The “High Spectral Resolution synthetic
radiances for Geostationary imagers” project
is performed to provide simulations of geostationary top of atmosphere (TOA)
radiances at high spectral resolution.
HYGEOS/LOA will provide EUMETSAT with at least two full disks at MSG/SEVIRI spatial grid (3km at nadir) and high spectral resolution (between 0.5nm and 0.25 cm-1) for spectral range covering 0.354 to 15.5 μm. Using the same spectral resolution, at least four scenes (1000 x 1000 pixels) at higher spatial resolution (~500m at nadir) will be provided.
The principal driver for the acquisition of such synthetic data by EUMETSAT is to enable evaluation of geostationary satellite imagery (i.e. level 1) quality and characteristics given uncertainties or variability in detector array SRFs. For example with detector arrays such as present on the FCI ( MTG ),
the degree of striping and development of methods to reduce striping may be evaluated.
A secondary driver is to enable the exercising of Atmospheric Motion Vectors on synthesised IRS Level-1 products.
Top of the atmosphere radiances for the full range of representative atmospheric and surface conditions are generated. The sun and view geometries are taken from SEVIRI observations for selected repeat cycles. The spatial grid is the SEVIRI/MSG one. For each pixel, the surface and atmosphere is realistically described based on ancillary information obtained for dates and time of required simulation (among which OCA products for clouds coupled with ECMWF water content profile, CAMS reanalysis for aerosols profiles, ECMWF reanalysis for atmospheric state, MODIS surface BRDF product and thermal infrared climatology for land properties). For high spatial resolution scenes, MODIS or VIIRS cloud products will be used.
To compute TOA radiance, the simulator uses ARTDECO radiative transfer tool in the UV to SWIR domain and RTTOV in the thermal infrared domain. The computation is done individually (on-the-fly) for each pixel and each spectral channel (each wavelength). The scene definition (aerosol, cloud, gas and ground) is made consistent between the two spectral domains.