visual-range formula

From Glossary of Meteorology
The formula for the daytime visual range V,
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where there is a contrast C between the horizon target and its background viewed through an atmosphere of extinction coefficient σ by an observer whose momentary threshold contrast is ε.
In practice, an important application of this formula is to the case of a black target (for which C = 1); hence
ams2001glos-Ve17
In calculations of the meteorological range, the threshold contrast is also assigned a constant value.
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