Repeated close-distance visual inspections with an AUV

Underwater structures like oil and gas production systems, ship hulls or the foundations of buildings, piers and offshore wind facilities have to be regularly inspected to evaluate the state of the structure and to plan future interventions for repair and maintenance. These inspections are currently done by remotely operated vehicles (ROVs) or by divers but they are time-consuming, expensive and need to be planned a long time in advance. Therefore a current trend in the offshore industry is to look into sub-sea resident autonomous underwater vehicles (AUVs) as inspection systems. There is a big difference between the currently available survey AUVs and inspection AUVs with respect to their primary mission capabilities. Whereas a survey AUV needs to map a wide area and have a high precision relative position between the scans, an inspection class AUV needs to find the inspection targets repeatedly. Within this paper we introduce the navigation problem in detail and the methods used for the inspection. We also present the initial tests with the FlatFish AUV applying the new approach to address this problem.