Daily Global Methane Super-Emitter Detection and Source Identification With Sub-Daily Tracking
Geophysical Reseach Letters
Tobias A. de Jong, Joannes D. Maasakkers, Itziar Irakulis-Loitxate, Cynthia A. Randles, Paul Tol, Ilse Aben
Key Points
Methane super-emitter attribution and quantification at 0.75 km resolution using Visible Infrared Imaging Radiometer Suite (VIIRS) including concurrently with TROPOMI super-emitter detection
Cross-validation of multi-band multi-pass method by comparison of co-located TROPOMI and Suomi-NPP VIIRS measurements
At least 4 times per day global coverage by combining three VIIRS instruments with Sentinel-3 Sea and Land Surface Temperature Radiometer data
Conclusion and Outlook
We have shown that under favorable conditions, the VIIRS instruments aboard the JPSS satellites can be used to detect and image super-emitter methane plumes, similar to other band imagers. This is a unique addition to the rapidly expanding suite of satellite instruments able to observe methane super-emitters, for three reasons. First, the co-location within 5 min of the Suomi-NPP VIIRS instrument with TROPOMI means that for every methane plume detected with TROPOMI, a higher resolution VIIRS observation of the same plume is available. This enables attribution of (transient) emissions to specific sources for mitigation. Second, for each event, one to four additional VIIRS observations are available through the complete JPSS constellation at intervals of 25 or 50 min. This gives significant insight in the temporal evolution of emissions, in particular for transient emissions. Using TROPOMI, VIIRS and SLSTR together to monitor emissions thus gives a much more complete picture. Third, the co-location of Suomi-NPP with TROPOMI allows for cross-validation of MBMP methods with TROPOMI measurements, both on the level of estimated emission rates, but also directly on the level of obtained methane enhancements. This enables identification of error sources of the widely applied MBMP methods. In particular, we have shown that water vapor concentration variation has a strong influence on the methane retrieved using MBMP methods. Although this does not prevent localization, a method directly correcting for water vapor would improve the quantification accuracy.
Looking to the future, everything described here will also be applicable to future combinations of high-precision spectral imagers with high-resolution band imagers, such as the methane measurements of Sentinel-5 and the VIIRS-like METimage, both aboard the Metop-SG-A satellite. DLR's METimage has a spatial resolution of 500 m and has bands around 900 nm that could be used to correct for water vapor (Wallner et al., 2017). All current and future band imagers can build on the cross-validation between TROPOMI and VIIRS. Nevertheless, spectral imagers are needed to accurately assess and remedy the emissions of smaller sources and additional instruments are needed to fill the gap in temporal coverage in the local afternoon. Combining all these instruments with different overpass times within the framework presented here greatly enhances the completeness of our ability to monitor methane super-emitters around the world.