Assessing Satellite-Based Data Products Estimating Daily Means of Solar Irradiance at Surface over South Cameroon Plateau and Potential Improvements

Abstract

The assessment of satellite-derived solar radiation products has been performed over several parts of the world by various authors. The case of Central Africa has so far hardly been addressed. This study takes a step forward by evaluating the performance of three existing state-of-the-art satellite-based data products, namely CAMS-RAD 4.6, CERES SYN1deg Ed4.2 and SARAH-3, in estimating the daily mean surface solar irradiance at five ground-based stations located in the South Cameroon plateau. The correlation coefficient varies between 0.59 and 0.92, with the highest level always seen for CAMS-RAD 4.6 data at each station. The bias (RMSE) is large and always positive for satellite products, confirming a general overestimation. It ranges between 34 W m−2 and 77 W m−2 (40 W m−2 and 86 W m−2), i.e., 22 % and 53 % (26 % and 60 %) in relative value. The lowest (highest) bias is seen with CERES SYN1deg Ed4.2 (SARAH-3) data when each station is taken individually. An approach for improvement based on a simple linear regression model without the intercept was developed with CAMS data. In general, the approach significantly reduces the bias by at least 30 W m−2, i.e., 20 % in relative value at each station. The RMSE also clearly reduces, by at least 30 W m−2, i.e., a reduction of at least 20 % in relative value. This work shows the way toward further improvements.