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Space weather negatively affects all geodetic measurement methods that are based on observing microwave signals/radiation (VLBI, Galileo and GPS as well as DORIS). Usually, corrections have to be calculated in order to evaluate the corresponding measurements. Therefore, the Federal Agency for Cartography and Geodesy (BKG) operates space weather sensors as part of its microwave methods department at the Geodetic Observatory Wettzell (GOW). Further, this arrangement creates synergies due to knowledge transfer and the joint use of technical infrastructure.

As we monitor the European Galileo services, space weather is of interest for two reasons. On the one hand, it poses a significant source of disturbances of satellite navigation itself. On the other hand, space weather events must be reliably distinguished from system-related malfunctions of the Galileo services. In addition to space weather probing, other key tasks in the area of Galileo monitoring are the near-real-time verification of satellite orbit information on the basis of SLR measurements and the signal quality assessment employing the radio telescopes at the GOW, which are primarily used for geodetic VLBI.

Our focus lies particularly on the aspects of space weather that can have an impact on satellite navigation. On the one hand, this includes the influence of solar activity on the ionosphere. On the other hand, the sun can directly interfere with GNSS receivers through strong radiation in the radio range (solar radio bursts). In this case, the sun basically acts like a jammer.

The infrastructure set up at GOW in this context includes sensors for direct solar observations as well as for monitoring the sun's influence on the earth's ionosphere and magnetic field. With the Solar Flux Telescope CLT, the radiation intensity of the sun is directly observed in the radio range. Among other things, the solar radio flux index (F10.7 index) is measured. The F10.7 index measures the solar radio flux per unit frequency at a wavelength of 10.7 cm corresponding to a frequency of 2.8 GHz. The F10.7 index is an excellent indicator of overall solar activity and it strongly correlates with the sunspot number. Consequently, it serves as a fundamental input parameter for space weather models and forecasts, including models used in satellite navigation to correct for ionospheric propagation delay. Further, F10.7 index is used as a measure of the energy input into the upper atmosphere to estimate the density and thus the flow resistance acting on LEO satellites.

Additionally, a frequency band around 1.4 GHz, i.e. close to the GNSS bands, is continuously monitored in order to detect direct interference effects on GNSS receivers due to solar radiation. The remaining frequency bands may also be used for modelling and forecasting space weather. Apart from this, these additional measurements are important to notice radio frequency interference. At night (when the sun is below the horizon), the CLT will be used to measure and characterize signal quality of individual Galileo satellites.

In order to link solar activity with effects on the Earth's magnetic field, magnetometers are installed in the vicinity of the observatory, since magnetic field fluctuations potentially affect the ionosphere and thus impair satellite navigation. Additionally, the current electron content and ionospheric scintillations are continuously monitored, to characterize the actual ionospheric conditions.