## 3 Results
### Validation of Diurnal Radiation  
Figure 4A displays the R\({}^{2}\) values depicting the correlation between the diurnal estimates of Heliosat-2 GHI and ground data. Meanwhile, Figure 4B,C exhibit the MB and RMSE, respectively. In Figure 4A, the median R\({}^{2}\) values exhibit an inclining trend as we transition from CAB to KSA locations and a declining nature from KSA to HON, with most values surpassing 0.8, excepting CAB and CNR. The interquartile range (IQR) for the KSA is the narrowest, followed by GOB and VUW, while it is widest for CAB, followed by CNR. The widest ranges of IQR, in the two locations of CAB and CNR, show that for at least 25% of days, the estimated GHI and ground measurements had R\({}^{2}\) values of less than 0.65 and 0.75, respectively.  
Figure 3: Comparisons of mean diurnal ground and Heliosat-2 GHI estimates in terms of scatter plots for (**A**) CAB, (**B**) CNR, (**C**) ABS, (**D**) TAT, (**E**) GOB, (**F**) VUW, (**G**) KSA, (**H**) ASO, and (**I**) HON sites, irrespective of clear and cloudy days. The 1:1 line indicates where ground and Heliosat-2 data are identical. The zero standard deviation line (magenta) overlaps with the best-fit line. The negative standard deviation lines lie below the best-fit line, while the positive standard deviation lines lie above it.  
The MB fluctuates significantly across the dataset, ranging from \(-\)130.7 to +145.2 W\(\cdot\)m\({}^{-2}\) (Figure 4B). Analyzing the median MB, Heliosat-2\({}^{\prime}\)s estimates show a nominal bias in CAB and CNR, lying close to zero, while they have the highest range and IQR among all of the locations in this study. A slight underestimation of daily radiation values, averaging \(-\)5.1 W\(\cdot\)m\({}^{-2}\), was observed in TAT. Conversely, in ABS, there is an average overestimation of approximately +5.2 W\(\cdot\)m\({}^{-2}\). Assessing the MB across the African sites, Heliosat-2\({}^{\prime}\)s estimates portray a tendency towards underestimation (\(-\)29.8 W\(\cdot\)m\({}^{-2}\)) for the majority of daily radiation values in GOB, while in VUW, a minor overestimation (+3.4 W\(\cdot\)m\({}^{-2}\)) is observed, based on median values of MB throughout the study period (Figure 4B). The MB analysis in the KSA location of Saudi Arabia indicates that Heliosat-2 estimates slightly underestimate daily radiation values (clear + cloudy days) by a median value of approximately \(-\)10.5 W\(\cdot\)m\({}^{-2}\). Both of the Indian locations show a nominal median MB, close to zero. The HON location shows less uncertainty in terms of lower MB IQR and MB range across the study period for India.  
Moreover, the RMSE data for Japan, depicted in Figure 4C, suggests relatively higher variability compared to the Middle East, with daily values ranging from 5.2 W\(\cdot\)m\({}^{-2}\) to 195.0 W\(\cdot\)m\({}^{-2}\) and an average median value of 71.9 W\(\cdot\)m\({}^{-2}\), irrespective of sky conditions. Similarly, the analysis of RMSE data for the African region, as shown in Figure 4C, indicates a range of RMSE values between 9.6 W\(\cdot\)m\({}^{-2}\) and 185.0 W\(\cdot\)m\({}^{-2}\), with an average median  
Figure 4: Comparisons of ground and Heliosat-2 GHI estimates in terms of (**A**) R\({}^{2}\), (**B**) MB (in W\(\cdot\)m\({}^{-2}\)), and (**C**) RMSE (in W\(\cdot\)m\({}^{-2}\)) values for the diurnal radiation, irrespective of clear and cloudy days.  
value of 52.7 W\(\cdot\)m\({}^{-2}\) on a daily time scale (inclusive of clear and cloudy days). The ASO location in India has the highest variability of RMSE values, ranging from 0 to nearly 341.7 W\(\cdot\)m\({}^{-2}\).