G2.2

G2 EDI

The International Terrestrial Reference System (ITRS) and its realizations are nowadays widely used for all applications in geosciences. A new realization, the ITRF2020 is being released, based on the combination of DORIS, GNSS, SLR and VLBI station coordinate time series provided by the IAG/IERS technique services.

The goal of this session is to provide a forum to discuss the following topics:
- Contribution of IAG/IERS technique services;
- Evaluation of state of the art GNSS, VLBI, DORIS and SLR position time series (similar to ITRF2020 input data) and associated datum parameters by comparing them with:
* new coordinate series based on enhanced data modeling strategies or combination at the observation level;
* non-tidal loading displacement models.
- Combination strategy and results using ITRF2020 input data;
- Evaluation of the combined terrestrial reference frames derived with ITRF2020 input data;
- Discrepancies between local ties and space geodesy results. Advanced local tie data acquisition and analysis. Study of station coordinate bias at co-location site;
- Impact of terrestrial reference frame station coordinate modeling (pseudo-periodic signals and post-seismic deformations) on Earth science applications and operational geodetic activities.

Contributions are sought from the individual technique services, space geodetic data analysts, the ITRS combination centres and ITRF users. Methodological and theoretical studies on the use of the ITRS realizations on a global or regional scale are also welcome.

Convener: Xavier Collilieux | Co-conveners: Mathis BloßfeldECSECS, Susanne Glaser, Claudio Abbondanza
Presentations
| Mon, 23 May, 11:05–11:50 (CEST), 13:20–14:50 (CEST)
 
Room -2.91

Presentations: Mon, 23 May | Room -2.91

Chairpersons: Susanne Glaser, Xavier Collilieux, Mathis Bloßfeld
11:05–11:07
11:07–11:13
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EGU22-10401
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On-site presentation
Petr Stepanek and Vratislav Filler

Geodesy Observatory Pecný (GOP) analysis center is one of the International DORIS Service (IDS) analysis centers. GOP fully contributed to the IDS combination of the ITRF2020, reaching various improvements in comparison to the ITRF2014 reprocessing. GOP also participates in the IDS operational solutions. A major progress has been reached in the data preprocessing strategy, South Atlantic Anomaly mitigation and satellite orbit & attitude modeling.  improvements in the internal strategy together with an updating of external models to the recent standards resulted in the significant improvement in the station positioning including of the stability of the transformation parameter time series. Also the pole coordinates estimation accuracy has been increased. This improvement is illustrated comparing the statistics of GOP contributions to the IDS combination for the ITRF2014 and ITRF2020. Important improvement in the GOP processing capability is the adaption of the software tools to the RINEX data processing, getting closer to raw DORIS measurement. In addition, we present initial results of the data processing and a modeling verification for the post-ITRF2020 data from the DORIS satellites Sentinel-6A, HY-2C and HY-2D.

How to cite: Stepanek, P. and Filler, V.: The GOP DORIS analysis center: data processing and innovation strategy , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10401, https://doi.org/10.5194/egusphere-egu22-10401, 2022.

11:13–11:19
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EGU22-5212
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Virtual presentation
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Erricos C. Pavlis, Vincenza Luceri, Antonio Basoni, David Sarrocco, Magdalena Kuzmicz-Cieslak, Keith Evans, and Giuseppe Bianco

The member ACs of the ILRS Analysis Standing Committee—ASC, evaluated the preliminary release of ITRF2020—ITRF2020P.  For the most part, this evaluation is based on the reanalysis of part or all of the SLR data from geodetic spherical targets in the model; in particular, we focused on the two LAGEOS and two Etalons from 1993 to the end of 2020, extended by one year of data NOT included in the model: all of 2021. The evaluation report was submitted to ITRS for consideration in the finalization of the ITRF2020 model. Some ACs used additional data that do not contribute to ITRF development for testing. The reanalysis used the same improved modeling that was used for the development of the ILRS contribution to ITRF2020.

We will focus on the implementation of the new approach in handling systematic errors at the stations and how users will need to adapt their data analysis procedures to benefit the most from the new model. The 2021 ILRS contribution to ITRF2020 minimized the scale difference between SLR and VLBI below 2 mm (ITRF2014 ~9 mm). The reanalysis incorporates an improved “target signature” model (CoG) for better separation of true systematic errors from errors in describing the target’s signature. This model will be periodically updated from now on, so that it represents accurately the state of operations at all sites in the ILRS network of tracking stations. SLR data users should make sure from now on to use each ITRF model with the appropriate (consistent) Data Handling file and “target signature” model.

The presentation will provide an overview of the analysis procedures and models, and it will demonstrate the level of improvement with respect to the previous ILRS product series, focusing especially on the Core ILRS sites.

How to cite: Pavlis, E. C., Luceri, V., Basoni, A., Sarrocco, D., Kuzmicz-Cieslak, M., Evans, K., and Bianco, G.: The ILRS Analysis Centers’ Report on the Evaluation of ITRF2020P, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5212, https://doi.org/10.5194/egusphere-egu22-5212, 2022.

11:19–11:25
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EGU22-5116
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ECS
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Virtual presentation
Hendrik Hellmers, Sadegh Modiri, Sabine Bachmann, Daniela Thaller, Mathis Bloßfeld, Manuela Seitz, and John Gipson

The ITRF2020 is the upcoming realization of the International Terrestrial Reference Frame. As the successor of the ITRF2014, it is based on an inter-technique combination of all four space-geodetic techniques, i.e., VLBI, GNSS, SLR and DORIS, and it is based on contributions from different institutions around the world. In this context, the Combination Centre of the International VLBI Service for Geodesy and Astrometry (IVS) – operated by the Federal Agency for Cartography and Geodesy (BKG, Germany) and the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM, Germany) – generates the VLBI intra-technique combination for ITRF2020 utilizing the individual contributions of multiple IVS Analysis Centres (AC).

For the contribution to the ITRF2020 solution, sessions containing 24h VLBI observations from 1979 until the end of 2020 are reprocessed by 11 ACs and submitted to the IVS Combination Centre. All individual sessions include datum-free normal equations containing station coordinates and source positions as well as full sets of Earth Orientation Parameters (EOP) in the required SINEX format. For ensuring consistently combined solutions, time series of EOP and station coordinates, as well as a VLBI-only Terrestrial Reference Frame (VTRF), have been investigated.

This contribution focuses on detailed investigations concerning the session-dependency of the scale and the impact of the individual AC contributions to the combination. Thereby significant differences of the scale estimates from the different session types are investigated. Also, the evaluation of the ACs’ contributions to the combined solution will be presented.

How to cite: Hellmers, H., Modiri, S., Bachmann, S., Thaller, D., Bloßfeld, M., Seitz, M., and Gipson, J.: Evaluation of the IVS contribution to the ITRF2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5116, https://doi.org/10.5194/egusphere-egu22-5116, 2022.

11:25–11:31
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EGU22-6932
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Highlight
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Virtual presentation
Manuela Seitz, Detlef Angermann, Matthias Glomsda, Mathis Bloßfeld, Sergei Rudenko, and Julian Zeitlhöfler

As one of the ITRS Combination Centres of the IERS, DGFI-TUM is in charge of computing an ITRS 2020 realisation. Since the ITRS 2014 realisation, many innovations have occurred. These include the six years longer observation period, but also new observation stations and satellites, and the use of refined background models in the analysis of the space-geodetic techniques. In addition, the combination strategy of the DTRF has also been improved. Namely, non-tidal loading (NTL) corrections over the full observation period and for all three components (atmospheric, hydrological and oceanic) are taken into account, as well as modelled post-seismic deformations (PSD). Both corrections are carried out - according to the combination strategy of DGFI-TUM - on the level of the normal equation (NEQ) by reducing each input NEQ.

Due to all the improvements mentioned above, ranging from observation to analysis and combination, it can be assumed that all ITRS 2020 realisations are not only more up-to-date but also more accurate than their predecessors. In the presentation, we demonstrate the DTRF2020 solution as well as first comparisons and analyses. We will also present the DTRF2020 release which will include SINEX files and an EOP file, plus the time series of SLR translations, NTL and PSD corrections, and station position residuals.

How to cite: Seitz, M., Angermann, D., Glomsda, M., Bloßfeld, M., Rudenko, S., and Zeitlhöfler, J.: The ITRS 2020 realization of DGFI-TUM: DTRF2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6932, https://doi.org/10.5194/egusphere-egu22-6932, 2022.

11:31–11:37
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EGU22-3221
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Highlight
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On-site presentation
Richard Gross, Claudio Abbondanza, T. Mike Chin, Mike Heflin, and Jay Parker

JPL's newly developed software for determining terrestrial reference frames, known as SREF (Square-root REference Frame 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 upon a square-root information filter and smoother, determines the reference frame sequentially from the input station position time series. 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 (consisting of a piecewise linear trend, annual and semi-annual periodic terms, and a sum of exponential terms to represent postseismic motion) 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. The result of using SREF to determine JTRF2020 will be presented.

How to cite: Gross, R., Abbondanza, C., Chin, T. M., Heflin, M., and Parker, J.: A Sequentially Estimated Terrestrial Reference Frame: JTRF2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3221, https://doi.org/10.5194/egusphere-egu22-3221, 2022.

11:37–11:43
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EGU22-3958
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Highlight
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On-site presentation
Zuheir Altamimi, Paul Rebischung, Xavier Collilieux, Laurent Metivier, and Kristel Chanard

More than 30 years of space geodetic data have been reprocessed
by the International Association of Geodesy technique services
and submitted to compute the new realization of the
International Terrestrial Reference System (ITRS). The new
realization, ITRF2020, is intended to replace ITRF2014. It is
provided in the form of an augmented reference frame so that in
addition to station positions and velocities, parametric
functions for both post-seismic deformation (PSD) and seasonal
signals (expressed in the Center of Mass frame derived from
Satellite Laser Ranging data) will also be delivered to the
users. The presentation summarizes the main results of ITRF2020
analysis and evaluates its internal consistency via some key
performance indicators. In particular, the paper discusses the
level of the scale agreement between the four techniques, its
linear and nonlinear time evolution, and the strategy adopted
for the ITRF2020 scale definition. In addition, we evaluate the
performance of the parametric functions for both seasonal
signals and PSD and the level of consistency between the four
techniques at colocation sites.

How to cite: Altamimi, Z., Rebischung, P., Collilieux, X., Metivier, L., and Chanard, K.: ITRF2020: main results and key performance indicators, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3958, https://doi.org/10.5194/egusphere-egu22-3958, 2022.

11:43–11:50
Lunch break
Chairpersons: Claudio Abbondanza, Mathis Bloßfeld, Xavier Collilieux
13:20–13:22
13:22–13:28
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EGU22-3897
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On-site presentation
Guilhem Moreaux

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 2021.0 as benchmark to investigate the characteristics of the three ITRF2020 realizations. This set of DORIS station positions correspond to the 1456 weekly solutions delivered by the International DORIS Service (IDS) as the DORIS contribution to the ITRF2020.

After presentation of the overall performance of these three 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, ITRF2020 and JTRF2020 solutions. Then, we make benefit of the almost complete year (2021) since the ending of the ITRF2020 time period to evaluate these three 2020 ITRF solutions in terms of prediction of the DORIS station positions.

How to cite: Moreaux, G.: DORIS Assessment of the 2020 ITRF Realizations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3897, https://doi.org/10.5194/egusphere-egu22-3897, 2022.

13:28–13:34
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EGU22-3417
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On-site presentation
Janusz Bogusz, Anna Klos, and Guilhem Moreaux

We examine DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) position time series processed by the IDS (International DORIS Service) within “ids21wd02” reprocessing, serving as an official input into the newest International Terrestrial Reference Frame, namely ITRF2020. The ids21wd02 set includes the North, East and Up coordinate time series of the 201 stations located at the 87 DORIS sites since 1993.0. These coordinate time series were delivered by the IDS as a byproduct of the IDS contribution to the 2020 realization of ITRF (International Terrestrial Reference Frame). From a number of 201 stations distributed globally, we choose a number of 115 sites, whose time series are longer than 5 years.  Position time series are carefully pre-processed by means of removing outliers and offsets. To reliably describe the DORIS position time series, we use a time series model of long-term non-linear signal, linear trend, seasonal oscillations and a stochastic part. Both deterministic and stochastic components are determined using maximum likelihood estimation. Our analysis is performed in three different ways. Firstly, we search for a preferred noise model and demonstrate, that there is an ongoing improvement of noise parameters over years. This is related to the persisting improvement in background models, antenna types, etc. Then, both deterministic and stochastic parameters are compared to the ITRF2014 IDS solution, to find the usefulness of a newly applied models or strategies, especially to prove an impact of the new C STAREC antenna type. Finally, we compare DORIS position time series to the GPS (Global Positioning System) position time series for a number of 267 co-located stations (official input of International GNSS Service into ITRF2020); both deterministic and stochastic components are compared, with a special attention paid to the differences of velocities and their errors, as they are employed for kinematic reference frames realization or in geodynamical interpretations.

How to cite: Bogusz, J., Klos, A., and Moreaux, G.: Assessment of IDS contribution to ITRF2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3417, https://doi.org/10.5194/egusphere-egu22-3417, 2022.

13:34–13:40
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EGU22-10320
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On-site presentation
Andreja Susnik, Graham Appleby, and Jose Rodriguez

SLR data of LAGEOS-1/2 and Etalon-1/2 satellites were used for generating weekly solution sets containing station coordinates, Earth Rotation Parameters, as well as accommodating systematic range errors, for the period from 1993 to 2020. The solutions follow the approach developed within the ILRS Analysis Standing Committee, with smoothed systematic range errors applied to station range normal points where required. The satellite centre-of-mass corrections developed by Rodriguez et al (2019), and his continuing updates, were applied to the NP ranges. The solutions were used for an evaluation of the ITRF2020P reference frame and to conduct comparisons to ITRF2014. Following our previous investigations into the impact on the scale of the ITRF of systematic range errors, we investigate in particular the difference in scale of the reference frame from our current solutions when mapped using weekly Helmert transformations onto ITRF2014 and onto ITRF2020P.

How to cite: Susnik, A., Appleby, G., and Rodriguez, J.: Evaluation of the ITRF2020P reference frame by means of Satellite Laser Observations (SLR) data analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10320, https://doi.org/10.5194/egusphere-egu22-10320, 2022.

13:40–13:46
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EGU22-13464
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On-site presentation
Karine Le Bail, Tobias Nilsson, Rüdiger Haas, and Fredrik Nyström Lindé

Preliminary results of the ITRF2020 show that the Very Long Baseline Interferometry 
(VLBI) solution appears to have a scale problem, with larger scatter of the scale factor and a 
potential scale drift after around 2014. There are several possible reasons that have been 
brought into discussion, ranging from specific VLBI stations having technical problems to 
the use of various geophysical models in the VLBI data analysis, such as atmospheric 
pressure loading and post-seismic deformation models, and other models to account for, e.g., 
thermal and gravitational deformation of radio telescopes. This work focuses on the impact of 
such reasons on the VLBI scale. We first investigate the VLBI contribution of the Onsala 
Observatory which made used of the software package ASCOT and that enters in the IVS 
combined solution, and we then expand to the IVS combined solution and other individual 
contributions. 

How to cite: Le Bail, K., Nilsson, T., Haas, R., and Nyström Lindé, F.: Investigating the VLBI scale behavior , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13464, https://doi.org/10.5194/egusphere-egu22-13464, 2022.

13:46–13:52
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EGU22-9240
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ECS
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On-site presentation
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Iván Herrera Pinzón and Markus Rothacher


In this contribution we highlight the challenges of the combination of space geodetic techniques through local ties, during the rigorous estimation of geodetic parameters, for the realisation of a global Terrestrial Reference Frame (TRF). Local ties at geodetic fundamental sites play an important role in the determination of a TRF, providing the necessary links to connect the different geodetic techniques. Moreover, the growing demands on the accuracy and stability of the ITRF, have turned the analysis of the quality of these ties into a crucial element to achieve a highly consistent frame, providing additionally the opportunity to identify technique-specific systematic biases  when comparing the space geodetic results with local measurements.

To study the impact of the local ties at fundamental sites, we use the Very Long Baseline Interferometry (VLBI) observations collected during the CONT17 campaign, together with simultaneous Global Navigation Satellite System (GNSS) observations of a subset of the International GNSS Service (IGS) global network. To this end, our approach performs the rigorous estimation of all parameter types common to the two techniques, namely station coordinates, troposphere zenith delays and gradients, and the full set of five Earth Orientation Parameters (EOPs) and their rates, and we include their full variance-covariance information during the combination process. In the central step of this processing scheme, we realise the GNSS-VLBI combination via the "official" ITRF coordinate ties, using and evaluating different weighting schemes, to obtain a unique set of consistent parameters. Moreover, we study the impact of tropospheric ties between the collocated VLBI and GNSS stations, which are essential for the height estimates. Thus, based on the analysis of the station coordinate repeatabilities and the characteristics and behaviour of the EOPs, we discuss the impact of the accuracy and weighting of the local coordinate and troposphere ties on the estimation of the different geodetic parameters.

How to cite: Herrera Pinzón, I. and Rothacher, M.: Local Tie Analysis at Fundamental Sites in the CONT17 Campaign, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9240, https://doi.org/10.5194/egusphere-egu22-9240, 2022.

13:52–13:58
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EGU22-6387
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ECS
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On-site presentation
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Jungang Wang, Maorong Ge, Susanne Glaser, Kyriakos Balidakis, Robert Heinkelmann, and Harald Schuh

The international celestial and terrestrial reference frames (ICRF and ITRF) are two important realizations of the global geodetic reference frame (GGRF). As the basis for high-accuracy astrometry and space exploration, ICRF is currently determined by the Very Long Baseline Interferometry (VLBI) technique solely and independently from the ITRF, whereas a consistent determination of TRF and CRF by a combination of different techniques is highly desirable. We conduct the Global Navigation Satellite Systems (GNSS) and VLBI integrated processing on the observation level and investigate the impact of applying global ties (that is, Earth Orientation Parameters, EOP), local ties, and tropospheric ties on the precision of both TRF and CRF. The GNSS and VLBI observations in VLBI continuous campaigns from CONT05 to CONT17 are processed simultaneously in the common least-squares estimator using the Positioning And Navigation Data Analyst (PANDA) software. We present that the precision of the VLBI station coordinates is significantly improved in the integrated solution, such as the horizontal components by global ties and the vertical components by local and tropospheric ties. Focusing on the precision of active galactic nuclei (AGN) coordinates, we demonstrate that the global ties can slightly reduce the AGN coordinate formal errors by up to 4%, and the local ties mainly improve the declination precision by about 10%. As for the tropospheric ties, the formal error of AGN coordinate can be reduced by 10% on average, and the repeatability can also be improved, especially the declination (10%). Moreover, the southern AGN are more improved than the northern ones, due to the observation geometry of the VLBI ground station distribution.

How to cite: Wang, J., Ge, M., Glaser, S., Balidakis, K., Heinkelmann, R., and Schuh, H.: On the contribution of global, local, and tropospheric ties to TRF and CRF in GNSS and VLBI integrated solution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6387, https://doi.org/10.5194/egusphere-egu22-6387, 2022.

13:58–14:04
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EGU22-5530
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On-site presentation
Arturo Villiger, Rolf Dach, Lars Prange, Daniel Arnold, Maciek Kalarus, Stefan Schaer, Pascal Stebler, and Adrian Jäggi

The release of the next International Terrestrial Reference Frame (ITRF) 2020 is based on the four geodetic techniques, namely Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radio-positioning Integrated by Satellite instrument (DORIS). The upcoming release will presumably define the scale based on the first two techniques.

The GNSS scale is mainly driven by the z-component of the satellite antenna phase center offsets. With the disclosure of the Galileo metadata by the European GNSS Agency (GSA) the satellite antenna pattern became available to the public and enabled the GNSS scale determination.

We aim to analyze the consistency between the preliminary ITRF 2020 solution and the GNSS based scale. In addition, we will extend our study with all available TRF solutions and compare their consistency with the GNSS derived scale and discuss the resulting comparisons. 

How to cite: Villiger, A., Dach, R., Prange, L., Arnold, D., Kalarus, M., Schaer, S., Stebler, P., and Jäggi, A.: Compatibility between the preliminary ITRF2020 solution and GNSS antenna phase center offsets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5530, https://doi.org/10.5194/egusphere-egu22-5530, 2022.

14:04–14:10
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EGU22-4436
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ECS
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On-site presentation
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Wen Huang, Benjamin Männel, Andreas Brack, and Harald Schuh

The deviations of phase center offsets (PCOs) of GPS satellites were and still are significant bias sources for GPS-based terrestrial reference frames (TRF). Because of the strong correlation between the scale of the TRF and the satellite PCOs in the z-direction (z-PCOs), a no-net-scale (NNT) condition relative to, for instance, the International Terrestrial Reference Frame (ITRF) is commonly applied. Based on the released Galileo metadata, the GPS z-PCOs have been calibrated without introducing a scale determined by other techniques in the third re-processing of the International GNSS Service (IGS). Another approach purely based on GNSS is by integrating low Earth orbiters (LEOs) into the estimation of the GPS z-PCOs and the realization of the scale. Within this study, we estimated the GPS z-PCOs based on zero-difference ionosphere-free observations from six low LEOs and ground networks with different numbers of stations in 2019 and 2020. Besides the study based on six LEOs in two years, a twelve-year-based estimation of GPS z-PCOs and scale realization is done by using the two satellites of the GRACE mission.

We jointly estimate orbits (GPS and LEOs), station coordinates, z-PCOs of GPS satellites, and some other parameters in an integrated processing. The NNT condition on the ground network is not applied in the processing. By adding six LEOs, the correlation coefficients between the GPS z-PCOs and the scale is reduced significantly (from about 0.85 to 0.30). It means that the GPS z-PCOs and the scale have been decorrelated efficiently, and consequently the precision of the estimation is improved. For GPS satellites operated in 2019 and 2020, excluding GPS III, their estimated z-PCOs have an average difference of -231 mm compared to the values in igs14_2134.atx and the corresponding scale to the IGS14 reference frame is +1.89 part per billion. These results agree well with the solutions based on the metadata of Galileo. The improvement due to different numbers of LEOs and the impact of LEO z-PCO errors on the estimation is studied, where more LEOs decorrelate the GPS z-PCOs and the scale more efficiently. The accuracy of the LEO z-PCOs is critical to the solution. A one-millimeter accuracy of the z-PCOs of the LEOs is required to achieve a one-millimeter scale on the surface of the Earth. Thanks to the long-term available data of LEO missions in the last decade and even longer, the LEO-based method has an advantage on the real-data-based estimation of PCOs of former GPS satellites over the Galileo-based method. The z-PCOs of satellites of GPS blocks IIA, IIR, IIRM, and IIF are estimated by integrating the two GRACE satellites from 2004 to 2015. A twelve-year scale relative to the ITRF is realized simultaneously. The performance of the LEO-based method is shown by the long-time series.  

How to cite: Huang, W., Männel, B., Brack, A., and Schuh, H.: LEO-based solution of GPS PCOs and impact on terrestrial scale , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4436, https://doi.org/10.5194/egusphere-egu22-4436, 2022.

14:10–14:16
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EGU22-1394
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ECS
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Virtual presentation
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yingying ren, hu wang, and jiexian wang

The current international and regional reference frame research is mainly realized by single GPS (Global Position System) technology. With the full deployment of BDS (Beidou Navigation System), it is urgent to study and establish the corresponding terrestrial reference frame. Since 2019, the global and regional BDS service performance has been evaluated and tested, and the long-term BDS observations of MGEX (Multi GNSS Experiment) sites distributed worldwide provide the possibility for the preliminary construction of the BDS terrestrial reference frame. We aim to preliminarily realize and evaluate the CTRF2020 (COMPASS/BDS Terrestrial Reference Frame at the epoch of 2020.0) that can be expressed with the coordinates and velocities of a series of reference sites at the epoch of 2020.0. Firstly, the actual BDS global service performance evaluation reflects BDS satellite's high visibility and change trend in recent three years, which provides primary input data for the frame. Then, the BDS observations of about 100 global sites in the recent three years are calculated by PPP (Precise Point Positioning) and NET solution, to obtain the global high-precision BDS coordinate time series. Then, the BDS time series of the two solutions are fitted and compared with the IGS14 velocity field. The results show that the series accuracy of PPP-BDS and NET-BDS solutions is equivalent, and there is an mm-level systematic deviation with IGS14 solutions. The horizontal series fitting accuracy of PPP-BDS and NET-BDS solutions is better than that of the vertical direction, the accuracy of NET-BDS solution is slightly better than PPP-BDS, and the difference of fitting accuracy is 0.12, 0.13, and 0.50 mm in the NEU direction. The velocity field accuracy of PPP-BDS and NET-BDS solution is the same, and the overall three-dimensional velocity difference is less than 0.2 mm/a. The velocity fields of PPP-BDS and NET-BDS solution have little difference from IGS14, and the overall difference is less than 0.5 mm/a. Finally, we give the limitations and improvement points of CTRF2020. The preliminary realization and evaluation of CTRF2020 may be expected to provide a reference for the future realization of a comprehensive terrestrial reference framework dominated by BDS technology and supplemented by multi-source space geodetic technology.

How to cite: ren, Y., wang, H., and wang, J.: The preliminary realization and evaluation of BDS3 global terrestrial reference framework (CTRF2020), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1394, https://doi.org/10.5194/egusphere-egu22-1394, 2022.

14:16–14:22
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EGU22-10229
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ECS
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On-site presentation
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Lin Wang, Dimitrios Ampatzidis, Antonios Mouratidis, and Kyriakos Balidakis

The Hermert-like constrain condition is commonly used in various space geodetic reference frame alignment and reference frame definition, this often demands discussions on the proper constrain strength, selection of fiducial network, and more. Thus, the published and constrained reference frame products/solutions are often demanded the transformation to alternative constrain condition due to the area of interest change, reduction of the coverage, or other reasons.

We present an efficient methodology to transform reference reframe product to a posterior selection of the constrained condition from the product which either minimum or redundant datum constraints have been imposed. This analytical methodology significantly reduces the computation effort for datum alignment, especially for the large GNSS network. By avoiding the expensive normal equation system reconstruction and the subsequent inversion thereof, we achieved computational complexity reduction with an inversion of an auxiliary matrix of up to 14X14 dimension, while the computation is validated analytically as well as numerically to the truncation error level. This Fast Constraints Transformation (FCT) method can be conveniently applied to the widely used space geodetic solution files following the Solution Independent Exchange (SINEX) format, especially with our provided software package written in Matlab. We validate and evaluated FCT with two globally distributed GNSS-derived solutions and one South America terrestrial reference frame. The results confirm the numerical equivalence of the classical method and FCT. We also present the discussion on the computation efficiency with the above networks as well as numerical simulations. For the large network of up to 5000 stations, The FCT accelerates the transformation by more than 100 times compared to the classical strategy.

FCT method could serve as a beneficial procedure to many TRF-related applications, including but not limited to:

  • Deploy Over Constain condition to an existing solution
  • Transforming an Over Constrained solution to a Minimal Constrained solution
  • Re-computation of a specified Minimal Constrained solution from an Over Constained or loosely-constrained solution.
  • For global networks with a large number of stations the FCT significantly reduces the computation effort.
  • For the cases of regional and local TRFs, the methodology shows significant advantages since the final product can be considered an Over Constrain solution.
  • FCT could be applied for local and regional networks removing the imposed constraints and deriving the initial GNSS network.

How to cite: Wang, L., Ampatzidis, D., Mouratidis, A., and Balidakis, K.: Solution-Level Fast Constraints Transformations with Case Studies for GNSS Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10229, https://doi.org/10.5194/egusphere-egu22-10229, 2022.

14:22–14:28
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EGU22-5578
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ECS
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On-site presentation
Yujiao Niu, Paul Rebischung, Zuheir Altamimi, Na Wei, and Min Li

Temporally and spatially correlated noise has long been reported in Global Navigation Satellite System (GNSS) station position time series. Accounting for the temporal correlations of the noise is crucial to obtain realistic uncertainties for deterministic parameters, e.g., station velocities, while accounting for its spatial correlations is beneficial to various applications such as offset detection, velocity estimation and detection of local geophysical signals. The origins of the spatio-temporally correlated noise in GNSS series are however still unclear, and a realistic spatio-temporal noise model also remains to be elaborated. In this study, we therefore analysed GNSS residual time series from the International GNSS Service (IGS) third reprocessing (repro3), corrected from loading deformation models, with the purpose of characterizing and modeling their spatio-temporal correlations in detail.

We first estimated spectral correlation coefficients as a function of both the distance between GNSS stations and the temporal frequency. Different spatial correlation regimes could thus be evidenced for different frequency bands. Spatial correlations are in particular higher, and range longer distances, at the frequencies of the periodic (e.g., draconitic, fortnightly) errors in GNSS time series. Broadband spatial correlations are consequently reduced when these periodic errors are filtered out from the series.

To investigate possible spatial non-stationarities of the noise, we then estimated its spatial covariance, as a function of the distance between stations, over different regions. While the estimated spatial covariance is similar to the global average in Europe, Eastern US and Australia, it is consistently higher in Eastern South America, New Zealand and Western US. This may point to a partially geophysical origin of the spatially correlated noise in the latter regions, possibly attributable to unmodeled hydrological loading and tectonic deformation, respectively.

We finally converted the globally averaged spatial covariance of the residual repro3 series into a spatial power spectrum, i.e., power as a function of the spherical harmonic degree. It thus turns out that the average spatial covariance is well described by a spatial power-law model attenuated at the lowest degrees.

How to cite: Niu, Y., Rebischung, P., Altamimi, Z., Wei, N., and Li, M.: Analysis of spatio-temporal correlations of IGS repro3 station position time series, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5578, https://doi.org/10.5194/egusphere-egu22-5578, 2022.

14:28–14:34
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EGU22-2985
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ECS
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On-site presentation
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Maylis de La Serve, Paul Rebischung, Zuheir Altamimi, Xavier Collilieux, and Laurent Métivier

In historical versions of the International Terrestrial Reference Frame (ITRF), the time evolution of station positions was described by piece-wise linear models. These kinematic models have been extended with exponential and logarithmic functions in ITRF2014 to account for post-seismic displacements, then with annual and semi-annual sine waves in ITRF2020 to account for the seasonal deformation of the Earth. However, part of the Earth’s surface deformation, such as inter-annual hydrological loading deformation, or high-frequency atmospheric loading deformation, is still not captured by such deterministic functions.

A reference frame in the form of a time series could allow such aperiodic displacements to be taken into account. This would require the aperiodic motions sensed by the different space geodetic techniques to be tied in a common frame by means of co-motion constraints. However, common aperiodic displacements between co-located space geodetic stations have not been evidenced at a global scale so far, and the relevance of such constraints is thus debatable. In this study, in order to investigate the possible existence of common aperiodic displacements at ITRF co-location sites, we use the solutions provided by the technique services for ITRF2014. Those solutions are first carefully aligned to a common reference frame in order to minimize differential network effects and obtain comparable position time series across techniques. The obtained position time series are then cleaned from linear, post-seismic and periodic signals (including seasonal deformation and technique systematic errors). The remaining aperiodic displacements are finally inter-compared at co-location sites.

Modest correlations are thus evidenced between the GNSS residual position time series and the other space geodetic techniques, mostly in the vertical component. The magnitude of the common aperiodic displacements evidenced in this study is finally discussed.

How to cite: de La Serve, M., Rebischung, P., Altamimi, Z., Collilieux, X., and Métivier, L.: Study of common aperiodic displacements at ITRF co-location sites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2985, https://doi.org/10.5194/egusphere-egu22-2985, 2022.

14:34–14:40
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EGU22-1183
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Highlight
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On-site presentation
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Alvaro Santamaría, Roelof Rietbroek, Thomas Frederikse, Paul Rebischung, and Juliette Legrand

GNSS velocities estimated by different analysts can significantly differ due to the choices made concerning the GNSS data processing (corrections applied and noise level of the series), the completeness of the series, the removed position discontinuities and the alignment to a terrestrial reference frame. The position discontinuities that populate the GNSS time series have probably the biggest impact on the error or dispersion of the velocity estimates at the same sites. Even when using exactly the same position series, different analysts may provide different velocity estimates and uncertainties mainly due to the choice of removing different position discontinuities.

The IAG Joint Working Group 3.2 (2019 – 2023) aims at providing a global combined GNSS velocity field that takes into account the repeatability, the alignment and the relative weighting of the velocity estimates by different groups. We expect that this IAG’s unified GNSS velocity field will be useful for the scientific community inside, but especially outside, the geodetic community in areas such as tectonics, sea-level change and GIA modeling among others.

In this contribution, we present the current status of the global combined velocity field, aligned to the recently released ITRF2020, and based on the velocity fields provided by several other groups.

How to cite: Santamaría, A., Rietbroek, R., Frederikse, T., Rebischung, P., and Legrand, J.: Towards an IAG combined global GNSS velocity field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1183, https://doi.org/10.5194/egusphere-egu22-1183, 2022.

14:40–14:50