EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-2652 EarthCARE MSI Level-1 Data: First In-Orbit Calibration and Validation Bley Sebastian https://orcid.org/0000-0003-1119-7067 1 Hünerbein Anja https://orcid.org/0000-0002-1424-4546 1 Baudrez Edward 5 Madenach Nils 1 Docter Nicole 1 Preusker Rene 2 Eisinger Michael 3 Marnas Fabien 4 Ludewig Antje 6 Ruiz Saldaña Manuel Ángel 7 Bean Cameron 7 Agarwal Shweta 7 Zimmermann Lennart 8 Hummel Timon 9 Leibniz Institute for Tropospheric Research, Leipzig, Germany Freie Universität Berlin (FUB), Berlin, Germany European Space Agency (ESA), ECSAT, Harwell, United Kingdom European Space Agency (ESA), ESTEC, Noordwijk, The Netherlands Royal Meteorological Institute of Belgium, Brussels, Belgium Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands GMV, Airspeed 2, Eighth Street, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RL, United Kingdom Airbus Defence and Space GmbH, Germany European Space Agency (ESA), ESRIN, Frascati, Italy 10 06 2026 2026 1 30 Copyright: © 2026 Sebastian Bley et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2652/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2652/egusphere-2026-2652.pdf

The successful launch of the EarthCARE satellite on 28 May 2024, with its unique combination of active and passive instruments, enables new insights into advanced cloud-aerosol-radiation interactions in the atmosphere. The Multi-Spectral Imager (MSI) onboard the EarthCARE satellite provides horizontal observations of reflected visible, near-infrared, and short-wave infrared (VNS) radiation and emitted thermal infrared (TIR) radiation across a 150-km swath. Following 1.5 years of calibration and validation, the MSI instrument is performing very well.</p> <p>This paper focuses on the main findings of the validation and calibration of the MSI Level-1 data since the launch. One major improvement in the MSI Level-1 processing was the introduction of band-specific pixel geolocation and inter-band coregistration corrections. These improvements have been shown to achieve the necessary instrument performance, successfully meeting the specifications for geolocation accuracy of &plusmn;500 meters and coregistration accuracy of &plusmn;0.3 pixels.</p> <p>The radiometric accuracy of MSI was assessed against the Flexible Combined Imager (FCI) onboard the Meteosat Third Generation (MTG) satellite using collocated cloud scenes. The results showed systematic offsets in MSI Level-1 VNS radiances compared to the corresponding FCI spectral bands. These findings led to the conclusion to perform an ad-hoc vicarious calibration of the MSI VNS radiances against FCI. The initial verification results for the improved and reprocessed MSI Level-1 <em>BA</em> dataset confirm the successful mitigation of the observed offsets between MSI and FCI with relative biases below 1 %.</p> <p>In addition, the VNS reflectances exhibited unexplained across-track variations that could not be attributed to the radiance measurements. Monitoring of the spectral solar irradiance, measured by MSI's onboard diffusers, revealed across-track artifacts and day-to-day variations exceeding expected solar variability. Therefore, the measured spectral solar irradiance has been replaced by theoretical values in the MSI Level-1 product. All of these updates led to a significantly improved radiometric and geometric stability.