Path following of underactuated marine surface vessels in the presence of unknown ocean currents

Unmanned marine crafts constitute a priority area within several fields of study, and there are still many challenges related to making such vessels autonomous. A basic task of an autonomous marine craft is to follow a general path in the presence of unknown ocean currents. This paper presents a method to achieve this for surface vessels. The results are an extension of the results in [1] regarding path following of space curves when no ocean currents are present, and introduce a virtual Serret-Frenet reference frame that is anchored in and propagates along the desired path. The closed-loop system consists of an ocean current observer, a guidance law, a controller and an update law to drive the Serret-Frenet frame along the path, and is shown to be UGAS. Simulation results are presented to verify the theoretical results.