4.1.1 噪音時頻譜 ...................................................... 27
4.1.2 風速資料 .......................................................... 28
4.2 噪音位準分析 ..................................................... 29
4.2.1 聲壓位準與風速 .............................................. 31
4.3 不明高位準訊號處理 ......................................... 36
4.4 統計分析 ............................................................. 37
第五章 結果分析與討論 ........................................... 38
5.1 季節變化分析 ..................................................... 38
5.2 每月變化分析 ..................................................... 42
5.2.1 颱風效應 .......................................................... 43
5.3 每日變化分析 ..................................................... 47
5.3.1 頻率每日變動比較 ........................................ 51
5.3.2 時段變動分析 .................................................52
5.4 噪音位準預估 ..................................................... 55
5.4.1 迴歸分析 .......................................................... 56
第六章 結論與建議 ................................................... 60
6.1 噪音變動統計 ..................................................... 60
6.2 噪音估算 ............................................................. 60
6.3 建議 ..................................................................... 65
參考文獻 .................................................................... 66

[1] R. J. Urick, Principles of Underwater Sound, McGraw-Hill,1993
[2] R. J. Urick, Ambient Noise in the Sea, Peninsula, 1984.
[3] J. A. Shooter , T. E. Demary, and A. F. Wttenborn, “Depth Dependence of Noise Resulting From Ship Traffic and wind”, IEEE Journal of Oceanic Engineering, 15(4), October 1990, pp.292-298.
[4] Knudsen, V. O., Alford, R. S., and Emling, J. W., “Underwater Ambient Noise”, J. Mar. Res. 7, 410, 1948.
[5] K. R. Curtis, B. M. Howe, and J. A. Mercer, “Low-frequency Ambient Sound in the North Pacific: Long Time Series Observations”, J. Acoust. Soc. Am., 106(6), December, 1999, pp.3189-3200.
[6] S. W. Marshall, “Depth Dependence of Ambient Noise”, IEEE Journal of Oceanic Engineering, 30(2), April 2005, pp.275-281.
[7] H. C. Graber and W. G. Large, “Oceanic Winds Estimated from Underwater Ambient Noise Observations in SWADE”, IEEE Journal of Oceanic Engineering, 1(4), September, 1996, pp.45-51.
[8] J. F. Lynch, H. X. Wu, and R. Pawlowicz, ”Ambient Noise Measurements in the 200-300 Hz Band from the Greenland Sea Tomography Experiment”, J. Acount. Soc. Am., 94(2), August, 1993, pp.1015-1033.
[9] A. S. Burgess and D. J. Kewley, “Wind-Generated Surface Noise Source Levels in Deep Water East of Australia”. J. Acount. Soc. Am., 73(1), January ,1983, pp.201-210.
[10] A. J. Perrone, “Deep-Ocean Ambient Noise Spectra in the Northwest Atlantic”, J. Acoust. Soc. Am., 46, September , 1969, pp.762-770.
[11] J. A. Shooter and M. L. Gentry. ”Wind-Generated Noise in the Parece Vela Basin“, J. Acount. Soc. Am., 70(6), December , 1981, pp.1757-1761.
[12] E. M. Arase and T. Arase, “Ambient Sea Noise in the Deep and Shallow Ocean”, J. Acount. Soc. Am., 42(1), July , 1967, pp.73-77.
[13] R. L. Pirie, A Study of Ambient Noise in Shallow Water, Florida Atlantic University, 1999.
[14] G. M. Wenz, “Acoustic Ambient Noise in the Ocean: Spectra and Source”, J. Acoust. Soc. Am., 34, 12, 1962.
[15] B. B. Ma, and J. A. Nystuen, “Passive Acoustic Detection and Measurement of Rainfall at Sea”, Acoustical Society of America, 22, August, 2005, pp.1225-1248.
[16] B. B. Ma, J. A. Nystuen, and Ren-Chieh Lien, “Prediction of underwater sound levels from rain and wind”, J. Acount. Soc. Am., 117(6), June, 2005, pp.3555-3565.
[17] H. M. Walkinshaw, “Measurements of Ambient Noise Spectra in the South Norwegian Sea”, IEEE Journal of Oceanic Engineering, 30(2), April , 2005, pp. 262-266.
[18] D. E. Newland, Random Vibrations, Spectral and Wavelet Analysis, 3th Edition, Longman Scientific&Technical, 1993.
[19] W. W. Crouch and P. J. Burt, “The Logarithmic Dependence of Surface-Generated Ambient-Sea-Noise Spectrum Level on Wind Speed,” J. Acoust. Soc. Am., 51(3), March, 1972, pp.1066-1072.
[20] R. Marrett & N. R. Chapman, “Low-Frequency Ambient-Noise Measurements in the South Fiji Basin,” IEEE Journal of Oceanic Engineering, 15(4), October, 1990, pp.311-315.
[21] 蒙以正，數位信號處理應用MATLAB。
[22] 劉金源，水中聲學-水聲系統之基本操作原理，國立編譯館，2001。
[23] 原著Walpole. Meyer，譯者傅冶天、陶治中、林定玉，工程機率與統計。
[24] 徐義人，工程機率統計學。
[25] 原著G. L. Pickard and W. J. Emery，譯者范光龍，物理海洋學導論，國立編譯館出版，1991。
[26] 林文斐，風延遲效應對海洋環境噪音之影響研究，國立中山大學海下技術研究所碩士論文， 民國90年。
[27] 陳勇杰，淺海環境噪音之深度相依研究，國立中山大學海下技術研究所碩士論文， 民國91年。
[28] 劉志昇，南海低頻環境噪音之分析，國立中山大學海下技術研究所碩士論文, 民國92年。
[29] 魏瑞昌、湛翔智，台灣周邊水下背景噪音模式研究(ΙΙ)－結案報告，中山大學（2004）。
[30] 苑梅俊，淺海水域之水下音傳不確定性分析與偵測效能之研究，國立臺灣大學工程科學與海洋工程研究所博士論文。
[31] 國立成功大學近海水文中心http://www.comc.ncku.edu.tw/
[32]中央氣象局網址http://www.comc.ncku.edu.tw/