Andrea Munafò

Secure cooperation of autonomous mobile sensors using an underwater acoustic network.

Methodologies and algorithms are presented for the secure cooperation of a team of autonomous mobile underwater sensors, connected through an acoustic communication network, within surveillance and patrolling applications. In particular, the work proposes a cooperative algorithm in which the mobile underwater sensors (installed on Autonomous Underwater Vehicles—AUVs) respond to simple local rules based on the available information to perform the mission and maintain the communication link with the network (behavioral approach). The algorithm is intrinsically robust: with loss of communication among the vehicles the coverage performance (i.e., the mission goal) is degraded but not lost. The ensuing form of graceful degradation provides also a reactive measure against Denial of Service. The cooperative algorithm relies on the fact that the available information from the other sensors, though not necessarily complete, is trustworthy. To ensure trustworthiness, a security suite has been designed, specifically oriented to the underwater scenario, and in particular with the goal of reducing the communication overhead introduced by security in terms of number and size of messages. The paper gives implementation details on the integration between the security suite and the cooperative algorithm and provides statistics on the performance of the system as collected during the UAN project sea trial held in Trondheim, Norway, in May 2011.

Thesaurus project: design of new autonomous underwater vehicles for documentation and protection of underwater archaeological sites

The Thesaurus Project, funded by the Regione Toscana, combines humanistic and technological research aiming at developing a new generation of cooperating Autonomous Underwater Vehicles and at documenting ancient and modern Tuscany shipwrecks. Technological research will allow performing an archaeological exploration mission through the use of a swarm of autonomous, smart and self-organizing underwater vehicles. Using acoustic communications, these vehicles will be able to exchange each other data related to the state of the exploration and then to adapt their behavior to improve the survey. The archival research and archaeological survey aim at collecting all reports related to the underwater evidences and the events of sinking occurred in the sea of Tuscany. The collected data will be organized in a specific database suitably modeled.

Enhancing AUV localization using underwater acoustic sensor networks: Results in long baseline navigation from the COLLAB13 sea trial

This work proposes a novel approach to enhance Autonomous Underwater Vehicles (AUVs) navigation through the addition of localisation services to networked acoustic communication. The approach is based on the inclusion of timing information within acoustic messages through which it is possible to know the exact time of an acoustic transmission in relation to its reception. The exploitation of such information at the network level makes it possible to create an interrogation scheme similar to that of a long-baseline (LBL). The advantage is that the AUVs themselves become the transponders of the baseline, and hence there is no need for dedicated instrumentation. Results are given from the COLLAB13 experimental campaign, where a three node network was deployed off the coast of La Spezia, Italy.

Interval methods based AUV localization in the context of an acoustic network with experimental results

This article presents an application of interval methods for the dynamic localization of an autonomous underwater vehicles (AUV) using acoustic measurements of range and/or bearing to one or more underwater or surface nodes. A node can be either a vehicle or a buoy equipped with an acoustic modem and positioning aid. The position and speed vector of each node is communicated acoustically underwater to all of the other nodes. Popular methods used in solving localization problems use a probabilistic approach (e.g. Kalman filtering or Particle filtering). While such methods consider the probabilistic distribution of variables, the interval methods consider sets of possible values of a variable. The interval methods are deterministic in nature and have certain advantages over probabilistic methods such as native handling of non linear equations or solving problems of high dimension, guaranteed result under the right assumptions, and handling inconsistent data. The interval localization method is tested on a dataset acquired during an experiment on the Mediterranean sea.

AUV active perception: Exploiting the water column

Autonomous Underwater Vehicles (AUVs) present a low-cost alternative or supplement to existing underwater surveillance networks. The NATO STO Centre for Maritime Research and Experimentation is developing collaborative autonomous behaviours to improve the performance of multi-static networks of AUVs. In this work we lay the foundation to combine a range-dependent acoustic model with a three dimensional measurement model for a linear array within a Bayesian framework. The resulting algorithm is able to provide the vehicles with an estimation of the target depth together with the more usual information based on a planar assumption (i.e. target latitude and longitude). Results are shown through simulations and as obtained from the REP16 sea trial where for the first time a preliminary implementation of the method was deployed in the C-OEX vehicles.

Switching control of an underwater glider with independently controllable wings

Abstract This paper presents a control-oriented dynamic model of an underwater glider with independently controllable wings. We show that this particular feature is particularly useful to improve the vehicles maneuverability. The only actuators here used are a ballast tank and two hydrodynamic wings. A switching control strategy, together with a backstepping control scheme, is designed to limit the action of the ballast tank and hence to enforce energy-efficient maneuvers. We consider a case study in which the vehicle has the hydrodynamic wings behind its main hull. This structure is motivated by the recently-introduced concept of the underwater wave glider, that is a vehicle capable of both surface and underwater navigation. The control algorithm is validated via numerical simulations of the vehicle performing three-dimensional path-following maneuvers.

Experimental evaluation of Net-LBL: An acoustic network-based navigation system

This paper describes the use and in-field evaluation of a Networked-Long Base Line system (Net-LBL) where a network of underwater nodes cooperate to support the localisation and navigation of mobile vehicles. To avoid the use of dedicated transponders, as for traditional long baseline systems, each node of the network makes use of its underwater acoustic modem to transmit both data and positioning information. The use of the proposed Net-LBL systems has been validated and evaluated during two at-sea campaigns. More specifically, this paper investigates how the use of different communication schemes to reserve the shared underwater channel (i.e. Time Division Multiple Access (TDMA) and Carrier Sensing Multiple Access (CSMA)) impact on the acquisition of range measurements and on the localisation results. The collected results show that CSMA, being more flexible and responsive, can obtain a reduction of the impact on the localisation error by 30% on average and up to 90% with respect to TDMA.

MOOS middleware and node adaptivity in underwater sensor networks: results from the UAN11 sea trial

The EU funded FP7 UAN - Underwater Acoustic Network - project has among its goals the investigation of networked communication modalities in which mobile nodes are located in the environment to optimize the communication characteristics of the acoustic channel. The mobile nodes in UAN are placed on Autonomous Underwater Vehicles (AUVs) carrying acoustic modems and capable of autonomous decisions. The AUVs must be able to autonomously react to changes in the environment that affect the communication, and to appropriately relocate themselves to guarantee some quality of service performance in the communication task. The autonomous decisions must be taken in a distributed way, also in presence of lack of communication among the network nodes, and must in any case guarantee the fulfillment of a general mission task (surveillance). Each node of the network communicates, at application level, using the MOOS publish/subscribe middleware, which also embeds network security procedures (cryptography, authentication...