Modified linear terminal guidance for docking and a time-varying ocean current observer

Unidirectional docking of a torpedo-type underactuated AUV (Autonomous Underwater Vehicle) has been developed. In this paper, guidance scheme considering drift caused by ocean currents will be investigated. To compensate drift, we design an ocean current observer. The observer is based on kinematic equations of the AUV. We also suggest a guidance scheme based on linear terminal guidance using the observer. The LTG (Linear Terminal Guidance) is in the framework of optimal control but there is no compensation against external disturbances. The conventional linear terminal guidance is modified to be adapted to unidirectional docking compensating the effect of ocean currents. Simulation results are also included.