THE COMPUTATION OF INFRARED TRANSMISSION BY ATMOSPHERIC WATER VAPOR

Abstract

A basic problem in atmospheric radiation is the computation of flux transmission (hemispheric radiation) for a narrow interval of the water-vapor spectrum. Individual lines are spaced more or less at random and have widely divergent intensities. Even inside a narrow spectral interval, the line half-width and the variation of line intensity with temperature vary appreciably from line to line. With the assumption of a completely random line spacing, the above problem can be formulated rather simply for the limiting cases of thick layers and thin layers, even for an arbitrary atmosphere and spectrum. With the additional assumption of a logarithmic ogive for line intensities, a flux-transmission function can be developed, dependent on only two parameters, which gives reasonable accuracy over the entire transmission range. This accuracy can be further improved by semi-empirical corrections to the two basic parameters. If the requisite spectral parameters are considered known precisely, the method proposed should yield values of the flux divergence, as required for calculations of radiative heating and cooling, with relative errors of the order of 2 to 3 per cent. Because these errors are largely random, the techniques can be applied with confidence in computations involving integrations over the entire spectrum.