If an object is viewed against a background sky under uniform illumination conditions and through a uniform haze, bN0/bNr — 1 and Eq. (19) becomes r Cn
Equation (20) forms the basis for using teleradiometer contrast measurements for approximating the extinction coefficient. If C0 and distance r are known, 6ext can be calculated.
The distance at which Cr approaches a threshold contrast of between —0.02 or -0.05 defines the visual range, Vr. If |C„| = 1 (black object) and -0.02 is taken to be a threshold contrast, then Eq. (20) becomes
Equation (21) allows visual range data to be interpreted in terms of extinction and vice versa, extinction measurements to be interpreted in terms of visual range. There is some debate as to what threshold contrast to use.
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