Underwater structure observation by the AUV with laser pointing device

To observe underwater structures such as artificial piles in harbors by taking visual images, the autonomous underwater vehicles (AUVs) have advantages that they have no problem related to the umbilical cable which may get entangled with the target object and surrounding obstacles. It is usually difficult to measure the precise configuration of such objects by using acoustic measurement systems because of poor resolution and diffused reflection of sound. This paper proposes sensing and navigation methods to observe such objects based on images by a CCD camera with laser pointers, on the assumption that the visibility is enough for taking their visual images. The navigation system cannot provide accurate enough position. Thus, AUVs change over their navigation basis from navigation system to relative position to the target so as to trace the shape of that. The proposed method was implemented in the testbed AUV Tri-Dog 1 and proved experimentally through tank tests. The vehicle accomplished the mission that autonomously detects 3 piles of 1 meter in diameter that are modeled on actual piles in a harbor, and turns around them. Based on the proposed system, AUVs will be able to carry out surveys of the target object without any help from outside.