## 3 Results
### SNR Degradation Experiment
A second \(R_{2M}\) baseline is added while getting rid of the reflector of the secondary antenna in order to test how the system works with an important Signal-to-Noise Ratio (SNR) degradation. **(b)** Secondary receivers’ detail. The first secondary receiver (corresponding to the nominal baseline) is pointed towards the reflector in order to have a proper SNR. The second secondary receiver feeder horn antenna is pointing directly towards the satellite, causing an important degradation in the SNR. Figure 5: September–October 2019. Interferometric phase measurements corresponding to the Astra 1M satellite transmitting DVB-S TV broadcasting signals from a 19.2°E longitude station. Despite the magnitude of the correlation dropping dramatically due to the SNR degradation, the quality of the phase information remains unaltered (RMSD 0.18 rad). This demonstrates the robustness of the system, allowing it to work with weak signals. fluctuations around noon indicates an atmospheric turbulence origin, taking into account the warm air temperatures (above 22 \({}^{\circ}\)C) and high relative humidity (96%) during the days of the acquisition. Figure 6 shows a comparison between the experimental phase data, obtained with the interferometric measurement system, and the simulated data, obtained from the North American Aerospace Defense Command (NORAD) Two-Line Element (TLE) set information propagated with the geosynchronous dynamical model described in Section 2.2. The right axis of the figure shows the Solar Radiation (SR) measurements obtained from an automatic weather station next to the site where the interferometric system is deployed, in Zona Universitaria (Barcelona). The station is property of Servei Meteorologic de Catalunya, and the data were validated by their team. During sunny days (solar radiation higher than 600 W/m\({}^{2}\)), the troposphere is turbulent, and it generates noisy observations. Moreover, temperature effects on the experimental measurements are very significant when the solar radiation is highest, causing an important deviation from the simulated data. On the other hand, during the night and cloudy days (solar radiation lower than 600 W/m\({}^{2}\)), it remains more steady and the measurements are cleaner, showing a good fit between the experimental and simulated data. Hence, the system must be designed in order to minimize the impact of temperature drifts, in particular minimizing the length and solar exposure of radiofrequency cabling. In summary, the most notable phase perturbations are caused by temperature and atmospheric effects. The errors caused by the limited SNR of the system are not comparable since they undergo two stringent filters, which reject most of the noise: the large processing gain of the correlator and the GEO dynamical model. Figure 6: Detail of four days of interferometric measurements. R\({}_{\rm 1M}\) and R\({}_{\rm 2M}\) correspond to the baselines formed by the main antenna and the Secondary 1 and Secondary 2 receivers, respectively. Phase measurements (experimental and simulated) are referenced to the left axis. Solar Radiation (SR) measurements are referenced to the right axis. The experimental data, obtained with the interferometric measurement system, are compared against the simulated data, obtained from the North American Aerospace Defense Command (NORAD) Two-Line Element (TLE) information and the geosynchronous orbital model. During sunny days (SR higher than 600 W/m\({}^{2}\)), the troposphere is turbulent, which increases the interferometric phase random fluctuations. Moreover, temperature effects on the experimental measurements are very significant when the solar radiation is highest, causing deviations from the simulated data. On the other hand, during the night and cloudy days (SR lower than 600 W/m\({}^{2}\)), the phase measurements are cleaner, showing a better fit between experimental and simulated data.