Davide Fenucci

Typhoon at CommsNet13: Experimental experience on AUV navigation and localization

The CommsNet 2013 experiment took place in September 2013 in the La Spezia Gulf, North Tyrrhenian Sea. Organized and scientifically led by the NATO S&T Org. Ctr. for Maritime Research and Experimentation (CMRE, formerly NURC), with the participation of several research institutions, the experiment included among its objectives the evaluation of on-board acoustic Ultra-Short Base Line (USBL) systems for navigation and localization of Autonomous Underwater Vehicles (AUVs). The ISME groups of the Universities of Florence and Pisa jointly participated to the experiment with one Typhoon class vehicle. This is a 300 m depth rated AUV with acoustic communication capabilities originally developed by the two groups for archaeological search. The CommsNet 2013 Typhoon, equipped with an acoustic modem/USBL head, navigated within the fixed nodes acoustic network deployed by CMRE. This allows the comparison between inertial navigation, acoustic self-localization and ground truth represented by GPS signals (when the vehicle was at the surface). The preliminary results of the experiment show that the acoustic USBL self-localization is effective, and it has the potential to improve the overall vehicle navigation capabilities.

The project V-fides: A new generation AUV for deep underwater exploration, operation and monitoring

The proposed work is in the framework of the V-Fides project, aiming at developing a new generation of agile, over-actuated, long endurance Autonomous Underwater Vehicles, for deep underwater exploration, operation and monitoring. The project is co-funded by Tuscany Region (Italy) and is developed by a team lead by WASS S.p.A. (Whitehead Sistemi Subacquei, Livorno) with the participation of several partners including two research institutions of the University of Pisa and Small-Medium Enterprises in the Pisa-Livorno area. The vehicle is a general purpose, 3000m depth rated underwater vehicle with highly maneuverability capabilities, which can operate both as AUV and ROV. The vehicle is equipped with seven thrusters, with asymmetric input-output characteristic, and with a sensors payload for autonomous navigation, composed by: a tactical grade Inertial Measurement Unit (IMU), a Doppler Velocity Logger (DVL), a depth sensor, a magnetic compass and an acoustic modem for underwater communication and localization. This contribution gives an overview of the developed general architecture of the Navigation and Control module of the vehicle, from the algorithmic and system implementation stand-points.

Thesaurus: AUV teams for archaeological search. Field results on acoustic communication and localization with the Typhoon

The Thesaurus project, funded by the Tuscany Region, had among its goals the development of technologies and methodologies for archaeological search with Autonomous Underwater Vehicles working as a team in exploration missions. This has led to the design and realization of a new AUV class, the Typhoon, on the basis of the archaeological requirements, and of an appropriate acoustic simultaneous communication and localization scheme. The paper describes the project background, the technical characteristics of the Typhoon AUVs, and the field results in acoustic localization as obtained in the CommsNet13 cruise, led by the NATO CMRE (Centre for Maritime Research and Experimentation), to which the Thesaurus project teams of the University of Pisa and Florence took part. In particular, the fields result reports the performance of acoustic localization through on-board USBL communicating with fixed modems placed in initially unknown locations.

Fusing acoustic ranges and inertial measurements in AUV navigation: The Typhoon AUV at CommsNet13 sea trial

The paper presents some experimental results of autonomous underwater navigation, based on the fusion of acoustic and inertial measurements. The work is in the framework of the Thesaurus project, funded by the Tuscany Region, aiming at developing techniques for systematic exploration of marine areas of archaeological interest through a team of Autonomous Underwater Vehicles (AUVs). The test was carried out with one Typhoon vehicle, a 300m depth rated AUV with acoustic communication capabilities, during the CommsNet13 experiment, organized and scientifically coordinated by the NATO S&T Org. Ctr. for Maritime Research and Experimentation (CMRE, formerly NURC), with the participation of several research institutions. The fusion algorithm is formally casted into an optimal stochastic filtering problem, where the rough estimation of the vehicle position, velocity and attitude, are refined by using the depth measurement, the relative measurements available on the acoustic channel and the vehicle surge speed.

Toward underwater acoustic-based simultaneous localization and mapping. Experimental results with the Typhoon AUV at CommsNet13 sea trial

An algorithmic framework and experimental results on acoustic self-localization and mapping for an AUV equipped with an USBL modem are reported. The methodology proposed is quite general and applicable to a wide range of AUV and of navigation needs; however, the results presented refer to the Typhoon AUV and to the experimental configuration as available in the CommsNet13 cruise, led by the NATO S&T Ctr. for Maritime Research and Experimentation. The obtained results show that, even with a low cost, inertial motion units, and in presence of hostile acoustic channel conditions, the approach is able to keep the navigation error bounded and within 3-4 times GPS accuracy.

A passivity-based framework for coordinated distributed control of AUV teams: Guaranteeing stability in presence of range communication constraints

This paper presents a cooperative, distance-based, distributed control law for multiple Autonomous Underwater Vehicles (AUVs) executing a mission while meeting mutual communications constraints. The classic graph theory provides the essential tools to model the whole network of interacting robots, which is then handled within the energy-based, port-Hamiltonian framework. The virtual interaction forces generated over each link are represented by visco-elastic couplings. The passivity theory allows the construction of a Lyapunov function for the closed loop system to demonstrate the stability in large of the whole network with the synthesized control law. Moreover, always using passivity-based techniques, the behaviour of the group is made as flexible as possible with arbitrary split and join events. Several software simulations, involving a team or sub-teams of agents that perform typical missions in marine environment, show the effectiveness of the proposed approach.

Marine Robots in Environmental Surveys: Current Developments at ISME—Localisation and Navigation

Despite the growing interest that marine engineering has received during the past few decades, autonomous underwater navigation can be still considered a daunting task. Unfavourable environmental conditions and limitations on the typologies of available sensors increase the difficulties autonomous vehicles encounter during the execution of planned missions. As of today, one of the main challenges researchers face is the precise localisation of underwater vehicles, where the limitation of the error drift over time becomes extremely important for long navigation missions. In recent years, the authors, within ISME—Interuniversity Center of Integrated Systems for the Marine Environment, extensively worked on autonomous underwater navigation, with special focus on positioning techniques. Working in parallel, research was conducted on the topics of both the improvement of state-of-the-art navigation techniques and on the employment of local sensor networks to periodically reset position errors. This contribution reports the most significative results obtained by the authors during these years.

Towards an autonomous underwater vehicles test range: At-sea experimentation of bearing-only tracking algorithms

Abstract Underwater navigation performance of Autonomous Underwater Vehicles (AUVs) strongly affects the quality of the collected data. Scientific literature extensively addresses the AUV tracking and self-localisation problems. However, no standard evaluation methods for vehicle navigation exist. Therefore, the authors’ visionary perspective is to develop and implement an Underwater Test Range (UTR) to certify the vehicle compliance with long-term underwater navigation. This paper describes a first step along this research path represented by an in field validation of such conceived measurement network. Experiments are soundly based on extensive simulation analysis presented in previous works. In particular, an underwater network composed of acoustic modems with Ultra Short BaseLine capabilities is deployed as measurement rig. This setup, through bearing-only measurements, allows the tracking of an Autonomous Surface Vehicle (ASV) equipped with Differential GPS as position ground truth. Results show how the proposed methodology performs in a real marine scenario with challenging conditions due to shallow waters and magnetically noisy environment.

Magnetometers independent heading estimation strategy for UUV based on position and speed observations

For Unmanned Underwater Vehicles (UUV), the problem of position estimation is crucial for many different aspects ranging from good navigation performance to suitable geo-referencing capabilities of the payload data. The possibility of accurately estimating the UUV orientation has a positive impact on it, as the most of position estimation algorithms rely on the orientation signal. Among the orientation degrees of freedom, the heading angle has the highest importance in this process. Because its determination is strongly based on the use of magnetometers, it is also the one mostly affect by environmental unpredictable disturbances. In the recent past, the authors worked on a complementary filter capable of detecting and ignoring the magnetometers samples affected by disturbances. This way the navigation system of the vehicle can always exploit a reliable orientation information. In order to allow the UUV working under strongly disturbed conditions (e.g. inspections of modern wrecks), in this paper the bases for a heading estimation strategy that could completely avoid the use of magnetometers is proposed. The only involved devices are positioning sensors (Global Positioning System — GPS on the surface or Ultra-Short BaseLine USBL system underwater) velocity sensor (Doppler Velocity Log — DVL) and gyroscopes. The results of an observability analysis are provided highlighting that the heading degree of freedom results observable except for few trajectories along which a real vehicle reasonably never travels. Experimental results are provided as a first validation of the proposed approach. MARTA AUV was controlled to complete a mission on an area free of magnetic disturbances; the outcome of the proposed algorithm is compared with the one of the onboard orientation estimation algorithm that could exploit also the magnetometers signal. The slightly difference between the two estimations is a first encouraging result towards its on-line application.

Bearing-only AUV tracking performance: The effect of uncertainty in underwater nodes position

We analyze a specific practical problem of bearing-only localization of a stationary target using noisy measurements from three sensors. It is well understood that the performance of any target position estimator is considerably influenced by the sensor-target geometry. The performance achievable can be measured in terms of the Cramer-Rao lower bound (CRLB) on the algorithm covariance. However, the CRLB is calculated assuming exact knowledge of sensors location, which in practice is not true. In this paper, the effect of unavoidable uncertainty in network sensor positions is numerically evaluated in terms of Mean Square Error (MSE), offering detailed comparison with the ideal case of exact sensors location often assumed in the literature. The problem is cast into a probabilistic framework based on Monte Carlo simulations with a static target whose position is estimated through an Extended Kalman Filter (EKF). The positions of the sensors for each simulation are sampled from a Gaussian distribution with a mean equal to the nominal position while the standard deviation takes into account both the placement error during the deployment and the sensor position measurement uncertainty. The presented results confirm the need of our preliminary analysis for the following design of a test range for Autonomous Underwater Vehicles (AUVs).