對於聲納或水中通訊而言，海洋環境噪音是影響因素之ㄧ，無論在監聽或主動偵測上，都會干擾聲納系統的效能，也會到影響水中通訊的品質。由於海水溫度、密度變化的因素，使環境噪音具有方向特性，運用波束形成法的計算，便可分析其能量的方向性。然而傳統波束形成法是以平面波訊號做為計算基礎，再運用線性累加各角度能量。但海洋中聲波的傳遞受到邊界及能量損耗影響，使陣列接收的訊號在空間相關性上會有所變化，若進行傳統波束形成計算，便無法符合其基本的假設，亦可能造成波束解析度及訊雜比的下降的缺陷。因此本研究以噪音空間相關性來探討對波束形成解析度的影響，並使用通訊系統中的適應性演算法來改善波束解析度。首先以模擬方式分析平面波聲場與非平面波聲場的空間相關性，並以波束解析結果進行比較。另外，本研究也將以ASIAEX實驗資料探討不同狀態下的噪音相關性情形，以及對波束形成的影響。結果指出隨著頻率逐漸增高，噪音空間相關性就越低，且當噪音空間相關性較低時，的確會使波束解析度變差，在此情況下，本研究使用適應性波束形成法來改善波束解析度。從傳統波束形成與適應性波束形成的比較結果指出，主波瓣寬度的改善程度最高可達到42.9 %，且波束訊雜比最高可增加6 dB。另一方面，在ASIAEX實驗資料的應用中，主波瓣寬度的改善程度最高可達到40.0 %，波束訊雜比最高可增加8 dB，不僅噪音缺口現象更為顯著，也提升噪音方向性分析的精確性。

Ocean ambient noise is one of factors that can affect the performance of sonar and underwater communication system, it can degrade the performance of sonar system on listening or active detection, and also can affect the quality of underwater communication. Due to the variation of temperature and density in the ocean which make ambient noise has directionality. Beamforming can analyze the directionality of noise energy. Conventional beamforming is based on the assumption of plane wave sound field, so the energy from each angle is obtained by linear accumulation of every element. However plane wave assumption may not be satisfied because of the boundary interactions of sound propagation and energy attenuation of water column, therefore conventional beamforming may have poor beam resolution and SNR in applications. This research is to study of the influence of spatial coherence of ambient noise on beam resolution, and to improve the beam resolution by using the adaptive algorithm from the communication system theory. Firstly, simulations were performed to study spatial coherence between plane wave and non-plane wave in ambient noise, and the results were compared with beam resolution. This research also analyzes the influence of different conditions of noise spatial coherence on beamforming with ASIAEX data. The results showed that ambient noise has lower spatial coherence at high frequency, and the beamforming has poor beam resolution because of the lower spatial coherence in noise. Therefore, the adaptive beamforming were performed to improve the beam resolution, and compared with the conventional beamforming. The results showed that the highest improvement on beam resolution is 42.9 %, and increased SNR by 6 dB. On the other hand, the application of ASIAEX data show that, the highest improvement on beam resolution is 40.0 %, and increased SNR by 8 dB. The noise notch of ambient noise became more significant by increasing in beam resolution, and it also promoted the accuracy of analysis on noise directionality.

摘要 ............................................................................. i
Abstract ...................................................................... ii
目錄 ............................................................................ iii
表目錄 ........................................................................ vi
圖目錄 ........................................................................ viii
第一章 緒論 ............................................................... 1
1.1 研究背景 .............................................................. 1
1.1.1聲納系統 ............................................................ 1
1.1.2海洋環境噪音 .................................................... 3
1.1.3聲學量測陣列 .................................................... 5
1.2 海洋環境噪音之方向特性 .................................. 6
1.3 海洋環境噪音之空間相關性 .............................. 9
1.4 適應性天線系統 .................................................. 11
1.5 研究目的 .............................................................. 15
第二章 基礎理論與實驗架構 .................................... 16
2.1實驗地理位置與實驗佈署 ................................... 16
2.1.1 垂直線陣列 ....................................................... 17
2.1.2 陣列訊號檔案格式 ........................................... 18
2.1.3 時頻譜圖 ........................................................... 19
2.1.4 水文環境資料 ................................................... 19
2.2 傳統波束形成法 .................................................. 21
2.3 相關性理論 .......................................................... 23
2.4 適應性演算法 ...................................................... 24
2.4.1 最小均方演算法 .............................................. 24
2.4.2 適應性波束形成法 .......................................... 28
2.5 波束訊雜比與主波瓣寬度 .................................. 29
2.6 陣列傾斜修正法 .................................................. 31
第三章 波束形成解析度探討 .................................... 34
3.1 訊號模擬架構 ...................................................... 34
3.2 不同陣列及分析頻率的差異 .............................. 36
3.3 噪音空間相關性對解析度的影響 ...................... 38
3.3.1 平面波聲場 ....................................................... 38
3.3.2 低空間相關的聲場 ........................................... 42
3.4 陣列傾斜修正結果 ............................................. 44
3.5 實驗資料的比較與分析 ..................................... 46
3.5.1 不同資料筆數平均 ........................................... 46
3.5.2 實驗資料與模擬結果 ....................................... 47
3.5.3 各頻率的空間相關性變化 ............................... 53
3.5.4 高低風速的影響 ............................................... 55
3.5.5 近船噪音的影響 ............................................... 58
第四章 適應性演算法之應用 .................................... 62
4.1雜訊消除 ................................................................ 62
4.2傳統與適應性之波束形成模擬比較 .................... 64
4.2.1 不同型式陣列 .................................................... 64
4.2.2 非平面波聲場 .................................................... 66
4.3實驗資料的波束解析度改善 ................................ 68
4.3.1 環境噪音方向性 ................................................ 68
4.3.2 船舶噪音方向定位 ............................................ 69
4.3.3 噪音缺口分析 ................................................... 70
4.3.4 各頻率噪音之方向性 ....................................... 71
第五章 結論與建議 .................................................... 76
5.1結論 ....................................................................... 76
5.2建議 ....................................................................... 77
參考文獻 ..................................................................... 78

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