MICRU: an effective cloud fraction algorithm designed for UV–vis satellite instruments with large viewing angles

Abstract. Clouds impact the radiative transfer of Earth's atmosphere and strongly influence satellite measurements in ultraviolet–visible (UV–vis) infrared (IR) spectral ranges. For trace gases absorbing UV–vis range, particularly clouds ultimately determine vertical sensitivity profile, mainly by reducing for trace-gas columns below cloud. The Mainz iterative cloud retrieval utilities (MICRU) algorithm is specifically designed to reduce error budget retrievals, such as those nitrogen dioxide (NO2), which depends on accuracy small fractions (CFs) particular. MICRU governed an empirical parameterisation viewing-geometry-dependent background surface reflectivity taking instrumental physical effects into account. Instrumental are degradation polarisation effects; due anisotropy reflectivity, e.g. shadowing plants sun glitter. applied main science channel (MSC) measurement device (PMD) data collected between April 2007 June 2013 Global Ozone Monitoring Experiment 2A (GOME-2A) instrument aboard MetOp-A satellite. CFs retrieved at different bands 374 758 nm. results MSC PMD wavelengths intercompared study CF precision accuracy, depend wavelength spatial correlation. Furthermore, compared FRESCO (fast scheme from oxygen A band) OCRA (optical recognition algorithm) operational products. We show that retrieves with 0.04 or better entire 1920 km wide swath a potential bias −0.01 −0.03. shorter less affected adverse heterogeneities. comparison algorithms shows significantly reduces dependence viewing angle, time, Systematic along coasts its dedicated treatment land ocean surfaces. spectroscopic instruments ranging GOME Sentinel-5P/Tropospheric Instrument (TROPOMI) but also applicable imagers like Advanced Very High Resolution Radiometer (AVHRR), Moderate Imaging Spectroradiometer (MODIS), Visible Infrared Suite (VIIRS), Sentinel-2.