Abstract
This paper describes an algorithm to make the treatment, segmentation, skeleton and characteristics extraction from acoustic images obtained from a side scan sonar. The fundamental goal is to implement a system that endows a autonomous vehicle with the capacity to know its own distance to the marine bottom and to features located on the marine environment. This features extraction would improve vehicle navigation and allow it to navigate relative to features like an underwater piper on the sea floor or a vertical wall. This paper was made based on Imagenex Sport Scan (side scan sonar) whose function is the observation of environment. Also the autonomous surface vehicle (ASV) ZARCO was used to transport the side scan sonar. Both the vehicles belong to The OceansSys Group DEEC-FEUP. A communication interface between the ASV ZARCO, Imagenex Sport Scan, and a static laptop that allows the observation of sonar data in real time is also described in this paper. The algorithms and routines implemented were validated with real acoustic images acquired during a mission. Results from algorithms application and features extraction are shown in this paper.

Abstract
This paper describes the full development process of TriMARES, a hybrid AUV/ROV designed to fulfil the requirements of a consortium for the inspection and periodic monitoring of a large dam reservoir. The demand of robotic systems for underwater operations is growing exponentially and there are many scenarios for which the commercial solutions are not adequate. Such was the case with TriMARES, where it was possible to take advantage of previous designs to achieve a custom solution in a short time. We describe the initial requirements for the underwater system, we present the main solutions adopted for the vehicle subsystems, and we provide some data from the first in-water tests, performed only 6 months after the beginning of the project.

Abstract
In this work, we address the modeling and control problems in the domain of underwater vehicles. We focus on a prototype of an autonomous underwater vehicle. Although the work presented here is applied to a particular vehicle with four controllable degrees of freedom, the method may be easily extended to several submerged bodies. In the engineering area, modeling of systems is done frequently, as it yields a mathematical translation of their behavior. Since models can become, an important tool to solve problems related to its motion or even to the design of controllers, we obtain a model with six degrees of freedom for such a vehicle. Robust control of underwater vehicles is an area in which many efforts were applied over the last two decades. However, due to nonlinear dynamics, it may be hard to design robust controllers that yield the expected behavior, and there is no general procedure to develop them. Here, we propose an approach that combines nonlinear controllers based on the deduced model and on the Lyapunov theory to control the velocities of the vehicle with linear controllers that control the vehicle's position. We derive control laws to perform several maneuvers, both in the vertical and the horizontal planes, in a decoupled way, which is made possible through the configuration of thrusters. Finally, we present realistic simulations and experimental results that validate the proposed approach in the definition of the control laws.

Abstract
In this paper, we present an approach to control an autonomous underwater vehicle in the vertical and the horizontal planes while pitching down or up (theta = +/-pi/2). Such a capability is explored in MARES, a small-sized, torpedo-shaped hovering AUV with four degrees of freedom. Despite the fact that roll angle is not controllable, we find a guidance law that makes the vehicle reach any point in the horizontal plane while maintaining the vehicle in the vertical position.

Abstract
This paper addresses the simultaneous localization and control of an AUV using a single acoustic beacon. To determine its horizontal position, the AUV fuses distances to the single beacon with dead reckoning data, heading and longitudinal velocity. A particle filter and an extended Kalman filter are implemented and compared in terms of performances. As this is an ill-posed problem, special guidance laws are derived so that the overall horizontal positioning error remains bounded. Besides presenting the derivation of such guidance and control laws, as well as procedures to estimate the horizontal position, we also demonstrate the performance of the proposed system by means of simulation results.

Abstract
In this paper, we address the control of a small-sized autonomous underwater vehicle (AUV), the MARES. We focus on the vertical motion of the vehicle while contemplating an alternative actuator configuration which may operate in the presence of a possible fault. We present a method to detect the occurence of a fault and to identify the faulty thruster. In normal operation, the MARES AUV makes use of two through-hull thrusters for accurate vertical positioning. Nevertheless, the vehicle depth is still controllable with only one of these but an adequate operation requires the redefinition of the control law. Two modes of operation are made possible by deriving a new feedback control law for the configuration with only one vertical thruster. Based on the Lyapunov theory and on the backstepping method, we determine a control law that makes the vehicle tend to the reference with null error. As a demonstration of the performances of our approach, we present some results obtained from field experiments.