A procedure is described for determining the amount and distribution of water vapor along a slant path through the atmosphere above 13.7 km. A multilayer analysis is used in which the transmittance of each layer is calculated and the accumulative effect obtained at the altitude of observation. The method depends upon the contribution of each line to the absorptance in a finite spectral region.
Robert F. Calfee and David M. Gates, "Calculated Slant-Path Absorption and Distribution of Atmospheric Water Vapor," Appl. Opt. 5, 287-292 (1966)