Mission integrated collision avoidance for USVs using laser range finder

In this paper, an approach for a collision avoidance system for small Unmanned Surface Vehicles (USV) is presented. These kind of USVs are typically used for measuring tasks and thus, the collision avoidance algorithm has to take the mission objective and information about obstacles and other vessels into account. It generates an evasive trajectory that either leads around the obstacle, reduces the velocity to let another vessel pass or combines evasive manoeuvres and velocity changes. For the evasive path generation, a specialized A∗ algorithm is used that allows velocity variations and considers different turning circles for different velocities. It is applied to a grid representation of the environment that is built using a laser range finder. The laser range finder detects obstacles above the surface like other vessels, pillars or jetties. An additional tracking module is used to determine the dynamic state of moving obstacles such as other vessels. The complete collision avoidance system is integrated into a small USV and results of real world tests for environment mapping and target tracking are presented. The collision avoidance performance is shown for simulated measurement scenarios.