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In recent years several sets of potential corrections to the current precession and nutation models IAU2006 and IAU2000 have been obtained by different teams, in whose derivation have participated a number of members of the IAU/IAG JWG on Improving theories and models of Earth rotation (ITMER). It was created to assist the development of the 2019 Resolution 5 of the IAG and has worked in close cooperation with IERS and GGOS through the participation in their 2019 and 2022 Unified Analysis Workshops, and also got an IAU high support with the approval of its 2021 Resolution B2.Regarding forced nutations, most sets of corrections are simply obtained by a refit of some lunisolar nutations. On the other hand, the sets derived by us include also corrections to the nutations of planetary origin. These corrections are far from being irrelevant, since their effect on the weighted root mean square of the celestial pole offsets series is comparable to that of the lunisolar terms.As for the free core nutation, most models follow the well-known sliding window approach that provides more insight into the underlying physics, although alternative approaches, like the multiband one, also may reduce the variance.The different teams have used various methodologies and basic input data. Our approach pays more attention to ordinary VLBI solutions, looking for minimizing the numerical effects that appear in the derivation of daily CPO series.This contribution presents a summary of the performance of those sets of potential corrections, including their behavior in VLBI data analysis., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

At present, the most precise method for obtaining reliable observations of Celestial Pole Offsets (CPO) is through the use of Very Long Baseline Interferometry (VLBI). The CPO data includes a variety of components, such as the free core nutation (FCN), trends, and harmonics, which result from shortcomings in the IAU 2006/2000A precession-nutation model, geophysical disturbances and observational noise. In consequence, the possibility of forecasting CPO is limited. One possible step forward in improving these predictions is to utilize more sophisticated models. On the other hand, there is a compelling need to identify next-generation time-series algorithms to be integrated into an operational processing chain to make advanced CPO predictions. Of specific interest is the emergence of machine learning regression algorithms.The goal of this study is to advance our understanding of CPO prediction developing new models/methodologies/tools. With the support of UAVAC (University of Alicante VLBI Analysis Center), we perform a global VLBI analysis to determine empirical corrections to the precession offsets and rates, and to the amplitudes of a wide set of terms included in the IAU 2006/2000A precession-nutation theory. Additionally, we explore new strategies to get more precise FCN models. Finally, based on these empirical corrections and novel FCN models, we use a diversity of advanced machine learning regression algorithms to make CPO prediction ranging from 1 to 365 days. The performance of the trained machine learning models is investigated by comparing their predictions vs. the corrected/updated CPO time series. The validation results suggests that the trained models produce reliable estimates., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The positions of the radio sources in the ICRF3 catalog, representing the newest realization of the Celestial Reference Frame (CRF), are given as a time invariant coordinate pair. However, systematic changes of source positions at different spacial and temporal scales are well documented. Failing to acknowledge such source behavior might lead to a deterioration in the quality of the frame, and thus in all derived variables, e.g. the orientation parameters of the Earth (EOP). One approach to overcome these shortcomings is the parametrization of source positions, similar to what is applied to the positions of the station. We present a feasible approach to parameterize all the source positions observed within the IVS data archive and produce a celestial reference frame based thereon, together with a list of consistent defining sources. We compare the resulting frame with the conventional ICRF3 as well as the Gaia frame to uncover eventual deformations and their origin. Further we examine the resulting EOP and station positions and give an evaluation of the precision and accuracy of the parameters.

RAEGE (Red Atlántica de Estaciones Geodinámicas y Espaciales / Rede Atlântica de Estações Geodinâmicas e Espaciais) commenced in 2011 with a Memorandum of Understanding between the Governments of Azores and Spain to set up a Very Long Baseline Interferometry VLBI observing network consisting of four antennas situated at Yebes near Madrid, and on the islands of Santa Maria, Gran Canaria and Flores, to meet the international requirements needed for VGOS, the VLBI Global Observing System. Currently the VGOS-antennas at Yebes and Santa Maria are operational, the other two are in the planning stage.The key feature of this network is its distribution over three tectonic plates (Eurasian, African and NorthAmerican), which will augment the estimates of the movements between the plates, both in direction and speed and thus improve the TRF (Terrestrial Reference Frame). Major improvements are expected for constraining the rotational component of the African plate, where we have currently only one VLBI station in South Africa and a very sparse network of about 30 IGS-GNSS antennas over the entire continent. Within this study we simulate VLBI observations for all four antennas and evaluate their performance regarding the TRF as well as the EOP. In the latter chase we will also explore the capabilities of this network to independently derive dUT1, and in conjunction with selected IVS stations, the observation of the entire set of the EOP., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)