Abstract
In this paper, we present a low-cost versatile device developed to support the navigation of autonomous underwater vehicles. Unlike the usual transponders extensively used for LBL acoustic navigation of a single vehicle, this device allows the navigation of multiple vehicles and the remote tracking of their positions, without any extra acoustic signals being transmitted. The navigation beacon has a radio buoy connected to an underwater reconfigurable multi-frequency transponder. A remote tracking station receives data from the buoy and monitors the position of the vehicles in real time. We describe the mechanical, electronic and software modules involved, as well as the tracking algorithm, and we also present experimental data from an operational mission.

Abstract

Abstract
In this paper, we address the current developments of the "PISCIS" project. We focus on the experimental results from recent operational missions with an AUV in a estuarine environment. Besides describing mission planning and logistic details, we also present tools for oceanographic data processing and visualization. This will be demonstrated with some examples of collected data.

Abstract
This paper describes the interaction between the kinematic model of the AUV MARES, and the measurement and observation of the environment through images obtained with the sonar use. Three types of Sonar are discussed in this paper; there are forward-look, side scan and multibeam. But the sonar used to develop this work was the side scan sonar. The type of observations and characteristics of the environment provided by the sonar are described here. The method, which connects the sensory part of the vehicle with the observations of the sonar, was the Kalman filter (EKF). In this paper, are presented two simulations of filters for two different characteristics. Both filters estimate the characteristics of natural landmarks, creating an environment map, but both of them consider different states of the vehicle. Results of the simulation are obtained. The features that are considered are an underwater pipe on the floor and a wall. It also generated a control for the vehicle that provides the capacity to move along the feature/landmark from a reference distance.

Abstract
This paper tackles the problem of localization of an acoustic pinger by a team of cooperative marine robots. A pinger, whose location is unknown, intermittently emits an acoustic ping which is sensed by hydrophones mounted on marine robots. In addition to position, the instant of emission is unknown. A team of robots carrying a total of four hydrophones is therefore (theoretically) required to estimate the position without ambiguity. The precision of the estimate and the uncertainty critically depend on the position of the hydrophones. In order to obtain the best possible estimation, we explore the possibility of using a cooperative method that leads the robots to points where the overall observability is improved.

Abstract
In this paper we investigate the creation of an heterogeneous underwater network with static and mobile assets cooperating together in coordinated missions using acoustic links. Each underwater device combines communication, networking, and sensing capabilities, and cooperates with the other devices to accomplish a given task. The flexibility and capability of the proposed system allows to overcome the limitations of commercial solutions currently available in the market which typically focus on point to point communications. SUNSET framework has been used to provide acoustic communication and networking capabilities to AUVs, ASVs and moored systems developed by the Oceans Systems Group, at the University of Porto, in Portugal. New solutions have been developed and tested allowing to combine together acoustic data transmission and ranging estimation, to control the underwater nodes acoustically and to instruct the vehicles on keeping a given formation using acoustic links. To validate the proposed approach several experiments with increasing complexity have been conducted at the laboratory and in the field. The experimental results confirm the validity, efficiency and reliability of the proposed solution opening to several possibilities for future developments.