Progress of CO2M implementation, the Copernicus mission for monitoring anthropogenic carbon dioxide from space

The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing as part of the EC’s Copernicus Sentinel expansion programme, a space-borne observing system for quantification of the emissions of the main greenhouse gases: anthropogenic carbon dioxide (CO₂) and methane (CH₄). The anthropogenic CO₂ monitoring (CO2M) mission will be implemented as a constellation of three identical LEO satellites, to be operated over a period of at least 7 years and measuring CO₂ concentration in terms of column-averaged dry air mole fraction (denoted as XCO₂). Each satellite will continuously image 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 better than 2 x 2 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 mission requirements necessitate a payload composed of four instruments, which simultaneously perform co-located measurements. The main instrument, called CO2I, consists of a push-broom imaging spectrometer which will perform co-located measurements of top-of-atmosphere radiances in the Near Infrared (NIR) and Short-Wave Infrared (SWIR) at high to moderate spectral resolution (NIR: 747- 773nm @0.1nm, SWIR-1: 1595-1675nm @0.3nm, SWIR-2: 1990-2095nm @0.35nm) for retrieving XCO₂ and XCH₄. These observations are complemented by a second instrument called NO2I in the same spectrometer acquiring measurements in the visible spectral range (405-490 nm @0.6nm), providing vertical column measurements of nitrogen dioxide (NO₂) that serve as a tracer to high temperature combustion of fossil-fuel and related emission plumes. High quality retrievals of XCO₂ will be ensured even in the presence of aerosol loading, thanks to co-located measurements of aerosol properties resulting from a third instrument called Multiple Angle Polarimeter (MAP). Polarimetric measurements are performed over 40 angular views and in six spectral channels in the range 410 nm to 865 nm. A fourth instrument is a three-band Cloud Imager (CLIM) that will provide the required capacity to detect small tropospheric clouds and cirrus cover with an accuracy of 1% to 5% and a sampling better than 400 m. Indeed, cloud contamination has a strong impact on the XCO₂ retrieval.

Starting by 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. CO2M is now in phase D, with manufacturing, integration and testing of the first two flight models (PFM and FM2) on-going.