Percorrer por autor "Salema, Carlos"
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- Comparative Study of Computational Electromagnetics Applied to Radiowave Propagation in WildfiresPublication . Faria, Stefânia; Vala, Mário; Coimbra, Pedro; Felício, João; Leonor, Nuno; Fernandes, Carlos; Salema, Carlos; Caldeirinha, RafaelIn this paper, a comparative study of four computational electromagnetic techniques to model the 2-dimensional radiowave propagation phenomena in wildfires, is proposed. The fire dynamics for a small tree specimen is studied, in which gases released from the combustion process are used to investigate the generation of an ionised plasma and, thus, to evaluate the gradient of the medium refractive index using the cold plasma model. Consequently, the presence of fire has been demonstrated to introduce additional losses in the radio path that may be critical to radio communication systems that are widely used in mission critical applications. The gradient of the refractive index across the vegetation volume yielded by the cold plasma model is used as input parameter to different numerical methods and electromagnetic solvers at 385 MHz (i.e. TETRA frequency band in Portugal) and, subsequently, their applicability to wildfires is assessed.
- Experimental Setup for Radio Characterization of Fire at Microwave FrequenciesPublication . Coimbra, Pedro; Faria, Stefânia; Vala, Mário; Felício, João; Fernandes, Carlos; Leonor, Nuno; Caldeirinha, Rafael; Salema, CarlosWildfires are a recurring phenomenon in many countries around the world, either due to natural causes or negligent human behavior. Emergency communication services used by firefighters at the theater of operations must be highly reliable, in order to ensure the safety and coordination of the teams that are fighting the wildfire, contributing to extinguishing it as quickly as possible with minimum use of resources. Emergency communication networks strongly rely on wireless links that may be impaired by the flames. In this work, we present an experimental setup for characterization of fire at microwave frequencies. Preliminary results show that we are able to extract very low dielectric constant (<1.1) using ultrawideband signals. Moreover, we characterize the attenuation introduced by fire in small-scale scenario. Future work will include the characterization of fire in larger-scale scenarios.
- A Framework for the Analysis of Wildfire Effects in Emergency Communication SystemsPublication . Leonor, Nuno; Fernandes, Carlos A.; Salema, Carlos; Caldeirinha, RafaelThis paper aims at the development of a simulation framework to enhance the quality, performance and the resilience of the emergency radio communication systems during a wildfire event. To this extent, this research work includes several studies that will contribute for the better understanding of the propagation effects on radio signals under fire environments, the development of a fire-front building up model, the development of a radio propagation tool to obtain coverage maps based on relevant models for propagation in rural areas, particularly in highly dense forest areas, taking into account the topography and clutter in the radio path and the integration of wildfire build up models into the radio propagation tool for an all encompassing radio coverage tool to aid ground forces in realtime with identification of radio exclusion zones in real-time as fire-front develops.
- Radiowave Propagation Modelling of Dual Wildfire Front Spreading over Hilly Terrain at 700 MHzPublication . Faria, Stefânia; Vala, Mário; Coimbra, Pedro; Leonor, Nuno; Felício, João; Fernandes, Carlos A.; Salema, Carlos; Caldeirinha, Rafael F. S.In this paper, a study of a fire front spreading over flat and sloped terrains and how these fire fronts may have impact on radiowave communications are presented. The phenomenon is modelled using Fire Dynamics Simulator (FDS) and the Cold Plasma Model (CPM), using pine needles as fuel heap. Fire parameters such as Heat Release Rate (HRR), Mass Loss Rate (MLR) and fuel consumption are presented and analysed. Attenuation effects at 700 MHz are calculated considering the Full-Stack Model (FSM) and Transmission Line Model (TLM). Simulation results clearly demonstrate that the slope of the terrain profile in the presence of a dual fire front spreading up the hill has significant impact on the additional excess loss of around 2.5 dB, yielding an overall excess loss of 3.5 dB for such a small-scale fire simulation.