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Koschmieder's law

law relating the apparent contrast, Cd, of an object against a sky background, at a given distance of observation, d, to the inherent contrast, C0, and to the atmospheric transmissivity, T, which is assumed to be uniform

       

where d0 is the length specified for the definition of T

NOTE 1 The formula is sometimes written

       

where the exponent, δ, in Tδ is the numerical value of d measured with d0 as "unit".

NOTE 2 Taking into account the relationship given in "meteorological optical range" between T and the meteorological optical range v, this law can be also written as

        .

NOTE 3 The contrast is taken to be the ratio of the difference between the luminance of the object and the luminance of the background, to the luminance of the background.

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