Temperature distributions in inhomogeneous hot gases were determined from line-of-sight infrared spectral measurements. Radiance and transmittance of combustion products of flat flames were measured at each of several CO2-band frequencies near 4.3 µ. Measurements of isothermal samples showed how the CO2 transmittance varied with temperature. Radiance measurements were made on samples with known nonisothermal temperature profiles. Radiance equations were so formulated that they could be solved for the temperature profile of the nonisothermal sample by an iterative procedure, using the transmittance and radiance data described above. Temperature profiles obtained by this procedure were in good agreement with the predetermined thermal structures of the specimens.
Burton Krakow, "Spectroscopic Temperature Profile Measurements in Inhomogeneous Hot Gases," Appl. Opt. 5, 201-209 (1966)