CO2 Profiling with Automated Scanning Raman Lidar

Carbon dioxide is the most important anthropogenic greenhouse gas. Therefore, measuring its distribution and variability in the atmosphere with high precision, accuracy, and resolution is key to a better understanding of the carbon cycle and radiative forcing. Especially, continuous profiling at the same location over longer periods of time provides insights about local sources and sinks. Since most of these are located on the ground, ground-based lidar systems with their ability of range-resolved measurements are particularly interesting because passive remote sensing satellites (e.g. OCO-2/3) cannot provide range-resolved data close to the surface. To realize carbon dioxide measurements, we integrated an additional channel into our eye-safe, fully automated ground-based Raman lidar ARTHUS (Atmospheric Raman Temperature and HUmidity Sounder) [1]. So far, more than 90 nights of CO₂ profiles have been collected at the Land-Atmosphere Feedback Observatory (LAFO) of the University of Hohenheim, Stuttgart, Germany [2]. Profiles of CO₂, temperature, and humidity, as well as particle extinction and particle backscatter coefficients, are measured simultaneously with five receiver channels. With averaging of 1 h and 400 m under nocturnal, cloud-free conditions, the uncertainties of the CO₂ mixing ratio measurements are only <2.8 ppm up to a distance of 2 km . When averaging over the full night, e.g., 13 hours and 400 m, the uncertainties are <1 and <2 ppm up to distances of ~2.5 and 4.0 km, respectively. Compared to measurements presented at last year’s EGU General Assembly [3], the lidar CO₂ signal intensity could be improved by a factor of up to 8.

Since 2025, a newly installed two-mirror scanner enables measurements in any direction. In December 2025, we performed measurements with an elevation angle of 2° close to the surface in order to investigate CO₂ sources and sinks. Furthermore, nearby in-situ CO₂ sensors on towers at 2 and 10 m height above ground at distances of 600 and 1000 m to the lidar now allow for improved calibration and comparisons. We will present and discuss these new low-level scans at the conference.

 

References:

[1] Lange, D. et al.: Compact Operational Tropospheric Water Vapor and Temperature Raman Lidar with Turbulence Resolution. Geophys. Res. Lett. (2019). DOI: 10.1029/2019GL085774

[2] Späth, F., et al.: The land–atmosphere feedback observatory: a new observational approach for characterizing land–atmosphere feedback. Geoscientific Instrumentation, Methods and Data Systems (2023). DOI: 10.5194/gi-12-25-2023

[3] Schumacher, M., D. Lange, A. Behrendt, V. Wulfmeyer: CO₂ Measurements with Raman Lidar in the Lower Troposphere. EGU25-8872 (2025) DOI: 10.5194/egusphere-egu25-8872