Relative navigation of an AUV using a light-section ranging system

Autonomous underwater vehicles (AUVs) are suitable for condition survey of the surface of artificial structures such as pillars and caissons in harbors. This paper introduces a method for AUVs to trace artificial structures using a light-section ranging system. This system acquires the profile of the target objects over a wide area using a sheet laser beam. The vehicle navigates by referencing the principal shape of the structure, and traces its surface while taking video images of it. This ranging system also enables 3D mapping of its surroundings based on high accuracy positioning. The method is implemented on the testbed AUV "Tri-Dog 1" and its performance is verified through tank tests. It is shown that the AUV navigates robustly against small obstacles and floating particles. Precise depth mapping of the tank floor is also carried out using the same system.