The Terrestrial Reference Frame is fundamental for monitoring Earth rotation in space and for all geoscience applications that require absolute positioning and precise orbit determination of artificial satellites. The goal of this session is to provide a forum to discuss reference systems theory, realization and applications in geosciences and society, with a special emphasis on the scientific applications of the International Terrestrial Reference Frame (ITRF), and namely the ITRF2014. Participants can discuss concerns not only related to the contributing technique services, but also all ITRF uses, ranging from local, regional to global applications. Contributions are sought from the individual technique services and various ITRF users, covering the complete range of topics, such as data analysis, parameter estimation and correction models. Of special interest is the assessment of the impact of non-linear station motions, e.g. periodic signals and post-seismic deformations. Contributions by the technique services related to the preparation of ITRF2020 focusing especially on identifying and mitigating technique systematic errors are highly appreciated. Contributions on local tie survey methodology are also welcome.

Convener: Xavier Collilieux | Co-conveners: Claudio Abbondanza, Susanne GlaserECSECS
| Attendance Mon, 04 May, 16:15–18:00 (CEST)

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Chat time: Monday, 4 May 2020, 16:15–18:00

Chairperson: X. Collilieux, S. Glaser, C. Abbondanza
D1856 |
Vincenza Luceri, Erricos C. Pavlis, Antonio Basoni, David Sarrocco, Magdalena Kuzmicz-Cieslak, Keith Evans, and Giuseppe Bianco

The International Laser Ranging Service (ILRS) Analysis Standing Committee (ASC) plans to complete the re-analysis of the SLR data since 1983 to end of this year by early 2021. This will ensure that the ILRS contribution to ITRF2020 will be available to ITRS by February 2021, as agreed by all space geodetic techniques answering its call. In preparation for the development of this contribution, the ILRS completed the re-analysis of all data (1983 to present), based on an improved modeling of the data and a novel approach that ensures the results are free of systematic errors in the underlying data. The new approach was developed after the completion of ITRF2014, the ILRS ASC devoting almost entirely its efforts on this task. A Pilot Project initially demonstrated the robust estimation of persistent systematic errors at the millimeter level, leading us to adopt a consistent set of a priori corrections for data collected in past years. The initial reanalysis used these corrections, leading to improved results for the TRF attributes, reflected in the resulting new time series of the TRF origin and scale. The ILRS ASC will now use the new approach in the development of its operational products and as a tool to monitor station performance, extending the history of systematics for each system that will be used in future re-analysis. The new operational products form a seamless extension of the re-analysis series, providing a continuous product based on our best knowledge of the ground system behavior and performance, without any dependence whatsoever on a priori knowledge of systematic errors (although information provided by the stations from their own engineering investigations are always welcome and taken into consideration). The presentation will demonstrate the level of improvement with respect to the previous ILRS product series and give a glimpse of what is to be expected from the development of a preliminary version of the ITRF2020.

How to cite: Luceri, V., Pavlis, E. C., Basoni, A., Sarrocco, D., Kuzmicz-Cieslak, M., Evans, K., and Bianco, G.: A Status Report on the ILRS Contribution to ITRF2020, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7218, https://doi.org/10.5194/egusphere-egu2020-7218, 2020.

D1857 |
Guilhem Moreaux, Frank Lemoine, Hugues Capdeville, Petr Štěpánek, and Pascale Ferrage

To provide its contribution to the next realization of the International Terrestrial Reference Frame (ITRF2020), the International DORIS Service (IDS) plans to complete the re-analysis of the DORIS data from 1993.0 to 2021.0 by early 2021. In preparation for the development of its contribution, the IDS completed several pilot studies for a better modelling of the solar radiation pressure, to mitigate the effect of the South Atlantic Anomaly on the DORIS receivers, to improve the stability of the DORIS scale. The complete re-analysis is divided in several parts depending on the time evolution of the DORIS constellation and on modelling issues.

IDS Analysis Center contributions for first time period, which corresponds to the observations from the DORIS satellites with the first generation of the DORIS receivers: 1993.0-2002.3 (start of Envisat – first DORIS 2G receiver), are expected by the end of the first quarter of 2020.

After presentation of the status of the main guidelines of the DORIS contribution to the ITRF2020, we will analyze the first time period of the DORIS contribution to ITRF2020 in terms of (1) geocenter and scale solutions; (2) station positions and week-to-week repeatability; (3) EOPs. In addition, we will compare this new DORIS solution with the IDS contribution to ITRF2014. Then, we will present updated results on the latest IDS pilot studies.

How to cite: Moreaux, G., Lemoine, F., Capdeville, H., Štěpánek, P., and Ferrage, P.: The IDS Contribution to the ITRF2020: Preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11252, https://doi.org/10.5194/egusphere-egu2020-11252, 2020.

D1858 |
| Highlight
Juliette Legrand and Carine Bruyninx

When using a network approach, expressing reliably GNSS position and velocities in a given reference frame (ITRF2014, IGS14, …) requires the identification of ‘stable’ and ‘rebliable’ reference stations. The choice of these reference stations can have a non-negligible impact on the estimated positions and velocities and of course on the derived geodynamic interpretations.

This study will present the work done to address this issue within EUREF and help the users of the EUREF products (more specifically of the EPN multi-year position and velocity solution) to identify the best reference stations in the EUREF Permanent Network (EPN). To that aim, a new station classification was developed based on a set of criteria.

First, the position time series of the stations were analyzed in terms of seasonal signals and scattering.

Then, we quantified the reliability of the velocity estimation: The EPN multi-year position and velocity solution is estimated using CATREF software (Altamimi et al., 2007). We used more realistic velocity error estimates taking into account a temporal correlated noisederived from the Hector software (Bos et al., 2013) and compared the velocity estimates from Hector and CATREF.

Finding a suitable reference station is particularly difficult when dealing with a different period of observations compared to the reference solution. Therefore, finally, we looked for a criterion to assess the stability of the station over its full history. For this, we quantified the velocity variability over time of a station by comparing the velocities estimated using various time spans with velocities from the full time span of the station.

Based on those criteria, the information has been organized and thresholds have been defined in order to end up with a simple station classification, which is currently under evaluation within EUREF. Based on this classification, we also developed a web tool in order to help the user to select the best reference stations in a considered area and for a given period of observation.

How to cite: Legrand, J. and Bruyninx, C.: Quality assessment of GNSS reference stations: Criteria and Thresholds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20320, https://doi.org/10.5194/egusphere-egu2020-20320, 2020.

D1859 |
Pakize Kurec Nehbit, Robert Heinkelmann, Harald Schuh, and Haluk Konak

The quality of geodetic networks can be determined with the sensitivity and the internal reliability magnitudes when the mathematical model established for the network adjustment is questioned. Internal reliability is used for controlling an observation with the help of the other observations in the network and describes the magnitude of the undetectable gross errors by using hypothesis testing. The sensitivity level is explained as the minimum value of the undetectable gross error in the adjusted coordinate differences. In VLBI the observed sources are of major importance for the quality of the observations.  In this study, it is investigated how the sensitivity levels of the sources impact the internal reliability of the observations during the continuous VLBI campaign CONT14. It is aimed to detect the poor sources and their effects statistically in the VLBI data analysis. If the sources having worst sensitivity value such as 0506-612, 3C454.3, NRAO150, and 3C345  have been excluded, the internal reliability values of the observations get better. For the rest of the sources the sensitivity distributions have been obtained as better. It can be concluded that the source structure might be significant for the quality of the observations.

How to cite: Kurec Nehbit, P., Heinkelmann, R., Schuh, H., and Konak, H.: Investigation of the relationship between sensitivity level of the sources and the internal reliability value of VLBI observations during CONT14, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18184, https://doi.org/10.5194/egusphere-egu2020-18184, 2020.

D1860 |
Xiaoping Wu, Bruce Haines, Michael Heflin, and Felix Landerer

A Kalman filter and time series approach to the International Terrestrial Reference Frame (ITRF) realization (KALREF) has been developed and used in JPL. KALREF combines weekly or daily SLR, VLBI, GNSS and DORIS data and realizes a terrestrial reference frame in the form of time-variable geocentric station coordinate time series. The origin is defined at nearly instantaneous Center-of-Mass of the Earth system (CM) sensed by weekly SLR data and the scale is implicitly defined by the weighted averages of those of weekly SLR and daily VLBI data. The standard KALREF formulation describes the state vector in terms of time variable station coordinates and other constant parameters. Such a formulation is fine for station positions and their uncertainties or covariance matrices at individual epochs. However, coordinate errors are strongly correlated over time given KALREF’s unique nature of combining different technique data with various frame strengths through local tie measurements and co-motion constraints and its use of random walk processes. For long time series and large space geodetic networks in the ITRF, KALREF cannot keep track of such correlations over time. If they are ignored when forming geocentric displacements for geophysical inverse or network shift geocenter motion studies, the covariance matrices of coordinate differences cannot adequately represent those of displacements. Consequently, significant non-uniqueness and inaccuracies would occur in the results of studies using such matrices. To overcome this difficulty, an advanced KALREF formulation is implemented that features explicit displacement parameters in the state vector that would allow the Kalman filter and smoother to compute and return covariance matrices of displacements. The use of displacement covariance matrices reduces the impact of time correlated errors and completely solves the non-uniqueness problem. However, errors in the displacements are still correlated in time. Further calibrations are needed to accurately assess covariance matrices of derivative quantities such as averages, velocities and accelerations during various time periods. We will present KALREF results of the new formulation and their use along with newly reprocessed RL06 GRACE gravity data in a new unified inversion for geocenter motion.

How to cite: Wu, X., Haines, B., Heflin, M., and Landerer, F.: An Advanced Formulation of Kalman Filter Time Series Reference Frame Realization for Geophysical Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6546, https://doi.org/10.5194/egusphere-egu2020-6546, 2020.

D1861 |
Benedikt Soja, Claudio Abbondanza, T. Mike Chin, Richard Gross, Michael Heflin, Jay Parker, and Xiaoping Wu

The ITRF2014 candidate solutions DTRF2014 and JTRF2014 provide time-dependent station coordinates accounting for irregular station motions. DTRF2014 by DGFI-TUM expands the secular coordinate model via non-tidal loading corrections caused by changes in the atmosphere and continental water storage. JTRF2014 by JPL follows a time series approach to TRF determination based on Kalman filtering, providing weekly updates to station coordinates. The process noise model of the Kalman filter is derived from non-tidal loading deformations.

Global features in station displacements have been studied in the past by determining coefficients of spherical harmonics. So far, studies have mostly focused on individual coordinate components at a time. Typically, the vertical coordinate component is of most interest, since it most often contains the largest signals.

In this work, we apply the concept of vector spherical harmonics (VSH) to study temporal variations in station displacements of DTRF2014 and JTRF2014. The advantage of VSH compared to scalar spherical harmonics is that all three coordinate components can be considered at the same time. We estimate VSH coefficients up to degree-2, which includes dipole and quadrupole deformations. Degree-1 deformations represent translations and rotations of the frame, while degree-2 terms contain, inter alia, information on the oblateness of the Earth. We use VSH to analyze station displacements of DTRF2014 and JTRF2014 individually and to conduct comparisons between the two frames. Furthermore, since the temporal variations in both DTRF2014 and JTRF2014 are linked to non-tidal loading deformations, our analysis of temporal variations in VSH coefficients allows for geophysical interpretation.


How to cite: Soja, B., Abbondanza, C., Chin, T. M., Gross, R., Heflin, M., Parker, J., and Wu, X.: Temporal variations in ITRF station displacements analyzed with vector spherical harmonics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10823, https://doi.org/10.5194/egusphere-egu2020-10823, 2020.

D1862 |
Lizhen Lian, Chengli Huang, and Jin Zhang

The reprocessed time series (weekly from SLR, daily from GNSS, and 24h session-wise from VLBI) of co-located station position solutions spanning their full observation histories up to the end of 2014 are analyzed with the goal to detect nonlinear time-variable effects in station positions, such as periodic variations or discontinuities caused e.g. by instrumental changes or earthquakes. This information is then used to assess the reliability of the results about the nonlinear changes of all technique stations in each colocation site since they can be verified with each other. Next, the iterative adjustment is performed, i.e. jumping changes, post-seismic deformation and periodical signals are determined altogether for accurate estimation of station velocity. Finally, the information of the relative motion among the stations equipped with different technique instruments per colocation site is determined which can offer a reference for the necessary arrangement of local resurvey in the future.

How to cite: Lian, L., Huang, C., and Zhang, J.: Comparative Analysis of non-linear position variations using the time series of station coordinates in some ITRF co-location sites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6812, https://doi.org/10.5194/egusphere-egu2020-6812, 2020.

D1863 |
Anna Zessner-Spitzenberg, David Mayer, Andreas Hellerschmied, Markus Mikschi, and Sigrid Böhm

The next International Terrestrial Reference Frame (ITRF), ITRF2020, will be released in early 2021 and preparations are entering the final phase. It will be realized by using the observations of the space geodetic techniques Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS).
The Vienna VLBI group is planning to contribute to the ITRF2020. This poster will present the goals, the methodology and preparations for our contribution. In order to analyse the VLBI observation sessions, the Vienna VLBI and Satellite Software (VieVS) will be used. The poster will focus on the influence of applying the gravitational deformation and the atmospheric loading on the individual solutions and the ITRF.  For this purpose, a selected list of more than 800 sessions of the last 40 years, which was released by the International VLBI Service for Geodesy and Astrometry (IVS) to verify the latest changes in the implementation, will be analysed and the results will be presented.

How to cite: Zessner-Spitzenberg, A., Mayer, D., Hellerschmied, A., Mikschi, M., and Böhm, S.: Preparations for the ITRF2020 at TU Wien, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8712, https://doi.org/10.5194/egusphere-egu2020-8712, 2020.

D1864 |
Sahar Shoushtari, Susanne Glaser, Kyriakos Balidakis, Robert Heinkelmann, James Anderson, and Harald Schuh

On the impact of gravitational deformation on VLBI-derived parameters

Sahar Shoushtari1,2, Susanne Glaser1, Kyriakos Balidakis1, Robert Heinkelmann1,2, James M. Anderson1,2, Harald Schuh1,2

(1) GFZ German Research Centre for Geosciences, Section 1.1 Space Geodetic Techniques, Telegrafenberg, 14473 Potsdam, Germany

(2) Technische Universität Berlin, Chair of Satellite Geodesy, Strasse des 17. Juni 135, 10623 Berlin, Germany

Very Long Baseline Interferometry (VLBI) is a highly accurate space geodetic technique that observes extragalactic radio sources to measure the time delay between arrival times of a plane wavefront at two distant radio telescopes. The gravitational deformation of the VLBI telescopes as a function of pointing direction, caused by gravitational forces acting on the massive telescope structures, mainly impacts the estimated station heights and can reach centimeter-level for large antennas. Thus far, this effect has not been considered in operational VLBI data analysis. In the next realization ITRF2020, it is envisaged to model this effect in an effort to reduce the persistent scale discrepancy in ITRF2014 between VLBI and Satellite Laser Ranging. Currently, there are models for only a minority of antennas available, six in total: Effelsberg, Gilcreek, Medicina, Noto, Onsala, and Yebes, which are provided by the International VLBI Service for Geodesy and Astrometry (IVS). In this study, the impact of the gravitational models on station positions, Earth orientation parameters and the network scale is assessed within VLBI data analysis. The standard 24-hours IVS-R1 and -R4 sessions are analyzed using the PORT (Potsdam Open-source Radio Interferometry Tool) software package. First results show that the gravitational models of the six antennas change the station heights by a few mm and the horizontal components by less than 1 mm (in case of Medicina).

How to cite: Shoushtari, S., Glaser, S., Balidakis, K., Heinkelmann, R., Anderson, J., and Schuh, H.: On the impact of gravitational deformation on VLBI-derived parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5100, https://doi.org/10.5194/egusphere-egu2020-5100, 2020.

D1865 |
Markus Mikschi, Johannes Böhm, and Matthias Schartner

With the number of available VGOS (VLBI Global Observing System) sessions rising, precise coordinates for the participating stations become more important. While station coordinates can be estimated during the VLBI (Very Long Baseline Interferometry) analysis, the definition of the geodetic datum via Not-Net-Rotation (NNR) and No-Net-Translation (NNT) conditions requires at least three participating stations with precise a priori coordinates. The VGOS station network is currently independent of the International Terrestrial Reference Frame (ITRF), as none of the stations have participated in a solution for the ITRF in VGOS mode. By estimating the VGOS station coordinates based on ITRF coordinates, originating from local surveying and solutions of S/X observations by now converted stations, a link to the ITRF can be established. First a global solution, which is the combination of individual sessions on the normal equation level, of the five VGOS CONT17 sessions was calculated. The datum was defined by WESTFORD, ISHIOKA and WETTZ13S whereby the coordinates of the first two stations are known from S/X observations and of the latter from local surveying. With velocities from adjacent stations, the estimated coordinates were used to calculate a global solution of the 2019 VGOS sessions. The obtained coordinates were assessed on basis of formal errors, coordinate repeatability and comparisons of estimated Earth Orientation Parameters (EOP) time series with fixed station coordinates to the 14 C04 a priori dataset.

How to cite: Mikschi, M., Böhm, J., and Schartner, M.: Estimation of VGOS Station Coordinates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8710, https://doi.org/10.5194/egusphere-egu2020-8710, 2020.

D1866 |
Ingrid Fausk, Michael Dähnn, and Ann-Silje Kirkvik

Where is a software package developed by the Norwegian Mapping Authority (NMA). The software will provide a useful contribution to the International Terrestrial Reference Frame, by analysis of data from Very-long-baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR).

Where is written in Python, and is taking advantage of well-tested code like the SOFA and IERS libraries. The architecture is easily maintainable and extendable. Python makes it easy to write, and utilizes external libraries written in faster languages.
Both the NMA and the Instituto Geografico Nacional, Spain, are in a test phase of deliveries of VLBI analysis results to the IVS with the Where software. After some improvements of the software, we will also deliver analysis results to the ILRS. Our goal is to receive full status as operational analysis center for both VLBI and SLR, and to contribute to ITRF2020.
Sharing and cooperating with other institutions is made possible by making Where an open source project on GitHub.

How to cite: Fausk, I., Dähnn, M., and Kirkvik, A.-S.: Where - A Software for geodetic Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17532, https://doi.org/10.5194/egusphere-egu2020-17532, 2020.

D1867 |
Dzana Halilovic and Robert Weber

The European GNSS Galileo became almost fully operational with 22 usable satellites in orbit and two testing satellites on the extended orbit. Since the introduction of the first Galileo satellite in December 2005, it became an important complement in GNSS applications to the already established GPS and GLONASS. The combination of Galileo with GPS observations allows to achieve an increased accuracy of precise parameter estimation.

GNSS-based applications are one of the most important methods to derive estimates of the pole coordinates x, y and the LOD (Length-of-Day). In previous work, the potential to improve GNSS observations for the estimation of hourly earth rotation parameters (ERP), based on a Multi-GNSS approach, has been investigated. The analysis covered a 6 month’s (August 2017 – December 2017) time period and considered a globally distributed network of approximately 160 GNSS stations. For around 75 stable stations, an NNR (No-Net-Rotation) constraint to their ITRF2014 coordinates was applied and precise GPS+Galileo ephemerides provided by ESA were used (based on an improved SRP apriori box-wing model for the Galileo satellites). On top solar radiation pressure coefficients were estimated using the empirical CODE orbit model (ECOM). Two solutions were applied, a GPS-only and a combined GPS+Galileo solution.

Meanwhile a reprocessing of the same time series was performed, based on an upgraded stable GNSS station network. Again, a GPS-only and a combined GPS+Galileo solution was carried out. The processing of the new time series has been extended for the whole year of 2017 and the first half of 2018, to provide more reliable results.

In this presentation, comparisons of 1- and 3-day arc ERP solutions with the IERS reference model IERS2010XY will be examined and discussed. Additionally, the different solution types (GPS-only and GPS+Galileo) from the first and reprocessed run were compared. From both GNSS solutions, amplitude corrections for tidal waves were estimated and analyzed w.r.t. the IERS2010XY reference model.

How to cite: Halilovic, D. and Weber, R.: Contribution of Galileo observations to improve the quality of daily and sub-daily earth rotation parameter estimates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3625, https://doi.org/10.5194/egusphere-egu2020-3625, 2020.

D1868 |
Benjamin Männel, Andre Brandt, Markus Bradke, Andreas Brack, Pierre Sakic, and Thomas Nischan

Based on a large network of continuously operated GNSS tracking stations, the International GNSS Service (IGS) has a valuable contribution to the realization of the International Terrestrial Reference System. In order to provide the highest accurate and consistent solution, the IGS refined the strategy and the set of associated models for the ongoing third reprocessing campaign. Beyond updated background models, a major improvement is the combined reprocessing of three GNSS, namely GPS, GLONASS, and Galileo. Furthermore, signal-specific receiving antenna calibrations for Galileo and scale-free transmission phase center positions are applied. These modifications will allow exciting new investigations based on the delivered products. Hosting an IGS Analysis Center and an Analysis Center of the IGS Tide Gauge Benchmark Monitoring Project (TIGA), GFZ will contribute with two solutions to the IGS reprocessing efforts.

In this contribution, we will present the first outcomes of the ongoing preparations and preliminary results of the GFZ reprocessing activities. In the first part, we will present selected results of dedicated tests with a special focus on correction models and parametrization options. Secondly, we will present the initial results of the AC solution as a basis to discuss also further applications of the derived products (e.g., orbits, Earth rotation parameters). Finally, the first results of our TIGA-related reprocessing will be presented which are based on the previously discussed orbits and satellite clocks.

How to cite: Männel, B., Brandt, A., Bradke, M., Brack, A., Sakic, P., and Nischan, T.: Status of IGS repro3 activities at GFZ , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7980, https://doi.org/10.5194/egusphere-egu2020-7980, 2020.

D1869 |
Michiel Otten, Tim Springer, Francesco Gini, Volker Mayer, Erik Schoenemann, and Werner Enderle

For the previous ITRF calls for participation ESOC reprocessed the historic data from the IDS, IGS, and ILRS. Our three solutions were computed with a single software package (NAPEOS), running on the same machine and using, as far as possible, identical settings. Any systematic differences between the technique dependent reference frame solutions must therefore be caused by the techniques themselves, and not because of model differences or errors. Our three technique dependent solutions gave us a good understanding of the technique dependent effects, helping us to improve our models.

At ESOC we have now made a significant step forward by including all satellite geodetic techniques (SLR, DORIS and GNSS) into one solution. This allows us to combine the ILRS, IDS and IGS reference frames by using “space ties”. Of course these space ties are not perfectly known but they still allow for a rigorous combination of the different reference frames. Furthermore, and very important for the GNSS technique, they allow for the direct estimation of the GNSS satellite transmitter phase centre offset. We solve not only for integer ambiguities of the GPS satellites but also for those of the LEO satellites, which is also providing GPS phase observations on two frequencies. 

Our poster presents an overview of this multi-technique combination approach at observation level (COOL). We have included all observations provided by the following satellites in a single parameter estimation process: GNSS, JASON, SPOT, Sentinels, GRACE, LAGEOS and Etalon satellites. We demonstrate the benefits of such a rigorous approach compared to processing the various space geodetic techniques separately.

How to cite: Otten, M., Springer, T., Gini, F., Mayer, V., Schoenemann, E., and Enderle, W.: The benefits for ITRF2020 from multi-technique combination at the observation level (COOL) processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21925, https://doi.org/10.5194/egusphere-egu2020-21925, 2020.

D1870 |
Manuela Seitz, Mathis Blossfeld, Matthias Glomsda, and Detlef Angermann

For the ITRS realization 2020 input data series of high quality from SLR, VLBI, GNSS and DORIS will be provided by the respective Technique Services ILRS, IVS, IGS and IDS. The observation data are currently reprocessed applying agreed state-of-the-art models. Between ITRF2014 and the ITRS realization 2020, many model changes had to be implemented for the individual techniques which nearly all have an impact on the realized scale. To mention the most important ones: (i) For SLR, estimated mean range biases will be introduced for each station and satellite. (ii) In VLBI analysis, the gravitational deformation of the telescopes will be considered for some stations. (iii) In GNSS analysis, highly-precise Galileo satellite phase center calibrations allow for the realization of the scale from Galileo observations. Calibrating GPS phase center corrections accordingly might even allow for a scale realization from the complete GNSS time series history. (iv) In case of DORIS, which was not involved in the ITRS scale realization up to now (as wasn’t GNSS), a new antenna type and changes in elevation cut-off and observation down-weighting will also have an impact on the scale.

It is a fact, that many of the model changes are not analyzed in detail with respect to their impact on the ITRF scale, and neither is the combination of model changes. The situation is even more complex since the ITRS realizations 2014, ITRF2014 on the one hand and DTRF2014 and JTRF2014 on the other hand, differ significantly with respect to the realized scale.

The poster summarizes and categorizes the various model changes and their impact on the scale. It critically discusses the new situation, which is a challenge for ITRS 2020 scale realization and will lead to significant differences between ITRF2020 and its predecessor ITRF2014.

How to cite: Seitz, M., Blossfeld, M., Glomsda, M., and Angermann, D.: ITRS 2020 realization: the new situation for scale realization , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5914, https://doi.org/10.5194/egusphere-egu2020-5914, 2020.

D1871 |
Toshio Mike Chin, Claudio Abbondanza, Richard Gross, Michael Heflin, Jay Parker, Benedikt Soja, and Xiaoping Wu

The JTRF2014 realization of terrestrial reference frame has adopted a weekly time series representation that can track dominant non-linear station motions including periodic and random variations.  The realization is based on the Kalman filter and smoother algorithms whose time sequential nature would also be suitable for continuous updating of an existing frame as soon as new geodetic data become available.

As a part of preparation for the next reference frame realization, we have been examining alternative filter and smoother algorithms based on the square-root information filter (SRIF), known generally for improved numerical accuracy of the covariance matrix represented by a square-root matrix.

The new algorithms offer a number of other advantages over the conventional filter/smoother algorithms used in JTRF2014.  Namely, the new approach allows us to (1) avoid using some fictitious covariance matrix to initialize the filter, (2) avoid the random-walk constraints for the Helmert parameter sequences, and (3) handle cross-temporal EOP data such as the week-long segments reported by the SLR and DORIS networks.  We have also been enhancing the stochastic models of the station position motion to be used by the filter and smoother, including models for non-tidal deformation.

How to cite: Chin, T. M., Abbondanza, C., Gross, R., Heflin, M., Parker, J., Soja, B., and Wu, X.: Realization of time sequential estimation of terrestrial reference frame using square-root information filter and smoother, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10805, https://doi.org/10.5194/egusphere-egu2020-10805, 2020.

D1872 |
Francesco Matonti, Adam Miller, and Nejc Krasovec

GNSS networks are required to continue meeting the ever-increasing demand for global positioning applications operating in a global reference frame. Meanwhile, the requirements of applications based in a local (regional) official reference frame must still be met. Using Bernese GNSS software (Dach, 2015), we can process GNSS networks in the ITRF2014 reference frame and, using Leica GNSS Spider, deliver GNSS corrections in ITRF2014, whilst continuing to serve those with local demands.  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. To ensure the daily solution runs with correct data, we maintain a database of all reference station equipment changes. Using the daily solution, 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 daily solution and monitoring of GNSS networks are 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. This includes the computation and monitoring of approximately 5000 GNSS reference stations worldwide, including those part of the HxGN SmartNet GNSS network.  

KEYWORDS: GNSS reference station network, Bernese GNSS 5.2, Leica CrossCheck, Leica GNSS Spider, HxGN SmartNet 

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 Krasovec, N.: ITRF use for global applications and estimation of linear velocities of dense networks , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17353, https://doi.org/10.5194/egusphere-egu2020-17353, 2020.

D1873 |
Elena Mazurova, Igor Stoliarov, and Vladimir Gorobets

     At the present time the Russian  state geodetic reference frame of the new generation consists of the three hierarchical levels that include: 1. fundamental astronomical-geodetic reference frame ; 2. high-precision geodetic reference frame; 3. satellite-based geodetic reference frame of the first category.  The spatial coordinates of the networks of these three levels are determined by satellite methods.   However, only the points of the fundamental astronomical-geodetic reference frame are continuously operating reference stations.  Many surveying engineers, geodesists, map-ping specialists, as well as scientists from different backgrounds, are using RINEX files every day freely downloading them from the site //rgs.centre.ru

    At the same time, private networks of Continuously operating reference stations are developing rapidly in Russia. These networks are owned by various corporations, both private and public, as well as stations owned by private individuals.  Now,  a center is being created, the main task of which is to unite all Continuously operating reference stations located on the territory of Russia into a unified network.

    This paper addresses the current state of the Continuously operating reference stations network  in Russia and plans for enhancing it within the next few years.

Key words: Russian continuously operating reference stations network

How to cite: Mazurova, E., Stoliarov, I., and Gorobets, V.: Continuously operating reference stations in Russia: current state and future enhancements , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3364, https://doi.org/10.5194/egusphere-egu2020-3364, 2020.

D1874 |
Kwo-Hwa Chen, Kuo-En Ching, Ray Y. Chuang, Ming Yang, and He-Chin Chen

Taiwan’s current horizontal coordinate system, TWD97[2010], is a static geodetic datum located at the boundary between Eurasian and Philippine Sea plates. Due to the relative motions between different plates, the accuracy of TWD97[2010] has been constantly decreasing. To maintain the internal accuracy of a national coordinate system at a high level, establishing a semi-kinematic reference frame is a practical solution. The semi-kinematic reference frame includes a static datum and a surface deformation model that is composed of velocity grid models and displacement grid models. In this study, observations of 437 continuous GNSS stations from January 2003 to December 2019 were adopted to estimate the horizontal velocity fields in Taiwan. We also integrated twelve horizontal velocity fields between 2003 and 2018 from 785 campaign-mode GNSS sites surveyed by the Central Geological Survey to derive the horizontal grid velocity models using the Kriging spatial interpolation method. Six coseismic displacement grid models from 2010 to 2018 were constructed using the dislocation model based on published coseismic source models. Independent GNSS observations of 1400 stations collected by the National Land Surveying and Mapping Center (NLSC) between 2013 and 2018 were also used for exterior checking on the accuracy of the surface deformation model. In addition, the network-based RTK system in Taiwan established by NLSC, named e-GNSS, is proposed to be used for assessing the accuracy of the velocity model and for the decision on the timing of velocity model renewal.

How to cite: Chen, K.-H., Ching, K.-E., Chuang, R. Y., Yang, M., and Chen, H.-C.: Taiwan Semi-kinematic Reference Frame Based on Surface Deformation Model Derived from GNSS Data, 2003 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1922, https://doi.org/10.5194/egusphere-egu2020-1922, 2020.

D1875 |
Jianqing Cai, Dalu Dong, and Nico Sneeuw

A newly developed Converted Total Least Squares (CTLS) algorithm is introduced, which is to take the stochastic design matrix elements as virtual observations, and to transform the TLS problem into a traditional Least Squares problem. This new algorithm has the advantages that it can not only easily consider the weight of observations and the weight of stochastic design matrix, but also deal with TLS problem without complicated iteration processing, which enriches the TLS algorithm and solves the bottleneck restricting the application of TLS solutions. The notable development of the CTLS reveals also that CTLS estimator is identical to Gauss-Helmert model estimator in dealing with EIV model, especially in the case of similarity coordinate transformation. CTLS has been successfully applied to the estimation of the transformation parameters, their rates and related transformed residuals between actual ITRF realizations of ITRF2014 and ITRF2008 with obvious improvement of their accuracies.

How to cite: Cai, J., Dong, D., and Sneeuw, N.: New Total Least Squares Algorithm and Model with Applications to the Transformation among ITRF Realizations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8188, https://doi.org/10.5194/egusphere-egu2020-8188, 2020.