EarthCARE MSI Level-1 Data: First In-Orbit Calibration and Validation

Bley, Sebastian; Hünerbein, Anja; Baudrez, Edward; Madenach, Nils; Docter, Nicole; Preusker, Rene; Eisinger, Michael; Marnas, Fabien; Ludewig, Antje; Ruiz Saldaña, Manuel Ángel; Bean, Cameron; Agarwal, Shweta; Zimmermann, Lennart; Hummel, Timon

doi:10.5194/egusphere-2026-2652

Sebastian Bley, Anja Hünerbein, Edward Baudrez, Nils Madenach, Nicole Docter, Rene Preusker, Michael Eisinger, Fabien Marnas, Antje Ludewig, Manuel Ángel Ruiz Saldaña, Cameron Bean, Shweta Agarwal, Lennart Zimmermann, and Timon Hummel

Abstract. 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.

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 ±500 meters and coregistration accuracy of ±0.3 pixels.

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 BA dataset confirm the successful mitigation of the observed offsets between MSI and FCI with relative biases below 1 %.

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.

Received: 11 May 2026 – Discussion started: 10 Jun 2026

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