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.

Abstract
Height mapping of shallow water areas is an important task for many commercial and scientific applications like river navigability, infrastructure maintenance or natural resource monitoring. The use of an autonomous boat presents several advantages that case the use of synthetic aperture images to create three-dimensional topographic maps through interferometric techniques. Sample data obtained during test trials illustrate how synthetic aperture can be used to generate imagery and bathymetry data.

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 an interferometric synthetic aperture sonar system based on an unmanned surface vehicle customized for shallow water environments. Synthetic aperture sonar enables imagery of high resolution that is independent of range by using the displacement of the sonar platform to create a large virtual array. If two geometrically displaced images are obtained, the construction of three-dimensional topographic maps is possible through the use of interferometric techniques. The use of an unmanned surface vehicle presents several advantages that alleviate some problems related to the formation of synthetic aperture images, which are mainly related to the fact that a precise navigation system can be used for the boat control and sonar imagery motion compensation. Also, a small unmanned surface vehicle is advantageous in terms of cost of operation, maintenance and ease of deployment. Mapping of shallow water areas is an important task for many commercial and scientific applications like river navigability, infrastructure maintenance and natural resource monitoring. These tasks can be done efficiently with this system. Sample data obtained during test trials illustrate how synthetic aperture can be used to generate underwater imagery and bathymetric data.

Abstract
Autonomous Underwater Vehicles (AUVs) are routinely being used to provide the scientific community with detailed ocean data at very reasonable costs. In typical operations, AUVs are programmed to follow pre-defined geo-referenced trajectories, while collecting the relevant information about the underwater environment, with a clear separation between navigation and payload sensors. Under the adaptive sampling paradigm, the AUVs are able to interpret some of the payload data in order to change the sampling pattern and concentrate measurements in the regions of interest. In this paper, we describe an implementation of such paradigm, in which a small sized AUV is able to process CTD data, in real time, and change depth in order to maintain tracking of the thermocline region. We demonstrate the developed algorithms with data from field experiments in a dam reservoir, which show a very good performance, even in very shallow waters with hardly detectable features. The implementation ensures the safety of the AUV, by resuming to standard yo-yo patterns if the thermocline is not detected.