4. Fault Detection/Tolerance Strategies for AUVs and ROVs

Abstract

Autonomous Underwater Vehicles (AUVs) and Remotely Operated Vehicles (ROVs) received increasing attention in the last years due to their significant impact in several underwater operations. Examples are the monitoring and maintenance of off-shore structures or pipelines, or the exploration of the sea bottom; see, e.g., reference [321] for a complete overview of existing AUVs with description of their possible applications and the main subsystems. The benefit in the use of unmanned vehicles is in terms of safety, due to the possibility to avoid the risk of manned missions, and economic. Generally, AUVs are required to operate over long periods of time in unstructured environments in which an undetected failure usually implies loss of the vehicle. It is clear that, even in case of failure detection, in order to terminate the mission, or simply to recover the vehicle, a fault tolerant strategy, in a wide sense, must be implemented. In fact, simple system failure can cause mission abort [154] while the adoption of a fault tolerant strategy allows to safely terminate the task as in the case of the arctic mission of Theseus [118]. In case of the use of ROVs, a skilled human operator is in charge of command the vehicle; a failure detection strategy is then of help in the human decision making process. Based on the information detected, the operator can decide in the vehicle rescue or to terminate the mission by, e.g., turning off a thruster.