Abstract A numerical iteration technique for determining both the temperature and CO 2 concentration profiles of axisymmetric combustion-gas flow from low resolution infrared spectral measurements has been developed. The technique includes inversion of the temperature profile from emission measurements when the CO 2 concentration distribution is known, inversion of the CO 2 concentration profile from transmittance measurements when the temperature distribution is known, and inversion of both temperature and CO 2 concentration profiles simultaneously from emission and transmittance data of the combustion-gas flow. The iteration technique is accurate, efficient, and effective even under structured temperature distributions. The effects of temperature, optical thickness, wave number, and band model parameters on the determined profiles are analyzed. It is found that a deviation of 40% in CO 2 concentration results in a difference of only about 5% in the determined temperature profile. This implies a possibility of passive scanning. The determined temperature profile of a laboratory combustion-gas flow agrees well with probe measurements.