We present BKG´s current activities in the field of combined data processing of different space-geodetic techniques. The primary goal of the combined analyses is the improvement of the consistency between the techniques through common parameters, mainly Earth Rotation Parameters (ERP), and thereby to improve also the resulting ERPs. In previous studies, we have investigated different combination approaches using VLBI and GNSS data and generated ERP series with latencies of about 1-2 or 14 days, depending on the input data used. In this way, we achieved a significant improvement in accuracy, especially for the dUT1 series, compared to the individual technique-specific solutions. The processing is based on datum-free normal equations (provided via SINEX files), which allow a rigorous combination on the normal equation level instead of the observation level.

Our current activities in the area of multi-technique combination are focused on augmenting the combination of GNSS and VLBI data with SLR data. It is expected that the SLR technique has the potential to improve the combined ERP solution, especially the highly variable dUT1 parameter, by providing a stable LOD contribution. Due to its short latency of about 1 day, the SLR-DAILY product is basically well suited to expand the database of our Rapid EOP series, which is currently only based on GNSS Rapid and VLBI Intensives data. However, the official SLR-DAILY product of the ILRS is a 7-day solution that explicitly contains polar motion (only as constant offsets over 24 hours) and LOD, but no dUT1 parameters and no polar motion rates. Therefore, this solution is not optimal for our combination approach because the parameterization of the ERPs is not identical to the other techniques that uses offsets and rates for all ERPs. However, the in-house ILRS Analysis Center allows us to generate a customized SLR solution that has an improved parameterization of the ERPs and, thus, is optimized for the multi-technique combination. We investigated the SLR data with respect to the quality of the resulting ERP series and integrated the data into our combination process. We present the impact of SLR on the combined ERP product and the challenges of extending the combination with this data.

How to cite: Klemm, L., Thaller, D., König, D., Flohrer, C., and Walenta, A.: Consistently combined Earth Rotation Parameters at BKG - Adding SLR data to VLBI and GNSS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9457, https://doi.org/10.5194/egusphere-egu24-9457, 2024.

Accurate knowledge of the Earth’s orientation and rotation in space is essential for a broad variety of scientific and societal applications such as near-Earth and deep space navigation, global positioning and satellite orbit determination as well as monitoring geodynamics and climate change phenomena. Consequently, an essential basis for any of the above-mentioned applications is the accurate determination and prediction of Earth Orientation Parameters (EOP), which describe the instantaneous relation between reference frames fixed to the Earth and to inertial space at any epoch. High-precision EOP are determined by combining the observations of four different geodetic space techniques.

Due to different standards for the processing of the observations – most notably the parameterisation of the EOP in the observation-type-specific processing softwares – current EOP combination approaches lack consistency. Such inconsistencies represent a major limiting factor of today’s accuracy of determined EOP as well as of short-term EOP predictions, which are an essential prerequisite for any application in (near-)real time.

This study identifies current deficiencies that limit the consistency and achievable accuracy of combined EOP series. It provides recommendations on how to improve the parameterisation and processing standards of the technique-specific input, and it outlines strategies to achieve a more consistent and accurate EOP combination. The proposed processing strategies shall serve as a basis for improved EOP prediction algorithms in a later stage of the study.

How to cite: Seitz, F., Kehm, A., Bloßfeld, M., Duan, B., Hugentobler, U., and Dill, R.: Current deficiencies and potential for improvement in the realisation of consistently combined Earth Orientation Parameter time series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14969, https://doi.org/10.5194/egusphere-egu24-14969, 2024.

The VLBI technique provides an extremely precise measurement of the geometric relationship between the receiving radio observatory and the celestial target. It utilizes methods of recording the signals at each antenna. These recordings are physically brought together and played back into a processing device, known as a correlator, which combines the signals in such a way that delivers the fundamental observables of geodetic VLBI, the time delays between signals arriving at the individual antennas as a function of time. Nowadays, numerous correlator software and strategies are employed which may result in inconsistencies on the geodetic products.

In this study, we empirically assess the consistency between the different correlators by analyzing the R1/R4 VLBI sessions from 2002 to 2022 to reflect the impact on the EOP estimates. To compare the different pairs of EOP time series estimates, we calculated the Weighted Mean (WM) of the differences and the Weighted Root Mean Square (WRMS) differences between each of them. Besides, we empirically evaluate the consistency, systematics, and deviations of the IAU 2006/2000A precession-nutation model using several CPO time series derived from the different correlators, providing a new set of empirical corrections to the precession offsets and rates, and to the amplitudes included in the nutation models. Finally, we study the impact on the estimation of new free core nutation (FCN) models.

This research was supported partially by Generalitat Valenciana (SEJIGENT/2021/001) and the European Union—NextGenerationEU (ZAMBRANO 21-04); and also by Spanish Projects PID2020-119383GB-I00 funded by Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033/) and  PROMETEO/2021/030 funded by Generalitat Valenciana.

How to cite: Belda Palazón, S., Karbon, M., Escapa, A., Ferrándiz, J. M., Azcue, E., Moreira, M., and Modiri, S.: Consistency assessment of EOP estimated by different VLBI correlators, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16150, https://doi.org/10.5194/egusphere-egu24-16150, 2024.

One of the key determinants influencing the accuracy and reliability of Earth Orientation Parameters (EOP) is the network Very Long Baseline Interferometry (VLBI) geometry. VLBI is a high-precision radio astronomy technique that involves multiple radio telescopes spread across the globe, working together as a network. The geometric configuration of these telescopes plays a crucial role in the quality of the data collected and, consequently, the accuracy of EOP measurements. The distribution and arrangement of the VLBI network antennas impact the triangulation process used to determine the positions of celestial radio sources, contributing to the calculation of Earth's rotation parameters. An optimal VLBI geometry ensures a well-constrained and robust observational setup, leading to more precise EOP results crucial for many scientific applications.

In this study, we analyze the impact of using different VLBI networks on the EOP estimation. Due to its nature the Continuous VLBI Campaigns (CONT) give a good basis to investigate these effects. For this purpose, we artificially create different networks with distinct configurations (e.g. removing VLBI antennas located in the northern hemisphere and vice versa, taking out the longest north-south baselines or the east-west baselines…). This sensitivity analysis will contribute to the refinement of the EOP and will help to fulfill the stringent GGOS targets (i.e. a frame with accuracy at epoch of 1 mm or better and a stability of 0.1 mm/y).

Acknowledgment. This research was supported partially by Spanish Projects PID2020-119383GB-I00 funded by Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033); PROMETEO/2021/030 and SEJIGENT/2021/001, funded by Generalitat Valenciana; and the European Union—NextGenerationEU (ZAMBRANO 21-04).

How to cite: del Nido Herranz, L. D., Belda, S., Karbon, M., Azcue, E., Puente, V., and Ferrándiz, J. M.: Exploring the effect of different VLBI Networks on EOPs estimation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9388, https://doi.org/10.5194/egusphere-egu24-9388, 2024.

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.

How to cite: Modiri, S., Thaller, D., Belda, S., Halilovic, D., Klem, L., König, D., Bachmann, S., Flohrer, C., and Walenta, A.: Advancing EOP Prediction: Bridging the Gaps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15551, https://doi.org/10.5194/egusphere-egu24-15551, 2024.

Previous investigations have shown the potential of enhancing the accuracy of estimates of the direction of the rotational pole and velocity of rotation of the Earth by using improved pre-processing (along with improved optimal estimation codes) of atmospheric and/or ocean angular momentum data. (These data are useful for prediction of the Earth orientation parameters because of conservation of the angular momentum in the Earth system).  Recent investigations have shown that predictions of UT1 – UTC estimates can be improved by 45% for 1- day predictions and 30% for 7-day predictions. This poster is a continuation of previous efforts to investigate procedures to handle outliers in EOP input data using improved robust curve-fitting tools and improved optimal estimation tools.

How to cite: Stamatakos, N., McCarthy, D., Salstein, D., Psiaki, M., and Page, J.: Using Optimal Estimation and Robust Curve-Fitting Tools to Enhance Predicted Earth Angular Momentum for Earth Orientation , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3582, https://doi.org/10.5194/egusphere-egu24-3582, 2024.

Since more than 15 years, GFZ routinely provides daily updated hydrological effective angular momentum functions (HAM) and its 6 days-long forecasts for the study of Earth orientation parameter variability and for improving polar motion and UT1-UTC predictions. GFZ’s HAM time series are part of a consistent set of effective angular momentum functions (EAM) covering the Earth’s major subsystems atmosphere, oceans, and the terrestrial hydrosphere. In addition, all EAM products are consistent with the GRACE/GRACE-FO atmosphere-ocean dealiasing product AOD1B release 06 which is used for gravity field processing and precise orbit determination.

For the new HAM data set we switch our hydrological model setup from the Land Surface Discharge Model (LSDM) to the open source, high-resolution hydrological rainfall-runoff-routing model LISFLOOD (https://ec-jrc.github.io/lisflood/). We slightly adapted the latest LISFLOOD 0.05° version for geodetic applications by modifying the snow melting parameterization, the soil depth parameterization, and implementing a seasonal snow storage model for Antarctica to optimize the agreement of simulated terrestrial water storage with mass anomalies from the satellite gravimetry missions GRACE and GRACE-FO on different spatial and temporal scales. Due to (I) up-to-date surface parameter maps; (ii) increased temporal resolution of 3 hours; (iii) enhanced parameterization of hydrological processes such as evapotranspiration, soil infiltration, snow accumulation and dynamic river routing; and (iv) a much more extensive set of atmospheric forcing parameters from ECMWF’s latest global atmospheric reanalysis ERA5, the derived HAM time series could be substantially improved in terms of long-term stability, seasonal amplitudes, sub-seasonal and episodic variations, and short-term forecasts. Furthermore, the new HAM data set is consistent with the new AOD1B release 07.

How to cite: Dill, R., Jensen, L., and Dobslaw, H.: New Data Set of Hydrological Angular Momentum With its Associated 6 Days-Long Forecasts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19345, https://doi.org/10.5194/egusphere-egu24-19345, 2024.

In this study, we investigate the excitation of polar motion (PM) caused by changes in the distribution of hydrosphere mass. This phenomenon is expressed through hydrological angular momentum (HAM) series, which can be estimated using global models of the continental hydrosphere, Earth's gravity field variations, and numerical climate models.

The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions have provided crucial data for understanding the time-variable gravity field affected by changes in global mass distribution. These missions also reveal how mass variations in the continental hydrosphere and cryosphere affect PM. However, it has been identified that GRACE/GRACE-FO solutions have certain limitations when determining geopotential coefficients of lower degrees. As a remedy, it has become standard practice to replace the C₂₀ values obtained from GRACE/GRACE-FO solutions with corresponding estimates from Satellite Laser Ranging (SLR). Similar substitutions are also recommended for the C₂₁ and S₂₁ coefficients.

In our study, we employ hybrid SLR+GRACE/GRACE-FO time-variable gravity solutions, made available by the Institute of Geodesy at Graz University of Technology (ITSG) and Centre National D'Etudes Spatiales (CNES), to determine hydrological/gravimetric angular momentum (HAM). To evaluate the SLR+GRACE/GRACE-FO-based HAM series, we compare them with the hydrological signal in observed PM excitation, referred to as geodetic residuals (or GAO). Additionally, we compare these series with HAM derived from GRACE/GRACE-FO data, focusing on seasonal and non-seasonal variations.

Our findings indicate that the excitation functions derived from the hybrid solution closely align with the GAO. In fact, they are similar or even better consistent with GAO than the series derived from the GRACE/GRACE-FO data.

How to cite: Nastula, J., Śliwińska-Bronowicz, J., Wińska, M., and Partyka, A.: Exploiting the SLR+GRACE/GRACE-FO Hybrid Solutions to Determine Gravimetric Excitations of Polar Motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8315, https://doi.org/10.5194/egusphere-egu24-8315, 2024.

Variations in Earth’s rotation, encompassing polar motion (PM) and the length-of-day (LOD) changes, result from a variety of factors influencing mass distribution and movement. These factors include the redistribution of air and water masses within the climate system and the solid Earth, and exchanges of angular momentum between the core and mantle. The ability to differentiate between these diverse sources is crucial for comprehending processes occurring at or near the Earth's surface, as well as within its interior.

Fluctuations in the low-degree spherical harmonic coefficients of Earth's gravitational potential are linked to the redistribution of mass on a large scale within and on the planet. Observing changes in these coefficients provides a means to investigate the movement of mass within the Earth system. The degree-2 order-0 coefficient (C₂₀) of geopotential holds particular significance for Earth rotation studies since C₂₀ variations (ΔC₂₀) are directly linked to the corresponding excitations of LOD. ΔC₂₀ can be determined from various methods, of which Satellite Laser Ranging (SLR) measurements have the longest tradition. Launching Gravity Recovery and Climate Experiment (GRACE) in 2002 and GRACE Follow-On (GRACE-FO) in 2018 brought new measurements of changes in the Earth's gravitational field, including estimates of the ΔC₂₀. However, estimates of ΔC₂₀ from GRACE/GRACE-FO have limitations due to orbital geometry, the relatively short distance between the two satellites, and tide-like aliases. In practice, GRACE/GRACE-FO computing centres replace ΔC₂₀ with an estimate from SLR measurements. Combining GRACE/GRACE-FO and SLR observations could enhance the accuracy of determining low-degree coefficients of geopotential, including ΔC₂₀, ΔC₂₁, and ΔS₂₁.

In this study, we reassess the excitation of LOD over the period 2002–2023, estimated from five different data sources: SLR, GRACE/GRACE-FO, a combination of SLR+GRACE/GRACE-FO, geodetic observations, and geophysical fluid models. To each of the time series we apply the same processing to isolate long-period, seasonal and non-seasonal short-term fluctuations. For every component, we conduct a comparative analysis aiming to evaluate the consistency among various estimates and identify discrepancies between the series. We show that combining GRACE/GRACE-FO with SLR data improves the consistency between ΔC₂₀-derived and observed LOD excitation for the studied oscillations.

How to cite: Śliwińska-Bronowicz, J., Nastula, J., Wińska, M., and Partyka, A.: Revisiting excitation of length-of-day using recent GRACE/GRACE-FO, SLR, SLR+GRACE/GRACE-FO gravity solutions and geophysical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9835, https://doi.org/10.5194/egusphere-egu24-9835, 2024.

We study coupling mechanisms at the core-mantle boundary (CMB) of the Earth in the frame of nutations and Length-of-Day (LOD) variations. The CMB is usually considered to have a smooth spherical or elliptical shape inducing a Poincaré flow in the nutation case and a global rotation in the LOD case. However, in reality, the CMB is bumpy and there are mountains and valleys representing local height differences of the order of a kilometer. The existence of a topography induces inertial waves that need to be considered in the flow of the core. This is in addition to the Poincaré fluid motion when the nutations are computed and in addition to a relative rotation of the fluid opposite and of the same amplitude as that of the mantle for LOD variations. The additional pressure and the topographic torque depend on the shape of the CMB and can be related to the spherical harmonic coefficients of the CMB topography. We follow the philosophy of the computation of Wu and Wahr [Geophys. J. Int., 128(1), 18-42, 1997] and determine the coefficients of the velocity field in the core at the CMB in terms of the topography coefficients. We used an analytical approach instead of a numerical one. We confirm that some topography coefficients may enhance length-of-day variations and nutations at selected frequencies, and show that these increased rotation variations and nutations are due to resonance effects with inertial waves in the incremental core flow. While they could be at a detectable level for LOD, they are very small for nutations (except for the flattening of the core), enhancing the importance of the electromagnetic coupling at the CMB.

How to cite: Dehant, V., Rekier, J., Puica, M., Folgueira, M., and Van Hoolst, T.: Effects of topographic coupling at core-mantle boundary in rotation and orientation changes of the Earth., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3096, https://doi.org/10.5194/egusphere-egu24-3096, 2024.