Satellite Estimation of Solar Irradiance at the Surface of the Earth and of Surface Albedo Using a Physical Model Applied to Metcosat Data

Abstract

A physically based model is used to derive downward solar irradiance at the surface of the earth and surface albedo from Meteosat satellite measurements in the wavelength range between 0.40 and 1. 1 0 ?m. The model takes into account Rayleigh and Mie scattering, water vapor and ozone absorption. No threshold setting is necessary to distinguish between clear and cloudy conditions, thereby avoiding the problem of its arbitrary nature and to some extent allowing quicker and easier data processing. Comparison of noontime satellite estimates with analogous hourly solar irradiance measurements obtained from the French pyranometer network shows a correlation coefficient of 0.92 and a rms error of 109 W m?2 (20% of the mean solar irradiance). The maximum error occurs for values of insulation around 300 W m?2 and can be mostly attributed to the different spatial and temporal samplings of the systems being compared. Mean monthly estimates of the solar irradiance between 1100 and 1300 UT, at different locations, fit pyranometer measurements with a rms error of 37 W m?2 (6%). The method is finally used to product maps of solar irradiance albedo and net solar flux at the surface over France. These maps can be easily derived from the whole Meteosat frame, with resolution ranging from a few kilometers to several dozens of kilometers, which are scales suitable for agrimeteorology and climate studies respectively.