This computation involves the Level 2 processing algorithm applied to raw TROPOspheric Monitoring Instrument (TROPOMI) data. The one-step OFFL algorithm (S5P_TO3_GODFIT) comprises a non-linear least-squares inversion based on the direct comparison of simulated and measured backscattered
radiances. Simulated radiances are computed (again for a multiple scattering atmosphere) at all nominal wavelengths in the UV fitting window, along with corresponding analytically derived weighting functions for total ozone, albedo and effective temperature. The algorithm also contains closure fitting coefficients and a semi-empirical correction for Ring interference. Although more accurate, the S5P_TO3_GODFIT algorithm involves many more RT simulations than S5P_TO3_DOAS, and is, therefore, slower by an order of magnitude approximately. This is currently the main driver for the selection of S5P_TO3_DOAS for the
NRTI product. For more information on the processing of the O3 product please refer to the ATBD document.