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Atmospheric light scattering: Difference between revisions
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→The color of the horizon
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Thus, as the visibility increases from zero to infinity, the horizon first gets lighter until it reaches a brilliant white, then it darkens again. | Thus, as the visibility increases from zero to infinity, the horizon first gets lighter until it reaches a brilliant white, then it darkens again. | ||
=== Color shifts of the terrain === | |||
Rayleigh scattering on air molecules and small aerosol particles does not only cause the blue color of the sky - the same effect that occurs when looking through a column of air into space also occurs when looking through air onto terrain. Rayleigh scattering causes distant objects to appear at different colors. | |||
The actual color of an object seen in the distance is a competition between in- and out scattering. Along the ray of light connecting eye and the object, light coming from the object is scattered out, and as Rayleigh scattering preferentially affects the short wavelength, the remaining light is shifted towards red. However, at the same time, light hitting the air molecules from above is scattered into the direction of the eye, and for the same reason, this light is preferentially blue. As a result, distant terrain appears as if covered by a blue haze, but the colors underneath the haze are subtly shifted towards red. | |||
An example of increasingly stronger Rayleigh scattering on the terrain rendered in Flightgear is shown below: | |||
[[File:Rayleigh off.jpg|300px|No Rayleigh scattering]] | |||
[[File:Rayleigh half.jpg|300px|Medium Rayleigh scattering]] | |||
[[File:Rayleigh full.jpg|300px|Strong Rayleigh scattering]] | |||
=== Visibility and fog function === | === Visibility and fog function === | ||