Adaptive Coverage Path Planning for Underwater Sonar Scans in Environments with Changing Currents

This article considers underwater sonar scans that utilize a sonar-equipped Autonomous Marine Ship (AMS). The AMS finds an underwater object by towing a tow fish, having active sonars for imaging the sea bottom. This paper tackles the autonomous generation of the AMS’s coverage path, such that the AMS scans the entire survey region once it moves along the generated path. The presence of currents introduces undesired vehicle motion that can greatly complicate sonar data collection, especially when sonar data are to be processed into high-resolution SAS imagery. If the tow fish moves opposite to the current’s direction, then the tow fish can move straight along its intended course without using crabbing motions. In this situation, one can derive a clear sonar image appropriate for finding underwater objects. We planned the AMS’s coverage path so that the tow fish’s heading is opposite to the current’s changing direction, while covering the entire workspace. As far as we know, this paper is novel in planning the AMS’s coverage path adaptively, such that the tow fish’s heading is opposite to the current’s changing direction. Using computer-based simulations, we verify the outperformance of the proposed adaptive path planner by comparing it with a case where varying sea current was not considered by the path planners.