Aníbal Matos

Development and implementation of a low-cost LBL navigation system for an AUV

A reliable navigation system is a key factor for the success of an operational mission with an AUV in a real scenario. We address the main issues involved in the implementation of a long baseline (LBL) navigation system for a REMUS AUV. This system replaces both the original hardware and software of the vehicle with a simpler, faster, less expensive and more precise system, based on a Kalman filter. We also discuss the influence of transponder location in the overall performance of the LBL navigation, and present results obtained with this new system in operational missions.

The MARES AUV, a Modular Autonomous Robot for Environment Sampling

In this paper, we discuss the design aspects and the development of the MARES AUV, a 1.5 m long vehicle, weighting 32 kg, designed and built at the University of Porto, Portugal. This vehicle is highly maneuverable, with the ability to move in the vertical plane, controlling pitch and vertical velocity; forward velocity can also be determined, anywhere between 0 and 2 m/s. MARES can easily integrate any new payload within reason, finding applications in a wide range of areas, such as pollution monitoring, scientific data collection, sonar mapping, underwater video or mine countermeasures.

Localization of Mobile Robots Using an Extended Kalman Filter in a LEGO NXT

The inspiration for this paper comes from a successful experiment conducted with students in the “Mobile Robots” course in the fifth year of the integrated Masters program in the Department of Electrical and Computer Engineering, Faculty of Engineering, University of Porto (FEUP), Porto, Portugal. One of the topics in this Mobile Robots course is “ Localization of Mobile Robots using the Extended Kalman Filter in a LEGO NXT,” which gives the students the opportunity to study the concepts of localization. This experiment comes within the framework of teaching localization concepts in mobile robotics and focuses primarily on explaining the Kalman filter concept. It involves a specific tool developed by the authors and based on LEGO NXT technology. The work presented here could be a helpful guide for teaching concepts related to localization in mobile robotics to ensure adequate understanding of the concept and of the use of the extended Kalman filter (EKF). The LegoFeup robot described here was built using a LEGO Mindstorms NXT and tested both in simulation and in real scenarios. Based on the results obtained, the authors concluded that the developed tool is effective in motivating students. The implementation of the tool, the structure of the Mobile Robots course, and the criteria for student assessment are described in this paper.

A versatile acoustic beacon for navigation and remote tracking of multiple underwater vehicles

In this paper, we present a low-cost versatile device developed to support the navigation of autonomous underwater vehicles. Unlike the usual transponders extensively used for long baseline acoustic navigation of a single vehicle, this device allows the navigation of multiple vehicles and the remote tracking of their positions, without any extra acoustic signals being transmitted. The navigation beacon has a radio buoy connected to an underwater reconfigurable multifrequency transponder. A remote tracking station receives data from the buoy and monitors the position of the vehicles in real time. We describe the mechanical, electronic and software modules involved, as well as the tracking algorithm, and we also present experimental data from an operational mission.

Investigation of Underwater Acoustic Networking Enabling the Cooperative Operation of Multiple Heterogeneous Vehicles

In this paper, the authors 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.

Single beacon navigation: Localization and control of the MARES AUV

This paper addresses the simultaneous localization and control of an AUV using a single acoustic beacon. To determine its horizontal position, the AUV fuses distances to the single beacon with dead reckoning data, heading and longitudinal velocity. A particle filter and an extended Kalman filter are implemented and compared in terms of performances. As this is an ill-posed problem, special guidance laws are derived so that the overall horizontal positioning error remains bounded. Besides presenting the derivation of such guidance and control laws, as well as procedures to estimate the horizontal position, we also demonstrate the performance of the proposed system by means of simulation results.

Adaptive sampling of thermoclines with Autonomous Underwater Vehicles

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.

Modeling and Control of the MARES Autonomous Underwater Vehicle

This work addresses the modeling and control problems in the domain of underwater vehicles. The focus is on a prototype of an autonomous underwater vehicle. Although the work presented is applied to a particular vehicle with 4 controllable degrees of freedom, the method may be easily extended to several submerged bodies. In the engineering area, modeling of systems is done frequently, as it yields a mathematical translation of their behavior. Since models can become an important tool to solve problems related to its motion or even to the design of controllers, a model with 6 degrees of freedom for such a vehicle is obtained. Robust control of underwater vehicles is an area in which many efforts were applied over the last 2 decades. However, due to nonlinear dynamics, it may be hard to design robust controllers that yield the expected behavior, and there is no general procedure to develop them. Here, an approach is proposed that combines nonlinear controllers based on the deduced model and on the Lyapunov theory to control the velocities of the vehicle with linear controllers that control the vehicles position. Control laws are derived to perform several maneuvers, both in the vertical and horizontal planes, in a decoupled way, which is made possible through the configuration of thrusters. Finally, realistic simulations and experimental results that validate the proposed approach in the definition of the control laws are presented.

AUV navigation and guidance in a moving acoustic network

This paper addresses the navigation and guidance of an AUV operating in a network of moving acoustic beacons. In this network, the vehicle position is obtained from acoustic signals exchanged between the vehicle and the beacons and is computed in a reference frame associated with the moving beacons. The paper describes the operation of the acoustic network, the mission specification and guidance system that computes the references for the vehicle controllers, and the navigation system that produces all the data required by the guidance system.

Guidance and control of an ASV in AUV tracking operations

The following addresses the control of an autonomous surface vehicle (ASV) to follow the trajectory made by an autonomous underwater vehicle (AUV) when the last is performing any given pre-programmed mission. In fact, it has been proved to be of great interest to have an ASV that could follow on the surface and even catch up the trajectory performed by the AUV, when executing a given mission. In order to achieve this desired coordinated motion between AUV and ASV, it would make sense just to program each of the vehicles with the same mission. However, due to the nature of vehicles, missions and also due to the localization system used, with this kind of solution some problems would arise, namely related with timings and synchronization, which are indeed difficult to overcome. The solution proposed here tries to estimate the AUV position, by tapping the signals exchanged between the former and each of the beacons of the acoustic localization network, and control and actuate the ASV in accordance.