NEPHELOMETER ESTIMATES OF VISUAL RANGE

A survey of basic contrast brightness theory and integrating nephelometer operational theory shows the inherent difficulty of trying to derive the true meteorological visual range Vm from nephelometer measurements of scattering visibility Vs. The effects of background horizon sky spectral radiance, atmospheric spectral scattering coefficient and nephelometer spectral response on Vs Vm for different atmospheric conditions and nephelometer models have been calculated. For a polluted atmosphere Vs and Vm are nearly equal while for a relatively clean atmosphere Vs Vm might be as low as 0.65. The conversion of Vs to Vm for the latter case is not straightforward since the conversion factor varies with the Angstrom coefficient α for any particular instrument. © 1979.