CRAS - Indexed Articles in Conferences

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Browsing CRAS - Indexed Articles in Conferences by Author "5158"
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    Autonomous Tracking of a Horizontal Boundary
    ( 2014) Nuno Cruz ; Aníbal Matos ; 5155 ; 5158
    The ability to employ autonomous vehicles to find and track the boundary between two different water masses can increase the efficiency in waterborne data collection, by concentrating measurements in the most relevant regions and capturing detailed spacial and temporal variations. In this paper we provide a guidance mechanism to enable an autonomous vehicle to find and track the steepest gradient of a scalar field in the horizontal plane. The main innovation in our approach is the mechanism to adapt the orientation of the crossings to the local curvature of the boundary, so that the vehicle can keep tracking the gradient regardless of its horizontal orientation. As an example, we show how the algorithms can be used to find and track the boundary of a dredged navigation channel, using only altimeter measurements.
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    Cooperative deep water seafloor mapping with heterogeneous robotic platforms
    ( 2017) Pinto,A ; Dias,A ; Melo,J ; Alfredo Martins ; Abreu,N ; Almeida,J ; Almeida,R ; José Carlos Alves ; Carlos Filipe Gonçalves ; Ferreira,H ; Ferreira,B ; Nuno Cruz ; Silva,E ; Aníbal Matos ; Hugo Miguel Silva ; Eduardo Silva ; Vitor Hugo Pinto ; 5570 ; 258 ; 5155 ; 5158 ; 5429 ; 5473 ; 6852 ; 6920
    This paper describes the PISCES system, an integrated approach for fully autonomous mapping of large areas of the ocean in deep waters. A deep water AUV will use an acoustic navigation system to compute is position with bounded error. The range limitation will be overcome by a moving baseline scheme, with the acoustic sources installed in robotic surface vessels with previously combined trajectories. In order to save power, all systems will have synchronized clocks and implement the One Way Travel Time scheme. The mapping system will be a combination of an off-the-shelf MBES with a new long range bathymetry system, with a source on a moving surface vessel and the receivers on board the AUV. The system is being prepared to participate in round one of the XPRIZE challenge. © 2017 Marine Technology Society.
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    Critical object recognition in underwater environment
    ( 2019) Alexandra Nunes ; Ana Gaspar ; Aníbal Matos ; 5158 ; 6868 ; 6869
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    DART - A portable deep water hovering AUV
    ( 2017) Aníbal Matos ; Bruno Miguel Ferreira ; Almeida,RM ; Nuno Cruz ; 5158 ; 5238 ; 5155
    Autonomous Underwater Vehicles are remarkable machines that revolutionized the collection of data at sea. There are many examples of highly operational man-portable vehicles for shallow waters, but there was no similar solution for deep water operations. This paper describes the development of a portable, modular, hovering AUV for deep water operations. The vehicle has little over 50kg, 2.4m of length, and a depth rating of 4000m. The first version of the vehicle has been assembled, it has gone through the initial tests in water tanks, and it is being prepared for the first operations at sea. © 2017 Marine Technology Society.
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    Evaluation of Bags of Binary Words for Place Recognition in Challenging Scenarios
    ( 2021) Ana Gaspar ; Alexandra Nunes ; Aníbal Matos ; 5158 ; 6868 ; 6869
    To perform autonomous tasks, robots in real-world environments must be able to navigate in dynamic and unknown spaces. To do so, they must recognize previously seen places to compensate for accumulated positional deviations. This task requires effective identification of recovered landmarks to produce a consistent map, and the use of binary descriptors is increasing, especially because of their compact representation. The visual Bag-of-Words (BoW) algorithm is one of the most commonly used techniques to perform appearance-based loop closure detection quickly and robustly. Therefore, this paper presents a behavioral evaluation of a conventional BoW scheme based on Oriented FAST and Rotated BRIEF (ORB) features for image similarity detection in challenging scenarios. For each scenario, full-indexing vocabularies are created to model the operating environment and evaluate the performance for recognizing previously seen places similar to online approaches. Experiments were conducted on multiple public datasets containing scene changes, perceptual aliasing conditions, or dynamic elements. The Bag of Binary Words technique shows a good balance to deal with such severe conditions at a low computational cost. © 2021 IEEE.
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    An Hierarchical Architecture for Docking Autonomous Surface Vehicles
    ( 2019) Aníbal Matos ; Andry Maykol Pinto ; Pedro Nuno ; Renato Jorge Silva ; 7626 ; 5446 ; 5158 ; 7627
    Autonomous Surface Vehicles (ASVs) provide the ideal platform to further explore the many opportunities in the cargo shipping industry, by making it more profitable and safer. This paper presents an architecture for the autonomous docking operation, formed by two stages: a maneuver module and, a situational awareness system to detect a mooring facility where an ASV can safely dock. Information retrieved from a 3D LIDAR, IMU and GPS are combined to extract the geometric features of the floating platform and to estimate the relative positioning and orientation of the moor to the ASV. Then, the maneuver module plans a trajectory to a specific position and guarantees that the ASV will not collide with the mooring facility. The approach presented in this paper was validated in distinct environmental and weather conditions such as tidal waves and wind. The results demonstrate the ability of the proposed architecture for detecting the docking platform and safely conduct the navigation towards it, achieving errors up to 0.107 m in position and 6.58 degrees in orientation.
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    Occupancy Grid Mapping from 2D SONAR Data for Underwater Scenes
    ( 2021) Alexandra Nunes ; Ana Gaspar ; Aníbal Matos ; 5158 ; 6868 ; 6869
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    A PHD Filter for Tracking Multiple AUVs
    ( 2014) Aníbal Matos ; Melo,J ; 5158
    In this paper we address the problem of tracking multiple AUVs using acoustic signals. Using For this challenging scenario, we propose to use a Probability Hypothesis Density Filter and present a suitable implementation of the Sequential Monte Carlo PHD filter. It will be demonstrated that a particle filter implementation of the aforementioned filter can be used to successfully track multiple AUVs, changing in number over time, using range measurements from the vehicles to a set of acoustic beacons. Simulation results will be presented that allow to evaluate the performance of the filter.
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    REX 16-Robotic Exercises 2016 Multi-robot field trials
    ( 2019) Marques,F ; Bruno Miguel Ferreira ; Aníbal Matos ; Lobo,V ; Marques,MM ; Mendonca,R ; Ramalho,T ; Castelao,I ; Simoes,N ; 5238 ; 5158
    Nowadays, one of the problems associated with Unmanned Systems is the gap between research community and end-users. In order to emend this problem, the Portuguese Navy Research Center (CINAV) conducts the REX 2016 (Robotic Exercises). This paper describes the trials that were presented in this exercise, divided in two phases. The first phase happened at the Naval Base in Lisbon, with the support of divers and RHIBs (Rigid-Hulled Inflatable Boats), and the second phase, also with divers' support, at the coast of Lisbon-Cascais. It counted with many participants and research groups, including INESC-TEC, UNINOVA, TEKEVER and UAVISION. There are several advantages of doing this exercise, including for the Portuguese Navy, but also for partners. For the Navy, because it is an opportunity of being in contact with recent market technologies and researches. On the other hand, it is an opportunity for the partners to test their systems in a real environment, which usually is a difficult action to accomplish. Therefore, the paper describes three of the most relevant experiments: underwater docking stations, UAV and USV cooperation and Tracking targets from UAVs.