ASSOCIATE LABORATORY
INSTITUT FOR SYSTEMS AND ROBOTICS
LISBON
Activities Plan
2004-2011
Strategic Planning and Long Term Perspectives
1. Introduction
When ISR-Lisbon was awarded the Associate Laboratory status, a contract was signed with FCT setting the obligations of both parties. FCT, apart from keeping the level of pluriannual financing (base+programatic) set by the last international evaluation to the research units constituting the Associate Laboratory, would reinforce the programmatic funds in a scheduled manner in order that the Associate Laboratory could contract 14 researchers (holding a Ph.D.) and 4 technicians (holding university degrees).
ISR-Lisbon had to pursue research and development activities according to the approved plan (Annex to this document).
As we emphasize in the activities reports concerning 2002 and 2003, FCT has not honored the contract and did not transfer the funds as agreed. The details about this situation can be found in the Introduction to the 2003 Activities Report.
This instability created by the lack of financing has jeopardized the regular research activities and the research environment.
Despite this abnormal situation, the direction and the thematic areas managers have encouraged young researchers to keep their enthusiasm and energy focused on the research activities.
However we feel that, unless the situation returns to normal very quickly, it will be no longer possible to stop our researchers, in particular the younger ones, from accepting the very attractive positions abroad that they are being offered.
In the following we define for each thematic area the activities we plan to develop in the years to come if the institutional situation returns to normal.
THEMATIC AREA A
Technologies for Ocean Exploration
The main goal of the Associate Laboratory / Thematic Area A is:
“To carry out research and development in marine science and technology for a better understanding of the oceans, and to use this knowledge for the sustainable benefit of society”.
This far-reaching goal sets the stage for the work program and main objectives of the Associated Laboratory. The proposed research and development effort capitalizes on prior joint work of ISR/IST, IMAR-DOP/UAzores, and Creminer / FCUL, and encompasses a wide spectrum of activities that touch upon theoretical and practical issues on marine science and technology. The activities planned adopt as a starting point a scenario of adequate financial stability and take into account the expected impact of new equipment acquisition brought about by the recent outcome of the re-equipment call evaluation. The program targets the Azores with its network of abyssal plains, seamounts, island margins, islands, and a large extension of the Mid-Atlantic Ridge, as a natural laboratory for the study of a number of challenging scientific issues in the fields of biological, chemical, geological, and physical oceanography.
This document sets the ISR-Lisbon (Associate Laboratory) strategic plan for Theme A, over a time window that ends in 2011 (10 year period in the original contract). The document defines practical goals and discusses important related theoretical issues in the following areas:
I. Dynamical Systems and Marine Robotics
II. Ocean Acoustics
III. Marine Science
In order to allow for a comparison with the original plan, the milestones for Years 5 and 10 are explicitly discussed and in some cases refined whenever appropriate. Other major achievements are also introduced for some of the areas, namely Marine Science.
I. Dynamical Systems and Marine Robotics
Two main lines action have been selected
i) Design, construction, and operation of autonomous robots for marine science applications. This includes the development of new prototype vehicles as well as the operation of existing vehicles including the CARAVELA, DELFIM, and DELFIMx autonomous surface craft, and the INFANTE autonomous underwater vehicle.
ii) Research in key enabling methodologies that are essential to the design and development of highly performing navigation, guidance, and control systems for autonomous robots.
The first topic has a direct bearing on the cooperation forged over the years with IMAR-DOP/UAzores and CREMINER in that it will contemplate the development of vehicles and the realization of scientific missions at sea. The second topic is at the core of autonomous systems design and development. It encompasses a large range of issues that range from dynamical system theory and navigation and control algorithms to software / hardware architectures for real-time systems implementation.
In terms of vehicle development, the following two milestones will be achieved by the year 2006:
i) Development of an ROV capable of diving to depths on the order of 1000 meters. The vehicle will be equipped with systems for image acquisition, as well as automatic systems for precise trajectory tracking, path following, and target hovering. Foreseen applications include time-series studies on the Menez Gwen hydrothermal site. This development effort was initiated in the scope of the DREAM project of the FCT, in cooperation with CREMINER and the Lab. Guia of the Faculty of Sciences of the University of Lisbon.
ii) Development of a modular, miniaturized AUV for commercial and scientific operations at sea (in collaboration with the National Institute of Oceanography, Dona Paula, Goa, India). This development effort was initiated in the scope of the MAYA project of the AdI, in cooperation with the IMAR/DOP-Azores and the company of naval engineers RINAVE.
iii) Development of a platform for automatic inspection of rubble-mound breakwater structures above and underwater, using an autonomous surface craft equipped with an echousounder and a laser beam. This development effort was initiated in the scope of the MEDIRES project of the AdI, in cooperation with the National Laboratory of Civil Engineering (Laboratório Nacional de Engenharia Civil – LNEC). Its main goal is to develop the means to automatically monitor the state of human-made structures in harbours and to aid in the decision making process relative to the timing of their maintenance, or even repair, works.
At a more theoretical level, work will focus on the topics listed below, in cooperation with partners from a number of institutions that include but are not restricted to the following:
· Naval Postgraduate School, Monterey, CA, USA
· University of São Paulo, Brasil,
· National Instititute of Oceanography, Goa, India,
· Dept. Engineering Cybernetics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
· School of Engineering, University of Plymouth, UK.
· Dept. of Aerospace, Power & Sensors, Royal Military College of Science,
Cranfield University, UK.
· Department of Electrical & Computer Engineering, University of California, Santa Barbara, CA, USA.
· Institute of Informatics and Applications, Escola Politècnica Superior - Campus de Montilivi, Girona .
· Department of Electrical Engineering, University of Genova, Genova, Italy
· Istituto Automazione Navale, Genova, Italy
· University of Lecce, Department of Innovation Engineering, Lecce, Italy
I.1 Linear and Nonlinear Systems Theory: Navigation, Guidance, and Control.
The main problem addressed in this topic is that of developing advanced algorithms for navigation, guidance, and control of air and marine robots. There are challenging theoretical issues that must be tackled and solved, of which the following are but representative examples.
I.1.1 Navigation and Positioning
Navigation refers to the problem of computing the linear position and the attitude of an autonomous platform - and respective linear and rotational rates - using a system installed on-board that platform. By positioning it is simply meant the problem of computing the position of an autonomous platform using a surface-born system. The two are often connected (for example, when the positioning system relays positioning information back to the underwater platform via a cable and an acoustic channel in the case of a remotely operated vehicle (ROV) and an autonomous underwater vehicle (AUV), respectively). However, for clarity of presentation, the two will be presented separately in the text below. In some instances, for example when one is interested in determining the position of a marine mammal underwater and follow its evolution, positioning is often referred to as tracking.
Navigation is probably the hardest and most complex task underwater. In fact, once a platform submerges, it ceases to have GPS fixes and accurate navigation can only be achieved by resorting to either a true inertial system or to the integration of moderate cost attitude and heading reference units with complementary systems that rely on the propagation of acoustic waves (long and short-baseline systems, Doppler units, etc.). The first option is prohibitive and clearly not an option if one is to develop underwater robots with a strong impact on a wide range of scientific and commercial operations. The second option requires fusing data from different sources, dealing with multipath effects and drop-outs, and addressing explicitly the problems that arise because data are available with variable latency (due to the finite speed of propagation in the water) and at different sampling frequencies (multirate characteristics).
At ISR/IST, navigation system design has been typically approached using the theory of multi-rate, polytopic, and linear parametrically varying systems. The main goal is to develop methodologies that can afford system designers with frequency-like design / analysis tools, thus extending to the time-varying and nonlinear settings the highly practical and intuitively appealing complementary filtering structures that are commonly used in aeronautics. The applications envisioned fall in the areas of marine and air robotics. Work will continue along these lines to obtain navigation algorithms with stability and performance guarantees. At the same time, and in order to bridge the gap between theory and practice, efforts will continue to design and build a high precision, miniaturized, inertial unit of low of moderate cost. This is certainly within reach because the performance of small, highly performing accelerometers and rate gyros increases steadily, while their price decreases. The development of such a unit is important for three main reasons: i) it will significantly reduced the price of marine platforms to be built in the future, ii) the unit can be used as an advanced testbed for testing increasingly sophisticated navigation algorithms, and lastly iii) there is great potential for the transfer of this kind of technology to the industry.
Underwater Positioning. Classical approaches to underwater vehicle positioning include the use of Long Baseline (LBL) and Short Baseline (SBL) systems, to name but a few. More recently, a number of methods have been proposed to somehow "reproduce" the idea of GPS in the underwater environment. For example, the so-called GIB system (GPS Intelligent Buoy system), which was purchased by ISR/IST. This system consists of four surface buoys equipped with DGPS receptors and submerged underwater hydrophones. Each of the buoys receives the acoustic impulses emitted periodically by a synchronized pinger installed on-board an underwater vehicle and records their times of arrival. The buoys communicate via radio with a central station (typically on-board a support vessel) where the position of the underwater vehicle is computed. Due to the fact that position estimates are only available at the central station, this system is naturally suited for tracking applications. Unfortunately, the algorithms for target tracking available with the commercial unit exhibit very poor performance. In view of this, and given the very good quality of the hardware purchased, considerable effort was placed on re-doing the positioning algorithms to obtain a system capable of yielding precise estimates of the position of an underwater vehicle given a set of ranges from the underwater vehicle to known buoy locations. Work will continue along these lines to obtain a reliable unit that can be used to track underwater vehicles and even marine mammals or fish carrying miniaturized pingers. Future work will also address the integration of the modified GIB system with the dead reckoning navigation system existent on-board the underwater vehicle. In this configuration, position estimates will be periodically transmitted to the underwater platform via an acoustic modem. There are also plans to build such a tracking unit from scratch, using hardware developed in-house. Again, this development should prove beneficial in reducing costs, providing a new testbed for algorithm performance assessment, and potentiating the transfer of technology to the industry.
From a theoretical point of view, the problem of target positioning can be tackled by resorting to triangulation techniques, which require that at least three range measurements be available at the end of each acoustic emission-reception cycle. This is hardly feasible in practice, due to unavoidable communication and sensor failures. It is therefore of interest to develop an estimator structure capable of dealing with the case where the number of range measurements available is time-varying. This can be done by tackling the problem in the framework of Extended Kalman Filtering (EKF), whereby the vehicle-to-buoy range measurements drive a filter (tracker) that relies on the kinematic model of the underwater vehicle. It is important to recall that due to the finite speed of propagation of sound in water, the range measurements are obtained at the buoys with different latencies. To overcome this problem, a methodology has been developed at ISR/IST that utilizes the measurements as they arrive, by incorporating a backwards and forward fusion approach. Simulation, as well as preliminary experimental results obtained show that the estimator proposed holds great promise for practical applications. Future work will address the development of non-EKF based estimation structures (for example, using the theory of Linear Parametrically Varying Systems) so as to obtain guaranteed stability and performance.
I.1.2 Landmark Based Navigation. In the two above problems, navigation and positioning are done by resorting to “inertial” systems. In this case the navigational accuracy achieved is directly related to the quality of the equipment used. Unfortunately, there simply is no remedy to this situation when the vehicles execute missions in open water, far away from the seabed and the sea surface, that is, with no clear landmarks “on sight”. The situation is completely different when the vehicle is asked to repeatedly survey an area where there are conspicuous landmarks (e.g. conspicuous terrain features, strong magnetic or gravimetric signatures, etc.). In this case, it is best to try and use this information to develop navigation system capable of correcting for the drift that is inherent to “inertial navigation” systems. This justifies the worldwide interest in the area of landmark based navigation, which has received considerable attention in the area of land robots.
Future work to be carried out under Theme A of the Associated Laboratory includes extending existing concepts and techniques for landmark-based navigation to underwater applications. So far, the work carried out has been focused on the use of particle filters for underwater navigation using a single beam echosounder to acquire bathymetric information of the area being surveyed. Encouraging simulation results obtained with a digital terrain map of the D. João de Castro seamount in the Azores show the potential of the filter to the development of terrain based navigation systems. Future work will address other means of doing local navigation by using more than one echosounder / multibeam sonar to explore spatial diversity, or even a magnetometer to acquire the magnetic signature of the terrain being covered. The applications envisioned are focused on the navigation of autonomous underwater vehicles to aid in marine habitat mapping of selected areas in the Azores.