CO2M MAP and CLIM Top-Of-Atmosphere simulations
Context
The CO2M mission is dedicated to the monitoring of anthropogenic CO2 emissions. The Multi-Angle Polarimeter (CO2M-MAP) instrument is supporting the CO2CH4 main instrument retrievals from CO2M with the detection of aerosol properties and by correcting the forward calculation of the geometrical light-path due to aerosol scattering in the retrieval. The accuracy of the retrieved air-column weighted total column CO2 strongly depends on the accurate knowledge of the effective light path. The presence of clouds, even small optically thick and thin cirrus clouds, can significantly alter the light path leading to systematic errors. Thus, the CO2 monitoring mission will use simultaneous measurements from a dedicated cloud imager (CLIM) to detect clouds, particularly in those categories, and filter CO2 data for cloud-contaminated cases.
Among the various activities related to CO2M, the accurate and efficient processing of the payload data down-linked from the orbiting platforms is of outstanding importance to the primary users. For the preparation of the CO2M mission and its ground processor developments, it is therefore necessary to simulate realistic data from all instruments on the platform. The project concerns the provision of simulated TOA radiance test-data for MAP and CLIM instruments over complete orbits but outside dark-side eclipse. This includes transition to the sun-illuminated part of the orbit at high SZA, changes of observation geometries for dedicated “sun-glint” observation orbits, covering of a realistic scale of surface and atmospheric conditions, from dark to bright surface, as well as high latitude to tropical atmospheric conditions.
HYGEOS activities
HYGEOS used the radiance simulator developed over past EUMETSAT projects to simulate 6 orbits of data corresponding to L1B for MAP and CLIM sensors. The simulator was adapted to match the study constraints and instruments specifications. Among the constraints, it was critical to use the same scene definition (ancillary data for atmosphere and surface characterisation) as the one used for the main CO2M instruments (CO2I/NO2I) test data production. In addition to the MAP and CLIM test data corresponding to radiance spectrally integrated in Spectral Response Function of the instruments, spectrally over-sampled test data were produced for a sub-set of the 6 orbits to assess error propagation to Level 2 related to spectral miscalibration. As an optional task, MAP data in L1C sampling was produced allowing assessing the error related to the co-registration of all L1B pixel to the L1C common geolocated grid.
RGB composite of radiances (left) and polarized radiance (right) of MAP instrument simulated for the orbit on 3rd July 2025.
