G2.2 | Terrestrial Reference Frame: data analysis, evaluation and applications
EDI
Terrestrial Reference Frame: data analysis, evaluation and applications
Convener: Kristel ChanardECSECS | Co-conveners: Claudio Abbondanza, Mathis BloßfeldECSECS, Susanne Glaser
Orals
| Mon, 24 Apr, 14:00–15:45 (CEST)
 
Room -2.91
Posters on site
| Attendance Mon, 24 Apr, 16:15–18:00 (CEST)
 
Hall X2
Posters virtual
| Attendance Mon, 24 Apr, 16:15–18:00 (CEST)
 
vHall GMPV/G/GD/SM
Orals |
Mon, 14:00
Posters on site |
Mon, 16:15
Posters virtual
Mon, 16:15
The Terrestrial Reference Frame (TRF) is critical for monitoring the Earth's rotation in space, as well as for many geoscientific applications that need absolute positioning and exact orbit determination of near-Earth artificial satellites. Its new realization, the ITRF2020 has been released based on the combination of DORIS, GNSS, SLR, and VLBI station coordinate time series provided by the IAG/IERS Technique Services.
The objective of this session is to bring together contributions from individual Technique Services, space geodetic data analysts, ITRS combination centres and all ITRF users, with a broad range of applications from geosciences to society, to discuss the results and scientific applications of ITRF2020 and other realizations. The assessment of observed non-linear, and particularly periodic, station motions through space geodetic techniques by comparison with physics-based deformation models is of particular interest. Moreover, contributions to geocenter motion determination are encouraged. Finally, contributions that focus on identifying and mitigating technique-related systematic errors as well as different combination strategies, e.g., space and tropospheric ties are encouraged because they may potentially enhance future ITRF solutions.

Orals: Mon, 24 Apr | Room -2.91

Chairpersons: Kristel Chanard, Claudio Abbondanza, Susanne Glaser
14:00–14:05
5-minute convener introduction
14:05–14:15
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EGU23-3962
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On-site presentation
Towards an ITRF2020 plate motion model 
Zuheir Altamimi, Laurent Métivier, Paul Rebischung, Xavier Collilieux, and Kristel Chanard

For various geodetic and geophysical applications, users need to have access to a Plate Motion Model (PMM) that is consistent with the ITRF2020 frame. The aim of this paper is to evaluate different possible approaches for determining a PMM from the horizontal velocities of a subset of the ITRF2020 sites away from plate boundaries, Glacial Isostatic Adjustment regions and other deformation zones. Compared with the ITRF2014-PMM, we assess in particular the performance of a PMM based on ITRF2020 velocity field, which contains more sites in some large tectonic plates, such as North and South Americas, Australia, and to some extent Antarctica. Using a global inversion of all plates all together, with full variance-covariance information, the angular velocities of these plates are expected to be improved in the ITRF2020 plate motion model. We also investigate the impact of subtracting GIA horizontal velocity predictions of different models before adjusting for angular plate velocities. Early results will be presented and discussed.

How to cite: Altamimi, Z., Métivier, L., Rebischung, P., Collilieux, X., and Chanard, K.: Towards an ITRF2020 plate motion model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3962, https://doi.org/10.5194/egusphere-egu23-3962, 2023.

14:15–14:25
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EGU23-2117
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On-site presentation
JTRF2020: Results and Next Steps 
Richard Gross, Claudio Abbondanza, Mike Chin, Mike Heflin, and Jay Parker

JPL's newly developed software for determining terrestrial reference frames, known as SREF (Square-root Reference frame Estimation Filter), has been used to produce JTRF2020, a combined terrestrial reference frame determined from the input SINEX files submitted by the IVS, IGS, ILRS, and IDS for ITRF2020. SREF, being based on a square-root information filter and smoother, determines the reference frame sequentially from the input station position time series. For JTRF2020, 525 GNSS, 194 DORIS, 116 SLR, and 96 VLBI, or a total of 931, station position time series were used. Incorporating process noise in SREF, determined from geophysical fluid loading models, allows the observed station positions to be smoothed between discontinuities caused by earthquakes and equipment changes. Reference frames determined by SREF, like JTRF2020, are represented by this set of smoothed station position time series. SREF also fits a model to the station's observations and uses the model to fill gaps in the station's observing history, to forecast the position of the station after it stopped observing, and to hindcast its position before it started observing. For JTRF2020, the model consists of a piecewise linear trend, an annual periodic term, and a sum of exponential terms to represent postseismic motion for those stations that experience postseismic motion. The result of using SREF to determine JTRF2020 will be presented.

How to cite: Gross, R., Abbondanza, C., Chin, M., Heflin, M., and Parker, J.: JTRF2020: Results and Next Steps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2117, https://doi.org/10.5194/egusphere-egu23-2117, 2023.

14:25–14:35
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EGU23-12029
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Virtual presentation
DTRF2020: Strategy, Results and Data Set 
Manuela Seitz, Mathis Blossfeld, Matthias Glomsda, Detlef Angermann, Sergei Rudenko, Julian Zeitlhoefler, and Florian Seitz

The DTRF2020 is the ITRS 2020 realization of the ITRS CC at DGFI-TUM.It was published earlier this year. The calculation of the DTRF2020 is based on a two-step approach: First, after a data pre-analysis, one TRF (normal equation system, NEQ) per technique, i.e. VLBI, SLR, GNSS and DORIS, is calculated. Second, the TRF NEQs are combined to the DTRF2020 solution. For the first time, all previously modeled non-tidal loading (NTL) components provided by IERS GGFC, i.e., the atmospheric, hydrological, and oceanic parts, are considered to reduce NTL signals in the station motions from the input NEQ. Post-seismic deformation (PSD) signals in station position time series are approximated by combinations of logarithmic and exponential functions and reduced from the NEQ in the same way as the NTL signals in the first step of our approach.

 

The published dataset includes the DTRF2020 solution itself, i.e., station positions at the reference epoch 2010.0 and station velocities, as well as the consistently estimated EOP series. In addition, the model-based NTL time series used in the DTRF2020 calculation, the parameters of the PSD approximation functions, and the corresponding time series of the approximation signal considered in DTRF2020 (over the DTRF2020 time period) are provided for the users. Furthermore, residual time series of station positions and SLR translation time series are made available (the latter indicate the deviation of the instantaneous from the mean center of mass realized in DTRF2020).

 

In this presentation, we discuss the final results of DTRF2020 and give an overview of the DTRF2020 dataset and the features it provides for its application. We also discuss the consistency of DTRF2020 with respect to its predecessor DTRF2014 and the limits of accuracy of reference frames. Further, we address the need for consistency with respect to datasets that will be used in DTRF2020 applications, such as the SLR Data Handling File and GNSS satellite PCV.

How to cite: Seitz, M., Blossfeld, M., Glomsda, M., Angermann, D., Rudenko, S., Zeitlhoefler, J., and Seitz, F.: DTRF2020: Strategy, Results and Data Set, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12029, https://doi.org/10.5194/egusphere-egu23-12029, 2023.

14:35–14:45
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EGU23-3399
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ECS
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On-site presentation
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Toward a realistic spatio-temporal description of GNSS station position time series 
Kevin Gobron, Paul Rebischung, Julien Barnéoud, Kristel Chanard, and Zuheir Altamimi

Today, Global Navigation Satellite Systems (GNSS) are widely used to study the kinematics of the Earth's surface and provide a fundamental contribution to the establishment of terrestrial reference frames. GNSS station position time series are derived by different analysis centres, which have achieved tremendous progress over the years. Nevertheless, GNSS station position time series remain polluted by stochastic variations – often called "noise" – which hinder their geophysical interpretation and contribution to terrestrial reference frames.

Many studies have evidenced that these stochastic variations exhibit both temporal and spatial correlations. On the one hand, temporal correlations have been analyzed in detail and are known to be well approximated by a combination of white noise and flicker noise. The presence of flicker noise, whose origin remains unknown, is a major source of uncertainty in the estimation of long-term station positions and velocities. Consequently, most geodetic studies now routinely take these temporal correlations into account to avoid inferring unrealistically optimistic uncertainties. On the other hand, the stochastic variations in GNSS station position time series are also spatially correlated up to distances reaching a few thousand kilometres. The origins of these large-scale correlations, whether non or poorly-modelled ground deformation, positioning errors, or a combination of both, remain to be understood. Although this spatially correlated noise is known to obscure geophysical signals and affect the estimation of parameters of interest, it is hardly ever modelled or accounted for.

This presentation introduces a realistic spatio-temporal correlation model for the stochastic variations in GNSS station position time series. Based on the analysis of position time series from the IGS repro3 campaign (over 1,300 stations) and the Nevada Geodetic Laboratory analyzes (over 11,000 stations), we first provide a diagnosis of the spatial correlations of the white and flicker noise processes separately. We then introduce three-dimensional spatial correlation models for each process. Finally, we discuss the implications of these spatio-temporal correlations on the uncertainty of long-term station positions and velocities.

How to cite: Gobron, K., Rebischung, P., Barnéoud, J., Chanard, K., and Altamimi, Z.: Toward a realistic spatio-temporal description of GNSS station position time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3399, https://doi.org/10.5194/egusphere-egu23-3399, 2023.

14:45–14:55
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EGU23-10251
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ECS
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On-site presentation
From noise-to-signal: enhancing the sensitivity of long-term GNSS by explaining non-linear station motions 
Roland Hohensinn and Yehuda Bock

Reducing uncertainties in long-term GNSS is crucial for providing the most stable realization of terrestrial reference frames. Besides the epoch-wise handling of errors in the GNSS processing of the raw observations, this includes the description of linear and non-linear station motions by using functional and stochastic time series models (trajectory models). While the state-of-the-art trajectory models explain common signals (such as station velocity, periodic motions and offsets), a main challenge is to explain the variety of signals that are still present in the residuals (i.e., transients and artifacts).

We take the time series of almost 2000 stations from Europe and the Western U.S., and fit extended trajectory models (ETMs) using the Hector software. We show that correcting the vertical observations by geophysical loadings and common-mode errors (CME) enhances median GNSS sensitivity by a factor of two, which we demonstrate for important parameters of the ETM, for both, linear and non-linear motions. The analysis reveals a median sensitivity of 0.5 mm/year for station velocity, and 0.6 mm for annual seasonal motions. Supported by the comparison with the CME-corrected case, we highlight potential shortcomings of the non-tidal atmospheric and hydrological loading models (related to phase shifts and the presence of transients), and demonstrate biasing effects on uncertainty.

Based on the post-fit residuals of the ETMs and unsupervised learning methods, yet unexplained geophysical transients can be classified and clustered, which is a significant step towards automatic data interpretation and quality control. In view of an optimal GNSS station deployment, this approach also helps to separate stable from unstable regions, for example regions of irregular subsidence.  We conclude, that this algorithmic framework cannot only be successfully used for GNSS data, but also for other geodetic time series data.

How to cite: Hohensinn, R. and Bock, Y.: From noise-to-signal: enhancing the sensitivity of long-term GNSS by explaining non-linear station motions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10251, https://doi.org/10.5194/egusphere-egu23-10251, 2023.

14:55–15:05
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EGU23-13235
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On-site presentation
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Exploiting the full potential of ocean tide models for space geodetic techniques 
Torsten Mayer-Guerr, Felix Oehlinger, Roman Sulzbach, and Henryk Dobslaw

The influence of ocean tides plays a major role for geodetic space methods in the modeling of satellite orbits, Earth rotation, and short-period station motions.

Current ocean tide models are published with a large number of individual constituents that are representative for the entire tidal spectrum. The analysis requires interpolation of the constituents onto the spectrum using admittance theory. The application of admittance is non-trivial, as it explicitly and implicitly refers to historical conventions that are hard to retrace for users. Further linear admittance theory is non-unique and requires some insight into the principles of ocean tidal dynamics.

Nonetheless, the error-prone implementation of admittance is mostly left to the user, which can easily induce confusion and errors. For example, the IERS2010 conventions describe only one method for the outdated FES2004 model that does not apply directly to current models. While there is a conventional routine for calculating the ocean loading displacement, it needs to consider recent developments and therefore does not exploit the full potential of current ocean tide models.

In this presentation, a unified approach is presented for discussion to exploit the full potential of current ocean tide models in satellite orbit calculation and for station displacements. This approach aims to set up a framework for tidal correction that is userfriendly, model-independent, and applies to many geophysical observables.

How to cite: Mayer-Guerr, T., Oehlinger, F., Sulzbach, R., and Dobslaw, H.: Exploiting the full potential of ocean tide models for space geodetic techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13235, https://doi.org/10.5194/egusphere-egu23-13235, 2023.

15:05–15:15
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EGU23-15354
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On-site presentation
Implementation of ITRF2020 in the ILRS Operational Products 
Vincenza Luceri, Antonio Basoni, David Sarrocco, Erricos C. Pavlis, Magda Kuzmicz-Cieslak, Keith Evans, Mathis Bloßfeld, and Giuseppe Bianco

The ILRS contributed to the development of ITRF2020 via the combined products submitted to ITRS. The combined products were the result of the combination of individual AC contributions where a new approach in handling systematic errors at the stations was implemented. A set of a priori estimated mean biases was considered for the main period 1993-2020 that includes data from LAGEOS, LAGEOS-2 and the Etalons, whereas an adjusted 15-day average bias at each station for the 1983-1993 period was considered to accommodate systematic and target signature errors, if a priori mean biases were missing. The implementation of ITRF2020/SLRF2020 in SLR operational products required an extended version of the SSEM model, SSEM-X, which led to the finalization of a new DH file. Considering this updated set of long-term mean biases, all ACs produced a solution set based on models used for REPRO2020 and SLRF2020 as input to a combined product intended for the IERS RS/PC at USNO. These EOP series will be used for the calibration of EOP biases prior to the release the final version of the new Bulletin A. The new bias model SSEM-X will be publicly available and maintained current over the coming years.

How to cite: Luceri, V., Basoni, A., Sarrocco, D., Pavlis, E. C., Kuzmicz-Cieslak, M., Evans, K., Bloßfeld, M., and Bianco, G.: Implementation of ITRF2020 in the ILRS Operational Products, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15354, https://doi.org/10.5194/egusphere-egu23-15354, 2023.

15:15–15:25
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EGU23-13970
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ECS
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On-site presentation
Current status and future perspectives of VLBI global solutions 
Lisa Kern, Hana Krasna, Johannes Böhm, and Matthias Madzak

The realization of a terrestrial and celestial reference frame is a fundamental requirement for all ground- and space-based observations, making the interpretation of key global processes on Earth possible and therefore contributing to a better understanding of the Earth system. In this matter, the space-geodetic technique called Very Long Baseline Interferometry (VLBI) provides the perfect link between stations on the Earth's surface and extragalactic sources with a quasi-fixed position. In the process of an intra-technique combination, it is possible to estimate parameters that are common to all VLBI sessions in a common least squares adjustment, resulting in, e.g., catalogs of station and source positions (and station velocities) at a certain reference epoch. 

We present the current status of our new state-of-the-art and stand-alone Python software for the combination of VLBI sessions developed at the VLBI Analysis Center in Vienna. The combination process is based on homogenized, datum-free normal equations from SINEX (solution independent exchange format) files. In the future, we are planning on implementing filter solutions to ensure an optimal state estimation of the dynamical system Earth and further expanding the capabilities of our software by, e.g., allowing a combined analysis of different space-geodetic techniques (inter-technique combination) to further improve the consistency and accuracy of the resulting reference frames and Earth Rotation Parameters (ERPs). 

How to cite: Kern, L., Krasna, H., Böhm, J., and Madzak, M.: Current status and future perspectives of VLBI global solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13970, https://doi.org/10.5194/egusphere-egu23-13970, 2023.

15:25–15:35
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EGU23-14501
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On-site presentation
DORIS based precise orbit and reference frame determination using multiple altimetry satellite missions 
Reinhold Anton, Schreiner Patrick, Neumayer Karl Hans, and König Rolf

The German Research Centre for Geosciences (GFZ) is one of the Associate Analysis Centers (AAC) of the International Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) Service (IDS).

In the framework of a future contribution to the DORIS part of the International Terrestrial Reference Frame (ITRF) a repertoire of well-known satellite altimetry missions equipped with DORIS receiver, in particular Topex, Envisat, Jason-1/2, Cryosat-2, Saral, Jason-3, Sentinel-3A/B and Sentinel-6A Michael Freilich, have been processed.

Therefore, Precise Orbit Determination (POD) is performed for these missions, and orbits are generated based on DORIS-only and on the combination of DORIS and Satellite Laser Raging (SLR) observations.

The quality of the orbits is subsequentely analyzed internally and in comparison with external orbit solutions.

For external comparisons, the combined orbit solutions of the Copernicus POD quality working group (CPOD-QWG), which is assumed to have superior absolute accuracy and minimal residual systematic errors, are used for the Sentinel missions, while for the remaining missions orbit products by Centre National D’Etudes Spatiales (CNES) are used.

Eventually, starting from the DORIS only solutions, weekly local terrestrial reference frames (TRFs), are computed for each single satellites, as well as a combined solution for the entire analysis interval with all satellite missions is generated.

The TRF solutions thus generated are evaluated with respect to the reference frame defining parameters, i.e. origin, scale, and orientation, in comparison to the a piori TRF.

How to cite: Anton, R., Patrick, S., Karl Hans, N., and Rolf, K.: DORIS based precise orbit and reference frame determination using multiple altimetry satellite missions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14501, https://doi.org/10.5194/egusphere-egu23-14501, 2023.

15:35–15:45
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EGU23-12556
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ECS
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On-site presentation
Impact of Local Ties in GNSS and VLBI Integrated Solution 
Jungang Wang, Susanne Glaser, Maorong Ge, Kyriakos Balidakis, Robert Heinkelmann, and Harald Schuh

In the multi-technique integrated solution, different space geodetic techniques are combined via common parameters and external observations, such as global ties (Earth Orientation Parameters, EOPs) and local ties (LTs), respectively. Local ties, which directly link the coordinates of co-location stations, are currently used in determining terrestrial reference frames (TRFs). We investigate the impact of global and local ties in Global Navigation Satellite Systems (GNSSs) and Very Long Baseline Interferometry (VLBI) integrated solutions in five VLBI continuous (CONT) campaigns. Compared to a baseline solution where GNSS and VLBI have separate minimal constraints implemented (no-net-rotation and no-net-translation, NNR+NNT), applying additional GTs and LTs improves the VLBI TRF and EOP estimates. As LTs are supposed to transfer the datum information between GNSS and VLBI, we further investigate the scenario where the VLBI datum is linked to GNSS via LT, without NNR+NNT applied to the VLBI network. We demonstrate that in this scenario the VLBI solution is deteriorated, especially the east-west component of station coordinates and UT1-UTC estimates, mainly due to the insufficient accuracy of the currently used LTs. We thus emphasize the importance of improving the accuracy of LT measurements and applying additional ties, for example, space ties and atmospheric ties.

How to cite: Wang, J., Glaser, S., Ge, M., Balidakis, K., Heinkelmann, R., and Schuh, H.: Impact of Local Ties in GNSS and VLBI Integrated Solution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12556, https://doi.org/10.5194/egusphere-egu23-12556, 2023.

Posters on site: Mon, 24 Apr, 16:15–18:00 | Hall X2

Chairpersons: Kristel Chanard, Claudio Abbondanza, Susanne Glaser
X2.20
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EGU23-3212
An Insight on Scale Definition in JTRF2020 
Claudio Abbondanza, Toshio Chin, Richard Gross, Michael Heflin, and Jay Parker

JTRF2020 is the latest TRF solution computed at JPL by assimilating frame input data submitted by the IVS, IGS, ILRS, and IDS for ITRF2020. Determined with SREF (Square-root Reference frame Estimation Filter), a computational code based on a square-root information filter and Dyer-McReynolds smoother algorithm, JTRF2020 adopts a time-series based representation: Its daily time series determined from observations of a multi-technique space-geodetic network of 931 stations describe, through their Cartesian coordinates, the deformation of solid Earth as a function of time. Such coordinates are inherently expressed in Earth’s Center of Mass as sensed by SLR and give access to the quasi-instantaneous scale implied by the underlying frame.  JTRF2020, like its predecessor JTRF2014, traditionally adopts a scale relying on VLBI and SLR observations only. In this presentation, we will guide the readers through the process we adopted to define and construct the scale of JTRF2020, from the determination and analysis of the scale differences between VLBI and SLR to the way in which the time-variable scale bias between VLBI and SLR is handled within the J2020 assimilation.     

How to cite: Abbondanza, C., Chin, T., Gross, R., Heflin, M., and Parker, J.: An Insight on Scale Definition in JTRF2020, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3212, https://doi.org/10.5194/egusphere-egu23-3212, 2023.

X2.21
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EGU23-12442
The introduction of ITRF2020 in global positioning applications 
Francesco Matonti, Adam Miller, and Joanna Wnuk

With the integration of positioning solutions into mass-production autonomous driving systems, together with the ever-increasing demand for global positioning applications the use of a global reference frame is now a requirement that global correction service providers need to support and deliver, whilst still maintaining support of local (regional) official reference frames. To maintain high precision of the GNSS network we perform a daily solution, which is computed based on precise orbits and following the guidelines of the EPN Analysis Centres. Using the daily solutions, we are estimating the linear velocity of reference stations within GNSS networks and are also considering jumps due to equipment changes. The estimated velocities give the opportunity to monitor the long-term stability of the network as well as the quality of reference station coordinates. The transition between ITRF2014 and ITRF2020 on a large GNSS reference stations worldwide, including the computation of the HxGN SmartNet GNSS network consisting of more than 5300 GNSS reference stations, will be investigated to evaluate the impact that this could have on the users using the correction services.

The daily solution and monitoring of GNSS networks, such as HxGN SmartNet, is executed by the Leica Geosystems solution named Leica CrossCheck, which is based on Bernese GNSS software. Leica CrossCheck is capable to monitor GNSS networks of all scales.

KEYWORDS: GNSS reference station network, Bernese GNSS 5.4, Leica CrossCheck, Leica GNSS Spider, HxGN SmartNet, Leica GeoMoS Now!


References:
Dach, R., S. Lutz, P. Walser, P. Fridez (Eds); 2015: Bernese GNSS Software Version 5.2. User manual, Astronomical Institute, Universtiy of Bern, Bern Open Publishing. DOI: 10.7892/boris.72297; ISBN: 978-3-906813-05-9.

How to cite: Matonti, F., Miller, A., and Wnuk, J.: The introduction of ITRF2020 in global positioning applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12442, https://doi.org/10.5194/egusphere-egu23-12442, 2023.

X2.22
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EGU23-12089
New website of the ITRS CC at DGFI-TUM: dtrf.dgfi.tum.de 
Florian Seitz, Manuela Seitz, Mathis Bloßfeld, Matthias Glomsda, Detlef Angermann, Sergei Rudenko, and Julian Zeitlhöfler

The ITRS CC at the Deutsches Geodätisches Forschungsinstitut of the Technical University of Munich (DGFI-TUM) has created the new DTRF website https://dtrf.dgfi.tum.de. On this site, DGFI-TUM provides background information and data access to the current and all previous DTRF solutions. In particular, the DTRF2020 processing strategy is presented and the results are described and explained. In addition to the actual solution, the DTRF2020 release contains further datasets that are necessary for a highly accurate application of the DTRF2020. The website clearly presents and makes available all datasets, partly map-based. Our poster gives an overview of the new DTRF website and provides examples of its use.

How to cite: Seitz, F., Seitz, M., Bloßfeld, M., Glomsda, M., Angermann, D., Rudenko, S., and Zeitlhöfler, J.: New website of the ITRS CC at DGFI-TUM: dtrf.dgfi.tum.de, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12089, https://doi.org/10.5194/egusphere-egu23-12089, 2023.

X2.23
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EGU23-3452
IDS evaluation of the DORIS versions of the DGFI and IGN TRF2020 solutions 
Guilhem Moreaux and Hugues Capdeville

In the context of the 2020 realization of the International Terrestrial Reference Frame, the three IERS Production Centers (DGFI, IGN and JPL) delivered three independent solutions from the contributions of the four space geodetic techniques (DORIS, GNSS, SLR and VLBI). Even if these three ITRF2020 realizations are based on the same input, they differ on several points such as the space geodetic techniques weighting, the coordinate time series discontinuities and on the modelling of the station displacements.

In this study, we use the coordinate time series of the two hundred DORIS stations from 1993.0 to 2022.5 as benchmark to investigate the characteristics of the ITRF2020 and DTRF2020 realizations.

After presentation of the overall performance of these two TRF realizations in terms of geocenter, scale and mean velocities, we assess the quality of the weekly restitution of the DORIS station positions by the DTRF2020, and ITRF2020 solutions. Then, we make benefit of the one and a half year since the ending of the ITRF2020 time period to evaluate these two 2020 TRF solutions in terms of prediction of the DORIS station positions. Finally, we will estimate the impact of the DTRF2020 and ITRF2020 solutions on DORIS precise orbit determination.

How to cite: Moreaux, G. and Capdeville, H.: IDS evaluation of the DORIS versions of the DGFI and IGN TRF2020 solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3452, https://doi.org/10.5194/egusphere-egu23-3452, 2023.

X2.24
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EGU23-11703
Impact of SLR long-term mean range biases on the orbits of altimetry and SLR satellites for ITRS2020 realizations 
Sergei Rudenko, Mathis Bloßfeld, Julian Zeitlhöfler, Alexander Kehm, and Denise Dettmering

In 2022-2023, new (2020) realizations of the International Terrestrial Reference System (ITRS) were published, namely ITRF2020, DTRF2020, and JTRF2020. One of the differences for these realizations with respect to the previous (2014) ones is the application of Satellite Laser Ranging (SLR) station-specific long-term mean range biases for the four geodetic satellites LAGEOS-1, -2 and Etalon-1 and -2. These range biases were subtracted at the observation level from the SLR observations used to derive the ITRS2020 realizations. In this context, a question arises if these range biases should be applied in SLR-observation-based precise orbit determination for any satellite to obtain the highest orbit quality possible, when using ITRS2020 realizations as the a priori reference frame. We present results of a study on the application of the SLR long-term mean range biases derived from LAGEOS-1, -2 and Etalon-1 and -2 for precise orbit determination of some altimetry and other spherical SLR satellites using ITRS2020 realizations as the a priori reference frame and make a conclusion on the necessity of application of these biases. Furthermore, we present results of precise orbit determination for altimetry satellites based on long-term mean range biases explicitly determined for the respective satellites.

How to cite: Rudenko, S., Bloßfeld, M., Zeitlhöfler, J., Kehm, A., and Dettmering, D.: Impact of SLR long-term mean range biases on the orbits of altimetry and SLR satellites for ITRS2020 realizations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11703, https://doi.org/10.5194/egusphere-egu23-11703, 2023.

X2.25
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EGU23-6235
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ECS
Different approaches in determining global geodetic parameters from SLR data - a simulation study 
Joanna Najder, Krzysztof Sośnica, Dariusz Strugarek, and Radosław Zajdel

Satellite laser ranging (SLR) is currently one of the four space geodetic techniques that provide a relevant contribution to the International Terrestrial Reference Frame (ITRF) realization as well as to the determination of global geodetic parameters including the low-degree harmonics of the Earth's gravity potential. ITRF realizations are mostly based on the observations to the two LAGEOS and two Etalon satellites, however, the impact of observations to Etalon satellites is marginal when compared to LAGEOS. Currently under consideration is an extension of the ITRF solution to include the LAser RElativity Satellite (LARES) and LARES-2 developed by the Italian Space Agency ASI and launched on July 13, 2022. The contribution of other satellites with retroreflectors is still being investigated.

This study aims to verify various approaches to estimating geodetic parameters depending on the number of determined empirical once-per-revolution parameters for satellite orbits and different approaches of parametrization for the Earth rotation parameters (ERP), including piecewise linear and piecewise constant parametrization. We analyze six parametrizations, where three of them are proposed in this study and the other three are used by research centers, such as the Center for Space Research (CSR), the International GNSS Service (IGS), and the International Laser Ranging System (ILRS). For IGS and ILRS, these are the approaches used in determining the ERPs based on GNSS and SLR data, respectively. To the constellation of geodetic satellites such as LAGEOS-1/-2, Etalon-1/-2, and LARES-1/-2, we add hypothetical SLR satellites such as LARES-3/-4 and LARES-5/-6 which supplement the current constellation in the simulation study. We check whether satellite parameters, such as satellite altitudes and inclination angles affect individual global geodetic parameters when using different approaches to ERP parameterization and the set of estimated empirical orbit parameters.

The obtained results show that the value of the obtained formal errors may depend not only on the choice of the estimated geodetic parameters but also on the number of satellites or satellite orbit parameters involved in the calculations.

How to cite: Najder, J., Sośnica, K., Strugarek, D., and Zajdel, R.: Different approaches in determining global geodetic parameters from SLR data - a simulation study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6235, https://doi.org/10.5194/egusphere-egu23-6235, 2023.

X2.26
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EGU23-11531
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ECS
Intra-technique VLBI combination by handling software-specific dependencies 
Hendrik Hellmers, Sadegh Modiri, Daniela Thaller, Mathis Bloßfeld, and Manuela Seitz

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 and releases the combined products of the International VLBI Service for Geodesy and Astrometry (IVS). These session-wise solutions are achieved by an intra-technique combination utilizing the individual contributions delivered by multiple IVS Analysis Centres (AC). For the IVS contribution to the ITRF2020, the re-processed sessions containing 24 h VLBI observations have been submitted by eleven different ACs, where a total number of seven different software packages are utilized. As a result, the session-wise SINEX files are delivered, including datum-free normal equations containing the station coordinates, the source positions and full sets of the Earth Orientation Parameters (EOP). As the same software packages are used by various ACs (e.g. CalcSolve by five ACs), the combined solution is in danger of being dominated by these contributions. The estimates of EOP and station coordinates are affected then mainly by the software specific modelling.

This work focuses on an optimal weighting strategy to handle dependencies due to identical software packages in the ACs’ contributions. Thereby, software specific sub-combinations are carried out in the first step to employ the strategy. Finally, the ultimate combination consists of the weighted individual contributions of each applied software. In order to assess the quality of the individual components of the combination - especially in comparison to the contributions of the individual ACs – the internal as well as the external comparisons of the estimated EOP are carried out, where the combined solution together with the external time series (e.g., IERS Bulletin A) serve as a reference.

How to cite: Hellmers, H., Modiri, S., Thaller, D., Bloßfeld, M., and Seitz, M.: Intra-technique VLBI combination by handling software-specific dependencies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11531, https://doi.org/10.5194/egusphere-egu23-11531, 2023.

X2.27
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EGU23-8636
VLBI-based assessment of the consistency of the conventional EOP series and the reference frames (terrestrial and celestial) 
Mariana Moreira, Esther Azcue, Maria Karbon, Santiago Belda, Víctor Puente, Robert Heinkelmann, David Gordon, and José Ferrándiz

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.

How to cite: Moreira, M., Azcue, E., Karbon, M., Belda, S., Puente, V., Heinkelmann, R., Gordon, D., and Ferrándiz, J.: VLBI-based assessment of the consistency of the conventional EOP series and the reference frames (terrestrial and celestial), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8636, https://doi.org/10.5194/egusphere-egu23-8636, 2023.

X2.28
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EGU23-8773
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ECS
Optimal geometry for reference frame rotation transformation using VLBI-GNSS space-tie onboard Galileo satellites 
Hakan Sert, Urs Hugentobler, Ozgur Karatekin, and Veronique Dehant

Each space geodetic technique realizes its own technique-specific terrestrial frame. Combining the individual techniques requires the links between those frames such as the local tie vectors. Co-location of different geodetic techniques on Earth orbiting satellites offers the unique opportunity of continuously measure ‘space-ties’ which can have a critical role for achieving the Global Geodetic Observing System (GGOS) goal of 1mm accuracy and 0.1mm/year stability of the Terrestrial Reference Frame (ITRF).

We simulate Very Long Baseline Interferometry (VLBI) observations of a broadband VLBI transmitter (VT) onboard Galileo satellites to evaluate the contribution of such a VT space-tie on the rotation transformation between the VLBI and GNSS frames. We investigate the contribution of a VT as space tie by evaluating the formal precision of orientation parameters between the VLBI and GNSS frames using different ground stations/baselines to find the observation geometry for the rotation transformation.

How to cite: Sert, H., Hugentobler, U., Karatekin, O., and Dehant, V.: Optimal geometry for reference frame rotation transformation using VLBI-GNSS space-tie onboard Galileo satellites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8773, https://doi.org/10.5194/egusphere-egu23-8773, 2023.

X2.29
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EGU23-8947
On the systematic differences between various GNSS solutions 
Janusz Bogusz, Paul Rebischung, and Anna Klos

Space geodesy is the branch of science that deals with determining the shape and dimension of the Earth using quasars and artificial satellites. However, the use of space techniques is not limited to geodesy, many recent geodynamical interpretations are based on the velocities determined using GNSS (Global Navigations Satellite System). In this regard, reference frame differences as well as processing strategies - Precise Point Positioning (PPP) or Network Solution (NS) - may induce systematic differences of significant values. A first comparison between NGL (Nevada Geodetic Laboratory) PPP-produced and IGS (International GNSS Service) NS-produced (repro3) products showed systematic differences between both sets of displacement time series. While the discrepancies in the noise parameters are quite understandable and interpretable, the systematic disagreements in the velocities or amplitudes of annual signals are concerning. The repro3 daily combined solutions are aligned in origin and orientation to the IGSR3 reference frame, which inherits its origin and orientation from ITRF2014. So the daily repro3 station positions are expressed with respect to the ITRF2014 origin, which follows CM on the long-term, but reflects CF at sub-secular time scales. NGL time series, just like the IGS ones, are aligned to a linear reference frame, IGS14 in their case. Since both the IGS repro3 and NGL time series are in fact with respect to the ITRF2014 origin, this cannot explain the annual amplitude differences we observe. A difference in scale may contribute though, because the NGL time series are aligned in scale to IGS14, but the repro3 time series are not aligned in scale to any reference frame. They inherit their scale from the radial satellite phase center offsets (z-PCOs) in igsR3.atx, so in general we may expect: (1) an average ~8 mm difference between the vertical positions in both sets of time series at epoch 2010.0, (2) an average ~0.2 mm/yr rate between the vertical positions in both sets of time series, (3) small differences in the vertical seasonal signals due to the network effect occurring when the NGL solutions are aligned in scale to IGS14. But the fact that the NGL solutions are aligned in scale to the reference frame, while the IGS solutions are not, might explain some other systematic differences. To verify that, we compared the aforementioned series to a set of special IGS repro3 time series produced at IGN and aligned not only in origin and orientation, but also in scale to the IGSR3 reference frame. The comparison between the series was made at 607 stations distributed around the world. The Up component was investigated, and the data have been cut to the same ranges in all three solutions (namely, IGS, NGL and IGN) to avoid misinterpretations and have a minimum length of 5 years. Velocities as well as amplitudes of annual and draconitic oscillations have been analyzed revealing very interesting spatial patterns in the differences.

How to cite: Bogusz, J., Rebischung, P., and Klos, A.: On the systematic differences between various GNSS solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8947, https://doi.org/10.5194/egusphere-egu23-8947, 2023.

X2.30
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EGU23-9320
ESA’s GENESIS mission: Advancing terrestrial reference systems by co-location of geodetic techniques in space. 
Özgür Karatekin and the GENESIS Team

Improving and homogenizing time and space reference systems on Earth and, more specifically, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1 mm and a long-term stability of 0.1 mm/year are crucial  to many scientific and societal endeavors. This is the purpose of the GENESIS mission, proposed as a component of the FutureNAV program of the European Space Agency (ESA) [1].  The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, such as those located at tide gauges, as well as the ground stations of tracking networks. In addition, numerous applications in geophysics require absolute millimeter precision from the reference frame, as, for example, monitoring tectonic motion or crustal deformation, contributing to a better understanding of natural hazards. The target TRF accuracy  is based on the scientific needs of various disciplines in Earth Sciences and is reflected in the consensus of various authorities, including the International Association of Geodesy (IAG). Moreover, the United Nations Resolution 69/266 states that the full societal benefits in developing satellite missions for positioning and Remote Sensing of the Earth are realized only if they are referenced to a common global geodetic reference frame at the national, regional and global levels. Yet, when combining all these techniques for the TRF generation, the process is today affected by the accuracy on which we may determine the differential coordinates between the reference point of each technique and several unmodelled systematic errors. 

The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. GENESIS will support the production of a more accurate TRF and enable the generation of an updated global model of Earth rotation, as well as a better-determined geocenter. The GENESIS mission would deliver exemplary science and societal benefits across a multidisciplinary range of Navigation and Earth sciences applications, constituting a global infrastructure that is internationally agreed to be strongly desirable. GENESIS got the green light at the  ESA Ministerials  held in Paris on November 2022. Here we will present the latest updates on the overall mission.

[1] Delva et al., 2023, GENESIS: co‐location of geodetic techniques in space, accepted in Earth, Planets and Space

How to cite: Karatekin, Ö. and the GENESIS Team: ESA’s GENESIS mission: Advancing terrestrial reference systems by co-location of geodetic techniques in space., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9320, https://doi.org/10.5194/egusphere-egu23-9320, 2023.

Posters virtual: Mon, 24 Apr, 16:15–18:00 | vHall GMPV/G/GD/SM

vGGGS.1
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EGU23-9417
Incorporating LARES-2 SLR Data in ILRS Products for ITRF Development 
Erricos C. Pavlis, Magda Kuzmicz-Cieslak, and Keith Evans

Geodetic network infrastructure has evolved with increasing pace the past decade with remarkable additions of modern hardware, replacing aging, ‘80s vintage equipment throughout the globe. SLR needs however more than updating the network to deliver the accuracy required today. New and improved design “targets” must also be used that support the required “1-mm accuracy”. LAGEOS was conceived and built in the early ‘70s with a ~5 mm accuracy in mind [Pearlman et al., 2019]. This limitation forced analysts to develop approaches of data analysis to ensure that even with such data one can reach the required 1-mm accuracy [Luceri et al., 2019]. Along with the network updates a parallel effort was thus initiated to modernize the space segment as well. Initially with the design and launch of LARES in 2012 [Pavlis et al., 2015] and following that, the design of LARES-2 [Ciufolini et al., 2017, Paolozzi et al., 2019], which was successfully launched on July 13, 2022 [https://www.nature.com/articles/d41586-022-02034-x]. The new mm-accurate target was quickly acquired first by the Italian station at Matera, only three days after launch and although very early in the mission, the data were of remarkably high quality and insignificant bias. This prompted a quick evaluation and a test inclusion of this target in the limited list of SLR targets supporting the ITRF development. With an orbit nearly identical to LAGEOS (with supplementary inclination), taking full advantage of all the appropriate models designed and applied to LAGEOS, we achieved 7-day orbital fits of 3-5 mm even without a tuned target signature correction. Using the approach described in [Kuzmicz-Cieslak, M. et al., 2022] and along with data from the other geodetic spheres, we have generated preliminary combination products for the development of the ITRF. We will present an overview of this initial analysis of LARES-2 data focusing on comparing these results to contemporaneously taken data from the standard four geodetic spheres only, (LAGEOS 1 & 2 and Etalon 1 & 2).

Pearlman et al. J Geod 93, 2181–2194 (2019). https://doi.org/10.1007/s00190-019-01228-y

Luceri et al. J Geod 93, 2357–2366 (2019). https://doi.org/10.1007/s00190-019-01319-w

Pavlis et al. EEEIC (2015), pp. 1989-1994. https://doi.org/10.1109/EEEIC.2015.7165479

Paolozzi et al. J Geod 93, 2437–2446 (2019). https://doi.org/10.1007/s00190-019-01316-z

Ciufolini et al. Eur. Phys. J. Plus 132, 336 (2017). https://doi.org/10.1140/epjp/i2017-11635-1

Kuzmicz-Cieslak, M. et al. (2022). https://doi.org/10.22541/essoar.167214343.32185093/v1

How to cite: Pavlis, E. C., Kuzmicz-Cieslak, M., and Evans, K.: Incorporating LARES-2 SLR Data in ILRS Products for ITRF Development, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9417, https://doi.org/10.5194/egusphere-egu23-9417, 2023.

vGGGS.2
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EGU23-9468
Updating Terrestrial Reference Frame using Sequential Computation Method 
Toshio Mike Chin, Claudio Abbondanza, Richard Gross, Michael Heflin, and Jay Parker

JTRF2020 is a recent contribution by NASA Jet Propulsion Laboratory to IERS as part of their effort to determine ITRF2020.  JTRF2020 is estimated daily using a sequential computational method (called "SREF") based on the SRIF and DMCS algorithms which are respective variants of the Kalman filter and smoother.  The filtering algorithm allows us to make timely update of the reference frame, as newer geodetic analysis data become available beyond those ingested into JTRF2020.  Benefits of such frame updating are examined using hindcasting experiments, which are presented here.  Also, some of the standard formulas used in terrestrial reference frame realizations are not immediately suitable for sequential formulation required by the algorithms like the Kalman filter.  We thus describe our sequential re-formulation of these formulas, including the intrinsic constraints, week-long EOP arcs, and lack of initial conditions.

How to cite: Chin, T. M., Abbondanza, C., Gross, R., Heflin, M., and Parker, J.: Updating Terrestrial Reference Frame using Sequential Computation Method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9468, https://doi.org/10.5194/egusphere-egu23-9468, 2023.