Baseline extraction algorithm for mixed absorption spectrum of multiple gases under different pressure

Abstract

This study developed an algorithm for determining gas pressure and concentration in a mixed absorption feature using direct absorption spectroscopy. Blending spectra is observed when multiple absorption lines are approached when conducting a laser scan and/or when the pressure begins to increase. The proposed blended-feature baseline fitting method estimated the baseline by coupling measured data with simulated fractional transmission at the peaks between absorption features. In this study, the CH4 and CO absorption lines in the range 4299.70 to 4300.10 cm −1 were selected to demonstrate the method. Three experiments were conducted at different pressures of 0.5, 1, and 2 atm, and a mixture of CH4 and CO with different concentrations was measured at each pressure. Subsequently, the transmission spectra under the optimal parameters were compared with the simulated transmission spectra. Finally, the three results obtained via the proposed common baseline fitting method were compared with simulation results to verify the accuracy of the method. The method of data analysis based on direct absorption spectroscopy was confirmed to be applicable for spectra with a mixture of features, and was suitable for scanning ranges with multiple intensive spectral absorption lines and high pressures.