Output feedback algorithm for position and attitude tracking control of underwater vehicles

The problem of tracking the position and the attitude of an underwater vehicle without using direct velocity feedback is addressed. To this purpose, a controller-observer scheme is devised and exponential convergence of tracking and estimation errors is proven via a Lyapunov argument. Noticeably, in order to avoid representation singularities of the orientation, unit quaternions are used to express the vehicle attitude. A simulation case study is carried out to show the effectiveness of the proposed control algorith