Understanding Earth's orientation parameters (EOP) is paramount for unraveling intricate mass redistribution, gravitational interactions, and geodynamic processes within the Earth's system. With a growing interest in EOP across diverse scientific disciplines such as Earth science, astronomy, and climate change studies, the demand for accurate and timely real-time information has become increasingly crucial. This is particularly evident in applications like satellite navigation, interplanetary spacecraft tracking, and weather forecasting. Despite the precision enabled by modern space geodetic techniques (e.g., Very Long Baseline Interferometry - VLBI, Global Navigation Satellite Systems - GNSS, and Satellite Laser Ranging - SLR), the complexity of data processing and associated delays necessitates significant progress in EOP prediction, especially for applications requiring timely information. This study addresses these challenges by introducing a redesigned prediction package that effectively bridges the gap between observational data and final estimated products. Utilizing a sophisticated combination of deterministic and stochastic methods, our prediction algorithm is applied to both the official International Earth Rotation and Reference Systems Service (IERS) EOP series and the Federal Agency for Cartography and Geodesy (BKG) single-specific and combined technique time series. The results of this study make a significant contribution to efforts that aim to enhance the accuracy of predicted Earth Orientation Parameters (EOP). By thoroughly exploring the selection of input data and prediction methods, our research strives to improve the dependability of EOP forecasts, especially for short-term predictions. By tackling crucial challenges in the field, this work not only deepens our understanding of Earth's dynamic processes but also opens doors for more accurate and timely applications across various scientific disciplines that rely on EOP data.

Real-time Earth Orientation Parameters (EOP) are crucial in various space geodetic applications, from satellite navigation to weather forecasting. This study introduces a refined prediction package leveraging diverse EOP series from the Federal Agency of Cartography and Geodesy (BKG), including rapid and final series, Satellite Laser Ranging (SLR) series, and International Earth Rotation and Reference Systems Service (IERS) C04. Our approach yields substantial improvements in EOP prediction accuracy. Results highlight superior performance in critical parameters such as Polar Motion, (UT1-UTC) dUT1, and Length of Day (LOD) predictions. Notably, our predictions surpass benchmarks from the Second EOP Prediction Comparison Campaign (2nd EOP-PCC)” organized by International Association of Geodesy (IAG) and IERS, showcasing the effectiveness of our methodology. Additionally, BKG’s Rapid EOP stands out with remarkable accuracy, featuring a shorter latency of 1 to 2 days. This study contributes to our understanding of Earth’s rotational dynamics. It provides practical advancements in real-time EOP predictions, demonstrating the potential impact on a wide range of scientific and operational applications.

Variations in Earth orientation parameters (EOP) are related to mass redistribution, gravitational, and geodynamic processes in the Earth system and have gained a great deal of attention in Earth science, astronomy, and climate change studies. In addition, real-time EOP information is needed for many space geodetic applications, including satellite navigation from the ground and low-Earth orbit, like tracking interplanetary spacecraft and forecasting the weather. Currently, the EOP can be estimated at the best possible accuracy with modern high-precision space geodetic techniques like Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), and Satellite Laser Ranging (SLR). However, the complex nature of data processing and the time it takes to process it always lead to delays. Consequently, predicting EOP is of great scientific and practical importance. Accordingly, several methods have been developed and applied to EOP prediction. In spite of this, the accuracy of EOP still needs to meet our expectations, even for forecasts of a few days into the future. We will therefore have to face two major challenges in order to provide the best prediction data: which input data to use and which prediction methods are superior to others. In order to answer these two questions, new methods or a combination of existing approaches are investigated to improve the accuracy of the predicted EOP time seires. Such in-depth investigations are currently conducted within the “Second EOP Prediction Comparison Campaign (EOP-PCC)” organized by IAG and IERS. In this study, we investigate a redesigned prediction package (input data and method) to improve the possibility of bridging the existing gap between the observation and the final estimated product.We will briefly present our contribution to EOP-PCC and illustrate the result of EOP data obtained from single space geodetic techniques provided by the department of geodesy at BKG. Then, we run our prediction algorithm with the official IERS EOP series and our BKG’s single-technique analysis products for VLBI and SLR using the combination of a deterministic and a stochastic method and compare it with different prediction techniques. Finally, we will show the potential of using a combination of VLBI and GNSS techniques to obtain real-time EOP estimates.

The ITRF2020 is the upcoming realization of the International Terrestrial Reference Frame. As the successor of the ITRF2014, it is based on an inter-technique combination of all four space-geodetic techniques, i.e., VLBI, GNSS, SLR and DORIS, and it is based on contributions from different institutions around the world. In this context, the Combination Centre of the International VLBI Service for Geodesy and Astrometry (IVS) – operated by the Federal Agency for Cartography and Geodesy (BKG, Germany) and the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM, Germany) – generates the VLBI intra-technique combination for ITRF2020 utilizing the individual contributions of multiple IVS Analysis Centres (AC). For the contribution to the ITRF2020 solution, sessions containing 24h VLBI observations from 1979 until the end of 2020 are reprocessed by 11 ACs and submitted to the IVS Combination Centre. All individual sessions include datum-free normal equations containing station coordinates and source positions as well as full sets of Earth Orientation Parameters (EOP) in the required SINEX format. For ensuring consistently combined solutions, time series of EOP and station coordinates, as well as a VLBI-only Terrestrial Reference Frame (VTRF), have been investigated. This contribution focuses on detailed investigations concerning the session-dependency of the scale and the impact of the individual AC contributions to the combination. Thereby significant differences of the scale estimates from the different session types are investigated. Also, the evaluation of the ACs’ contributions to the combined solution will be presented.

The ITRF2020 will be the next official solution of the International Terrestrial Reference Frame and the successor of the currently used frame, i.e., ITRF2014. Based on an inter-technique combination of all four space geodetic techniques VLBI, GNSS, SLR and DORIS, contributions from different international institutions lead to the global ITRF2020 solution. In this context, the IVS Combination Centre operated by the Federal Agency for Cartography and Geodesy (BKG, Germany) in close cooperation with the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM, Germany) generates the final contribution of the International VLBI Service for Geodesy and Astrometry (IVS). Thereby, an intra-technique combination utilizing the individual contributions of multiple Analysis Centres (AC) is applied. For the contribution to the upcoming ITRF2020 solution, sessions containing 24h VLBI observations from 1979 until the end of 2020 are processed by 10 to 12 ACs and submitted to the IVS Combination Centre. The required SINEX format includes datum-free normal equations containing station coordinates and source positions as well as full sets of Earth Orientation Parameters (EOP). For ensuring a consistently combined solution, time series of EOPs, source positions and station coordinates as well as a VLBI-only Terrestrial Reference Frame (VTRF) and a Celestial Reference Frame (CRF) were generated and further investigated. One possibility to assess the quality of the IVS contribution to the ITRF2020 solution is to carry out internal as well as external comparisons of the estimated EOP. Thereby, estimates of the individual ACs as well as external time series (e.g. IERS C04, Bulletin A, JPL-Comb2018) serve as a reference. The evaluation of the contributions by the ACs, the combination procedure and the results of the combined solution for station coordinates, source positions and EOPs will be presented.

In this article we investigate the impact of different realizations in framework of the generation of the International Terrestrial Reference Frame (ITRF), Earth Orientation Parameters (EOP), and scale resulting from Very Long Baseline Interferometry (VLBI) intra-technique combination. The first section reviews the input contribution of the International VLBI Service for Geodesy and Astrometry (IVS) to the ITRS realizations. The second section shows the results of using the three different inter-technique combined ITRS realizations as a priori station coordinates in the IVS combination process. We found significant differences in the scale when comparing the results to the respective a priori frames DTRF2014, ITRF2014, and JTRF2014. The scale differences are -0.01 ppb for DTRF2014, -0.59 ppb for ITRF2014, and 0.19 ppb for JTRF2014, with residual WRMS of 0.88 ppb for DTRF2014, 0.95 ppb for ITRF2014, and 0.78 ppb for JTRF2014. In terms of EOP, the differences of using DTRF2014, ITRF2014, and JTRF2014 as a priori values for station coordinates are less distinct. We found differences in particular parameters, i.e. x-pole, y-pole, LOD, and dUT1, using the three different TRS realizations as a priori station coordinates. However, the differences do not emphasize one or another ITRS realization as preferable TRF for VLBI combination. Moreover, we found significant differences in dUT1 when using IERS 08C04 or IERS 14C04 as EOP reference series, which might indicate inconsistencies between these two reference series. Introduction In this chapter we review the IVS contribution to the ITRF2014 and the adjunctive combination process before investigating the impact of the three ITRS realizations on VLBI combined Earth Orientation Parameters (EOP) and scale. The scale parameter is particularly interesting, as VLBI – together with Satellite Laser Ranging (SLR) – are the only space geodetic techniques with reliable access to this parameter. In the framework of the latest realization of the International Terrestrial Reference System (ITRS), each of the three ITRS Combination Centers of the IERS (DGFI-TUM, IGN, JPL) provides an inter-technique combined terrestrial reference frame (TRF) using different station coordinate parameterizations. DGFI-TUM provides the DTRF2014, using a piecewise linear station model with improved geophysical modeling of loading deformation (Seitz et al., 2016). The official ITRF solution, ITRF2014, is provided by IGN, using a piece-wise linear station model and an additional post-seismic deformation model (Altamimi et al., 2016). Finally, JPL provides the JTRF2014, using Kalman filtered weekly estimations of station coordinates with the noise of the time-series triggered by geophysical loading models (Abbondanza et al., 2017). In the following sections the internal VLBI evaluation of the scale parameter is discussed, then we compare the scale parameter between the combined solution resulting from the VLBI-only combination using

In this paper we investigate the impact of using the three ITRS realizations DTRF2014, ITRF2014, and JTRF2014 as a priori TRF for the VLBI combination on EOP and scale. The scale factor between the IVS routine combined solution and DTRF2014, ITRF2014, and JTRF2014 shows a significant offset of −0.59 ppb with respect to ITRF2014 and of 0.19 ppb with respect to JTRF2014. No significant offset was found for the DTRF2014-based solution. The investigation of the EOP of all four TRF-based solutions (DTRF2014-, ITRF2014-, JTRF2014- and VTRF2015q2-based) shows specific effects when comparing to the reference time series IERS 14C04, IGS, and ILRS. Relative to the VTRF2015q2-based solution, x-pole differences with respect to the DTRF2014-based solution (positive trend) and JTRF2014-based solution (scatter and negative trend), as well as an offset concerning the y-pole for all three TRF-based solutions with an additional scatter for the JTRF2014-based solution are recognized. No significant differences were found for pole rates, nutation, and LOD, but using ITRF2014 or JTRF2014 leads to marginal larger scatter with respect to the VTRF-based EOP series for LOD. In addition, a significant impact was found when comparing dUT1. All three TRF-based solutions show a significant offset comparing to IERS 14C04, whereas no offset is detected for the VTRF2015q2-based solution.

The next realization of the International Terrestrial Reference System, the ITRF2014, was released in the beginning of 2016. The VLBI input to ITRF2014 was provided by the International VLBI Service for Geodesy and Astrometry (IVS) and consists of a combination of all Analysis Center contributions. One of these single solutions was contributed by the Vienna Special Analysis Center of the Department of Geodesy and Geoinformation at TU Wien. In this paper we describe the characteristics of the Vienna contribution (calculated using the Vienna VLBI Software VieVS) to ITRF2014 and VTRF2014, respectively. We give a documentation of the included sessions and stations as well as some statistical information which shows the performance of the Vienna contribution compared to the other contributions in the IVS combination. In addition to that, a single TRF solution, VieTRF2014a, which is based on the Vienna input to ITRF2014, is presented and compared to previous TRF solutions. By and large the Vienna contribution does not exhibit any outstanding features when compared to the other submissions, except for the Earth rotation component dUT1, which shows large residuals with respect to the combined solution. The reason for this discrepancy is probably the different parameterization of EOP in VieVS as piecewise linear offsets, necessitating a transformation prior to the combination.

The consistent estimation of terrestrial reference frames (TRF), celestial reference frames (CRF) and Earth orientation parameters (EOP) is still an open subject and offers a large field of investigations. Until now, source positions resulting from Very Long Baseline Interferometry (VLBI) observations are not routinely combined on the level of normal equations in the same way as it is a common process for station coordinates and EOPs. The combination of source positions based on VLBI observations is now integrated in the IVS combination process. We present the studies carried out to evaluate the benefit of the combination compared to individual solutions. On the level of source time series, improved statistics regarding weighted root mean square have been found for the combination in comparison with the individual contributions. In total, 67 stations and 907 sources (including 291 ICRF2 defining sources) are included in the consistently generated CRF and TRF covering 30 years of VLBI contributions. The rotation angles \(A_1\), \(A_2\) and \(A_3\) relative to ICRF2 are −12.7, 51.7 and 1.8 \({\upmu }\) as, the drifts \(D_\alpha \) and \(D_\delta \) are −67.2 and 19.1 \(\upmu \) as/rad and the bias \(B_\delta \) is 26.1 \(\upmu \) as. The comparison of the TRF solution with the IVS routinely combined quarterly TRF solution shows no significant impact on the TRF, when the CRF is estimated consistently with the TRF. The root mean square value of the post-fit station coordinate residuals is 0.9 cm.

The contribution of the International VLBI Service for Geodesy and Astrometry (IVS) to the ITRF2014 generation is presented. The ITRF2014 is an inter-technique combined product of the IERS ITRS Center, combining contributions from the four space geodetic techniques -DORIS, GNSS, SLR, and VLBI. The VLBI contribution is provided by the IVS Combination Center at the German Federal Agency for Cartography and Geodesy (BKG), and is comprised of station coordinates and Earth Orientation Parameters derived from data collected between 1979 and 2014. The status and results of the IVS contribution, as well as a comparison with other space geodetic techniques, are shown.

Very Long Baseline Interferometry (VLBI) is a primary space-geodetic technique for determining precise coordinates on the Earth, for monitoring the variable Earth rotation and orientation with highest precision, and for deriving many other parameters of the Earth system. The International VLBI Service for Geodesy and Astrometry (IVS, http://ivscc.gsfc.nasa.gov/) is a service of the International Association of Geodesy (IAG) and the International Astronomical Union (IAU). The datasets published here are the results of individual Very Long Baseline Interferometry (VLBI) sessions in the form of normal equations in SINEX 2.0 format (http://www.iers.org/IERS/EN/Organization/AnalysisCoordinator/SinexFormat/sinex.html, the SINEX 2.0 description is attached as pdf) provided by IVS as the input for the next release of the International Terrestrial Reference System (ITRF): ITRF2014. This is a new version of the ITRF2008 release (Bockmann et al., 2009). For each session/ file, the normal equation systems contain elements for the coordinate components of all stations having participated in the respective session as well as for the Earth orientation parameters (x-pole, y-pole, UT1 and its time derivatives plus offset to the IAU2006 precession-nutation components dX, dY (https://www.iau.org/static/resolutions/IAU2006_Resol1.pdf). The terrestrial part is free of datum. The data sets are the result of a weighted combination of the input of several IVS Analysis Centers. The IVS contribution for ITRF2014 is described in Bachmann et al (2015), Schuh and Behrend (2012) provide a general overview on the VLBI method, details on the internal data handling can be found at Behrend (2013).