Using a portable EM27/SUN FTIR-spectrometer for validating the TCCON site-to-site consistency: The COCCON Travel Standard

The precise knowledge of the global atmospheric concentrations of green-house gases (GHG) are crucial for understanding and monitoring climate change.Satellites for measuring GHGs are offering a global coverage, however, they need precise ground-based reference data for validation.This reference data is provided by ground-based measurements, foremost the Total Column Carbon Observing Network (TCCON).The TCCON measures column averages of GHG abundances at about 25 stations around the globe using Fourier Transform Infrared (FTIR) spectrometer. For achieving the high data quality needed for the validation of current and upcoming GHG measuring satellite missions the control of site-by-site biases across the network is of utmost importance. So far, the verification of the individual TCCON sites mainly depends on the collection of collocated in situ measurements of GHG profiles, using airplane overflights or balloon air-core measurements, the use of calibrated HCl gas cells and on the evaluation of XAIR. In this work we present a new supplemental approach by using the portable EM27/SUN FTIR spectrometer, which is the standard instrument of the Collaborative Carbon Column Observing Network (COCCON). This instrument type has proven its high stability in various field campaigns and long-term studies. In the framework of the ESA project “Fiducial Reference Measurements for Green-House Gases II” we are exploiting the stability of the instrument to use it as a Travel Standard (TS) for the TCCON. We visited sites in Japan, Canada, Germany, Australia, France and the Canary Islands to perform side-by-side measurements with the local TCCON spectrometers. Between the visits, the stability of the TS was monitored using the Karlsruhe TCCON site and the COCCON reference spectrometer.This allows to compare the different TCCON sites to a common reference and hence, to verify the level of station-to-station consistency currently achieved by the TCCON and support further improvements. Here, we present the results of the TS visit at the TCCON site Tsukuba(Japan), Wollongong(Australia) and Izana(Canary Islands).