Toward Global Mapping of Methane With TROPOMI: First Results and Intersatellite Comparison to GOSAT

The TROPOspheric Monitoring Instrument (TROPOMI), launched on 13 October 2017, aboard the Sentinel-5 Precursor satellite, measures reflected sunlight in the ultraviolet, visible, near-infrared, and shortwave infrared spectral range. It enables daily global mapping of key atmospheric species for monitoring air quality and climate. We present the first methane observations from November and December 2017, using TROPOMI radiance measurements in the shortwave infrared band around 2.3 mu m. We compare our results with the methane product obtained from the Greenhouse gases Observing SAT-ellite (GOSAT). Although different spectral ranges and retrieval methods are used, we find excellent agreement between the methane products acquired from the two satellites with a mean difference of 13.6 ppb, standard deviation of 19.6 ppb, and Pearson's correlation coefficient of 0.95. Our preliminary results capture the latitudinal gradient and show expected regional enhancements, for example, in the African Sudd wetlands, with much more detail than has been observed before. Plain Language Summary Methane is the second most important anthropogenic greenhouse gas. Improved knowledge about methane variations and detection of localized sources is of great importance for scientists, policy makers, and private companies. One of the goals of the recently launched European Space Agency Sentinel-5 Precursor satellite, with on board the cutting-edge TROPOspheric Monitoring Instrument (TROPOMI), is to measure methane with an unprecedented combination of accuracy, spatial coverage, and resolution. This work presents the first TROPOMI methane measurements and shows that these are in excellent agreement with methane measurements from the validated Japanese Greenhouse gases Observing SATellite satellite.