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Discussion papers
https://doi.org/10.5194/amt-2019-371
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-371
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 11 Nov 2019

Submitted as: research article | 11 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Intercomparison of low and high resolution infrared spectrometers for ground-based solar remote sensing measurements of total column concentrations of CO2, CH4 and CO

Mahesh Kumar Sha1, Martine De Mazière1, Justus Notholt2, Thomas Blumenstock3, Huilin Chen4, Angelika Dehn5, David W T Griffith6, Frank Hase3, Pauli Heikkinen7, Christian Hermans1, Alex Hoffmann8, Marko Huebner8, Nicholas Jones6, Rigel Kivi7, Bavo Langerock1, Christof Petri2, Francis Scolas1, Qiansi Tu3, and Damien Weidmann8 Mahesh Kumar Sha et al.
  • 1Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
  • 2Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 3Karlsruhe Institute of Technology, IMK-ASF, Karlsruhe, Germany
  • 4Centre for Isotope Research, University of Groningen, Groningen, The Netherlands
  • 5European Space Agency, ESA/ESRIN
  • 6University of Wollongong, Wollongong, Australia
  • 7Finnish Meteorological Institute, Sodankylä, Finland
  • 8Rutherford Appleton Laboratory, United Kingdom

Abstract. The Total Carbon Column Observing Network (TCCON) has been the baseline network of instruments that record solar absorption spectra from which accurate and precise column-averaged dry air mole fractions of CO2 (XCO2), CH4 (XCH4), CO (XCO) and other gases are retrieved. The TCCON data have been widely used for carbon cycle science and validation of satellites measuring greenhouse gas concentrations globally. The number of stations in the network (currently about 25) is limited and the stations are distributed mostly in Northern America, Europe, Japan and Oceania leaving gaps in the global coverage. A denser distribution of ground-based solar absorption measurements is needed to cover various atmospheric conditions (humid, dry, polluted, presence of aerosol), various surface conditions (high and low albedo) and a larger latitudinal distribution. More stations in the southern hemisphere are also needed but a further expansion of the network is limited by its costs and logistical requirements. For this reason several groups are investigating supplemental portable low-cost instruments. The European Space Agency (ESA) funded campaign Fiducial Reference Measurements for Ground-Based Infrared Greenhouse Gas Observations (FRM4GHG) at the Sodankylä TCCON site in northern Finland aims at characterising the assessment of several low-cost portable instruments for precise solar absorption measurements of XCO2, XCH4 and XCO. The test instruments under investigation are three Fourier transform spectrometers (FTS): a Bruker EM27/SUN, a Bruker IRcube and a Bruker Vertex70; as well as a Laser Heterodyne spectro-Radiometer (LHR) developed by the UK Rutherford Appleton Laboratory. All four remote sensing instruments performed measurements simultaneously next to the reference TCCON instrument, a Bruker IFS 125HR, for a full year in 2017. The TCCON FTS was operated in its normal high-resolution mode (TCCON data set) and in a special low-resolution mode (HR125LR data set), similar to the portable spectrometers. The remote sensing measurements have been complemented by regular AirCore launches performed from the same site. They provide in-situ vertical profiles of the target gas concentrations as auxiliary reference data for the column retrievals which is traceable to the WMO SI standards. The timeseries, the bias relative to the reference instrument and its scatter and the seasonal and the day-to-day variations of the target gases are shown and discussed. The comparisons with the HR125LR data set gave useful analysis of the resolution dependent effects on the target gas retrieval. The solar zenith angle dependence of the retrievals is shown and discussed. The reference measurements performed with the Bruker IFS 125HR (TCCON and HR125LR data sets) were found to be affected by non-linearity. A non-linearity correction of the TCCON data was performed and compared with the test instruments and AirCore. The non-linearity corrected TCCON data show a better match with the test instruments and AirCore data as compared to the reference TCCON data. The intercomparison results show that the LHR data have a large scatter and biases with a strong diurnal variation relative to the TCCON and other FTS instruments. The LHR is a new instrument under development and these biases are being currently investigated and addressed. The campaign helped to characterise and identify the instrumental biases and possibly retrieval biases which are currently under investigation. Further improvements of the instrument are ongoing. The EM27/SUN, the IRcube, the modified Vertex70 and the HR125LR provided stable and precise measurements of the target gases during the campaign with quantified small biases. The bias dependence on the humidity along the measurement line-of-sight has been investigated and no dependence was found. These three portable low-resolution FTS instruments are suitable to be used for campaign deployment or long-term measurements from any site and offer the ability to complement the TCCON and expand the global coverage of ground-based reference measurements of the target gases.

Mahesh Kumar Sha et al.
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Status: open (until 06 Jan 2020)
Status: open (until 06 Jan 2020)
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Data sets

FRM4GHG raw dataset from the Sodankylä campaign M. K. Sha, M. De Mazière, J. Notholt, T. Blumenstock, H. Chen, D. Griffith, F. Hase, P. Heikkinen, A. Hoffmann, M. Huebner, N. Jones, R. Kivi, C. Petri, Q. Tu, T. Warneke, and D. Weidmann https://doi.org/10.18758/71021040

FRM4GHG level2 dataset from the Sodankylä campaign M. K. Sha, M. De Mazière, J. Notholt, T. Blumenstock, H. Chen, D. Griffith, F. Hase, P. Heikkinen, A. Hoffmann, M. Huebner, N. Jones, R. Kivi, C. Petri, Q. Tu, T. Warneke, and D. Weidmann https://doi.org/10.18758/71021048

Mahesh Kumar Sha et al.
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Short summary
We present the results of the FRM4GHG campaign in 2017 at the Sodankylä TCCON site aimed at characterising the assessment of several low-cost portable instruments for precise solar absorption measurements of column-averaged dry air mole fractions of CO2, CH4 and CO. The test instruments provided stable and precise measurements of these gases with quantified small biases. This qualifies the instruments to complement TCCON and expand the global coverage of ground-based measurements of these gases.
We present the results of the FRM4GHG campaign in 2017 at the Sodankylä TCCON site aimed at...
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