Mobile ground-based remote sensing of atmospheric CO2, CH4, and CO column densities above the Pacific Ocean
- 1University of Heidelberg, Institute of Environmental Physics, Atmospheric Remote Sensing, Germany
- 2Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Germany
- 3European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading, RG2 9AX, UK
- 4Max Planck Institute for Meteorology, Hamburg, Germany
Validation opportunities for model data and satellite observations in the short-wave infra-red spectral range are still sparse above the oceans. To provide such opportunities, we qualify a Fourier-transform spectrometer (FTS) for the regular use on ships. We use the EM27/SUN FTS [1] in direct-sunlight measurement geometry to retrieve total column densities of carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) [2] with solar absorption spectroscopy.
Performing direct-sunlight measurements from a moving platform poses significant challenges to the solar tracking. We use a solar tracker that compensates the vessel's movements in real time, keeping the pointing of the instrument relative to the center of the sun better than 0.05° for more than 99 % of the time [3]. The solar tracker is part of a newly developed enclosure that allows automated measurements and withstands environmental factors such as rain, humidity, and sea spray.
The instrument was deployed on board the German research vessel RV Sonne during the MORE-2 (Measuring Oceanic REferences 2) campaign on a longitudinal transect from Vancouver (Canada) to Singapore in June 2019. During the campaign we recorded 33800 direct sunlight spectra from which column-averaged dry-air mole fractions of CO2, CH4, and CO are retrieved. Our results are calibrated against World Meteorological Organization standards and the columns achieve a relative precision of 0.06 %, 0.06 %, and 1.02 % for CO2, CH4, and CO, respectively.
We compare our records to coincident observations of the Greenhouse gases Observing SATellite (GOSAT), the Orbiting Carbon Observatory-2 (OCO-2), and the TROPOspheric Monitoring Instrument (TROPOMI). Our CO2 records show a mean offset of -3.2 ± 1.1 ppm to OCO-2 and -1.4 ± 1.7 ppm to GOSAT observations. Furthermore, we find a mean CH4 offset of 17 ± 6 ppb to GOSAT and a mean CO offset of 3.5 ± 2.6 ppb to TROPOMI. The Copernicus Atmosphere Monitoring Service (CAMS) provided us with model data of CH4 and CO. We could show that the CO data agree well with our measurements, showing an offset of 3.5 ± 3.6 ppb.
[1] Gisi, M. et al.: XCO2-measurements with a tabletop FTS using solar absorption spectroscopy, Atmos. Meas. Tech., 5, 2969-2980, 2012
[2] Hase, F. et al.: Addition of a channel for XCO observations to a portable FTIR spectrometer for greenhouse gas measurements, Atmos. Meas. Tech., 9, 2303-2313, 2016
[3] Klappenbach, F. et al.: Accurate mobile remote sensing of XCO2 and XCH4 latitudinal transects from aboard a research vessel, Atmos. Meas. Tech., 8, 5023–5038, 2015
How to cite: Knapp, M., Kleinschek, R., Hemmer, B., Pfeifer, R., Hase, F., Agustí-Panareda, A., Inness, A., Barre, J., Kinne, S., and Butz, A.: Mobile ground-based remote sensing of atmospheric CO2, CH4, and CO column densities above the Pacific Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7345, https://doi.org/10.5194/egusphere-egu2020-7345, 2020
How to cite: Knapp, M., Kleinschek, R., Hemmer, B., Pfeifer, R., Hase, F., Agustí-Panareda, A., Inness, A., Barre, J., Kinne, S., and Butz, A.: Mobile ground-based remote sensing of atmospheric CO2, CH4, and CO column densities above the Pacific Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7345, https://doi.org/10.5194/egusphere-egu2020-7345, 2020
