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Atmospheric light scattering: Difference between revisions
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→Light scattering at dawn / dusk
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[[File:Sunrise side all.jpg|300px|Diffuse, Mie and Rayleigh scattering]] | [[File:Sunrise side all.jpg|300px|Diffuse, Mie and Rayleigh scattering]] | ||
[[File:Sunrise side mie.jpg|300px|Mie and Rayleigh scattering]] | [[File:Sunrise side mie.jpg|300px|Mie and Rayleigh scattering]] | ||
== Predawn light scattering == | |||
Before sunrise, there is no direct light from the sun available, all light which reaches the ground has scattered at least once in the upper atmosphere (which is already illuminated). In the context of the [http://en.wikipedia.org/wiki/Phong_reflection_model Phong reflection model], this means that the diffuse and specular lighting is absent. | |||
Since Rayleigh scattering dominates the upper atmosphere light scattering, predawn light is usually blue. However, this is not the whole story, as the perception of low intensity light is also biased towards blue (this is known as the [http://en.wikipedia.org/wiki/Purkinje_effect Purkinje effect] and the reason why moonlit scenes appear bluish in spite of the fact that moonlight is just reflected sunlight and has the same spectrum). The sudden change to the red direct light of the rising sun can create for a short time spectacular contrasts. | |||
However, in the presence of a high cloud or haze layer, direct light can be diffuse scattered towards the ground. In this case, the ground predawn light is actually brighter than for a clear sky, and it has a red color. The following screenshots illustrate this in Flightgear: | |||
[[File:Predawn-scatter1.jpg|400px|Usual predawn light]] | |||
[[File:Predawn-scatter2.jpg|400px|Predawn light with high haze layer]] | |||