Abstract
The concept of underwater docking stations has long been proposed to support the long term deployment of AUVs, but the number of successful solutions is still very disappointing. Hovering type AUVs can navigate arbitrarily slow, simplifying the docking maneuver and the requirements for the receiving structure. This paper describes a docking system that was developed to extend the mission duration of the MARES AUV, a man portable hovering type AUV. Given the wide range of operational scenarios and configurations of this AUV, one of the design requirements was to have a simple modular structure, that could easily be reconfigured to support different vehicle configurations, deployment scenarios and docking maneuvers. The paper provides details of the mechanical aspects, the onboard electronic subsystems, and the general operational procedure, as well as preliminary data from the first trials. © 2017 IEEE.

Abstract
There are several sources of error affecting the accuracy of underwater ranging using acoustic signals. These errors have a direct impact in the performance of Long Baseline (LBL) navigation system. This paper presents the results of experiments designed to characterize the most significant sources of errors in acoustic ranging. For the experiments, we use a set of acoustic devices and compare distances given by GPS differences with and acoustic ranges. We describe the experimental procedure and we process the results to provide a qualitative and quantitative analysis of the errors.

Abstract
The ability to employ autonomous vehicles to find and track the boundary between two different water masses can increase the efficiency in waterborne data collection, by concentrating measurements in the most relevant regions and capturing detailed spacial and temporal variations. In this paper we provide a guidance mechanism to enable an autonomous vehicle to find and track the steepest gradient of a scalar field in the horizontal plane. The main innovation in our approach is the mechanism to adapt the orientation of the crossings to the local curvature of the boundary, so that the vehicle can keep tracking the gradient regardless of its horizontal orientation. As an example, we show how the algorithms can be used to find and track the boundary of a dredged navigation channel, using only altimeter measurements. © 2014 IEEE.

Abstract
In this paper, we investigate the creation of an underwater acoustic network to support marine operations based on static and mobile nodes. Each underwater device combines communication, networking, and sensing capabilities and cooperates with the other devices in coordinated missions. The proposed system is built upon the SUNSET framework, providing acoustic communications and networking capabilities to autonomous underwater vehicles, autonomous surface vessels, and moored systems, using underwater acoustic modems. Specific solutions have been developed and tested to control the underwater nodes acoustically and to instruct the vehicles on keeping a given formation using acoustic links. One of the novelties of our approach has been the development and utilization of a realistic simulation infrastructure to provide a very accurate representation of all the dynamic systems involved in the network, modeling the vehicle dynamics, the acoustic channel, and the communication messages. This infrastructure has been extensively used to investigate and validate the proposed solutions under different environmental conditions before the actual deployment of devices. Several experiments were then conducted in the laboratory and in the field. The experimental results have confirmed the effectiveness of the proposed solutions and the reliability of the proposed simulation framework in estimating system performance.

Abstract
The design of an Autonomous Underwater Vehicle (AUV) is governed by a complex tradeoff between mission performance and required payload sensors, and taking into account possible constraints in fabrication, assembly and operational logistics. On a commercial level, the technology is relatively mature, with several companies offering off-the-shelf AUV solutions in a wide range of sizes and performance levels, for a wide variety of operational scenarios. However, to ensure proper performance in specific applications, such broad-range systems require factory customization, with the consequent impact in time and cost. This paper describes a program for the development of underwater vehicles based on modular building blocks. In this case, modularity encompasses both physical parts and also software and control systems. These modules can be rearranged, replaced or individually redesigned to yield a great variety of AUV configurations in a relatively short time. The paper describes the development of MARES, a small hovering AUV, and also TriMARES, a custom 3-body hybrid AUV/ROV, built from the same modules in little over 6 months.

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.

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