A new physical model of radiative transfer within the atmosphere for the estimation of daily surface solar exposure based on GMS-5 0.5 to 1.0 m observations has been developed. The two-band model is an extension of an earlier single-band model developed for data from GMS-4. It uses additional physics to account for the increased spectral bandwidth of the GMS-5 VISSR. The model has other improvements including use of real-time ozone estimates derived locally from the NOAA polar-orbiting series of satellites. The output from the model is validated against 2041 high quality pyranometer values from 12 sites covering the major Australian climatic zones from late July 1997 to late April 1998. Mean absolute percentage differences of model daily surface exposure from point pyranometer estimates are 6.2% (1.4 MJ m-2) overall, 3.1% (approximately 0.8 MJ m-2) in the least cloudy 35% of cases (mean daily cloud albedo less than 0.07), and 12.4% (approximately 1.6 MJ m-2) in the cloudiest 15% of cases (mean daily cloud albedo greater than 0.34). The spatial variability of exposure has been estimated in this study. It is shown that in typical grain growing areas of Australia, the satellite-based exposure estimates are more accurate than extrapolation over more than approximately 45 km (20 km in one case) from surface measurement sites having a total system error standard deviation of 5% of the observations.
Weymouth et al. (Sat,) studied this question.