VLBI-based assessment of the consistency of the conventional EOP series and the reference frames (terrestrial and celestial)

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) envisages stringent goals for the International Terrestrial Reference Frame (ITRF) realization in terms of accuracy (1 mm) and precision (0.1 mm/year). These requirements entail that the Earth Orientation Parameters (EOP) should be estimated with similar accuracy.

The conventional International Terrestrial Reference Frame (ITRF) is based on the combination of solutions from four space geodetic techniques, including observations until the end of 2020, incorporating updated data and models. On the other hand, the Celestial Reference Frame (CRF) is a VLBI-only solution based on data until 2015, provided by one sole VLBI-analysis centre. Additionally, the current conventional EOP series, IERS 14 C04, is also produced in a separate process following a different analysis and combination strategy. It is based on a combination of monthly EOP estimates obtained by the combination centres of each space geodetic technique. These disparate approaches might cause a slow degradation of the consistency among EOP and the reference frames or a misalignment of the current conventional EOP series. The recent release of the ITRF2020 brings an exciting opportunity to investigate this topic.

In this work, we empirically assess the consistency among the conventional terrestrial reference frame (TRF) and celestial reference frame (CRF), and EOP through the analysis of Very Long Baseline Interferometry (VLBI) historical data, taking different TRFs as alternative settings in the analysis: ITRF2020, VTRF2020, ITRF2014, and the terrestrial frame consistent with the newest Celestial Reference Frame (i.e., ICRF3). Additionally, Helmert transformations are computed to evaluate to which extent the behaviour that may be found in the previous point can be attributed to orientation differences of the TRFs themselves. Finally, different CRF realizations (ICRF2 and ICRF3) are tested to study their impact on the EOP, especially in the long term, paying attention to the appearance of biases and trends among the EOP series.

This study allows evaluation if the selection of the TRFs and/or the CRFs has a significant impact on the consistency of the estimated EOP and assesses its agreement with the conventional EOP series.