The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing as part of the EC’s Copernicus program, a space-borne observing system for quantification of anthropogenic carbon dioxide (CO2) emissions. The anthropogenic CO2 monitoring (CO2M) mission will be implemented as a constellation of identical Low Earth Orbit satellites, to be operated over a nominal period of more than 7 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 250km. Observations will be provided at a spatial resolution < 2 × 2km², with high precision (< 0.7ppm) and accuracy (bias < 0.5ppm), which are required to resolve the small atmospheric gradients in XCO2 originating from anthropogenic activities. The demanding requirements led to 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), NO2 serving as a tracer to high temperature combustion of fossil-fuel and related emission plumes. High quality retrievals of XCO2 will be ensured even in presence of aerosol loading, thanks to co-located measurements of aerosol properties resulting from a second instrument called Multiple Angle Polarimeter (MAP). The third instrument is a three-band Cloud Imager (CLIM) that will provide the capacity to detect small tropospheric clouds and cirrus cover.

Starting with a summary of the main scientific drivers, this paper will provide an overview of the progress of the space segment development: platform, payload as well as the end-to-end simulator. The consolidated design of the CO2M instruments which have passed their Critical Design Review, the results of the critical development models as well as the first delivery of the flight hardware are included in this paper.