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As part of the European Copernicus Programme, the European Commission (EC) and the European Space Agency (ESA) together with the support of Eumetsat and the European Centre for Medium-Range Weather Forecasts (ECMWF) are initiating the development of operational satellites for measurements of anthropogenic carbon dioxide (CO2) emissions. The CO2 Monitoring (CO2M) mission shall provide atmospheric CO2 measurements at 4 km2 spatial resolution and a precision and systematic error better than 0.7 ppm and 0.5 ppm respectively in column-average dry-air mole fractions of CO2 (XCO2). The demanding requirements necessitate a payload composed of several instruments, which simultaneously perform co-located measurements. The main CO2 instrument is a 250 km swath pushbroom imaging spectrometer allowing to retrieve XCO2 from reflectance measurements in the Near-Infrared (747-773 nm) and Short-Wave Infrared spectral regions (1590-1675 nm and 1990-2095 nm). The observations for CO2 concentration will be complemented by measurements of nitrogen dioxide (NO2) columns over the same area. The NO2 measurements from the visible region (405-490 nm) will serve as a tracer for plumes of CO2 emission resulting from high temperature combustion, which will facilitate plume identification and mapping from (fossil fuel) power plants and large cities. The third component of the payload is a multiple-angle polarimeter, performing high-precision measurements of aerosol (and cloud) properties. Its measurements of polarized radiance under various observation angles will allow a precise light path correction. The resulting improved knowledge of the effective optical path due to scattering will reduce XCO2 bias error. Retrievals will be successful not only under clear sky conditions, but also under moderate aerosols loading and hence significantly increase the yield of useful XCO2 retrievals. The strong sensitivity of the XCO2 retrieval to cloud contamination calls also for a cloud-imager capable of detecting small tropospheric clouds and cirrus cover with an accuracy of 1% to 5% and with a sampling better than 400 m.
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