- 學位論文
淺海水域之水下音傳不確定性分析與偵測效能之研究
Uncertainty Analysis of Underwater Acoustic Propagation and Detection Performance in Littoral Water
摘要
淺海海域受內波及地形影響，海洋環境極為複雜，本研究以ASIAEX獲得之南海海域海洋環境資料為基礎，利用「經驗正交法EOF」來分析造成海水溫度變化的影響因素。在南海海域之水文變化，主要受到內潮（Internal Tide, IT）及非線性內波（Nonlinear Internal Wave, NIW）作用影響為主。利用EOF法分析，可以有效偵測海水溫度變化的主因為內潮或是非線性內波。利用ASIAEX所規劃之音傳實驗路徑、實測海水溫度錨碇資料及聲學模式進行綜合分析，可知在大陸棚邊緣的水下聲波變動，海底地形的變化是主要影響因素。 此外，淺海水域的環境變動性，不論在時間與空間上其變化起伏均較大洋中高，惟各個海洋環境參數特性，例如水文、底質及水深等，則有不同程度的變化，針對這些變動性參數，可利用不確定性的方法加以定義其變動區間。本研究利用建構之環境分析模型，分析海洋環境特性對水下聲波之影響程度，其中以音源位置的不確定性影響聲波傳遞最大，其次為底質聲速、底質密度及衰減係數等參數。 聲波為偵測水下環境的有效能量，在探討水下聲學的特性時，多以波動方程式為基礎，配合適當起始與邊界條件所開發出來的聲學模式，用以分析水下聲波能量分佈的狀況，惟這些聲學模式的計算，必需有賴正確的海洋環境資訊，做為輸入參數，才能獲得正確水下聲波能量的計算結果，本研究建構一整合海洋環境與聲學模式間的耦合關係的計算模組，作為評估聲納偵測效能之計算工具。 最後應用學術界長年建立的海洋環境資料，進行台灣週邊水下聲學特性分析，以探討聲納的運用效能，建立一套適用台灣周邊海域，並依據海洋環境變動，計算水下聲波傳遞狀況的分析方法，以提昇海洋探測裝備效能，乃至聲納偵測的操作效益。
並列摘要
The ocean environment is very complicated due to the effect of internal wave activity and the bathymetry changing in littoral water. This research is based on the ocean mooring data in South China Sea during ASIAEX period and utilizes the decomposing EOF to analyze the variation of sea water temperature which is mainly effected by the internal tide and nonlinear internal wave. The EOF method can efficiently detect the activity of internal tide or nonlinear internal wave in water column. Based on the acoustic transmission track of ASIAEX and using the measuring ocean data as the input data for acoustic model can reach a conclusion of the dominance of the acoustic field in the shelf break area as follows. The bathymetry is the major factor of the underwater acoustic energy variation. The variation of ocean environment in littoral waters is always high than that in deep waters no matter in temporal and spatial scale. The individual parameters of ocean environment, such as seawater temperature, sediment and water depth, have different variation in scale. The variation range of these parameters can be presented by the method of uncertainty. To develop an ocean environment model can analyzes the acoustic field of effecting by ocean parameter. The parameters of most effecting acoustic field are position of source, sound speed of sediment, density and attenuation coefficient of sediment in order. The wave equation is the basis to describe the property of underwater sound with proper initial condition and boundary condition for acoustic model and to analyze the acoustic energy. The operation of acoustic model relies on precise ocean data as input in order to get correct acoustic field. This research constructs a computing module that can evaluate the sonar performance through coupling ocean environment and acoustic model. At the end of this research, to analyze the characteristic of underwater sound around Taiwan waters based on the ocean database collecting by academic is in order to explore the operation of sonar performance. This result gives a clear picture of sonar detection that can prompt the sonar operating ability.