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The Multi-Viewing -Channel -Polarisation Imager (3MI), planned to fly on the Metop-SGA satellites as part of the EUMETSAT Polar System - Second Generation (EPS-SG) programme in the timeframe beyond 2020, is a radiometer dedicated to aerosol and cloud characterisation 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 nm and 2130 nm), multi-polarisation (-60°, 0°, and +60°), and multi-angular (10 to 14 views) images of the Earth top of atmosphere outgoing radiance.
The 3MI concept is based on the PARASOL mission heritage. This heritage allows adapting techniques developed for PARASOL e.g. for the vicarious calibration methods. As PARASOL, 3MI does not have an onboard calibration facility and its radiometric and geometric performances will rely on vicarious calibration. However the monitoring of the SWIR (short wave infrared) channels will be the new challenge for the 3MI calibration as this spectral range was not present on PARASOL. Because the vicarious methods may have less accurate performance for absorption bands (763 nm, 910 nm, and more specifically the SWIR 1370 nm), the access to a moon observation during commissioning would be very beneficial, in addition to the characterization of many other radiometric aspects. The Metop-SGA satellite will also allow simultaneous temporal and geometrical acquisitions between the payload instruments. This synergy will be beneficial to support 3MI with cross-calibration (radiometric, spectral, and geometric). Indeed the Visible-Infrared Imager (METimage) and the UV-VIS-NIR-SWIR Sounder (Sentinel-5), the two other optical instruments covering the similar spectral regions will be both equipped with on-board calibration and provide valuable measurements for cross-calibration with 3MI.
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