Title

Improved calibration procedures for the EM27/SUN spectrometers of the COllaborative Carbon Column Observing Network (COCCON)

Authors

Carlos Alberti, Karlsruher Institut für Technologie
Frank Hase, Karlsruher Institut für Technologie
Matthias Frey, National Institute for Environmental Studies of Japan
Darko Dubravica, Karlsruher Institut für Technologie
Thomas Blumenstock, Karlsruher Institut für Technologie
Angelika Dehn, ESRIN - ESA Centre for Earth Observation
Paolo Castracane, ESRIN - ESA Centre for Earth Observation
Gregor Surawicz, Bruker Optics Inc.
Roland Harig, Bruker Optics Inc.
Bianca C. Baier, University of Colorado Boulder
Caroline Bès, CNES Centre National d'Etudes Spatiales
Jianrong Bi, Lanzhou University
Hartmut Boesch, University of Leicester
André Butz, Universität Heidelberg
Zhaonan Cai, Institute of Atmospheric Physics Chinese Academy of Sciences
Jia Chen, Fakultät für Elektrotechnik und Informationstechnik, Technische Universität München
Sean M. Crowell, University of Oklahoma
Nicholas M. Deutscher, Faculty of Science, Medicine and Health
Dragos Ene, National Institute of RandD for Optoelectronics Inoe 2000
Jonathan E. Franklin, Harvard John A. Paulson School of Engineering and Applied Sciences
Omaira García, State Meteorological Agency of Spain (AEMet)
David Griffith, Faculty of Science, Medicine and Health
Bruno Grouiez, Université de Reims Champagne-Ardenne
Michel Grutter, Universidad Nacional Autónoma de México
Abdelhamid Hamdouni, Université de Reims Champagne-Ardenne
Sander Houweling, SRON Netherlands Institute for Space Research
Neil Humpage, University of Leicester
Nicole Jacobs, University of Alaska Fairbanks
Sujong Jeong, Seoul National University
Lilian Joly, Université de Reims Champagne-Ardenne

Publication Name

Atmospheric Measurement Techniques

Abstract

In this study, an extension on the previously reported status of the COllaborative Carbon Column Observing Network's (COCCON) calibration procedures incorporating refined methods is presented. COCCON is a global network of portable Bruker EM27/SUN FTIR spectrometers for deriving column-averaged atmospheric abundances of greenhouse gases. The original laboratory open-path lamp measurements for deriving the instrumental line shape (ILS) of the spectrometer from water vapour lines have been refined and extended to the secondary detector channel incorporated in the EM27/SUN spectrometer for detection of carbon monoxide (CO). The refinements encompass improved spectroscopic line lists for the relevant water lines and a revision of the laboratory pressure measurements used for the analysis of the spectra. The new results are found to be in good agreement with those reported by Frey et al. (2019) and discussed in detail. In addition, a new calibration cell for ILS measurements was designed, constructed and put into service. Spectrometers calibrated since January 2020 were tested using both methods for ILS characterization, open-path (OP) and cell measurements. We demonstrate that both methods can detect the small variations in ILS characteristics between different spectrometers, but the results of the cell method indicate a systematic bias of the OP method. Finally, a revision and extension of the COCCON network instrument-to-instrument calibration factors for XCO2, XCO and XCH4 is presented, incorporating 47 new spectrometers (of 83 in total by now). This calibration is based on the reference EM27/SUN spectrometer operated by the Karlsruhe Institute of Technology (KIT) and spectra collected by the collocated TCCON station Karlsruhe. Variations in the instrumental characteristics of the reference EM27/SUN from 2014 to 2017 were detected, probably arising from realignment and the dual-channel upgrade performed in early 2018. These variations are considered in the evaluation of the instrument-specific calibration factors in order to keep all tabulated calibration results consistent.

Open Access Status

This publication may be available as open access

Volume

15

Issue

8

First Page

2433

Last Page

2463

Funding Number

4000121212/17/I-EF

Funding Sponsor

European Space Agency

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Link to publisher version (DOI)

http://dx.doi.org/10.5194/amt-15-2433-2022