The uncertainty of the HelioClim-3 DNI data under Moroccan climate

The purpose of this study is to evaluate the uncertainty of the DNI satellite-derived data from HelioClim-3 against those measured at ground level by calculating the classical statistical performance indicators for different time resolutions (hourly, daily and monthly). Correlations between the errors and the Aerosol optical depth (AOD) data measured by an AERONET sun photometer station at the University of Oujda were performed. Results show that the DNI data derived from Helioclim-3 can be considered as acceptable for satellite data with an RMSE of 19.7 % and a bias of 7.9 % for the hourly data. HelioClim-3 systematically over-estimates the daily DNI sums for the investigated site. The correlation to AOD at 550 nm can only be one of the reasons for the deviation. Corrections or site adaptation could help to increase the accuracy of the data base for that pixel.