The Copernicus Sentinel-5 Precursor (Sentinel-5P or S5P) satellite mission is one of the European Space Agency's (ESA) new mission family - Sentinels, and it is a joint initiative between the Kingdom of the Netherlands and the ESA. The sole payload on Sentinel-5P is the TROPOspheric Monitoring Instrument (TROPOMI), which is a nadir-viewing 108 degree Field-of-View push-broom grating hyperspectral spectrometer, covering the wavelength of ultraviolet-visible (UV-VIS, 270nm to 495nm), near infrared (NIR, 675nm to 775nm), and shortwave infrared (SWIR, 2305nm-2385nm). Sentinel-5P is the first of the Atmospheric Composition Sentinels and provides measurements of ozone, NO2, SO2, CH4, CO, formaldehyde, aerosols and clouds at high spatial, temporal and spectral resolutions. Spatial resolution is 5.5 km along-track and 7 km across-track at nadir. S5P is in a sun-synchronous orbit with an ascending node of ~13:30 which provides daily global coverage of the sun-lit Earth. Data are archived in enhanced netCDF-4 format. Beginning August 6th in 2019, S5P implemented along-track high spatial resolution (~5.5km at nadir). The near-real-time (NRT) data are generally available within three hours of measurement as required by the Land Atmosphere NRT Capability Earth Observing System (LANCE). Data granules are in five-minute intervals of an orbit, rather than a full orbit as provided for the standard products. NRT data are only archived for five days and not considered to be science-quality data. The data are intended for rapid turnaround assessments, for rigorous scientific analyses users should use the standard Version 3 product.

The retrieval algorithm for Sentinel-5P TROPOMI methane product is a physics based method that uses the Oxygen-A band (760 nm) and absorption bands in shortwave infrared spectrum. In Sentinel-5P/TROPOMI methane algorithm, the atmosphere forward model simulates the absorbing gas (oxygen, methane, water vapor, and carbon monoxide) optical properties, as well as aerosol optical properties with size distribution, refractive index, and number concentration. The inversion is performed based on the forward calculation, the measurement, and the prior information. Cloud filtering is critical in methane retrieval, S5P methane algorithm applies re-gridded Visible Infrared Imaging Radiometer Suite (VIIRS) cloud mask data. Additional cloud filters based on S5P/TROPOMI measurements and the FRESCO apparent surface pressure will be applied when VIIRS cloud data are not available. Other current data filters in the retrieval algorithm include land-only pixels (excluding mountainous areas), spectrum intensity, solar zenith angle and instrument zenith angle.
The S5P/TROPOMI methane retrieval is for non-time-critical (NTC) data stream only, and its main outputs include the column averaged dry air mixing ratio of methane, the random error, and the biased corrected dry air methane fraction data based on the retrieved surface albedo.

The Version 3 methane algorithm updated the internal cloud mask to no longer rely on convergence of the CO retrieval