Laser scanners for autonomous surface vessels in harbor protection: Analysis and experimental results

Autonomous surface vessels (ASVs) have been proposed, and in limited cases implemented in support of harbor and port protection missions. Such vessels can be used to extend the reach of existing shore-based sensors as well as warning and deterring would-be intruders or trespassers entering a restricted zone. In such a context, the ASV must co-exist with productive and innocuous authorized port traffic, and might be required to transit congested waterways and deal with dynamic traffic conditions. A laser scanner is one useful sensor for relatively close range object detection for obstacle avoidance, docking, approaching, or other controlled close-quarters positioning of an ASV. This paper presents a theoretical treatment of the utility and limitations of laser scanners aboard an ASV, a cost-benefit analysis comparing laser scanners to other sensors which might be used for similar purposes, and provides results of an experiment in which one of NURC´s ASVs was equipped with a commercial laser scanner. The ASV (a 4.7-meter RHTB) runs the MOOS-IvP suite of open-source software. Custom modules were added to MOOS to detect and track objects present in the field of view of the laser scanner. The tracks were then available for use by any active behaviors running on the ASVs backseat control computer. The detected objects were thus avoided or approached as appropriate, following the predefined mission goals.