Calibration of column-averaged CH4 over European TCCON FTS sites with airborne in-situ measurements M. C. Geibel1,*, J. Messerschmidt2, C. Gerbig1, T. Blumenstock3, H. Chen1,**, F. Hase3, O. Kolle1, J. V. Lavrič1, J. Notholt2, M. Palm2, M. Rettinger4, M. Schmidt5, R. Sussmann4, T. Warneke2, and D. G. Feist1 1Max Planck Institute for Biogeochemistry (MPI-BGC), Jena, Germany 2Institute of Environmental Physics (IUP), University of Bremen, Bremen, Germany 3IMK-ASF, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany 4IMK-IFU, Karlsruhe Institute of Technology (KIT), Garmisch-Partenkirchen, Germany 5Laboratoire des Sciences du Climat et l'Environnement (LSCE), Gif-sur-Yvette, France *now at: Department for Applied Environmental Research (ITM), Stockholm University, Stockholm, Sweden **now at: NOAA Earth System Research Laboratory, Boulder, CO, USA
Abstract. In September/October 2009, six European ground-based Fourier Transform Spectrometers
(FTS) of the Total Carbon Column Observation Network (TCCON) were
calibrated for the first time using aircraft measurements. The
campaign was part of the Infrastructure for Measurement of the European
Carbon Cycle (IMECC) project.
During this campaign, altitude profiles of several trace gases and
meteorological parameters were taken close to the FTS sites (typically within
1–2 km distance for flight altitudes below 5000 m). Profiles
of CO2, CH4, CO and H2O were measured
continuously. N2O, H2, and SF6 were later derived
from flask measurements. The aircraft data had a vertical coverage ranging
from approximately 300 to 13 000 m, corresponding to ~80% of
the total atmospheric column seen by the FTS.
This study summarizes the calibration results for CH4. The resulting calibration factor of 0.978 ± 0.002
(±1 σ) from the IMECC campaign agreed very well with the results
that Wunch et al. (2010) had derived for TCCON instruments in North America,
Australia, New Zealand, and Japan using similar methods.
By combining our results with the data of Wunch et al. (2010),
the uncertainty of the calibration factor could be reduced by a factor of three
(compared to using only IMECC or only Wunch et al. (2010) data).
A careful analysis of the calibration method used by Wunch et al. (2010)
revealed that the incomplete vertical coverage of the aircraft profiles can
lead to a bias in the calibration factor. This bias can be compensated with a
new iterative approach that we developed. Using this improved method, we
derived a significantly lower calibration factor of 0.974 ± 0.002
(±1 σ). This corresponds to a correction of all TCCON CH4
measurements by roughly −7 ppb.
Citation: Geibel, M. C., Messerschmidt, J., Gerbig, C., Blumenstock, T., Chen, H., Hase, F., Kolle, O., Lavrič, J. V., Notholt, J., Palm, M., Rettinger, M., Schmidt, M., Sussmann, R., Warneke, T., and Feist, D. G.: Calibration of column-averaged CH4 over European TCCON FTS sites with airborne in-situ measurements, Atmos. Chem. Phys., 12, 8763-8775, doi:10.5194/acp-12-8763-2012, 2012.