G3.5

The rapid determination of the Earth's phase of rotation, expressed through the Earth rotation parameter dUT1, is one of the core tasks of geodetic Very Long Baseline Interferometry (VLBI). To ensure a low latency between observation and analysis results, dedicated 1-hour-long VLBI sessions, so-called Intensives, are regularly observed. Two of these Intensive programs, namely INT2 and INT3, are organized and monitored by the joint IVS operation center DACH. 

Within this study, a detailed overview over the last five years of the VLBI Intensive observing programs INT2 and INT3 is provided. INT2 sessions are typically observed on Saturdays and Sundays using a single baseline and a recording rate of 256 Mbps. INT3 sessions are multi-baseline Intensives with up to five stations, observed on Mondays with a recording rate of 1 Gbps. 

Starting in 2019, the scheduling strategy of the INT3 sessions was significantly changed, leading to a reduction of the estimated average dUT1 formal errors by 25% (from (6.1 ± 2.0) µs to (4.5 ± 1.0) µs) for the 4-station network. The improvement w.r.t. dUT1 mean formal errors for the 5-station network is 45% (from (6.3 ± 1.7) µs to (3.5 ± 0.5) µs). 

The best performing INT2 baseline is observed between station MK-VLBA (USA) and WETTZELL (Germany). Mid-2020, the same change was applied for these INT2 sessions, leading to a reduction in the average dUT1 mean formal error of 44% (from (11.7 ± 5.7) µs to (6.6± 4.7) µs). 

Furthermore, comparisons of dUT1 estimates from various analysis centers w.r.t. IERS EOP C04 and JPL EOP2 are conducted. It is revealed that the previously mentioned INT2 baseline shows a bias of only -2.5 µs and 1.9 µs based on the estimates provided by the analysis centers Goddard Space Flight Center (GSF) and Bundesamt für Karthographie und Geodäsie (BKG), respectively, when compared with JPL EOP2. In contrast, the bias is 10.4 µs and 14.9 µs w.r.t. IERS EOP C04. 

Besides analyzing dUT1 formal errors, the latency of the dUT1 results is compared. For INT3 sessions, results are typically available within 24 hours, while it takes two to three days for INT2 sessions, due to observations occurring on weekends. This reveals that the increased data volume recorded by the up to five stations with 1 Gbps does not increase the latency of the analysis results and dUT1 estimates can be obtained within 24-hours. 

Overall, this work provides a detailed insight into the INT2 and INT3 session performances, revealing a strong positive trend in the precision of dUT1 measurements over the last few years.

How to cite: Schartner, M., Plötz, C., and Soja, B.: Investigating INT2 and INT3 VLBI session performance for the determination of dUT1, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8877, https://doi.org/10.5194/egusphere-egu22-8877, 2022.

Currently, accurate observations of the Celestial Intermediate Pole (CIP) can only be obtained by the Very Long Baseline Interferometry (VLBI) technique. The differences among the observed CIP and that derived from IAU 2006/2000A precession-nutation model are the Celestial Pole Offsets (CPO). CPO contain the free core nutation (FCN), trends, and harmonics due to limitations of IAU precession-nutation model, geophysical excitations, etc. as well as the noise of observations. FCN is a free rotational mode of the Earth and, in principle, cannot be predicted. It can be determined from CPO time series with the use of different empirical models. The development of such models, and the enhancing of the existing ones, has been suggested in the IAU/IAG Joint Working Group ”Improving Theories and Models of the Earth’s Rotation (ITMER)”, since FCN contribution is the main one of CPO. The accurate estimation of the free core nutation (FCN) period of about 430 days is a challenging prospect. Comparison of the FCN period obtained by different authors and methods shows slight discrepancies. But, is there any evidence that the period of the FCN varies with time? If so, then this would complicate making a model of it. The FCN phase drift in 2000 could be related to that, but the is no clear evidence. In this study, we tested different FCN periods using several subsets of the observed nutations derived from VLBI analysis with the purpose of finding the optimal configuration that provides the lowest residuals. That is why a large quantity of empirical FCN models were also estimated and tested with different sliding window lengths and FCN periods. This analysis could bring us significantly closer to meet the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e. 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the ITRF defining parameters.

This research was supported partially by Generalitat Valenciana (SEJIGENT/2021/001) and the European Union—NextGenerationEU (ZAMBRANO 21-04) (S.B). This research was also supported 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 (J.M.F., A.E.).

How to cite: Belda, S., Ferrándiz, J. M., Escapa, A., Modiri, S., Puente, V., Heinkelmann, R., and Schuh, H.: An empirical analysis of the free core nutation period from VLBI-based series of celestial pole offsets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9343, https://doi.org/10.5194/egusphere-egu22-9343, 2022.

We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI, GNSS and SLR data. The main goal of the combined analyses of the three different space-geodetic techniques is the improvement of the consistency between the techniques through common parameters, i.e., mainly Earth Rotation Parameters (ERPs). The combination is based on homogenized, datum-free NEQs which allow a rigorous combination on the normal equation level instead of the observation level.

Based on our previous combination studies using GNSS data and VLBI Intensive sessions on a daily and multi-day level, we generate a consistent, low-latency ERP time series with a regular daily resolution for polar motion and dUT1. We achieved in this way a significant accuracy improvement of the dUT1 time series and a slight improvement of the pole coordinates time series, comparing ERPs from the combined processing with the individual technique-specific ERPs.

In the second step, we extend the multi-day combination of GNSS and VLBI Intensive sessions by adding VLBI 24-hour sessions. The additional combination with VLBI R1/R4 data further stabilizes all ERPs twice per week and enables the estimation of high-precision ERP time series with a latency of about two weeks. With this combination approach, we obtained a further improvement in the dUT1 time series. For the pole coordinates time series, the accuracy of the estimates is almost at the same level as for the rapid combined solution.

In our recent studies, we want to investigate improvements in the representation of the ERP parameters of the VLBI 24-hour sessions. Furthermore, we want to extend the combination of GNSS and VLBI data by adding SLR sessions in order to exploit the benefit of the combination to its maximum extend. We expect that SLR improves the combined ERP solution in particular through a stable contribution of LOD. We analyse the impact of the combination on the global parameters of interest, i.e., mainly dUT1, polar motion and LOD, but also on station coordinates.

Based on the improved combination method, we intent to set up a new operational BKG-ERP product.

How to cite: Lengert, L., Flohrer, C., Girdiuk, A., Hellmers, H., and Thaller, D.: Combination of GNSS, VLBI and SLR data for consistent estimation of Earth Rotation Parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5059, https://doi.org/10.5194/egusphere-egu22-5059, 2022.

In addition to Very Long Baseline Interferometry (VLBI) the Earth rotation phase ∆UT1 can also be determined directly from Lunar Laser Ranging (LLR) data. With the other Earth Orientation Parameters (EOP) like terrestrial pole coordinates and nutation parameters, the determination of a full set of EOP is possible from LLR observations. In recent years LLR observations have been carried out with bigger telescopes (APOLLO) and at infrared wavelength (OCA, Wettzell). This resulted in a better distribution of LLR data over the lunar orbit and retro-reflectors with a higher accuracy. The aim of our recent study is to quantify, how much the EOP determination can be improved with the new high-accurate LLR data compared to previous years and if it can then be used to validate VLBI results. First, we focus on estimating ∆UT1 and terrestrial pole coordinates from different constellations such as single or multi-station data and for a different number of normal points per night. The accuracies of the results determined from the new LLR data (after 2000.0) have significantly improved, being less than 20 µs for ∆UT1, less than 2.5 mas for x_p, and less than 3 mas for y_p for nights selected from subsets of the LLR time series which have 10 and 15 normal points obtained per night. Second, we focus on the determination of corrections of the nutation coefficients to the MHB2000 model of the IERS Conventions 2010. Here we also see significant smaller correction values and accuracies with an improvement of one order of magnitude, that means accuracies better then 0.01 mas. Recent results will be presented and discussed.

This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2123 QuantumFrontiers – 390837967.

How to cite: Biskupek, L., Singh, V. V., Müller, J., and Zhang, M.: Estimation of Earth rotation parameters from Lunar Laser Ranging data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3377, https://doi.org/10.5194/egusphere-egu22-3377, 2022.

Ring lasers are now resolving the rate of rotation of the Earth with 8 significant digits. Technically they constitute a Sagnac interferometer, where a traveling wave resonator, circumscribing an arbitrary contour, defines the optical frequency of two counter-propagating resonant laser beams. Subtle non-reciprocal effects on the laser beam however, cause a variable bias, which reduces the long-term stability. Over the last two years, we have improved the performance of the G ring laser to the point that we obtain long-term stable conditions over more than 50 days. Advances in the modeling of the non-linear behavior of the laser excitation process as well as some small but signicant improvements in the operation of the laser gyroscope are taking us now right to the doorstep of the periodic part of the Length of Day signal. In this talk we outline the current state of the art of inertial rotation sensing in the geosciences. Furthermore we discuss the next steps for an enhanced stability. At this point in time there is no apparent fundamental limit of this technique in sight.

How to cite: Schreiber, K. U., Kodet, J., Hugentobler, U., Klügel, T., Brotzer, A., and Igel, H.: High Resolution Inertial Earth Sensing with Large Sagnac Interferometers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7119, https://doi.org/10.5194/egusphere-egu22-7119, 2022.

Precise positioning and navigation on the Earth’s surface and in space require accurate Earth Orientation Parameters (EOP) data and predictions. In the last few decades, the problem of EOP prediction has become a subject of increased attention within the international geodetic community, and many research centres from around the world have developed their own methods of forecasting the EOP. It is not surprising that those various predictions differ in many aspects such as accuracy and the length of the forecast horizon.

A re-assessment of the various EOP prediction capabilities is currently pursued in the frame of the 2^nd EOP PCC, which started in September 2021. The new campaign was prepared by the EOP PCC office run by the Space Research Centre of the Polish Academy of Sciences (CBK PAN) in cooperation with GeoForschungsZentrum (GFZ) and under the auspices of the International Earth Rotation and Reference Systems Service (IERS). The campaign will be continued until the end of the year 2022 and all interested scientists are invited to contribute with new predictions at any time.

In this presentation, we provide preliminary results of the 2^nd EOP PCC by focusing on the quality of EOP predictions up to 10 days into the future. The quality assessment includes metrics such as mean absolute error (MAE) and root mean square error (RMSE) for the ensemble of all predictions, but also more detailed assessments of individual predictions. The accuracy of EOP forecasts is determined using IERS 14 C04 solution as a reference. We will pay special attention to the impact of input data exploited by participants, including the Effective Angular Momentum functions.

How to cite: Nastula, J., Dobslaw, H., Śliwińska, J., Kur, T., Wińska, M., and Partyka, A.: Preliminary results from the Second Earth Orientation Parameters Prediction Comparison Campaign of the IERS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5234, https://doi.org/10.5194/egusphere-egu22-5234, 2022.

The real-time Earth orientation parameters (EOP) estimation is needed for many applications, including precise tracking and navigation of interplanetary spacecraft, climate forecasting, and disaster prevention. However, the complexity and time-consuming data processing always lead to time delays. Accordingly, several methods were developed and applied for the EOP prediction. However, the accuracy of EOP prediction is still not satisfactory even for prediction of just a few days in the future. Therefore, new methods or a combination of the existing approaches can be investigated to improve the predicted EOP. To assess the various EOP prediction capabilities, the international Earth rotation and reference systems service (IERS) established the working group on the 2nd Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC).
Our EOP prediction team provides the full set of EOP predictions weekly for one year ahead. The SSA+Copula method and the empirical free core nutation (FCN) model (named B16) are used for Earth rotation parameters and celestial pole offsets (CPO) prediction, respectively. 
Our preliminary results illustrate an improvement in EOP prediction compared to the current EOP prediction methods, especially on CPO. Additionally, the comparison with other method results indicates that the proposed techniques can efficiently and precisely predict the EOP at different terms (short, mid, and long term).

How to cite: Modiri, S., Thaller, D., Belda, S., Guessoum, S., Ferrandiz, J. M., Raut, S., Dhar, S., Heinkelmann, R., and Schuh, H.: Towards the improvement of EOP prediction: first results of the 2nd EOP PCC, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11411, https://doi.org/10.5194/egusphere-egu22-11411, 2022.

The accuracy and robustness to input data outages of near real-time estimates and short-term predictions of Earth orientation parameters (EOPs) may be enhanced by using atmosphere and ocean angular momentum data accounting for the global conservation of angular momentum in the Earth system. The US Navy Earth System Prediction Capability (ESPC) data that combines the motion and mass fields of the atmosphere angular momentum information from the NAVY Global Environmental Model (NAVGEM 1.2) with that of the ocean angular momentum information from the HYbrid Coordinate Ocean Model (HYCOM) provides a source that can be used to evaluate the nature of the possible contribution of these physical data to the operational determination of the EOPs.  The rates of change of the EOPs derived from the most recent angular momentum data are evaluated in comparison with observed values of polar motion and UT1-UTC rates from the IERS RS/PC EOP data series, and the stability of statistical models accounting for systematic errors in scaling and bias in the ESPC data was investigated.  Analyses of these data show good agreement and indicate the viability of the practical integration of the rate data alone as well as in combination with data from other techniques in the operational determination of EOPs. Two years of past ESPC data were analyzed to provide estimates of the possible precision of the resulting polar motion and UT1-UTC data.

How to cite: Stamatakos, N., McCarthy, D., Psiaki, M., and Salstein, D.: Using Atmosphere and Ocean Angular Momentum for Earth Orientation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3232, https://doi.org/10.5194/egusphere-egu22-3232, 2022.

Oceanic circulation and mass-field variability play important roles in exciting Earth’s wobbles and changes in length-of-day (ΔLOD), on time scales from days to several years. Quantifying these effects require estimates of ocean angular momentum (OAM), which are typically drawn from numerical forward models or coarse-resolution ocean state estimates. A little-tested alternative in this regard is the emerging suite of ocean reanalyses, operating at eddy-permitting horizontal resolution (1/4°) and with sequential data assimilation (DA) schemes. Here, we compute geophysical excitation series from three identically configured global ocean reanalyses that are based on the same hydrodynamic core and input data (e.g., altimetry, Argo, sea surface temperature) but different DA schemes. The resulting OAM time series are compared both with each other and with atmosphere-corrected geodetic excitation from 2007 to 2011. For periods less than 120 days, the reanalyses series typically explain 40–50% of the residual observed polar motion excitation, somewhat less than a widely used ocean state estimate. By contrast, the reanalyses’ skill in accounting for oceanic signals in ΔLOD is more varied, particularly when seasonal and longer time scales are included in the comparison. This result points to a misclosure of the global mass balance constraint among atmosphere, ocean, and terrestrial hydrology, in part depending on whether or not a specific reanalysis considers the discharge of continental freshwater into the ocean. Together, our analyses provide insight into the kinematic consistency of newly available ocean reanalyses and give a quantitative understanding of the influence of different DA schemes on OAM estimates.

How to cite: Börger, L. and Schindelegger, M.: Are ocean reanalyses useful for Earth rotation research?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4720, https://doi.org/10.5194/egusphere-egu22-4720, 2022.

Understanding the polar motion (PM) changes is one of the major tasks in geodesy. In order to understand this changes cause by internal forces, it is necessary to analyse the so called PM excitation functions of geophysical fluids layers, namely atmosphere, ocean, and land hydrology with cryosphere. The impact of atmosphere and oceans is pretty well understood, but the impact of land hydrology is not well known and the study of the Hydrological Angular Momentum (HAM) is still the main research topic in finding the agreement between observed geodetic changes in PM and geophysical ones. The study of different HAM excitations are possible, among other things, through the use and analysis of temporal gravity models, which are constantly being developed by numerous research centres around the world.

The main aim of this study is to compare the equatorial components of the PM excitation (χ1 and χ2) calculated using the ITSG (The Institute of Geodesy at Graz University of Technology) daily gravity field models (ITSG-Grace2014, ITSG-Grace2016, ITSG-Grace2018) with other daily models and reference data, in order to assess their accuracy. The comparison of successive versions of ITSG solutions (2014, 2016, 2018) will allow for the assessment of the improvement in the accuracy of the excitation functions determined on their basis. Their potential for use in future research will be evaluated. These models are an object of study due to the fact that they have a daily temporal resolution, unlike most models that offer a monthly resolution.

The ITSG-Grace models used in the study were created by researchers at Technische Universität Graz using data obtained from the GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Gravity Recovery And Climate Experiment-Follow-On) missions. The equatorial components of the PM excitation were calculated from the relationship between χ1, χ2 and degree-2, order-1 Stokes coefficients (∆C21, ∆S21) available in the ITSG-Grace models. In this study, HAM series from the LSDM (Hydrological Land Surface Discharge Model) delivered by GFZ (GeoForschungsZentrum in Potsdam) and GAO geodetic residuals, being a differences between geodetic angular momentum (GAM) and a sum of atmospheric and oceanic excitaions, provided by Observatoire de Paris were used for comparison with PM excitation series determined from ITSG-Grace models.

In order to compare the PM excitation determined from ITSG-Grace models with series obtained using other models, trends as well as seasonal and non-seasonal variations were determined. Correlations between the series, amplitude agreement and root mean square errors were calculated, on the basis of which their accuracy and relations with other models were assessed.

How to cite: Partyka, A., Nastula, J., Śliwińska, J., Kur, T., and Wińska, M.: Analysis of the polar motion excitation function based on ITSG daily models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-283, https://doi.org/10.5194/egusphere-egu22-283, 2022.

Interpretation of variations in polar motion (PM) excitation due to global mass redistribution of atmosphere, oceans, hydrosphere and cryosphere is an important task that takes place on the boundary between geodesy and geophysics. The role of Earth’s surficial fluids in PM excitation is usually assessed by analysing time series of atmospheric, oceanic, hydrological and cryospheric angular momentum (AAM, OAM, HAM and CAM, respectively). With the launch of the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions, a new era of using global gravity data to determine gravimetric excitation of PM has begun. This can be done due to linear relationship between degree-2 order-1 coefficients of geopotential and equatorial components of PM excitation.

A number of institutes around the world routinely process and deliver GRACE/GRACE-FO solutions; however, the non-negligible differences between PM excitation  estimates derived from data provided by various data centres exist. The choice of most appropriate GRACE/GRACE-FO solution for the purpose of HAM and CAM determination is a very complex task and depends on several factors like considered time period, analysed oscillation and assumed criterion of evaluation. The use of a combination of multiple GRACE/GRACE-FO solutions is a very common approach in various research tasks.

In this work, we create combined GRACE/GRACE-FO solutions to determine the total effect of HAM and CAM (HAM/CAM) on PM excitation. To do so, we use three-cornered hat method to estimate noise level of single GRACE/GRACE-FO solutions. We also consider unweighted and weighted mean of GRACE/GRACE-FO datasets as well as publicly available combined solutions such as that provided by the International Combination Service for Time-variable Gravity Field (COST-G). Our estimates of HAM/CAM based on the combined data are compared to the HAM/CAM determined from single solutions and to the hydrological plus cryospheric signal in observed (geodetic) excitation called geodetic residuals (GAO). As data form Satellite Laser Ranging (SLR) are also recommended to determine HAM/CAM, especially in the period of lack of GRACE or GRACE-FO measurements, we include SLR solutions to our analyses. Our work aims to check whether the combination of multiple solutions from different computing centres noticeable increases the compliance between HAM/CAM and GAO in several spectral bands like seasonal and non-seasonal oscillations.

How to cite: Śliwińska, J., Wińska, M., and Nastula, J.: Exploiting the combined GRACE/GRACE-FO solutions to determine gravimetric excitation of polar motion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7729, https://doi.org/10.5194/egusphere-egu22-7729, 2022.

Since 2020 a few research groups have reported new estimations of nutation amplitudes or precession parameters, usually presented as corrections to the nutation and precession theories IAU2000 and IAU2006, as well as new empirical models for the free core nutation (FCN). The main effect of those proposed corrections is reducing the unexplained variance of the celestial pole offsets (CPO) time series. The improvement of the accuracy of CPO models was encouraged by Resolution 5 of the 2019 General Assembly of the International Association of Geodesy (IAG), included among the recommendations of the GGOS/IERS Unified Analysis Workshop held that year, and also supported by Resolution B2 of the International Astronomical Union (IAU) in 2021.

The variance reduction attainable by refining the precession offsets and rates and the amplitudes of the forced nutations is noticeably larger than that resulting from the corrections needed for the consistency of the precession and nutation theories (Escapa et al 2018). However, the amount of the improvement depends strongly on the various fitting strategies, the input CPO series and the time periods chosen for benchmarking.

That fact is shown through the accuracy assessment of a selection of correction models proposed by the authors and other teams, either supplemented with FCN models or not, and for a selection of input CPO data and time spans.

How to cite: Ferrándiz, J. M., Belda, S., Juárez, M. Á., Baenas, T., Modiri, S., Heinkelmann, R., Escapa, A., and Schuh, H.: Accuracy of proposed corrections to the current precession-nutation models: A first assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4031, https://doi.org/10.5194/egusphere-egu22-4031, 2022.

The secular change in the length of day due to mass redistribution effects is revisited using the Hamiltonian formalism of the rotation of a two-layer deformable Earth. The dissipative effects at the core-mantle boundary are described through a coupling torque formulated by means of generalized forces. Taking advantage of the canonical procedure, a closed analytical formula for the secular deceleration of the rotation rate is obtained, which can be evaluated using frequency-dependent Love numbers corresponding to solid and oceanic tides.

Under the widespread assumption of totally coupled core and mantle layers in the long-term response, a secular angular deceleration of 1328.6 as/cy² is calculated, equivalent to an increase of 2.418 ms/cy in the length of day. Such an estimate is in very good agreement with recent observational values and theoretical predictions based on comparable modeling features. The complete research work can be consulted in the paper by Baenas, T., Escapa, A., and Ferrándiz, J. M. (2021), entitled “Secular changes in length of day: Effect of the mass redistribution” (A&A 648, A89).

This work has been partially supported by the 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: Escapa, A., Baenas, T., and Ferrándiz, J. M.: Secular changes in length of day induced by the redistribution potential, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3642, https://doi.org/10.5194/egusphere-egu22-3642, 2022.