EGU2020-7479, updated on 10 Jan 2024
https://doi.org/10.5194/egusphere-egu2020-7479
EGU General Assembly 2020
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Toward CO2 and CH4 measurements by ground-based observations of surface-scattered sunlight: Instrumentation and experiments

Benedikt Hemmer1, Philip Holzbeck1, Ralph Kleinschek1, Marvin Knapp1, Julian Kostinek2, Robin Müller1, Christin Proß1, Frank Hase3, and André Butz1
Benedikt Hemmer et al.
  • 1Institute of Environmental Physics, University of Heidelberg, Germany (benedikt.hemmer@iup.uni-heidelberg.de)
  • 2Institute of Atmospheric Physics, Deutsches Zentrum für Luft- und Raumfahrt e.V., Oberpfaffenhofen, Germany
  • 3Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Germany
Precise knowledge of sources and sinks in the carbon cycle is desired to understand its sensitivity to climate change, and to account and verify man-made emissions. An important role herein play extended sources like urban areas. While in-situ measurements of carbon dioxide (CO2) and methane (CH4) are highly accurate but localized, satellites measure column-integrated concentrations over an extended footprint. Our innovative measurement technique aims at determining CO2 and CH4 concentrations on the scale of a few kilometers near the ground, and therefore fills the sensitivity gap between in-situ and satellite measurements.
 
Our development starts out from the EM27/SUN Fourier transform spectrometer, which is a reliable, mobile and commercially available spectrometer for the measurement of CO2 and CH4 column densities using direct sunlight spectra. We increased the radiometric sensitivity of the instrument by enhancing optical throughput and replacing the detector module by a thermoelectrically cooled detector. This enables the measurement of surface scattered sunlight spectra in the range of 4000 - 11000 cm-1 under various viewing directions. Our setup is independent of sun position and exhibits a high sensitivity to the concentrations in the lower boundary layer, due to the near ground horizontal path component.
 
Here, we report progress on our instrumental developments, as well as first retrievals of column averaged CO2 and CH4 mole fractions from ground-scattered sunlight spectra recorded with this setup. We present the instrument modifications and extensions to the experimental setup: A Lambertian reflector allows for reference measurements without horizontal path component, a coaligned camera enables specific targeting and the motorized tracking system facilitates automated alternation between multiple targets. We characterize the setup with a spectral resolution of 0.54 ± 0.03 cm-1 a signal to noise ratio above 200 for solar zenith angles < 85°, and precision of 1.8 ppm and 9 ppb regarding the inferred column averaged CO2 and CH4 mole fractions obtained from retrievals with a simple radiative transfer model, neglecting atmospheric scattering.

How to cite: Hemmer, B., Holzbeck, P., Kleinschek, R., Knapp, M., Kostinek, J., Müller, R., Proß, C., Hase, F., and Butz, A.: Toward CO2 and CH4 measurements by ground-based observations of surface-scattered sunlight: Instrumentation and experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7479, https://doi.org/10.5194/egusphere-egu2020-7479, 2020.

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