New retrieval method boosts accuracy of open-path infrared gas sensing

A research team from the Anhui Institute of Optics and Fine Mechanics, the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, developed a new method that enhances the precision and reliability of trace gas analysis in open-path infrared spectroscopic remote sensing.

Their recent study was published in Analytical Chemistry.

Active infrared optical remote sensing enables real-time, long-distance monitoring of multiple trace gases along open paths. However, interference from water vapor absorption, combined with fluctuations in temperature and humidity, aerosol scattering, and optical turbulence, often leads to non-stationary variations in background spectra. These effects significantly reduce the accuracy of quantitative analysis, posing a major challenge for applying this technology in high-precision measurements.

To address this issue, the team developed an integrated retrieval method that combines Variable Decomposition Level Dual-Tree Complex Wavelet Transform (VDL-DTCWT) with Nonlinear Least Squares (NLLS) fitting. VDL-DTCWT adaptively reconstructs background signals across spectral bands, robustly extracting multi-scale and non-stationary features. Meanwhile, the NLLS forward model incorporates common interfering gases such as water vapor as independent absorption components alongside target pollutants, enabling joint inversion and effectively eliminating cross-talk.

Experimental results show that this method significantly reduces background interference and improves both accuracy and precision of pollutant concentration retrieval under complex environmental conditions. 

The findings provide a new solution for quantitative infrared spectral analysis in open-path scenarios and offer important methodological insights for advancing high-precision optical remote sensing in dynamic environments.