4,184 research outputs found

    Estimation of soil and vegetation temperatures with multiangular thermal infrared observations: IMGRASS, HEIFE, and SGP 1997 experiments

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    The potential of directional observations in the thermal infrared region for land surface studies is a largely uncharted area of research. The availability of the dual-view Along Track Scanning Radiometer (ATSR) observations led to explore new opportunities in this direction. In the context of studies on heat transfer at heterogeneous land surfaces, multiangular thermal infrared (TIR) observations offer the opportunity of overcoming fundamental difficulties in modeling sparse canopies. Three case studies were performed on the estimation of the component temperatures of foliage and soil. The first one included the use of multi-temporal field measurements at view angles of 0°, 23° and 52°. The second and third one were done with directional ATSR observations at view angles of 0° and 53° only. The first one was a contribution to the Inner-Mongolia Grassland Atmosphere Surface Study (IMGRASS) experiment in China, the second to the Hei He International Field Experiment (HEIFE) in China and the third one to the Southern Great Plains 1997 (SGP 1997) experiment in Oklahoma, United States. The IMGRASS experiment provided useful insights on the applicability of a simple linear mixture model to the analysis of observed radiance. The HEIFE case study was focused on the large oasis of Zhang-Ye and led to useful estimates of soil and vegetation temperatures. The SGP 1997 contributed a better understanding of the impact of spatial heterogeneity on the accuracy of retrieved foliage and soil temperatures. Limitations in the approach due to varying radiative and boundary layer forcing and to the difference in spatial resolution between the forward and the nadir view are evaluated through a combination of modeling studies and analysis of field data

    Radiation techniques for urban thermal simulation with the Finite Element Method

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    Modern societies are increasingly organized in cities. In the present times, more than half of the world’s population lives in urban settlements. In this context, architectural and building scale works have the need of extending their scope to the urban environment. One of the main challenges of these times is understanting all the thermal exchanges that happen in the city. The radiative part appears as the less developed one; its characterization and interaction with built structures has gained attention for building physics, architecture and environmental engineering. Providing a linkage between these areas, the emerging field of urban physics has become important for tackling studies of such nature. Urban thermal studies are intrinsically linked to multidisciplinary work approaches. Performing full-scale measurements is hard, and prototype models are difficult to develop. Therefore, computational simulations are essential in order to understand how the city behaves and to evaluate projected modifications. The methodological and algorithmic improvement of simulation is one of the mainlines of work for computational physics and many areas of computer science. The field of computer graphics has addressed the adaptation of rendering algorithms to daylighting using physically-based radiation models on architectural scenes. The Finite Element Method (FEM) has been widely used for thermal analysis. The maturity achieved by FEM software allows for treating very large models with a high geometrical detail and complexity. However, computing radiation exchanges in this context implies a hard computational challenge, and forces to push the limits of existing physical models. Computer graphics techniques can be adapted to FEM to estimate solar loads. In the thermal radiation range, the memory requirements for storing the interaction between the elements grows because all the urban surfaces become radiation sources. In this thesis, a FEM-based methodology for urban thermal analysis is presented. A set of radiation techniques (both for solar and thermal radiation) are developed and integrated into the FEM software Cast3m. Radiosity and ray tracing are used as the main algorithms for radiation computations. Several studies are performed for different city scenes. The FEM simulation results are com-pared with measured temperature results obtained by means of urban thermography. Post-processing techniques are used to obtain rendered thermograms, showing that the proposed methodology pro-duces accurate results for the cases analyzed. Moreover, its good computational performance allows for performing this kind of study using regular desktop PCs.Las sociedades modernas están cada vez más organizadas en ciudades. Más de la mitad de la población mundial vive en asentamientos urbanos en la actualidad. En este contexto, los trabajos a escala arquitectónica y de edificio deben extender su alcance al ambiente urbano. Uno de los mayores desafíos de estos tiempos consiste en entender todos los intercambios térmicos que suceden en la ciudad. La parte radiativa es la menos desarrollada; su caracterización y su interacción con edificaciones ha ganado la atención de la física de edificios, la arquitectura y la ingeniería ambiental. Como herramienta de conexión entre estas áreas, la física urbana es un área que resulta importante para atacar estudios de tal naturaleza. Los estudios térmicos urbanos están intrinsecamente asociados a trabajos multidisciplinarios. Llevar a cabo mediciones a escala real resulta difícil, y el desarrollo de prototipos de menor escala es complejo. Por lo tanto, la simulación computacional es esencial para entender el comportamiento de la ciudad y para evaluar modificaciones proyectadas. La mejora metodológica y algorítmica de las simulaciones es una de las mayores líneas de trabajo para la física computacional y muchas áreas de las ciencias de la computación. El área de la computación gráfica ha abordado la adaptación de algoritmos de rendering para cómputo de iluminación natural, utilizando modelos de radiación basados en la física y aplicándolos sobre escenas arquitectónicas. El Método de Elementos Finitos (MEF) ha sido ampliamente utilizado para análisis térmico. La madurez alcanzada por soluciones de software MEF permite tratar grandes modelos con un alto nivel de detalle y complejidad geométrica. Sin embargo, el cómputo del intercambio radiativo en este contexto implica un desafío computacional, y obliga a empujar los límites de las descripciones físicas conocidas. Algunas técnicas de computación gráfica pueden ser adaptadas a MEF para estimar las cargas solares. En el espectro de radiación térmica, los requisitos de memoria necesarios para almacenar la interacción entre los elementos crecen debido a que todas las superficies urbanas se transforman en fuentes emisoras de radiación. En esta tesis se presenta una metodología basada en MEF para el análisis térmico de escenas urbanas. Un conjunto de técnicas de radiación (para radiación solar y térmica) son desarrolladas e integradas en el software MEF Cast3m. Los algoritmos de radiosidad y ray tracing son utilizados para el cómputo radiativo. Se presentan varios estudios que utilizan diferentes modelos de ciudades. Los resultados obtenidos mediante MEF son comparados con temperaturas medidas por medio de termografías urbanas. Se utilizan técnicas de post-procesamiento para renderizar imágenes térmicas, que permiten concluir que la metodología propuesta produce resultados precisos para los casos analizados. Asimismo, su buen desempeño computacional posibilita realizar este tipo de estudios en computadoras personales

    Analysis of Climate Policy Targets under Uncertainty

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    Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/).Although policymaking in response to the climate change is essentially a challenge of risk management, most studies of the relation of emissions targets to desired climate outcomes are either deterministic or subject to a limited representation of the underlying uncertainties. Monte Carlo simulation, applied to the MIT Integrated Global System Model (an integrated economic and earth system model of intermediate complexity), is used to analyze the uncertain outcomes that flow from a set of century-scale emissions targets developed originally for a study by the U.S. Climate Change Science Program. Results are shown for atmospheric concentrations, radiative forcing, sea ice cover and temperature change, along with estimates of the odds of achieving particular target levels, and for the global costs of the associated mitigation policy. Comparison with other studies of climate targets are presented as evidence of the value, in understanding the climate challenge, of more complete analysis of uncertainties in human emissions and climate system response.This study received support from the MIT Joint Program on the Science and Policy of Global Change, which is funded by a consortium of government, industry and foundation sponsors

    Probabilistic Forecast for 21st Century Climate Based on Uncertainties in Emissions (without Policy) and Climate Parameters

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    Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/).The MIT Integrated Global System Model is used to make probabilistic projections of climate change from 1861 to 2100. Since the model's first projections were published in 2003 substantial improvements have been made to the model and improved estimates of the probability distributions of uncertain input parameters have become available. The new projections are considerably warmer than the 2003 projections, e.g., the median surface warming in 2091 to 2100 is 5.1°C compared to 2.4°C in the earlier study. Many changes contribute to the stronger warming; among the more important ones are taking into account the cooling in the second half of the 20th century due to volcanic eruptions for input parameter estimation and a more sophisticated method for projecting GDP growth which eliminated many low emission scenarios. However, if recently published data, suggesting stronger 20th century ocean warming, are used to determine the input climate parameters, the median projected warning at the end of the 21st century is only 4.1°C. Nevertheless all our simulations have a very small probability of warming less than 2.4°C, the lower bound of the IPCC AR4 projected likely range for the A1FI scenario, which has forcing very similar to our median projection. The probability distribution for the surface warming produced by our analysis is more symmetric than the distribution assumed by the IPCC due to a different feedback between the climate and the carbon cycle, resulting from a different treatment of the carbon-nitrogen interaction in the terrestrial ecosystem.his work was supported in part by the Office of Science (BER), U.S. Department of Energy Grant No. DE-FG02-93ER61677, NSF, and by the MIT Joint Program on the Science and Policy of Global Change

    Modelação multiescala de qualidade do ar urbana para cidades mais saudáveis

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    Ambient air pollution is nowadays a serious public health problem worldwide, especially in urban areas due to high population density and intense anthropogenic activity. Among the main urban air pollution sources, the road traffic sector is one of the major concerns and the largest contributor to nitrogen dioxide (NO2) concentrations, though regional background chemical conditions must also be considered. In this context, the use of modelling tools is crucial to understand atmospheric and social dynamics in multiple scales, as well as to support in defining the best air quality improvement strategies. The main objective of this thesis is to develop and apply a multiscale modelling system able to simulate air quality and health impacts in cities. For this purpose, the modair4health multiscale air quality and health risk modelling system was developed and operationalized. It includes the online model WRF-Chem, which provides air quality and meteorological fields from regional to urban scales, and the Computational Fluid Dynamics (CFD) model VADIS, which uses the urban WRF-Chem outputs to calculate flows and dispersion of traffic emissions-related air pollutants in urban built-up areas. A health module, based on linear and non-linear World Health Organization approaches, was also integrated in modair4health to assess the health impacts resulting from air quality changes, and the overall health damage costs are calculated based on economic studies. The application and assessment of the modair4health system allowed to identify the most appropriate configurations and input data, which were used to apply the system over the case study testing air quality improvement scenarios. One of the busiest road traffic areas of the city of Coimbra (Fernão de Magalhães Avenue) in Portugal was selected as case study. The application considered a 4 domains setup: three nested domains (25, 5 and 1 km2 resolutions) for the WRF-Chem, and the 4th domain (4 m2 resolution) over the target local study area and NO2 for the VADIS. WRF-Chem was applied along the year 2015 and VADIS was simulating two particular periods: one week in winter and another one in summer. Short-term health impacts were estimated and the non-linear approach led to lower health outcomes that seem better adjusted to the local reality. Finally, to assess the modair4health capabilities for decision-making support, two traffic management scenarios were tested over the case study: replacement of 50% of the vehicle fleet below EURO 4 by electric vehicles (ELEC), and introduction of a Low Emission Zone (LEZ). Air quality and health positive impacts were higher for the ELEC scenario. This study represents a scientific advance in multiscale air quality and health modelling. The modair4health system can be easily adapted and applied to other simulation domains, providing urban air pollution levels and subsequent health impacts for different case studies and supporting the assessment of air pollution control policies.A poluição atmosférica é atualmente um sério problema mundial de saúde pública, especialmente em áreas urbanas, devido à elevada densidade populacional e intensa atividade antropogénica. O setor dos transportes rodoviários é uma das principais preocupações e o que mais contribui para concentrações de dióxido de azoto (NO2) na atmosfera, embora as condições químicas de fundo regional devam também ser consideradas. Neste contexto, a utilização de ferramentas de modelação é crucial para compreender a dinâmica atmosférica e humana a diferentes escalas, e apoiar na definição das melhores estratégias para melhoria da qualidade do ar (EMQA). Esta tese tem como objetivo principal o desenvolvimento e aplicação de um sistema de modelação multiescala que permita simular qualidade do ar e impactos na saúde em cidades. Para isso, foi desenvolvido e operacionalizado o sistema modair4health - multiscale air quality and health risk modelling. Este sistema inclui o modelo online WRF-Chem, que fornece campos meteorológicos e de qualidade do ar da escala regional à urbana, e o modelo CFD VADIS, que utiliza os resultados do WRF-Chem para calcular o impacto das emissões do tráfego rodoviário no escoamento e dispersão de poluentes em áreas urbanas. Para avaliar os impactos na saúde humana, foi também integrado um módulo baseado nas abordagens linear e não-linear da Organização Mundial de Saúde (OMS), e os custos são calculados com base em estudos económicos. A aplicação e avaliação do sistema modair4health permitiram identificar as configurações e dados de entrada mais apropriados, que foram posteriormente utilizados para testar EMQA sobre o caso de estudo, que corresponde a uma das áreas de maior tráfego rodoviário da cidade de Coimbra (Avenida Fernão de Magalhães). O WRF-Chem foi configurado com 3 domínios aninhados (resoluções de 25, 5 e 1 km2), simulados para o ano 2015; enquanto que para o VADIS, foi definido um quarto domínio (resolução de 4 m2) sobre o caso de estudo para simular concentrações de NO2 em dois períodos específicos: uma semana no inverno e outra no verão. Para quantificar os impactos na saúde, as duas abordagens da OMS foram aplicadas ao caso de estudo para avaliar efeitos a curto-prazo. A abordagem não-linear apresentou resultados de saúde mais baixos que aparentemente estão melhor ajustados à realidade local. Por fim, foram avaliadas as potencialidades do sistema no apoio à tomada de decisão, testando dois cenários de gestão do tráfego rodoviário: substituição de 50% da frota de veículos abaixo de EURO 4 por veículos elétricos (ELEC), e introdução de uma Zona de Emissões Reduzidas (LEZ). O cenário ELEC potencia melhorias mais significativas na qualidade do ar e saúde. Este estudo representa um avanço científico na modelação multiescala da qualidade do ar e saúde. O sistema modair4health pode ser facilmente adaptado e aplicado a outros casos de estudo para avaliar a qualidade do ar urbana e impactos na saúde, bem como para testar medidas de controlo da poluição atmosférica.Programa Doutoral em Ciências e Engenharia do Ambient

    The role of the atmospheric aerosol in weather forecasts for the Iberian Peninsula: investigating the direct effects using the WRF-chem model

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    In the atmosphere, aerosols play an important role in climate change, the Earth’s environment and human health. The purpose of this study is to investigate the direct and semi-direct aerosol effects on weather forecasting, focusing on the Iberian Peninsula (IP). To that end, two Weather Research and Forecasting (WRF)-Chem simulations (with and without aerosol feedback) for an entire year (2015) were performed. The model setup includes two nested domains run in two-way mode, allowing the downscaling for the IP domain at a 5 × 5 km2 high-horizontal resolution. The results were explored through agreement of pairs of time series and their spatial variability in order to analyse the importance of including the online-coupled aerosol radiative effect on the meteorological variables: shortwave (solar) radiation, air temperature and precipitation. Significant variations of agreement were found when capturing both temporal and spatial patterns of the analysed meteorological variables. While the spatial distribution of temperature and precipitation is similar throughout the IP domain, with agreement values ranging from 0.87 up to 1.00, the solar radiation presents a distinct spatial pattern with lower agreement values (0.68–0.75) over ocean and higher agreement (0.75–0.98) over land regions. With regard to the spatial differences between simulations, the aerosol contributed to a considerable decrease in annual mean and maximum radiation (up to 20 and 40 Wm−2, respectively), slightly impacting the temperature variation (up to 0.5 °C). These results suggest that the aerosol feedback effects should be accounted when performing weather forecasts, and not only for purposes of air quality assessment.publishe

    A sensor view model to investigate the influence of tree crowns on effective urban thermal anisotropy

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    A sensor view model is modified to include trees using a gap probability approach to estimate foliage view factors and an energy budget model for leaf surface temperatures (SUMVEG). The model is found to compare well with airborne thermal infrared (TIR) surface temperature measurements. SUMVEG is used to investigate the influence of trees on thermal anisotropy for narrow field-of-view TIR remote sensors over treed residential urban surfaces. Tests on regularly-spaced arrays of cubes on March 28 and June 21 at latitudes of 47.6°N and 25.8°N show that trees both decrease and increase anisotropy as a function of tree crown and building plan fractions. In compact geometries, anisotropy tends to decrease with tree crown plan fraction, with the opposite in open geometries, though trees taller than building height cause anisotropy to increase for all building plan fractions. These results help better understand and potentially correct urban thermal anisotropy

    An acoustic view of ocean mixing

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    Knowledge of the parameter K (turbulent diffusivity/"mixing intensity") is a key to understand transport processes of matter and energy in the ocean. Especially the almost vertical component of K across the ocean stratification (diapycnal diffusivity) is vital for research on biogeochemical cycles or greenhouse gas budgets. Recent boost in precision of water velocity data that can be obtained from vessel-mounted acoustic instruments (vmADCP) allows identifying ocean regions of elevated diapycnal diffusivity during research cruises - in high horizontal resolution and without extra ship time needed. This contribution relates acoustic data from two cruises in the Tropical North East Atlantic Oxygen Minimum Zone to simultaneous field observations of diapycnal diffusivity: pointwise measurements by a microstructure profiler as well as one integrative value from a large scale Tracer Release Experiment
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