Matthias Frey, Karlsruhe Institute of Technology
Mahesh Kumar Sha, BIRA-IASB, Belgium
Frank Hase, Laboratoire des Sciences du Climat et de L'Environnement, IMK-A-SF, Karlsruhe Institute of Technology
Matthaus Kiel, Karlsruhe Institute of Technology, California Institute of Technology
Thomas Blumenstock, Laboratoire des Sciences du Climat et de L'Environnement, Karlsruhe Institute of Technology
Roland Harig, Bruker Optik GmbH
Gregor Surawicz, Bruker Optik GmbH
Nicholas M. Deutscher, University of WollongongFollow
Kei Shiomi, Japan Aerospace Exploration Agency
Jonathan E. Franklin, Harvard University
Hartmut Bosch, University of Leicester
Jia-Jia Chen, Karlsruhe Institute of Technology
Michel Grutter, Universidad Nacional Autonoma de Mexico
Hirofumi Ohyama, Japan Aerospace Exploration Agency, National Institute for Environmental Studies
Youwen Sun, Chinese Academy Of Sciences
Andre Butz, IMK-A-SF, Karlsruhe Institute of Technology, Ludwig Maximilian University of MunichFollow
Gizaw Mengistu Tsidu, Botswana International University of Science and Technology
Dragos Ene, National Institute for Research and Development in Optoelectronics
Debra Wunch, California Institute of Technology, University of TorontoFollow
Zhensong Cao, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences
Omar E. Garcia, Izana Atmospheric Research Centre, Izaña Atmospheric Research Centre, Spain
M Ramonet, Laboratoire des Sciences du Climat et de L'Environnement
Felix Vogel, Environment Canada
Johannes Orphal, Karlsruhe Institute of Technology



Publication Details

Frey, M., Sha, M. K., Hase, F., Kiel, M., Blumenstock, T., Harig, R., Surawicz, G., Deutscher, N. M., Shiomi, K., Franklin, J. E., Bosch, H., Chen, J., Grutter, M., Ohyama, H., Sun, Y., Butz, A., Mengistu Tsidu, G., Ene, D., Wunch, D., Cao, Z., Garcia, O., Ramonet, M., Vogel, F. & Orphal, J. (2019). Building the COllaborative Carbon Column Observing Network (COCCON): Long-term stability and ensemble performance of the EM27/SUN Fourier transform spectrometer. Atmospheric Measurement Techniques, 12 (3), 1513-1530.


In a 3.5-year long study, the long-term performance of a mobile, solar absorption Bruker EM27/SUN spectrometer, used for greenhouse gas observations, is checked with respect to a co-located reference Bruker IFS 125HR spectrometer, which is part of the Total Carbon Column Observing Network (TCCON). We find that the EM27/SUN is stable on timescales of several years; the drift per year between the EM27/SUN and the official TCCON product is 0.02 ppmv for XCO 2 and 0.9 ppbv for XCH 4 , which is within the 1σ precision of the comparison, 0.6 ppmv for XCO 2 and 4.3 ppbv for XCH 4 . The bias between the two data sets is 3.9 ppmv for XCO 2 and 13.0 ppbv for XCH 4 . In order to avoid sensitivity-dependent artifacts, the EM27/SUN is also compared to a truncated IFS 125HR data set derived from full-resolution TCCON interferograms. The drift is 0.02 ppmv for XCO 2 and 0.2 ppbv for XCH 4 per year, with 1σ precisions of 0.4 ppmv for XCO 2 and 1.4 ppbv for XCH 4 , respectively. The bias between the two data sets is 0.6 ppmv for XCO 2 and 0.5 ppbv for XCH 4 . With the presented long-term stability, the EM27/SUN qualifies as an useful supplement to the existing TCCON network in remote areas. To achieve consistent performance, such an extension requires careful testing of any spectrometers involved by application of common quality assurance measures. One major aim of the COllaborative Carbon Column Observing Network (COCCON) infrastructure is to provide these services to all EM27/SUN operators. In the framework of COCCON development, the performance of an ensemble of 30 EM27/SUN spectrometers was tested and found to be very uniform, enhanced by the centralized inspection performed at the Karlsruhe Institute of Technology prior to deployment. Taking into account measured instrumental line shape parameters for each spectrometer, the resulting average bias across the ensemble with respect to the reference EM27/SUN used in the long-term study in XCO 2 is 0.20 ppmv, while it is 0.8 ppbv for XCH 4 . The average standard deviation of the ensemble is 0.13 ppmv for XCO 2 and 0.6 ppbv for XCH 4 . In addition to the robust metric based on absolute differences, we calculate the standard deviation among the empirical calibration factors. The resulting 2σ uncertainty is 0.6 ppmv for XCO 2 and 2.2 ppbv for XCH 4 . As indicated by the executed long-term study on one device presented here, the remaining empirical calibration factor deduced for each individual instrument can be assumed constant over time. Therefore the application of these empirical factors is expected to further improve the EM27/SUN network conformity beyond the scatter among the empirical calibration factors reported above.

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