A comparison of data sources for creating a long-term time series of daily gridded solar radiation for Europe

Satellite-derived surface solar radiation estimates are an alternative to the solar radiation measured at weather stations or modelled from other measured meteorological variables. The advantage of satellite-derived solar radiation is its high spatial and temporal resolution in comparison with solar radiation derived from weather stations, which has to be spatially interpolated. Solar radiation estimates at approximately 3-5km resolution derived from geostationary Meteosat satellites are available for Europe through the EUMETSAT Satellite Application Facilities (SAFs). The SAF responsible for land monitoring (LSA-SAF) has been providing daily solar radiation estimates in near real-time since 2005. The SAF on climate monitoring (CM-SAF) provided a 23-year long (1983-2005) consistent dataset of daily solar radiation. In this study we examine if these two solar radiation datasets may effectively be merged to generate a long-term gridded solar radiation time series for Europe. Further, we evaluate whether the ERA-Interim reanalysis or interpolated measured solar radiation (JRC-MARS) can be used as a replacement for existing and possible future data gaps in the satellite-based dataset. We show that the root mean square error and mean absolute error of LSA-SAF's and the CM-SAF's solar radiation estimates are similar (p<0.05), calculated against measured solar radiation data. A grid-based comparison of LSA-SAF's and CM-SAF's datasets showed an average root mean square difference over Europe of 2MJm^-2 and a mean difference of 0.37MJm^-2. For replacing data gaps in satellite-based radiation, we recommend the use of the ERA-Interim reanalysis data; they correspond better to both the ground reference and satellite-derived solar radiation data as compared to interpolated JRC-MARS. We conclude that both satellite-based products can be concatenated to create long-term gridded time series of solar radiation for Europe.