CRAS - Indexed Articles in Conferences

Permanent URI for this collection

http://localhost:4000/handle/123456789/350

Browse

Browsing CRAS - Indexed Articles in Conferences by Title

  • Item
    Accounting for uncertainty in search operations using AUVs
    ( 2017) Nuno Miguel Abreu ; Nuno Cruz ; Aníbal Matos
    Traditional coverage path planners create lawnmower-type paths in the operating area completely ignoring the uncertainty in the vehicle's position. However, in the presence of significant uncertainty in localization estimates, one can no longer guarantee that the vehicle will cover all the area according to plan. Aiming to bridge this gap, we present a coverage path planning technique for search operations which takes into account the vehicle's position and detection performance uncertainties and tries to minimize this uncertainty along the planned path. The objective is to plan paths, using a localization error model as input, to reduce as much uncertainty as possible and to minimize the extra path length (swath overlap) while satisfying mission feasibility constraints. We introduce an algorithm that calculates what will be the best moments for bringing the vehicle to surface to ensure a bounded position error. We also consider time and energy constraints that may influence the planned trajectory as path overlap is increased to account for uncertainty. Additionally we challenge the assumption frequently seen in coverage algorithms where two observations of the same target are considered independent. © 2017 IEEE.
  • Item
  • Item
    ALARS - Automated Launch And Recovery System for AUVs
    ( 2018) Nuno Cruz ; Carlos Filipe Gonçalves ; Almeida,RM ; Vitor Hugo Pinto ; 6852 ; 6920 ; 5155
  • Item
    Altitude control of an underwater vehicle based on computer vision
    ( 2019) Nuno Cruz ; Rodrigues,PM ; Pinto,AM ; 5155
    It is common the use of the sonar technology in order acquire and posteriorly control the distance of an underwater vehicle towards an obstacle. Although this solution simplifies the problem and is effective in most cases, it might carry some disadvantages in certain underwater vehicles or conditions. In this work it is presented a system capable of controlling the altitude of an underwater vehicle using computer vision. The sensor capable of computing the distance is composed of a CCD camera and 2 green pointer lasers. Regarding the control of the vehicle, the solution used was based on the switching of two controllers, a velocity controller (based on a PI controller), and a position controller (based on a PD controller). The vehicle chosen to test the developed system was a profiler, which main task is the vertical navigation. The mathematical model was obtained and used in order to validate the controllers designed using the Simulink toolbox from Matlab. It was used a Kalman filter in order to have a better estimation of the state variables (altitude, depth, and velocity). The tests relative to the sensor developed responsible for the acquisition of the altitude showed an average relative error equal to 1 % in the range from 0 to 2.5 m. The UWsim underwater simulation environment was used in order to validate the integration of the system and its performance. © 2018 IEEE.
  • Item
    Analysis and Visualisation of Crowd-sourced Tourism Data
    ( 2016) Leal,F ; Dias,JM ; Benedita Malheiro ; Burguillo,JC
    The tourist behaviour has changed significantly over the last decades due to technological advancement (e.g., ubiquitous access to the Web) and Web 2.0 approaches (e.g., Crowdsourcing). Tourism Crowdsourcing includes experience sharing in the form of ratings and reviews (evaluation-based), pages (wiki-based), likes, posts, images or videos (social-network-based). The main contribution of this paper is a tourist-centred off-line and on-line analysis, using hotel ratings and reviews, to discover and present relevant trends and patterns to tourists and businesses. On the one hand, online, we provide a list of the top ten hotels, according to the user query, ordered by the overall rating, price and the ratio between the positive and negative Word Clouds reviews. On the other hand, off-line, we apply Multiple Linear Regression to identify the most relevant ratings that influence the hotel overall rating, and generate hotel clusters based on these ratings. © 2016 ACM.
  • Item
    Analysis of Phase Interrogated SPR Fiber Optic Sensors with Different Bimetallic Combinations
    ( 2014) Hamed Moayyed ; Leite,IT ; Luís Carlos Coelho ; José Luís Santos ; Ariel Guerreiro ; Diana Viegas
    Optical fiber sensors based on the phenomenon of plasmonic resonance can be interrogated applying different methods, the most common one being the spectral approach where the measurand information is derived from the reading of the wavelength resonance dip. In principle, a far better performance can be achieved considering the reading of the phase of the light at a specific wavelength located within the spectral plasmonic resonance. This approach is investigated in this work for surface plasmon based fiber optic sensors with overlays which are combinations of bimetallic layers, permitting not only to tune the wavelength of the plasmon resonance but also the sensitivity associated with the phase interrogation of the sensors. The metals considered for the present analysis are silver, gold, copper, and aluminum.
  • Item
    Analysis of phase interrogation in SPR-based sensing supported by tapered optical fibres
    ( 2013) Hamed Moayyed ; Leite,IT ; Luís Carlos Coelho ; José Luís Santos ; Diana Viegas
    An analytical model based on geometrical optics and multilayer transfer matrix method is applied to the surface plasmonic resonance supported by fibre taper structures in the context of optical sensing applications. Phase interrogation is considered in particular as a methodology to attain enhanced sensitivities, and the performance of the sensing heads as function of the metal clad and taper parameters is analyzed. General topics concerning the actual relevance of plasmonics are also presented, first in a global perspective and then when applied to sensing.
  • Item
    Analysis of phase interrogation of SPR fiber optic sensors with characteristics tailored by the application of different metal-dielectric overlays
    ( 2014) Hamed Moayyed ; Leite,IT ; Luís Carlos Coelho ; José Luís Santos ; Ariel Guerreiro ; Diana Viegas
    Optical fiber sensors based on the phenomenon of plasmonic resonance can be interrogated applying different methods, the most common one being the spectral approach where the measurand information is derived from the reading of the wavelength resonance dip. In principle, a far better performance can be achieved considering the reading of the phase of the light at a specific wavelength located within the spectral plasmonic resonance. This approach is investigated in this work for fiber optic SPR sensors with overlays which are combinations of metallic and dielectric thin films, permitting not only to tune the wavelength of the SPR resonance but also the sensitivity associated with the phase interrogation of the sensors.
  • Item
    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.
  • Item
    Autonomous tracking of a horizontal boundary
    ( 2015) Nuno Cruz ; Aníbal Matos
    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. © 2014 IEEE.
  • Item
  • Item
    BLUECOM plus : Cost-effective Broadband Communications at Remote Ocean Areas
    ( 2016) Rui Lopes Campos ; Tiago Telmo Oliveira ; Nuno Cruz ; Aníbal Matos ; José Miguel Almeida
    The ocean and the Blue Economy are increasingly top priorities worldwide. The immense ocean territory in the planet and its huge associated economical potential is envisioned to increase the activity at the ocean in the forthcoming years. The support of these activities, and the convergence to the Internet of Things paradigm, will demand wireless and mobile communications to connect humans and systems at remote ocean areas. Currently, there is no communications solution enabling cost-effective broadband Internet access at remote ocean areas in alternative to expensive, narrowband satellite communications. This paper presents the maritime communications solution being developed in the BLUECOM+ project. The BLUECOM+ solution enables cost-effective broadband Internet access at remote ocean areas using standard wireless access technologies, e.g., GPRS/UMTS/LTE and Wi-Fi. Its novelty lies on the joint use of TV white spaces for long range radio communications, tethered balloons for lifting communications nodes high above the ocean surface, multi-hop relaying techniques for radio range extension, and standard access networks at the ocean. Simulation results prove it is possible to reach radio ranges beyond 100 km and bitrates in excess of 3 Mbit/s using a two-hop land-sea communications chain.
  • Item
    Case-based replaiming of search missions using AUVs
    ( 2017) Nuno Miguel Abreu ; Aníbal Matos
  • Item
    Characterization of Measurement Errors in a LBL Positioning System
    ( 2016) Rui Miguel Almeida ; José Luís Melo ; Nuno Cruz
    There are several sources of error affecting the accuracy of underwater ranging using acoustic signals. These errors have a direct impact in the performance of Long Baseline (LBL) navigation system. This paper presents the results of experiments designed to characterize the most significant sources of errors in acoustic ranging. For the experiments, we use a set of acoustic devices and compare distances given by GPS differences with and acoustic ranges. We describe the experimental procedure and we process the results to provide a qualitative and quantitative analysis of the errors.
  • Item
    CloudAnchor: Agent-Based Brokerage of Federated Cloud Resources
    ( 2016) Bruno Miguel Veloso ; Benedita Malheiro ; Carlos Burguillo,JC
    This paper presents CloudAnchor, a brokerage platform conceived to help Small and Medium Sized Enterprises (SME) embrace Infrastructure as a Service (IaaS) cloud computing both as providers and consumers. The platform, which transacts automatically single and federated IaaS cloud resources, is a multi-layered Multi-Agent System (MAS) where providers, consumers and virtual providers, representing provider coalitions, are modelled by dedicated agents. Federated resources are detained and negotiated by virtual providers on behalf of the corresponding coalition of providers. CloudAnchor negotiates and establishes Service Level Agreements (SLA) on behalf of SME businesses regarding the provision of brokerage services as well as the provision of single and federated IaaS resources. The discovery, invitation, acceptance and negotiation processes rely on a distributed trust model designed to select the best business partners for consumers and providers and improve runtime.
  • Item
    Collaborative Filtering with Semantic Neighbour Discovery
    ( 2016) Bruno Miguel Veloso ; Benedita Malheiro ; Burguillo,JC
    Nearest neighbour collaborative filtering (NNCF) algorithms are commonly used in multimedia recommender systems to suggest media items based on the ratings of users with similar preferences. However, the prediction accuracy of NNCF algorithms is affected by the reduced number of items - the subset of items co-rated by both users typically used to determine the similarity between pairs of users. In this paper, we propose a different approach, which substantially enhances the accuracy of the neighbour selection process - a user-based CF (UbCF) with semantic neighbour discovery (SND). Our neighbour discovery methodology, which assesses pairs of users by taking into account all the items rated at least by one of the users instead of just the set of co-rated items, semantically enriches this enlarged set of items using linked data and, finally, applies the Collinearity and Proximity Similarity metric (CPS), which combines the cosine similarity with Chebyschev distance dissimilarity metric. We tested the proposed SND against the Pearson Correlation neighbour discovery algorithm off-line, using the HetRec data set, and the results show a clear improvement in terms of accuracy and execution time for the predicted recommendations.
  • Item
    Collision avoidance for safe structure inspection with multirotor UAV
    ( 2017) Fábio André Azevedo ; Oliveira,A ; Dias,A ; Almeida,J ; Moreira,M ; Santos,T ; Ferreira,A ; Martins,A ; Eduardo Silva
  • Item
    Comparative Study of Visual Odometry and SLAM Techniques
    ( 2018) Alexandra Nunes ; Matos,A ; Andry Maykol Pinto ; Ana Gaspar ; 5446 ; 6869 ; 6868
    The use of the odometry and SLAM visual methods in autonomous vehicles has been growing. Optical sensors provide valuable information from the scenario that enhance the navigation of autonomous vehicles. Although several visual techniques are already available in the literature, their performance could be significantly affected by the scene captured by the optical sensor. In this context, this paper presents a comparative analysis of three monocular visual odometry methods and three stereo SLAM techniques. The advantages, particularities and performance of each technique are discussed, to provide information that is relevant for the development of new research and novel robotic applications. © Springer International Publishing AG 2018.
  • Item
    Control of the MARES Autonomous Underwater Vehicle
    ( 2009) Aníbal Matos ; Bruno Miguel Ferreira ; Miguel Armando Pinto
    This paper focuses the control problem of a nonholonomic autonomous underwater vehicle, moving in the tridimensional space. The dynamic of a body in submarine environments is strongly nonlinear. This implies that classical linear controllers are often inadequate whereby Lyapunov theory is here considered. Methods based in this theory are promising tools to design controllers and are applied to the case of MARES, a small-sized autonomous underwater vehicle. Several controllers based only on Lyapunov theory are determined while others combine linear and nonlinear control theory in order to perform various maneuvers. Aiming to verify the correct performance of controllers, simulations and experiments are carried out.
  • Item
    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.