Validation of daily global solar irradiation images from MSG over Spain

Daily irradiation images over Spain – area that embraces a highly heterogeneous landscape, climatic conditions and relief – are calculated from the down-welling surface short-wave radiation flux (DSSF) product derived from the MSG SEVIRI images. Their analysis and validation is carried out using two different station networks along the year 2008. The first network covers the peninsular Spain and Balearic islands. A denser one, covering the Catalonian territory and including many stations located in rugged terrain, is found useful to assess the elevation correction to be applied to the images. The statistics from the validation using the first network shows a relative mean bias of about 1%, a relative mean absolute difference of 6%, and a mean absolute difference of 1.0MJm−2. The analysis of the second database shows that the elevation correction reduces the relative mean bias, for rugged terrains and for clear sky data, from 5% to 0.5%, whereas for the complete sampling the mean absolute difference of the derived daily irradiation images is 1.3MJm−2. A downscaling of the DSSF product is also carried out, and a methodology to obtain topographically-corrected daily irradiation images, based on merging the DSSF with a digital elevation model, is proposed. These images satisfactorily map the surface solar radiation at 1-km spatial resolution even in rugged terrains.