Ground-based infrared remote sensing greenhouse gas (GHG) observations are extensively used for the validation of GHG measurements from satellites like SCIAMACHY, GOSAT and OCO-2. TCCON (Total Carbon Column Observing Network) is a network of about 27 stations distributed globally and measuring the total column abundances of GHGs using a Fourier-transform infrared (FTIR) solar absorption spectrometer of the type Bruker IFS 125HR. TCCON was set up with the aim to provide precise and accurate measurements of GHGs to be used primarily for satellite validation. However, the TCCON network has shown some deficiencies in terms of the gaps in the coverage, especially in remote locations, locations with high/low albedo. The TCCON spectrometer is very expensive, not so easy to move, and requires special operational conditions, trained personnel for operation and maintenance, therefore, it is very costly if further expansion of the network is desired.
Several new portable spectrometers have been developed in recent years that have the potential to eliminate those deficiencies of the TCCON network: they are low cost, portable, easy to operate and maintain and require low operational cost. During the FRM4GHG 1.0 campaign their performances have been fully characterized through inter-comparison results with collocated measurements with TCCON and AirCore observations. The deployed instruments included Bruker's Fourier transform Infrared (FTIR) spectrometers of the type EM27/SUN, Vertex70, and IRcube, additionally, a Laser Heterodyne Spectroradiometer (LHR) and in-situ AirCore sampler was part of the campaign. The campaign took place for the duration of three years (2017 - 2019). During the first two years, all instruments were deployed next to the TCCON station in Sodankylä, Finland. In the third year, the IRcube was performing measurements in Australia at Wollongong and Darwin TCCON sites, while the rest of the instruments stayed and performed measurements in Sodankylä. In addition, regular AirCore launches were performed from Sodankylä site which provided in-situ reference profiles of the target gases, these were useful to verify the instruments calibration.
The focus of the campaign was on CO and CH4 in support of the Sentinel-5 Precursor (S-5P) validation. The campaign provided a significant dataset of GHG measurements that was used for validation purposes during the S-5P commissioning phase. Furthermore, it also provide a comparative characterization of the participating instruments with respect to the standard TCCON instrument in terms of the precision, accuracy, stability, portability and ease of deployment, cost factor, etc. A guideline for the further development of new observation sites to complement the TCCON network and provide better support for the validation of the existing and future satellite missions was provided as an outcome of the campaign.