利用單一聲標進行自主式水下載具定位之研究

Abstract

本研究利用單一聲音信標所發出來的聲音信號來輔助自主式水下載具在水中的航行與定位。自主式水下載具運用擴展式的卡爾曼濾波器來做為定位演算方法，利用運動模型與內部搭載的感知器回授值做為定位依據，並利用量測水中的信標發出的聲音推估載具本身與信標之間的距離達到輔助定位。 本研究的水下聲標為水聲海洋層析法網路中所設定的一個水下聲學節點，為了分辨水下聲學傳感器節點所量測到的時間訊號，本研究採用常數錯誤報警率偵測器來做為篩選多重路徑聲音到達時間的依據，選定到達時間即可計算聲音的傳遞時間，進而推估載具與聲標的距離。在沒有收到聲標信號時，水下載具採用其運動模型推估本身的位置，等量測值出現方進行狀態的更新。本文也討論載具與聲標間距離量測值對系統定位的不確定性的影響。

This work is a study of localization method of an autonomous underwater vehicle (AUV) moving in the water using acoustic signals from a single beacon. An Extended Kalman Filter is employed to improve the vehicle localization. According to the vehicle motion model and the sensor measurements, the AUV position can be calculated by the dead-reckoning and updated by the signal from the beacon. The beacon in the study is one of the sensor node for the ocean acoustic tomography which is a method to measure the current velocity and temperature field using the time-of-flight of acoustic signals. The AUV carries a node while it transmits and receives signals of m-sequence from one of the fixed sensor nodes. Time of flight between the AUV and the node is distinguished from several acoustic rays from a single beacon using the constant false alarm rate detector. The arrival time is used to estimate the distance from the AUV and the beacon. Error covariance of the AUV position estimates are compared with the GPS location of the AUV. The uncertainty of the position estimates are found to be affected by the distance of the AUV to the sensor node.