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

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