Potential capabilities of CO2 measurement in the atmospheric column using a near infrared laser heterodyne radiometer (LHR)

Vertical concentration distributions of atmospheric trace gases, depending on vertical air transport from the Earth’s surface to the tropopause, play crucial roles in air pollution, ozone depletion and climate change. Accurate determination of the mixing ratios of the greenhouse gases (GHGs) in the lower troposphere, is thus important in the current international context of fighting against global warming and climate change. Laser heterodyne radiometry (LHR) technique, which extracts target molecular absorption information from the broadband sunlight by beating it with a local oscillator for heterodyne measurement, is a highly effective method for ground-based remoting measurement of GHGs’ concentration and vertical profile in the atmospheric column [1].

A transportable, all-fiber-coupled LHR instrument has been developed at the LPCA for ground-based remote sensing of carbon dioxide (CO₂​) [2] in the atmospheric column by using a wide band tunable external-cavity diode laser (1520 – 1620 nm) as local oscillator. The measured LHR spectra of CO₂ in the atmospheric column demonstrate strong agreement with spectra recorded by FTIR spectrometer of the TCCON at Paris and simulated from atmospheric transmission model.

The main objective of this study is to quantify the contribution of the LHR to the measurement of tropospheric abundances of CO₂ in the atmospheric column from the ground. We present the LHR’s capabilities to measure CO₂ vertical profiles through a complete information content analysis, a channel selection and an error budget estimation, using the radiative transfer model ARAHMIS (Atmospheric Radiation Algorithm for High-Spectral Resolution Measurements from Infrared Spectrometers), developed at the LOA [3]. A comparison with the other ground-based instruments like the EM27/SUN and the IFS125HR of the TCCON networks are also presented.

 Acknowledgments

This work is partially supported by the French national research agency (ANR) under the Labex CaPPA (ANR-10-LABX-005) contract, the EU H2020-ATMOS project (Marie Skłodowska-Curie grant agreement No 872081), the regional CPER ECRIN program, and the CNES ATMOSFER project.

 References

[1] D. Weidmann, "Atmospheric trace gas measurements using laser heterodyne spectroscopy", Ch. 4, pp. 159-223, in Advances in Spectroscopic Monitoring of the Atmosphere, eds. by Weidong Chen, Dean S. Venables, Markus W. Sigrist, ISBN: 978-0-12-815014-6, Elsevier (2021).

[2] J. Wang, T. Tu, F. Zhang, F. Shen,J. Xu, Z. Cao, X. Gao, S. Plus, and W. Chen, "An external-cavity diode laser-based near-infrared broadband laser heterodyne radiometer for remote sensing of atmospheric CO₂", Optics Express 31 (2023) 9251-9263.

[3] M.T. El Kattar, F. Auriol, H. Herbin, “Instrumental Characteristics and potential greenhouse gas measurement capabilities of the Compact High-Spectral-Resolution Infrared spectrometer: CHRIS”, Atmospheric Measurement Technique 13 (2020) 3769-3786.