Recognition of sacrificial anodes using parallel lighting for fully automatic underwater inspection by autonomous underwater vehicles

In this paper, an automatic inspection method by AUVs (Autonomous Underwater Vehicles) is proposed. As an example, full-inspection of the bottom shell of IT Mega-Float (a very large floating artificial land which is located at Yokosuka) is addressed. The AUV moves by dead-reckoning navigation, while the position error is reset by a vision-based system using sacrificial anodes as a reference. These anodes are fitted at regular intervals to prevent corrosion of the structure. In order to identify a sacrificial anode that may also be covered with marine organisms, the parallel lighting method is proposed. Simulations of the proposed technique and field experiments have been carried out under the bottom of IT Mega-Float to demonstrate the efficiency of the proposed method.