Horizontal visibility and the measurement of atmospheric optical depth of lidar

In this paper we describe a generalized treatment of the atmospheric visibility distances for a variety of atmospheric conditions. In the development of the formula for the visibility distance, it is shown how a series of assumptions made in the early work of Koschmieder [Beitr. Phys. Atmos. 12, 33 (1924)] can be reduced to a single assumption covering more atmospheric conditions. Special attention is paid to the cases in which the extinction coefficient is wavelength-dependent. It is shown that neglecting such a dependence may produce errors as large as 20-100%, especially when long visibility distances are considered. The use of a dye-laser radar for the remote sensing of visibility distances is described and discussed.