南海聲納偵測距離之統計分析

Abstract

被動聲納系統常被應用於監測及其他工作上，但海洋環境的變動會使被動聲納的效能受到影響，對被動聲納系統的操作造成阻礙。因此本文主要利用亞洲海域國際聲學實驗中的環境及聲學資料，研究被動聲納系統的聲納效能與海洋環境變動的關係。 亞洲海域國際聲學實驗於西元2001年在南海舉行，其觀測到的環境資料顯示該海域的內波活動極為頻繁，除了造成海洋環境劇烈又快速的變動之外，也進而影響聲音傳播的穩定性。另外在南海的內波可因其週期的不同而分為內潮及非線性內波兩種，所以亞洲海域國際聲學實驗提供的資料可用來研究在這兩種不同的變動機制下聲納效能的變化情形。 由於亞洲海域國際聲學實驗只能提供接收陣列處的聲學資料，無法有效計算及呈現該環境中的聲納效能變動情形，所以本文利用實驗中量測得的環境資料來模擬完整的聲場，並使用接收陣列所紀錄的聲學資料來檢驗模擬結果的正確性。分析結果顯示模擬所得之聲場與實測資料一致，且傳播損耗皆有隨深度而減少的趨勢；比較在內潮及非線性內波作用下的聲場，可發現內潮作用下的傳播損耗大於非線性內波作用下的傳播損耗。這些現象都是由非線性內波造成聲音強烈地向下折射現象而引起。 本文中用來衡量聲納效能的參數有二：偵測距離及累積偵測機率，由於環境變動劇烈，所以使用統計分析的方法來分析以上二個參數。分析結果顯示以上二個參數都在非線性內波發生期間有較好的結果，這個現象在靠近海底的部份更是明顯。雖然非線性內波能帶來較好的聲納效能，但由於非線性內波也會同時造成比較大的變動，所以在應用時也需要特別考量。

The passive sonar system has been extensively used to detect and accomplish the other tasks. But the sonar performance of passive sonar system will be intensively affected by the ocean fluctuation, and will interfere the operation of passive sonar. This thesis thus studies the relationship between ocean environment fluctuation and sonar performance by using the environmental and acoustic data in Asian Seas International Acoustic Experiment (ASIAEX). The ASIAEX South China Sea Component was conducted in 2001, and the measured data reveal that the internal wave activities are persistent and violent. It not only causes the rapid fluctuations in ocean environment but also damages the stability of the acoustical propagation. Moreover, the internal wave field would be categorized into internal tide field and nonlinear internal wave field by the period and the reaction activity. So that the in situ data measured in ASIAEX could be provided to investigate the fluctuations of the sonar performance among these two typical dynamic ocean environments. Because the received signals from only vertical line array can not interpret the acoustic fields along the acoustic propagation path, the sonar performance along this path could not be obtained. In this thesis, the in situ temperature profile has been utilized to obtain the model-based acoustical propagation filed and has been compared with the acoustic data to inspect the accuracy of the simulation results. The results show the model-based sound field match well to the data and the transmission loss is decreasing with depth because of the downward refracting sound speed profile. Compare the results in these two dynamic ocean environments, i.e. internal tide and nonlinear internal wave fields, the analysis result show that the propagation loss in the internal tidal field is larger than that in the nonlinear internal wave field. Two parameters which used to analyze the sonar performance are detection range and probability of detection. Two parameters are analyzed statistically because of the violent fluctuation in the ocean environment. The results present that the sonar performance is better in the nonlinear internal wave field but also suffers higher variation in the nonlinear internal wave field.