Accurate measurements are needed to improve our understanding of the Earth Radiation Budget (ERB). Despite continuous efforts to improve the observation systems, models remain necessary to convert the raw measurements in a form usable by the scientific community. These models concern the spectral, the angular, the spatial, and the temporal properties of the radiation leaving the Earth at the top of the atmosphere. The geostationary orbit allows to resolve the full diurnal cycle and consequently there is no need for any temporal modeling. This is the main motivation to include the Geostationary Earth Radiation Budget (GERB) instrument on the Meteosat Second Generation satellites. However, using the geostationary orbit the spectral, angular, and spatial models are still needed. In this work, we address these modelings in the case of the GERB project.