Intercomparison of Sentinel-5P TROPOMI cloud products for tropospheric trace gas retrievals

Abstract. Clouds have a strong impact on satellite measurements of tropospheric trace gases in the ultraviolet, visible, and near-infrared spectral ranges from space. Therefore, gas retrievals rely information cloud fraction, albedo, height products. In this study, parameters different retrieval algorithms for Sentinel-5 Precursor (S5P) TROPOspheric Monitoring Instrument (TROPOMI) are compared: Optical Cloud Recognition Algorithm (OCRA) priori Retrieval Of Information using Neural Networks (ROCINN) CAL (Clouds-As-Layers) fraction top base height, ROCINN CRB (Clouds-as-Reflecting-Boundaries) Fast Scheme Oxygen A-band (FRESCO) interpolated FRESCO TROPOMI NO2 product, fitting window, O2–O2 Mainz Iterative Utilities (MICRU) Visible Infrared Imaging Radiometer Suite (VIIRS) fraction. Two versions products OCRA/ROCINN, FRESCO, product included comparisons (processor version 1.x 2.x). Overall, retrieved by show qualitative consistency good agreement 2.x with exception VIIRS which cannot be directly compared to other data. Differences between found especially small heights threshold 0.2, i.e. clouds that particularly relevant retrievals. The fractions 2 primarily differ over snow- ice-covered pixels scenes sun glint, only MICRU includes an explicit treatment. All some systematic problems related across-track dependence, where larger values at edges view. depends strongly how data filtered comparison, example, what quality value is used or whether excluded analysis. summary, clear differences were results various algorithms, but these reduced most recent