An investigation of the effects of spatially averaging brightness measurements from a geostationary satellite on the calculation of insolation is presented. The calculation of insolation from calibrated hourly visible GOES satellite data is based on the model described by Gautier and others. A series of experiments are reported in which averaging over scales varying by a factor of 8 to 64 from the initial resolution as well as averaging within the model itself have been performed. Results from these experiments have been intercompared and compared with surface measurements. They indicate that spatially averaged daily insolation can be estimated from mean hourly brightness measurements at an eight-times reduced resolution. Furthermore, the mean insolation is not sensitive to averaging of the physical processes up to the largest spatial averaging of 64. This result is important, since it may allow a sizable reduction in the data processing necessary to obtain accurate estimates of insolation for va... Abstract An investigation of the effects of spatially averaging brightness measurements from a geostationary satellite on the calculation of insolation is presented. The calculation of insolation from calibrated hourly visible GOES satellite data is based on the model described by Gautier and others. A series of experiments are reported in which averaging over scales varying by a factor of 8 to 64 from the initial resolution as well as averaging within the model itself have been performed. Results from these experiments have been intercompared and compared with surface measurements. They indicate that spatially averaged daily insolation can be estimated from mean hourly brightness measurements at an eight-times reduced resolution. Furthermore, the mean insolation is not sensitive to averaging of the physical processes up to the largest spatial averaging of 64. This result is important, since it may allow a sizable reduction in the data processing necessary to obtain accurate estimates of insolation for va...