Atmospheric Scattering

Student: Diogo Lopes
Supervisor: António Ramires

Abstract

The colour of the sky has always fascinated people throughout the ages. The blue sky, the colour of the sun, the orange of the sunsets, the clouds, etc…

For centuries, physicists and mathematicians tried to explain with formulae what artists like Leonardo da Vinci reproduced in their paintings, like the colour of the sky, the bluish colour of distant mountains, fog, and several other nature effects.

In the area of computer graphics there is a great interest in recreating these natural effects, observable everyday, as real as possible. The reproduction of these effects is essential for certain applications such as flight simulators, video-games and other scientific applications, hence, the relevance of rendering these effects in real time.

This project aims to present a state of the art on atmospheric scattering and so consolidate knowledge on the subject.

Much work has been done with the purpose of recreating these effects digitally. In result many algorithms, implemented using different techniques, are now available.

When evaluating atmospheric scattering there are several aspects that are considered such as the light source, the density and size of particles in the atmosphere, among others.

In this thesis, only daylight models will be considered and in these models, the sun is considered the only light source. The particles on the atmosphere can be divided in 2 main entities: air molecules and aerosol particles.

The phenomenon can be explained as the result of the interaction between the rays that come from the sun and the particles in the atmosphere. The most relevant interaction, regarding colour, is scattering.

The atmospheric scattering models present methods and techniques to evaluate and recreate this phenomenon. These models are very diverse but they base their techniques with the physics behind the phenomenon.

Their evolution showed a path that went from quality to efficiency. Part of this evolutionary trait came with the evolution on both hardware and software.

The early AS models had a greater concern in recreating with the most possible accuracy the atmospheric scattering phenomenon. That concern passed, over the years, to recreate this phenomenon the fastest way possible.

When talking about rendering the colours of the sky, is natural to want to render the other natural effects such as clouds and light shafts. Therefore it is also valuable to present information of some algorithms that can recreate these effects.

Thesis download (PDF)