使用側掃聲納掃瞄線輔助無人水下載具建立導航地圖

Abstract

無人水下載具常用來執行水下測繪、水下監控等任務。由於缺乏預設的地標，因此無人水下載具在未知環境下的導航仍是一大挑戰，發展海床即時特徵偵測能力對水下無人載具的導航有相當大的助益。本文提出一套利用側掃聲納掃描線即時偵測水下目標物的方法，此方法可以使無人水下載具在無特定結構的環境下建置海底地圖來做自身定位。此方法主要包含二部分：第一，訊號前處理，以增強資料訊號並降低資料量和運算時間; 第二，特徵偵測，以辨識出有包含目標物的掃描線並用適應性閥值突顯出目標物。在偵測過程之後，為了得到整體環境的地圖，使用了佔格格網圖的方法來融合每ㄧ條掃描線上的偵測值，最後，無人水下載具使用運動感測器來表達移動路徑，並整合導航測器的量測值與側掃聲納所偵測到的目標物，建構具有較高信任度的移動路徑以及水底地圖。利用此方法實作在無人載具上即時偵測水下目標物，實驗說明水下載具所建立之沙床上的水泥目標物特徵與水底格網圖，可以用來做為無人水下載具的導航依據。

Navigation of UUV in unstructured environments with accurate positioning capabilities still is a challenging problem due to the lack of predefined landmarks on the sea floor. The aim of this work is the development of a method for target detection by the processing of side-scan sonar scanlines. The detection method developed in this work enables UUVs to build seafloor map for the self localization in an unstructured environment. The detection procedure has two steps. Firstly, a pre-processing step is used to filter the data and to reduce computation time. Then a detector is designed to detect the target position in a scanline. After detection procedure, for the purpose to obtain the whole map of the environment, the occupancy grid mapping method was applied to combine the detect result and the acoustic wave of side-scan sonar in sea water. Finally, trajectory of the UUV could be estimated by motion of the vehicle. This procedure was implemented on an UUV to verify its landmark detection capability. Experimental results conducted on sandy seabed with concrete targets are demonstrated with their signal contents and the final grid maps that are useful for UUV navigation purpose.