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Abstract(s)
Na presente dissertação discute-se a interação entre partĂculas e gases na atmosfera com a
radiação electromagnĂ©tica, a luz. Enquanto a luz segue o seu caminho para a superfĂcie da Terra ela
interage com as partĂculas e os gases que compĂ”em a atmosfera. Ao interagir com a atmosfera perde-
-se energia luminosa. Este fenómeno é chamado de extinção da luz o que resulta da combinação de
dois fenómenos, absorção de luz e da difusão de luz. A extinção da luz é importante, devido ao facto
de esta ser a causa da degradação da imagem, o que por sua vez tem um efeito negativo sobre a
visibilidade.
O tema mais importante abordado neste trabalho é a correlação entre os coeficientes de
extinção medidos e o seu efeito sobre a visibilidade. O objetivo principal é de compreender e analisar
as causas de extinção da luz, a quantidade de luz extinta e os seus efeitos na visibilidade, comparando
vĂĄrios estudos.
Para atingir os objetivos estabelecidos esta dissertação foi estruturada e organizada como se
segue; uma introdução ao tema da dissertação, um resumo da radiação eletromagnetica e da
atmosfera, onde todas as informaçÔes sobre a estrutura e organização do ambiente são fornecidas
juntamente com a propagação natural da luz e a sua interação com a atmosfera circundante. De
seguida termina o capĂtulo com a quantificação do coeficiente de extinção. O capĂtulo 2 descreve a
neurofisiologia do olho humano e a percepção visual. O capĂtulo 3 descreve a visibilidade e as possĂveis
fontes naturais e antropogĂ©nicas que contribuem para a sua degradação. Este capĂtulo termina com a
descrição de alguns exemplos de como a degradação da visibilidade pode afectar o dia a dia.
A atmosfera contém diferentes materiais originados a partir de fontes diferentes, cada uma
com a sua Ășnica constituição, densidade, tamanho e concentração. Cada uma delas tem um impacto
Ășnico na propagação da luz visĂvel, que tambĂ©m terĂĄ um impacto sobre a sua prĂłpria visibilidade.
Houve diversos estudos nesta ĂĄrea, pois a visibilidade Ă© um parĂąmetro de grande interesse.
Algumas observaçÔes e sugestÔes foram deixadas para um estudo futuro que podem ser
desenvolvidos para melhorar a técnica e os resultados.
The present dissertation discusses the interaction between atmospheric particles and gases with the electromagnetic radiation â light. While electromagnetic radiation follows a given route to the earthâs surface it interacts with the atmospheresâ constituting particles and gases causing the final luminous energy to differ from the starting luminous energy. This phenomenon is called light extinction, which results from two other phenomenaâs, light absorption and light scattering. Light extinction is important due to the fact that the extinguishing light from the route of propagation is the cause of image degradation, which in turn has a negative effect on visibility. The most prominent topic addressed in this dissertation is the correlation between the extinction coefficient measurements and its effect on visibility. The main aim is to understand and analyze the causes for light extinction, how much light is being extinguished and how it affects visibility, by comparing information from similar studies. In effort to accomplish the objectives established, the dissertation was structured and organized as follows; an introduction of the dissertations topic, a summary of Light and the atmosphere, where all information about the structure and organization of the atmosphere is provided along with the natural propagation of light and light interaction with its surrounding atmosphere. It ends on the quantification of the extinction coefficient. Chapter 2 approaches the description of visual perception and neurophysiology of the human eye, one of which (perception) can be influenced by weather conditions. Chapter 3 describes visibility and possible natural and anthropogenic sources for its impairment. Also, it describes a few examples of how visibility impairment affects our day to day lives. The atmosphere contains different materials from different sources each with its unique constitution, density, size and concentration. Each of these has a unique impact on the propagation of visible light, that will also have a its own impact on visibility itself. There have been multiple studies in this area, because visibility is a parameter of great interest Some comments and suggestions were left for a future study that may be developed to improve the technique and the results.
The present dissertation discusses the interaction between atmospheric particles and gases with the electromagnetic radiation â light. While electromagnetic radiation follows a given route to the earthâs surface it interacts with the atmospheresâ constituting particles and gases causing the final luminous energy to differ from the starting luminous energy. This phenomenon is called light extinction, which results from two other phenomenaâs, light absorption and light scattering. Light extinction is important due to the fact that the extinguishing light from the route of propagation is the cause of image degradation, which in turn has a negative effect on visibility. The most prominent topic addressed in this dissertation is the correlation between the extinction coefficient measurements and its effect on visibility. The main aim is to understand and analyze the causes for light extinction, how much light is being extinguished and how it affects visibility, by comparing information from similar studies. In effort to accomplish the objectives established, the dissertation was structured and organized as follows; an introduction of the dissertations topic, a summary of Light and the atmosphere, where all information about the structure and organization of the atmosphere is provided along with the natural propagation of light and light interaction with its surrounding atmosphere. It ends on the quantification of the extinction coefficient. Chapter 2 approaches the description of visual perception and neurophysiology of the human eye, one of which (perception) can be influenced by weather conditions. Chapter 3 describes visibility and possible natural and anthropogenic sources for its impairment. Also, it describes a few examples of how visibility impairment affects our day to day lives. The atmosphere contains different materials from different sources each with its unique constitution, density, size and concentration. Each of these has a unique impact on the propagation of visible light, that will also have a its own impact on visibility itself. There have been multiple studies in this area, because visibility is a parameter of great interest Some comments and suggestions were left for a future study that may be developed to improve the technique and the results.
Description
Keywords
Visibilidade - Atmosfera terrestre Extinção da luz Absorção da luz Difusão da luz Coeficiente de extinção (Luz) Acuidade visual
Citation
Publisher
Universidade da Beira Interior