A multi-year global methane data set obtained by merging observations from TROPOMI and IASI

Data products of atmospheric methane (CH4) with improved vertical sensitivity in the lower tropo-
sphere are crucial for gaining a more comprehensive understanding of the impact of anthropogenic emissions.
This study presents a CH4 data product derived from the synergetic combination of level 2 (L2) data from
TROPOMI (Tropospheric Monitoring Instrument) and IASI (Infrared Atmospheric Sounding Interferometer),
specifically CH4 total column and CH4 profiles, respectively. IASI enables high-quality observation of CH4
mixing ratios in the upper troposphere and lower stratosphere, and TROPOMI observations excel in providing
sensitivity to the total column-averaged mixing ratio of CH4. By combining the IASI and TROPOMI L2 products
synergetically, we can detect tropospheric CH4 (mixing ratios averaged over a layer representing the lowermost
50 % of the atmosphere) that is not significantly affected by the strong CH4 variations around the tropopause.
This is not achievable by using IASI or TROPOMI data alone.
For the synergetic L2 data combination, we use the method as presented in detail in Schneider et al. (2022b),
and apply it to combine about 444 million individual and high-quality TROPOMI observations with about 805
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million individual and high-quality IASI observations made globally over 42 months (from January 2018 to June
2021). The combination method is fast; it uses a tool designed for efficient geo-matching between large data sets
and a computationally cheap Kalman filter for merging the data sets. We show that the combined data set has
a good global coverage. Moreover, we document that the sensitivity (response of the combined data product to
real atmospheric CH4 variations) is very satisfactory throughout the globe, and the uncertainties are generally
below 12–15 ppbv. Furthermore, we demonstrate the increased scientific value of the combined data product
when compared to the two individual data products.
The data set of the combined product consists of about 289 million individual data points, and it is provided
as NetCDF files. One file has a typical size of 85 MB and contains all data for observations made in one day
(the universal time of the TROPOMI observations are taken as the reference time). The data set is referenced
to https://doi.org/10.35097/wq583rnzpmd83m5g (Shahzadi et al., 2026) and also made freely available at https:
//www.imk-asf.kit.edu/english/CH4-synergy-IASI-TROPOMI_RemoTeC.php (last access: 8 March 2026)