Enrico Simetti

RT 2 : A Real-Time Ray-Tracing method for acoustic distance evaluations among cooperating AUVs

The paper deals with the problem of distributed acoustic localization of teams of Autonomous Underwater Vehicles (AUVs) and proposes a novel algorithm, Real-Time Ray-Tracing (RT2), for evaluating the distance between any pair of AUVs in the team. The technique, based on a modified formulation of the non-linear sound-ray propagation laws, allows efficiently handling the distorted and reflected acoustic ray paths, induced by the anisotropy of the underwater medium. Further it can be easily implemented on-board of low-cost AUVs. Indeed it just requires the presence, on each vehicle, of a simple acoustic modem and a pair of look-up tables, a-priori constructed via the assumed knowledge of the depth-dependent sound velocity profile. On such a basis, every AUV can easily on-line compute its distance w.r.t. to any other neighbour team member, through time-of-flight measurements and the exchanges of depth information only. Further, since the proposed RT2 algorithm makes available accurate distance evaluations (despite the distorted acoustic rays), the effective filtering techniques normally used by terrestrial mobile robots for distributed localization are expected to be transferable to the underwater field.

A Task & Subsystem Priority Based Control Strategy for Underwater Floating Manipulators

Abstract The need for actual autonomy in underwater vehicle is rapidly increasing. Many challenging issues derive from such a trend, one in all the need of controlling the motion of an I-AUV to accomplish complex tasks. To this aim, this work presents a control coordination strategy based on Task Priorities and Dynamic Programming techniques for an I-AUV endowed with a redundant manipulator. The resulting algorithmic structure is able to manage prioritized tasks of both equality and inequality type, while also establishing motion priorities among the composing mechanical subsystems. Simulative results are presented with respect to the floating manipulator which is currently under development within the EU-FP7 funded TRIDENT project.

Archimede: Integrated Network-Centric Harbour Protection System

Confined/inshore waters may represent the best type of environment for the conduct of clandestine operations, especially from the sea: the features of such an environment weaken the detection and identification processes carried out by the defenders, while allowing the covert execution of illegal activities, as well as a better exploitation of surprise. The most significant illegal activities conducted in such an environment include infiltration, drugs/weapons smuggling, sabotage/disruption of infrastructures, up to terrorist acts; these activities are accomplished through the use of a variety of means of transportation, which include cigarette boats and power boats, rigid hull inflatable boats (RHIBs), Ashing vessels, sailing/leisure boats, midgets, swimmers/divers (with open/closed breathing systems), and swimmer delivery vehicles (SDV). Requirements as flexibility, rapid reaction, resilience, fast deployment, high level automation, modularity, plug & play have a key role in modern surveillance architecture definition. The paper will describe the guidelines adopted to develop a CIP (Critical Infrastructure Protection) tactical architecture in accordance with the previous requirements. The CIP system integrates different types of sensors (e.g. radar, IR, TV, SONAR, underwater acoustic network) and classes of vehicles (Surface, Underwater, Air Unmanned Vehicles) which cooperate in a multi environmental scenario (above water, under water, sea surface, ground and air). The focus is to develop the following functionalities: fuse, classify, identify and present all the data provided by the sensors and consequently generate warnings on the Command and Control (C2) and interact automatically with the console. The integration is performed to guarantee flexibility and modularity by means of tactical gateways developed in order to decouple the C2 system from sensor systems and vehicles. In particular, these gateways are designed to translate the subsystem proprietary data in a unique format. This allows integrating every kind and numbers of systems tailoring each time the specific gateway without modifying sensors, vehicles or C2. The system shows Network-Centric features and a wide set of growth above capabilities, even vehicles/sensors swarms, due to the gateway implementing a flexible middleware oriented to publisher/subscriber philosophy.

Real-Time Ray-Tracing for Underwater Distance Evaluation with Application to Distributed Localization of AUV Teams

Abstract The paper deals with distributed acoustic localization of teams of Autonomous Underwater Vehicles (AUVs) and proposes a novel algorithm, Real-TimeRay-Tracing (RT2), for evaluating the distance between any pair of AUVs in the team. The technique, based on a modified formulation of the non-***linear sound-ray propagation laws, allows efficient handling of the distorted and reflected acoustic ray paths. The proposed algorithm can be easily implemented on-board of low-cost AUVs, requiring the presence, on each vehicle, of an acoustic modem and a pair of look-up tables, a-priori built on the basis of the assumed knowledge of the depth-dependent sound velocity profile. On such a basis, every AUV can compute its distance w.r.t. to any other neighbour team member, through time-of-flight measurements and the exchanges of depth information only.

Robotized Underwater Interventions

Working in underwater environments poses many challenges for robotic systems. One of them is the low bandwidth and high latency of underwater acoustic communications, which limits the possibility of interaction with submerged robots. One solution is to have a tether cable to enable high speed and low latency communications, but that requires a support vessel and increases costs. For that reason, autonomous underwater robots are a very interesting solution. Several research projects have demonstrated autonomy capabilities of Underwater Vehicle Manipulator Systems (UVMS) in performing basic manipulation tasks, and, moving a step further, this chapter will present a unifying architecture for the control of an UVMS, comprehensive of all the control objectives that an UVMS should take into account, their different priorities and the typical mission phases that an UVMS has to tackle. The proposed strategy is supported both by a complete simulated execution of a test-case mission and experimental results.

A task-priority based control approach to distributed data-driven ocean sampling

The paper illustrates the basic ideas and relevant algorithmic developments underlying the proposal for a task-priority based control approach to distributed data-driven ocean sampling applications. This approach is deemed allowing a better formalization of the overall motion problem of the involved team of agents; that apart the ultimate mission objective, also result characterized by other different control objectives directly related with both operability and safety aspects of the entire sampling system. Also, the proposed approach, other than leading to a unifying algorithmic structure, also seems allowing to foresee good possibilities for different types of downgrading toward efficient decentralized implementations.

Distributed Task-priority Based Control in Area Coverage & Adaptive Sampling

The paper presents the first simulative results and algorithmic developments of the task-priority based control applied to a distributed sampling network in an area coverage or adaptive sampling mission scenario. The proposed approach allowing the fulfilment of a chain of tasks with decreasing priority each of which directly related to both operability and safety aspects of the entire mission. The task-priority control is presented both in the centralized and decentralized implementations showing a comparison of performance. Finally simulations of the area coverage mission scenario are provided showing the effectiveness of the proposed approach.