1. German Aerospace Center (DLR), Institute for Solar-Terrestrial Physics, Kalkhorstweg 53, 17235 Neustrelitz, Germany
2. Department of Navigation and Positioning, Finnish Geospatial Research Institute (FGI), National Land Survey of Finland (NLS), Vuorimiehentie 5, 02150 Espoo, Finland
3. Department of Mathematics, Universitat Politècnica de Catalunya—Ionospheric Determination and Navigation Based on Satellite and Terrestrial Systems (UPC-IonSAT), IEEC-UPC, E08034 Barcelona, Spain
4. European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), 64293 Darmstadt, Germany