Temporal and spatial variability in Meteosat/SEVIRI images for the Global Space-based Inter-Calibration System (GSICS)

Inter-calibration of satellite instruments often require comparing observations from different instruments collocated in space, time and viewing geometry within certain thresholds. The choice of these thresholds directly impacts the uncertainty of the comparison, partially due to the scene variability within the range of the collocation criteria. Scene variability can be quantified as variograms by evaluating the root mean square difference of a series of observations sampled at different intervals in space or time. These are evaluated here using data from the infrared channels of the Meteosat/SEVIRI geostationary imager. The results suggest thresholds of 5 min and 3.5 km would each introduce random uncertainties of about 1-2 K into each collocation.