Instantaneous sampling accuracy of the Geostationary Earth Radiation Budget (GERB) experiment

Resolving uncertainties surrounding the nature of future climate change is currently one of the greatest challenges facing mankind. Validating climate model predictions of the currently much miss-represented cloud radiative feedback requires measurements made from orbit of the Earth Radiation Budget (ERB), specifically targeted at clouds. The ERB parameters for measure are the scattered solar or short wave (SW, 0.3-5 mum) and the emitted thermal or long wave radiance (LW, 5-100 mum). The Clouds and the Earth's Radiant Energy System (CERES), as part of NASA's Earth observing System, uses thermistor bolometer detectors to provide global high spatial resolution ERB measurements from polar orbiting space platforms. The Geostationary Earth Radiation Budget (GERB) experiment is a European Space Agency (ESA) project on board the spin stabilized Meteosat second Generation (MSG) platform. Location in geostationary orbit and the use of an array of thermopile detectors enables sampling of ERB radiances from the entire Earth disc at an optimum 5 minute temporal resolution. Taking full advantage of both GERB's time resolution and CERES's global coverage for climate science requires a radiometric cross calibration and validation between the two satellite programs. This study quantifies the instantaneous sampling errors incurred by the GERB instrument due to geo-location uncertainties and orbit spin axis miss-alignment. The results can therefore be characterized as a function of scene contrast, allowing an appropriate statistical weighting to be employed when making a radiometric comparison between the GERB and CERES instruments.