運用被動時間反轉法及聲線法建立水中聲源二維及三維定位之方法

2-D AND 3-D LOCALIZATION OF UNDERWATER SOUND SOURCE BY USING PASSIVE TIME REVERSAL MIRROR AND RAY METHOD

本研究應用被動時間反轉法與聲線法，建立水中聲源二維及三維定位的方法。二維定位方法中，利用一含有4支水聽器的垂直陣列收錄水中聲源發出的訊號，再利用基於聲線法發展出的BELLHOP程式，計算出水聽器收到的聲波經時間反轉後反向發出所產生的聲壓場，基於時間反轉法反向聚焦（retrofocus）的特性，聲壓最大處即為聲源位置。由於BELLHOP程式的限制，此種方法只能定位出聲源的深度及其與垂直水聽器陣列間的距離，而無法求出方位。本研究在拖航水槽及屏東縣鹽埔漁港外海進行聲源二維定位的實驗，試驗結果顯示利用本研究所發展的方法可得到二維定位不錯的結果。在聲源三維定位的方法上，本研究使用含垂直及水平陣列的十字形水聽器陣列。由於聲線法中二維圓柱座標（r,z）的聲線方程式與三維直角座標中（x,y）的聲線方程式兩者的型式完全相同；因此，先由垂直陣列上水聽器所接收到的聲音訊號，求出聲源的二維座標（r_(oe),Z_(oe)）如同上述二維定位方法，也利用BELLHOP程式，由水平陣列上水聽器所接收到的聲音訊號，計算（x,y）平面的聲場，求出聲源在（x,y）平面上的座標（X_(oe),Y(oe)）。由上述結果，即可得到水中聲源之三維位置（x_(oe),y_(oe),z_(oe)）。本研究所提出的水中聲源三維定位方法，經拖航水槽試驗證實此方法的可行性及準確性，後續可於實海域中進一步測試其實用性。

This study proposes techniques for the 2-D and 3-D localizations of underwater sound source based on passive time reversal method (TRM) and acoustic ray method. For the 2-D localization, a vertical array with four hydrophones was used to collect the sound signals emitted from a sound source. The ray-tracing code BELLHOP was then used to determine the acoustic pressure field generated by the time-reversed signals received by the hydrophones. Based on the retrofocus characteristic of the TRM, the location with the maximum pressure is the location of the sound source. The localization based on the BELLHOP code is limited to the 2-D position of the source, namely the distance and depth, without the bearing. Laboratory experiments performed in a towing tank and field tests conducted in the offshore region off Yanpu Harbor, Pingtung, revealed that the estimated source location is close to the actual one. For the 3-D localization, a cross-shaped hydrophone array consisting of a vertical array and a horizontal array was used to collect sound signals. Because the 3-D ray equations in the (x,y) plane of the Cartesian coordinates have the same form as the 2-D ray equation in the (r,z) plane of the cylindrical polar coordinates, after the 2-D position (r_(oe),z(oe)) of the source has been determined from the signals collected by the vertical hydrophones, the BELLHOP code was used to determine the pressure field in the (x,y) plane from the signals collected by the horizontal hydrophones, and the position with maximum pressure is set as the location of the source, (x_(oe),y_(oe)). Thus, the 3-D location of the source (x_(oe),y_(oe),z_(oe)) was obtained. Experiments conducted in a towing tank revealed that the estimated 3-D source location was close to the actual 3-D source location.