New 1km-version of the DUETT radiation data (using satellite and station data) based on the new Meteosat-FCI instrument

In recent decades, satellite-based observations of clouds and surface radiation (derived from estimated cloud albedo) are progressively improving in quality and have experienced a significant increase in spatial resolution with the new third generation of Meteosat satellites (MTG). Within the DUETT project, the German Meteorological Service (DWD) is pursuing the goal to supplement conventional solar radiation measurements at ground stations with satellite data and thus to increase the spatial coverage of solar radiation information over Germany. Data of solar radiation from 42 pyranometer stations are combined with corresponding data based on measurements from Meteosat-SEVIRI (with a spatial resolution of about 5 km). In a new version presented here, data from the new Meteosat-FCI instrument (1 km resolution) are used as input. In this version of DUETT hourly products of the global horizontal irradiance (GHI) and the sunshine duration (SDU) are provided on a 1 x 1 km grid for Germany in near real-time. In addition, new data of diffuse horizontal irradiance (DIF) will be provided in the course of 2026.

Merging is performed in four main steps: 1. Data aggregation 2. Adjustments regarding errors by snow cover and water vapour column 3. Global bias correction 4. Interpolation of residual local deviations. For SDU, the merging is based on satellite data of direct normal irradiance (DNI), which are ‘translated’ and compared with station data of SDU. Based on the combined gridded data, additional point data are determined at the coordinates of 576 measurement sites of DWD. These pseudo station data are optimized by a subsequent correction regarding the influence of surrounding topography. For both, grid and point data, uncertainties are estimated based on three known error sources. We present the latest data version for the three variables GHI, SDU and DIF. For the new DUETT variable DIF, the steps of the data combination are illustrated and validation results based on cross validation are presented for all three parameters. Furthermore, an outlook is given on planned improvements of the DUETT data in the near future.