Abstract
The measurement accuracy of trace gas detection based on infrared absorption spectroscopy is influenced by the overlap of absorption lines. A method for correcting the interference of overlapping absorption lines using second harmonic spectral reconstruction (2f-SR) is proposed to improve the measurement accuracy. 2f-SR includes three parts: measurement of gas temperature and use of the differences in temperature characteristics of absorption lines to correct the temperature error, 2f signal restoration based on laser characteristics to eliminate the influence of waveform change on overlapping absorption lines, and fast multi-peak fitting for the separation of interference from overlapping absorption lines. The CH4 measurement accuracy based on overlapping absorption lines is better than 0.8% using 2f-SR. 2f-SR has a lower minimum detection limit (MDL) and a higher detection accuracy than the separation of overlapping absorption lines based on the direct absorption method. The MDL is reduced by two to three orders of magnitude and reaches the part per million by volume level. 2f-SR has clear advantages for correcting the interference of overlapping absorption lines in terms of both MDL and measurement accuracy.
Highlights
Trace gas detection based on infrared absorption spectroscopy is widely applied in exploration geochemistry, medical diagnosis, and industrial analysis fields due to its advantages of high selectivity and high sensitivity [1,2,3,4,5]
Simulation results demonstrate that the measurement accuracy of overlapping absorption line measurement greatly affected laser parameters. accuracy
Is reported. 2f-SR includes three parts: gas temperature measurement using two well-isolated absorption lines to correct the interference of the gas temperature on overlapping absorption lines, 2f signal recovery based on laser characteristics to eliminate the effect of waveform change on overlapping absorption lines, and fast multi-peak fitting for the sep
Summary
Trace gas detection based on infrared absorption spectroscopy is widely applied in exploration geochemistry, medical diagnosis, and industrial analysis fields due to its advantages of high selectivity and high sensitivity [1,2,3,4,5]. Overlap may occur between adjacent absorption lines since the linewidths of absorption lines are widened by molecular collision, doppler shift, and the measurement instrument [6,7,8]. This overlap reduces the accuracy of the system and renders it more susceptible to environmental influences. It is difficult to avoid overlapping errors in some applications, and overlapping absorption lines are used to increase gas absorption and obtain lower minimum detection limits (MDL) [12,13,14,15]. To obtain more usable absorption lines and more accurate retrieved concentrations, a method to correct the interference of overlapping absorption lines is of great significance
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