An Infrared Band Ratio Technique for Temperature Determinations of Hot Gases

Abstract

A band ratio technique is developed for determining the temperature of optically thin hot gases from the infrared spectrum. The technique is based on the temperature variation of the integrated intensity of combination and overtone bands and not the Planck blackbody function. The technique can be applied to any fundamental, overtone, or combination band pair of a radiating molecule. In particular, the R-branch of the 2.7-μ fundamental band and the 1.87-μ and 1.34-μ combination bands of hot water vapor are investigated as a specific example of the technique. Characteristic band area ratios which can be used to determine the temperature from measured emissivity or radiance spectra are given for H2O. A comparison between temperatures determined from the band ratio technique and temperatures determined by independent experimental methods shows good agreement.