Abstract
We present results from observation, correlation and analysis of interferometric measurements between the three geodetic very long baseline interferometry (VLBI) stations at the Onsala Space Observatory. In total, 25 sessions were observed in 2019 and 2020, most of them 24 h long, all using X band only. These involved the legacy VLBI station ONSALA60 and the Onsala twin telescopes, ONSA13NE and ONSA13SW, two broadband stations for the next-generation geodetic VLBI global observing system (VGOS). We used two analysis packages: nu Solve to pre-process the data and solve ambiguities, and ASCOT to solve for station positions, including modelling gravitational deformation of the radio telescopes and other significant effects. We obtained weighted root mean square post-fit residuals for each session on the order of 10–15 ps using group-delays and 2–5 ps using phase-delays. The best performance was achieved on the (rather short) baseline between the VGOS stations. As the main result of this work, we determined the coordinates of the Onsala twin telescopes in VTRF2020b with sub-millimetre precision. This new set of coordinates should be used from now on for scheduling, correlation, as a priori for data analyses, and for comparison with classical local-tie techniques. Finally, we find that positions estimated from phase-delays are offset sim +3 mm in the up-component with respect to group-delays. Additional modelling of (elevation dependent) effects may contribute to the future understanding of this offset.
Highlights
Geodetic very long baseline interferometry (VLBI) is a space geodetic technique that is of major importance (Bachmann et al 2016) for the International Terrestrial Reference Frame (ITRF) (Altamimi et al 2016)
ON frequency channels were recorded as upper sideband (USB) while OE and OW data were recorded as lower sideband (LSB)
After fringe-fitting, the obtained VLBI delay observations were exported to the so-called VGOS databases (vgosDb) format (Bolotin et al 2015) that can be read by standard geodetic VLBI analysis software packages
Summary
Geodetic very long baseline interferometry (VLBI) is a space geodetic technique that is of major importance (Bachmann et al 2016) for the International Terrestrial Reference Frame (ITRF) (Altamimi et al 2016). Since 1979, the 20-m-diameter radio telescope, ONSALA60 (ON), is used for geodetic VLBI and contributes regularly to the observing program of the International VLBI Service for Geodesy and Astrometry (IVS). In order to use the new VGOS telescopes and observations together with the other existing space geodetic observations, the so-called local-tie vectors between the reference points of the new and the previously existing instrument have to be determined. In the case of co-located instrumentation of the same space geodetic technique, technique-inherent observations can be used to determine the local-tie vectors For this purpose, we performed during 2019 and 2020 a series of short-baseline local interferometry campaigns with the three co-located geodetic VLBI stations at Onsala, i.e. ON, OE and OW.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
