Detailed object observation by autonomous underwater vehicle with localization involving uncertainty of magnetic bearings

To observe underwater objects such as artificial piles and natural chimneys by taking visual images, autonomous underwater vehicles (AUVs) have advantages that they have no problem related to the umbilical cable which may get entangled with the target and surrounding obstacles. This paper proposes a navigation method for AUVs to observe such objects based on images by a CCD camera with simple laser pointers, on the assumption that the visibility is enough for taking their visual images. It includes a localization method under a distorted magnetic field. The proposed method was implemented in the developed testbed AUV "Tri-Dog 1", and proved experimentally through tank tests. The vehicle accomplished the observing mission that automatically detects three pile-objects and turns around them which were modeled on actual piles in a harbor. Based on the proposed method, AUVs are able to carry out a survey of the target object in detail without any help from outside.