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The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing as part of the EC’s Copernicus programme, six new missions to strengthen the already existing family of six Sentinels missions. The six new Sentinel Expansion missions cover four themes: Safeguarding the Artic, Monitoring Land and Natural Resources, Food Security and Management and Combating Climate Change. For this last theme, a space-borne observing system for quantification of anthropogenic carbon dioxide (CO2) emissions is in development. The anthropogenic CO2 monitoring (CO2M) mission will be implemented as a constellation of identical Low Earth Orbit satellites, to be operated over a period of more than seven years. Each satellite will continuously measure CO2 concentration in terms of column-averaged dry air mole fraction (denoted XCO2) along the satellite track on the sun-illuminated part of the orbit, with a swath width of 250 km. Observations will be provided at a spatial resolution of 4 km2, with high precision (⪅0.7 ppm) and accuracy (bias ⪅0.5 ppm), which are required to resolve the small atmospheric gradients in XCO2 originating from anthropogenic activities. The demanding requirements necessitate a payload composed of three instruments, which simultaneously perform co-located measurements: a push-broom imaging spectrometer in the Near Infrared (NIR) and Short-Wave Infrared (SWIR) for retrieving XCO2 and in the Visible spectral range (VIS) for nitrogen dioxide (NO2), a Multi Angle Polarimeter (MAP) and a three-band Cloud Imager (CLIM). Following the Satellite PDR, the industrial activities have concentrated in consolidating the design of the three instruments and the platform as well as completing the different development models. The paper presents the status of these activities which are leading to the Critical Design Review before entering into the flight manufacturing and assembly phase.
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