A novel method for underactuated UUV tracking unknown contour based on forward-looking sonar

Abstract

Tracking unknown contour is an essential problem for automated operations of Unmanned Underwater Vehicle (UUV). Applications such as harbor surveillance, island survey, and obstacle avoidance require UUV with the ability to track the contours of unknown marine structures. The absence of a priori information poses a great challenge in solving such problems. Most existing approaches follow the sense-act pattern by designing elaborate control laws to solve the problems under specific configurations. However, they demand much complexity to implement and lack generalizability in unstructured environments. This paper presents a novel unknown contour tracking method based on the sense-plan-act formulation and focuses primarily on the first two processes to make results applicable to conventional controllers. In terms of perception, forward-looking sonar (FLS) is used as the main device of data collection and a probabilistic perception model and a rolling occupancy grid map construction method based on this model are introduced. For planning, it is assumed that the UUV is underactuated and maneuvers in a 2D plane. Considering multiple tracking metrics, the problem is described as a multi-objective optimization problem and an emerging swarm intelligence algorithm is chosen as the solver. Notably, a contour prediction mechanism and a real-time risk assessment and replanning strategy are designed to ensure the continuity and navigational safety of the tracking process, respectively. Results demonstrate the effectiveness of the proposed method with contours extracted from real harbor and island.