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We present a model designed to estimate the incident solar radiation at the suface from GOES satellite brightness measurements in clear and cloudy conditions. In this simple physical model, the effect of Rayleigh scattering is taken into account. Water vapor absorption is also introduced by means of its climatological effects on shortwave radiation in southern Canada, but the main emphasis is on cloud effects. Cloud albedo and absorption are derived from brightness measurements on the assumption that they both are linearly related to the brightness. This simple treatment, however, applied to individual picture elements represents quite accurately the bulk effect of clouds, as illustrated by our results. Comparisons with daily insolation measurements from three pyranometers located in Toronto, Montreal and Ottawa in spring and summer 1978 showed that the satellite estimates were, on the average, within 9% of the ground measurements for a large variety of cloud conditions. The hourly variations monitored by the satellite also followed very closely the variations measured on the ground. This study has shown that a simple model is sufficient for the determination of the incident solar radiation when the high spatial and temporal coverage of a geostationary satellite is used.
Gautier et al. (Fri,) studied this question.