Estimating surface solar irradiance from METEOSAT SEVIRI-derived cloud properties

A satellite retrieval of surface solar irradiance based on METEOSAT SEVIRI-derived cloud properties is presented and validated for the Netherlands with one year of pyranometer measurements from 35 stations. The approach requires two independent steps: 1. Cloud properties are determined from narrow-band satellite radiances. 2. These cloud properties are used together with data on water vapor column and surface albedo to calculate the atmospheric flux transmittance. The retrieved irradiance is biased low by about 3–4 W/m2 throughout the year, corresponding to an underestimate in atmospheric flux transmittance of about 0.015 in summer and 0.04 in winter. From a least-squares linear regression, residual standard deviations of 56 W/m2 (0.072, 17.0%), 11 W/m2 (0.052, 10.8%), and 4 W/m2 (0.021, 4.2%) are found for hourly, daily and monthly mean irradiance (transmittance, relative error), respectively. These findings indicate that the accuracy of the retrieval is comparable to first-class pyranometers in the summer half year (5% of daily-mean values), but significantly lower in winter. Two aspects requiring further investigation have been identified: 1. For thin clouds, the atmospheric flux transmittance is strongly underestimated. 2. The retrieval accuracy is reduced for snow-covered surfaces.