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Atmospheric light scattering: Difference between revisions
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== Light scattering basics == | == Light scattering basics == | ||
The basic processes how light scatters in the atmosphere are [http://en.wikipedia.org/wiki/Rayleigh_scattering Rayleigh scattering] and [http://en.wikipedia.org/wiki/Mie_scattering Mie scattering]. | The basic processes how light scatters in the atmosphere are [http://en.wikipedia.org/wiki/Rayleigh_scattering Rayleigh scattering] and [http://en.wikipedia.org/wiki/Mie_scattering Mie scattering]. Rayleigh scattering occurs on scattering centers which are much smaller than the wavelength of light (typically the air molecules). In this limit, the outgoing light is scattered into every direction with equal likelihood (isotrope scattering), but the probability to scatter depends on the wavelength of the light - the shorter wavelengths (blue, violet) scatter more strongly. This is the cause for the color of a clear sky - there is much more diffuse Rayleigh scattering for blue light happening in the upper atmosphere than for red light, and as a result we see all the light that gets scattered out of the direct path from sun to eye as a diffuse blue glow - the sky. The same phenomenon causes the red color of sunrises - since the sun is close to the horizon, the path the light has to travel through the dense parts of the atmosphere is long and so by the time the light reaches the eye all blue light has been scattered out and only the red light remains. | ||
Mie scattering in contrast occurs for much larger particles (water droplets for instance). In this limit, the scattering is of equal strength for all wavelength (i.e. pure Mie-scattered light is white), but the scattering is strongly directional - the scattered light prefers to go close to its original direction. Mie scattering thus tends to create bright white halos around light sources. | |||
== Atmospheric haze == | == Atmospheric haze == | ||