Position change of the northernmost VLBI telescopes in Ny-Alesund, Svalbard

Abstract

Very Long Baseline Interferometry (VLBI) is a space geometric observing technique, the goal of which is to monitor the kinematics of interest points on Earth and in space. The observing instruments of VLBI are approximately 40 radio telescopes distributed throughout the world that simultaneously receive electromagnetic radiation emitted by compact objects in space, such as quasars. This technique has applications in geodesy, astrometry and astronomy (Nothnagel et.al., 2023). This master thesis aimed to analyze time series data from two of the northernmost VLBI telescopes, namely Nyales20 and Nyale13s, which are located in Svalbard, Norway. The thesis provided position time series data for both stations, which helped us to understand their position over the study period; to determine whether they exhibit discrepancies, especially in height biases; and finally, to analyze whether these changes could be related to factors such as glacier melting. Furthermore, this thesis evaluated the availability of sufficient parallel sessions for transferring velocity information from the legacy system (Nyales20) to the VGOS new generation (Nyale13s); then, it analyzed whether extending the working time of the legacy telescope Nyales20 is beneficial even though its working timespan has surpassed 30 years. Finally, this thesis compared the observed uplift trends from the VLBI and GNSS time series. The analysis was conducted using the Vienna VLBI Software (VieVS), which is a VLBI analysis software for geodesy and astrometry. Additionally, Vienna Scheduling software (VieSched++), which is part of VieVS, was used to generate and simulate IVS-R1 and IVS-R4 schedules, to address the objective of this study concerning the prolongation consideration of the legacy telescope Nyales20.The real data sets were directly downloaded in open-source vgosDB format, which is the IVS standard format for storing, transmitting, and archiving VLBI data (Webiste: NASA Earth Data). The results revealed height biases in the VLBI and GNSS time series data with respect to a priori catalog positions. This supported geophysical processes (e.g., glacier melting) as potential contributing factors. Furthermore, based on the velocities obtained for both stations, while also considering the number of parallel sessions (77 sessions), we were able to confirm that the transfer of velocities from the legacy telescope Nyales20 to the VGOS telescope Nyale13s can be achieved. Finally, addressing the impact of the Nyales20 telescope, our analysis revealed that excluding Nyales20 telescope led to an increase in mean formal error and repeatability values of several percent for Earth orientation parameters. This suggests that maintaining both telescopes within the network enhances accuracy. However, economic concerns and safety reasons influenced the decision to dismantle Nyales20 on August 14, 2023 (Garcia-Espada et.al., 2022). Despite its positive impact on quality of the data, the practical implications encourage its cancellation.