Vicarious calibration of the multiviewing channel polarisation imager (3MI) of the EUMETSAT Polar System-Second Generation (EPS-SG)

The Multi-Viewing -Channel -Polarization Imager (3MI), planned to fly on the Metop-SG satellite as part of the EPS-SG programme in the timeframe beyond 2020, is a radiometer dedicated to aerosol and cloud characterization for climate monitoring, atmospheric composition, air quality and numerical weather prediction. The purpose of the 3MI is to provide multi-spectral (12 channels between 410 and 2130 nm), multi-polarization (-60°, 0°, and +60°), and multi-angular (10 to 14 views) images of the Earth top of atmosphere outgoing radiance. 3MI does not have an onboard calibration facility and its radiometric and geometric performance will rely on vicarious calibration. The aim of this paper is to present the state of the art of vicarious calibration methods applicable to 3MI. The 3MI measurement principle is based on the French atmospheric mission PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) heritage [1]. This allows adapting the vicarious calibration methods of the PARASOL mission to the needs of 3MI. However, the monitoring of the SWIR (short wave infrared) channels will be a new challenge for the 3MI calibration as this spectral range was not present on PARASOL. The cross-calibration with other instruments flying on the same satellite will support the calibration of 3MI. Indeed the Metop-SG payload includes two other optical instruments covering the same spectral regions. METimage and Sentinel-5 will both be equipped with on-board calibration capabilities and provide valuable measurements for vicarious calibration of 3MI. Further cross-calibration with Earth observation instruments on other satellites, will be studied.