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Local VLBI-derived Vector Ties

Several old radio telescopes reach the end of their expected life time and new telescopes are erected to continue the operational VLBI observations either with the legacy S/X system or the new VGOS system. In order to take advantage of the long time series available for the old telescope, it is essential that the new telescope be tied to the old one and thus the time series be connected. A means of doing this is to implement overlap observations.

In addition to the overlap operations, however, also local tie sessions (using phase delay) should be observed between the old and the new telescopes. Furthermore, local tie surveys should augment the determination of the local tie vectors to facilitate an independent check. Here we provide a (non-exhaustive) compilation of local VLBI tie determinations.

Kokee Park.The site at Kokee Park sports two radio telescopes: a 20-m antenna and a 12-m antenna. The former has a long history of legacy S/X obervations, while the latter was built in 2015 as a new VGOS antenna. The following papers and presentations describe the efforts to determine the VLBI tie between the legacy and VGOS antennas:

  • Paper: Niell A., et al (2021), VLBI measurement of the vector baseline between geodetic antennas at Kokee Park Geophysical Observatory, Hawaii, Journal of Geodesy, doi:10.1007/s00190-021-01505-9.
  • Seminar: Niell A. (2021) VLBI tie between the legacy and VGOS geodetic antennas at Kokee Park Geophyiscal Observatory, Hawaii. Presented in the NASA GSFC Geodesy and Geophysics Laboratory Seminar series on June 15, 2021. The slides and a recording of the presentation are available on the IVS Outreach and Communications website:

Onsala.The site at Onsala supports three radio telescopes that participate in geodetic VLBI sessions: one 20-m antenna in legacy S/X sessions and two 13.2-m antennas in VGOS sessions. The VGOS twins were inaugurated in May 2017 and started to observe in VGOS sessions by the end of the same year. The Onsala group published a paper on their local tie efforts:

  • Paper: Varenius, E., Haas, R. and Nilsson, T. (2021) Short-baseline interferometry local-tie experiments at the Onsala Space Observatory. J Geod 95, 54. doi:10.1007/s00190-021-01509-5.
  • Presentation: Varenius E., Haas, R., and Nilsson, T. (2021) ONTIE: Short-baseline interferometry at Onsala Space Observatory. Presented at EVGA 2021 on March 15.

General Reviews. With more geodetic sites measuring and evaluating VLBI-derived local tie vectors, groups start to look at the results in a more holistic approach. Xu et al. published a paper with intra-site baselines for eight geodetic sites:

  • Paper: Xu, M., Savolainen, T., Bolotin, S., Bernhart, S., Plotz, C., Haas, R., Varenius, E., Wang, G., McCallum, J., Heinkelmann, R., Lunz, S., Schuh, H., Zubko, N., and Kareinen, N. (2023) Baseline Vector Repeatability at the Sub-Millimeter Level Enabled by Radio Interferometer Phase Delays of Intra-Site Baselines. J Geophys Res: Solid Earth, 128. e2022JB025198. doi.org/10.1029/2022JB025198.