Celebrating 40 years of astrometric and geodetic VLBI data – a solid foundation for celestial and terrestrial reference frames

Abstract

Very Long Baseline Interferometry (VLBI) is a measurement technique at radio wavelengths, which is used - among others - for astrometric and geodetic purposes providing a unique source of data for the creation of global celestial and terrestrial reference frames. Furthermore, it is the only measurement technique that provides the full set of Earth orientation parameters, which describe the connection between the two reference frames. In this talk, I introduce the latest VLBI celestial and terrestrial reference frames VIE2022 computed at TU Wien which include VLBI data until December 2022. They can be seen as an extension of the current International Celestial and Terrestrial Reference Frames, the ICRF3-sx and ITRF2020, which incorporate the VLBI observations at the standard S/X band frequencies (2.3/8.4 GHz) until March 2018 (ICRF3-sx) and December 2020 (ITRF2020). In the framework of the K band collaboration, a celestial reference frame at the frequency 24 GHz is also estimated at TU Wien. Over 99% of the K band single frequency data are produced by the Very Long Baseline Array (VLBA), which induces challenges in the data analysis connected to the geometry of the telescopes placed in the territory of United States. Furthermore, the latest terrestrial reference frames incorporate data from the novel VLBI Global Observing System (VGOS) which is based on the broadband delay using several frequency bands in the range from 2.5 to 14 GHz. The first test sessions were run in December 2017 and the regular observations started in January 2019. The challenges adherent to the position estimation of the newly built VGOS telescopes are addressed.