Method for demodulating the overlapping absorption spectra of CO and CH4

When measuring the concentrations of individual gases in gas mixtures via laser absorption spectroscopy, the widening of adjacent absorption spectral lines can cause them to overlap, which hinders the calculation of the gas concentrations. In this study, the causes of this hindrance are analyzed. By using the Partial Least Squares (PLS) algorithm, the relative error in the measured CO concentration for a mixture of CO and CH4 gases was less than 10% even when the volume ratio VCH4/CO (The ratio of CH4 gas concentration to CO gas concentration) reached 100. These results show that the PLS algorithm is able to determine accurate concentrations even with significant broadening and interference of spectral lines in mixed gases.