Sentinel-5P TROPOMI Methane CH4 1-Orbit L2 5.5km x 7km V2 (S5P_L2__CH4____HiR)

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.

Starting from orbit #12432 on March 7th of 2020, the S-NPP auxiliary cloud data source used in the methane product data processing has been transitioned from the VIIRS Cloud Mask (VCM) into the Enterprise Cloud Mask (ECM). The data are stored in an enhanced netCDF-4 format.