CRAS

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http://localhost:4000/handle/123456789/39
This performs research and development activities in autonomous robotic systems, mobile robotics and multi-robot mobile systems for inspection, monitoring and mapping, with applications in security, energy, environment, aquaculture, oceanography, marine biology, resource extraction, among other sectors. These activities are supported by research in perception, navigation, control, localization, coordination, and automatic data acquisition and processing.

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    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.
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    Accurate detection of spread-spectrum modulated signals in reverberant underwater environments
    ( 2015) Aparicio,J ; Jimenez,A ; Alvarez,FJ ; Urena,J ; De Marziani,C ; de Diego,D ; Nuno Cruz ; Campos,H
    In those positioning systems based on the detection of acoustic signals, an accurate detection of the arrival times is crucial for a correct estimation of the distance between nodes, and therefore, for the precise estimation of the node that wants to be located. In order to obtain this arrival time more accurately, acoustic signals can be coded using pseudorandom noise, but these coded signals are still affected by underwater channel phenomena. In this work, the detection of spread-spectrum modulated signals is analyzed in underwater environments that are highly affected by multipath and reverberation. A spread-spectrum signal, which consist of a modulated Kasami code, has been emitted through two different pools, reaching a receiver where it has been captured after following several line-of-sight and non-line-of-sight paths. Then, a correlation process has been performed offline to provide information about the arrival times (times-of-flight) that form the multipath structure. These times-of-flight are compared with those provided by an underwater acoustic propagation model, in order to test the performance of this model and its capacity to predict the outcome of signal detection in underwater environments with a strong multipath and reverberation component. That way, the validated propagation model could be later used in future studies to predict the detection of spread-spectrum signals and the performance of systems that use them in these adverse environments.
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    Active Learning Strategies for Sustainable Engineering
    ( 2022) Duarte,AJ ; Benedita Malheiro ; Manuel Santos Silva ; Ferreira,PD ; Pedro Guedes ; 5855 ; 8029 ; 5655
    Engineering aims to improve the quality of daily life on a planet with limited resources. This chapter describes how the European Project Semester offered by the School of Engineering of the Porto Polytechnic contributes to make engineering undergraduates conscious of their environmental and societal impact. The program is a project-based active learning framework where problem-solving is supported by intercultural communication and creativity, ethical and sustainable reasoning, and global contextual analysis. This analysis shows that it fosters scientific, technical, and interpersonal competencies, emphasizing ethical and sustainable design as recommended by several reference institutions through the testimonials left on the project reports and the evolution perceived by the participants during the semester. These findings are supported by a sample of 45 projects conducted by 228 students from 23 countries and 65 degrees. All projects aimed to have a lasting impact on the future engineering practice of participants and, somehow, transform the world positively.
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    ALARS - Automated Launch And Recovery System for AUVs
    ( 2018) Nuno Cruz ; Carlos Filipe Gonçalves ; Almeida,RM ; Vitor Hugo Pinto ; 6852 ; 6920 ; 5155
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    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.
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    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.
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    Analysis of Phase Interrogated SPR Fiber Optic Sensors With Bimetallic Layers
    ( 2014) Hamed Moayyed ; Leite,IT ; Luís Carlos Coelho ; José Luís Santos ; Diana Viegas
    An effective analytical model combining geometrical optics with the transfer-matrix theory for stratified optical media is applied to investigate the sensing properties of tapered optical fiber surface plasmon resonance (SPR) sensors incorporating Ag-Au bimetallic layers, particularly in the context of phase interrogation. The performance of the sensing structures is studied as a function of the tapering parameters and thickness of the metallic layers. It is shown that the Ag-Au bimetallic combination is capable of improving the resolution and tuning working region of SPR fiber-optic sensors and that by tapering the sensing structures enhanced sensitivity can be achieved when phase interrogation is considered.
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    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.
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    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.
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    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.
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    APASail—An Agent-Based Platform for Autonomous Sailing Research and Competition
    ( 2018) Alves,B ; Bruno Miguel Veloso ; Benedita Malheiro
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    Aptamer-based fiber sensor for thrombin detection
    ( 2016) Luís Carlos Coelho ; José Almeida ; José Luís Santos ; Pedro Jorge ; Martins,MCL ; Diana Viegas ; Queiros,RB
    The detection of thrombin based on aptamer binding is studied using two different optical fiber-based configurations: long period gratings coated with a thin layer of titanium dioxide and surface plasmon resonance devices in optical fibers coated with a multilayer of gold and titanium dioxide. These structures are functionalized and the performance to detect thrombin in the range 10 to 100 nM is compared in transmission mode. The sensitivity to the surrounding refractive index (RI) of the plasmonic device is higher than 3100 nmRIU(-1) in the RI range 1.335 to 1.355, a factor of 20 greater than the sensitivity of the coated grating. The detection of 10 nM of thrombin was accomplished with a wavelength shift of 3.5 nm and a resolution of 0.54 nM. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
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    Assessment of Robotic Picking Operations Using a 6 Axis Force/Torque Sensor
    ( 2016) Moreira,E ; Luís Freitas Rocha ; Andry Maykol Pinto ; António Paulo Moreira ; Germano Veiga
    This letter presents a novel architecture for evaluating the success of picking operations that are executed by industrial robots. It is formed by a cascade of machine learning algorithms (kNN and SVM) and uses information obtained by a 6 axis force/torque sensor and, if available, information from the built-in sensors of the robotic gripper. Beyond measuring the success or failure of the entire operation, this architecture makes it possible to detect in real-time when an object is slipping during the picking. Therefore, force and torque signatures are collected during the picking movement of the robot, which is decomposed into five different stages that allows to characterize distinct levels of success over time. Several trials were performed using an industrial robot with two different grippers for picking a long and flexible object. The experiments demonstrate the reliability of the proposed approach under different picking scenarios since, it obtained a testing performance (in terms of accuracy) up to 99.5% of successful identification of the result of the picking operations, considering an universe of 400 attempts. © 2016 IEEE.
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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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    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.
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    Autonomous Underwater Vehicles
    ( 2011) Nuno Cruz
    Autonomous Underwater Vehicles (AUVs) are remarkable machines that revolutionized the process of gathering ocean data. Their major breakthroughs resulted from successful developments of complementary technologies to overcome the challenges associated with autonomous operation in harsh environments. Most of these advances aimed at reaching new application scenarios and decreasing the cost of ocean data collection, by reducing ship time and automating the process of data gathering with accurate geo location. With the present capabilities, some novel paradigms are already being employed to further exploit the on board intelligence, by making decisions on line based on real time interpretation of sensor data. This book collects a set of self contained chapters covering different aspects of AUV technology and applications in more detail than is commonly found in journal and conference papers. They are divided into three main sections, addressing innovative vehicle design, navigation and con
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    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.