臺灣博碩士論文加值系統

本研究以西元2001年亞洲海域國際聲學實驗(Asian Seas International Acoustic Experiment, ASIAEX)在南海佈放垂直線陣列(Vertical Line Array, VLA)所收錄的淺海環境噪音資料為探討對象，使用波束形成(Beamforming)計算淺海環境噪音的垂直方向性，找出水下環境噪音的噪音能量在空間上的分佈及噪音垂直方向性與風速的相依性。由結果可以得知，低頻的聲音能量多來自水平方向，依照過去文獻已知的結果，推測水平角度來的環境噪音多為遠船噪音所貢獻，而表面風浪噪音則是影響水平以外較高角度的主要聲源。同時實驗期間通過的西馬隆(Cimaron)颱風，使得風速有劇烈的變化，因此研究中還有探討風速改變對垂直方向性的影響，由結果可知風浪噪音為影響垂直方向性中，高角度入射能量的主要貢獻源，在噪音頻率範圍越高時越明顯，而且風速越大垂直方向性受風浪噪音影響的頻率範圍越低，其中並驗證颱風影響的噪音垂直方向性的頻率門檻約為200 Hz。另外本研究在垂直方向性計算的過程中，注意到顯著的垂直方向性現象”噪音缺口”(Noise Notch)，在本文的最後部分，將會討論聲速剖面對噪音缺口的影響，而缺口現象在不同頻率上的表現，也將有所呈現，在最後並將結果和過去文獻做一個比較及驗證，並以波束能量差值的計算，量化噪音缺口出現的時間，為往後相關的研究提供一個依據。

This study is based upon the vertical line array (VLA) in South China Sea experiment of the Asian Seas International Acoustic Experiment (ASIAEX), dated from May 3, 2001 to May 16, 2001, in which the ambient noise in shallow water was measured. In this paper, we use the beamforming method to calculate the vertical directionality of ambient noise in shallow water, for discussing the noise source distribution, and environmental effects on vertical directionality. The results show that distant shipping noise was observed near the horizontal angles, and surface noise occurred at high grazing angles. It is also discussed that the wind speed effect on the vertical directionality in this paper. Because of the typhoon Cimaron passed the experimental area during the experiment, which make wind speed changed obviously, so it can be found out the wind effect of ambient noise. By analyze the noise fluctuation, it is concluded that the threshold frequency of wind wave affected ambient noise levels were about 400 Hz. And after analyzing the vertical directionality, it is verified that the threshold was lower to 200 Hz. On the other hand, we also note the phenomena of “noise notch” appeared at some duration when calculating the vertical directionality. The environmental effects (sound speed profile) on the notch, and the presentation of noise notch at different frequencies were discussed. In the end part of this paper, we determined the time when the notch occurred by using the power difference of vertical directionality, and we expect that the results would be important for similar researches in the future.

目 錄
摘要 .................................................................................................... i
Abstract ............................................................................................... ii
目錄 .................................................................................................... iii
圖目錄 ................................................................................................ vi
表目錄 ................................................................................................ viiii
第一章 緒論 ...................................................................................... 1
1.1 研究背景 ............................................................................... 1
1.2 相關文獻 ............................................................................... 4
1.3 研究目的 ............................................................................... 8
1.4 論文大網 ............................................................................... 9
第二章 實驗架構 .............................................................…………. 10
2.1 實驗描述 ............................................................................... 10
2.2 實驗環境……......................................................................... 12
2.2.1環境紀錄錨碇................................................................... 12
2.2.2 西馬隆颱風...................................................................... 13
2.3 主要聲學儀器......................................................................... 14
2.3.1 接收陣列 ........................................................................ 15
2.3.2 深海聲源 ................................….................................... 17
2.3.3 淺海聲源 ........................................................................ 19
2.3.4 燈炮聲源 ........................................................................ 20
2.4 儀器佈放時程........................................................................ 21
第三章 相關理論 .............................................................................. 23
3.1 波束形成法 ........................................................................... 23
3.2 取樣定理 ............................................................................... 25
3.3 濾波處理 ............................................................................... 26
第四章 訊號處理 .............................................................................. 28
4.1 聲音檔案格式 ....................................................................... 28
4.2 三維頻譜 ............................................................................... 29
4.3 訊號濾波 ..........…................................................................. 30
4.4 陣列測試 ............................................................................... 31
4.5 垂直方向性計算..................................................................... 32
4.5.1 計算過程及結果呈現 .................................................... 32
4.5.1 旁瓣的影響 .................................................................... 33
4.6 水文資料處理 ....................................................................... 35
4.6.1 溫度紀錄 ........................................................................ 35
4.6.2 聲速剖面 ........................................................................ 36
4.6.3 風速資料 ........................................................................ 37
第五章 結果分析 .............................................................................. 38
5.1 垂直方向性的頻率相依 ....................................................... 38
5.2 風速相依 ............................................................................... 39
5.2.1不同頻率的垂直方向性表現 ......................................... 40
5.2.1垂直方向性隨風速變化的趨勢分佈 ............................. 43
5.3 噪音缺口 ............................................................................... 43
5.3.1噪音缺口在不同頻率的表現 ......................................... 43
5.3.2風速對噪音缺口的影響 ................................................. 45
5.4 垂直方向性隨時間變化的分析 ........................................... 46
5.4.1風速相依的時間序列 ..................................................... 47
5.4.2噪音缺口出現時間的計算 ............................................. 50
第六章 結論與建議 ........................................................................ 53
6.1結論 ........................................................................................ 53
6.2 建議 ....................................................................................... 54
參考文獻 ............................................................................................ 55
附錄...................................................................................................... 57

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