Search

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.

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) is a collaborative contribution of the global geodesy community to the observation and monitoring of the Earth System. Geodetic observation techniques and analysis infrastructures, as well as the high-quality geodetic products, provide the foundation upon which advances in Earth and planetary system sciences and applications are built.One main objective of GGOS is to support actions and initiatives to communicate the value of Geodesy to society, as well as help to understand and solve complex issues facing the global geodetic community. Towards this objective, GGOS has completely redesigned its website, www.ggos.org, which serves as a “point of entry to geodesy” to facilitate discoverability and usability of geodetic data and products. This includes explanations about: IAG services, geodetic observations and geodetic products. With this, GGOS engages with diverse user communities to increase awareness of geodesy and the ever-expanding benefits of geodesy in every-day applications.In addition, GGOS recently produced short videos to explain the applications and importance of geodesy to non-geodesists. The new “Discover GGOS and Geodesy” video is available on YouTube in multiple languages.

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.

High-resolution regional applications require regional reference frames with dense networks of reference stations. These regional reference frames can be realised in the form of multi-year reference frames (that can be fixed to a specific tectonic plate like EUREF for Europe) or as epoch reference frames to represent non-linear phenomena such as earthquakes or loading effects (like SIRGAS for Latin America). Common to these realisations is that they are based on GNSS networks with a geodetic datum that is realised by alignment to the global reference frame (ITRF or IGS TRF).In consequence, the origin of these networks reflects the Earth’s centre of figure rather than the Earth’s instantaneous centre of mass. Moreover, the quality of the realised datum decreases over time, as the linearly-parameterised coordinates of the global reference frame have to be extrapolated beyond the observation period. These effects mean a significantly reduced value of station-specific displacement time series for the study of, e.g., local geophysical effects.This study presents an alternative approach for the realisation of a regional epoch reference frame for Latin America. The approach is based on the common weekly solution of global SLR, VLBI and GNSS networks combined at the normal equation level. Thereby, SLR determines the origin, SLR and VLBI jointly determine the scale, and a homogeneously distributed global GNSS network is used to realise the orientation. This GNSS network is densified by the stations of the regional sub-network, namely the stations of the Latin American SIRGAS network. The approach does not necessarily rely on fiducial points in the region of interest, which means that it is conceptually transferrable to other regional networks.In order to cope with system-specific deficiencies of SLR and VLBI, namely data gaps, low station performances and frequently changing observational networks deteriorating the realised datum parameters, we propose a strategy to stabilise the realised datum via filtering the input data of these techniques at the normal equation level before combination with GNSS.We evaluate the realised datum of the epoch-wise weekly solutions by comparison against the ITRF2014 as an independent multi-year realisation of the ITRS and against the JTRF2014 as an independent sub-secular realisation of the ITRS. Moreover, station-specific displacement time series are validated against non-tidal loading displacement time series derived from geophysical fluid models provided by ESMGFZ in order to demonstrate that the displacement time series reflect seasonal geophysical processes in a geocentric frame.

The Bureau of Products and Standards (BPS) is a key component of the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG). It supports GGOS in its goal to provide consistent geodetic products needed to monitor, map, and understand changes in the Earth’s shape, rotation, and gravity field. In its current structure, the Committees “Contributions to Earth System Modeling” and “Definition of Essential Geodetic Variables” as well as the Working Group “Towards a consistent set of parameters for the definition of a new Geodetic Reference System (GRS)” are associated to the BPS. This poster contribution presents the role of the BPS and it highlights some of the recent activities, which are focused on the updating of the IERS Conventions, mainly related to Chapter 1 "General definitions and numerical standards", the updating of the BPS inventory of standards and conventions used for the generation of IAG products to incorporate the latest developments in the field, the compilation of user-friendly descriptions of geodetic products published at the GGOS website, and the contribution to GGOS films for specific products. The BPS activities also comprise the interaction with IAG and other entities in the field of standards and conventions, such as the IAG Services, the IERS Conventions Center, the Commission A3 “Fundamental Standards” of the International Astronomical Union (IAU), ISO/TC 211 and the Working Group ``Data Sharing and Development of Geodetic Standards” of the UN-GGIM Subcommittee on Geodesy (SCoG).

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.

This presentation gives a summary of the role and the activities of the Bureau of Products and Standards (BPS) to support IAG’s Global Geodetic Observing System (GGOS) in its goal to provide observations and consistent geodetic products needed to monitor, map and understand changes in the Earth’s shape, rotation and mass distribution. In its present structure, the two Committees “Earth System Modeling” and “Essential Geodetic Variables” as well as the Working Group “Towards a consistent set of parameters for the definition of a new GRS” are associated with the BPS. A key objective of the BPS is to keep track and to foster homogenization of adopted geodetic standards and conventions across all IAG components as a fundamental basis for the generation of consistent geometric and gravimetric products. Towards this aim, an updated 2nd version of the BPS inventory of standards and conventions used for the generation of IAG products has been published in the Geodesist’s Handbook 2020. In the framework of the renewing of the GGOS website, the BPS supports the GGOS Coordinating Office in particular regarding the representation of geodetic products. Furthermore, the BPS contributes to the rewriting of the IERS Conventions as Chapter Expert for Chapter 1 “General definitions and numerical standards” and interacts with external stakeholders regarding standards and conventions, such as ISO, IAU, BIPM, CODATA and the UN GGIM Subcommittee on Geodesy, including its Working Group “Data Sharing and Development of Geodetic Standards”.

The new ITRS realization, the ITRF2020, will be computed and released in 2021. Many institutions contributing to the international IAG services IGS, IVS, ILRS and IDS did work hard during the last months to finalize the ITRF2020 input data until mid of February 2021. The resulting data are series of SINEX files of daily or weekly global GNSS, VLBI, SLR and DORIS solutions. The ITRS Combination Centres (CC) are in charge of the computation of three ITRS realizations based on a combination of these input data. The three realizations can be seen as independent to some extent, as the combination strategies realized by the three CC partly differ considerably. This provides the opportunity of a cross-validation between the computed frames and ensures a high reliability of the final ITRF product. The ITRS CC will start in February 2021 with the analysis of the final input data series and their combination.We will present first results of the analyses and computations performed at ITRS CC DGFI-TUM.

Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national levelling networks and therefore define a height system of a country. Thus, sea level research across countries is closely linked to height system unification and needs to be regarded jointly. The project aims to make use of a new observation technique, namely SAR positioning, which can help to connect the GNSS basic network of a country to tide gauge stations and as such to link the sea level records of tide gauge stations to the geometric network. By knowing the geoid heights at the tide gauge stations in a global height reference frame with high precision, one can finally obtain absolute sea level heights of the tide gauge stations in a common reference system and can link them together. By this method, on the one hand national height systems can be connected and on the other hand the absolute sea level at the tide gauge stations can be determined. By analyzing time series of absolute sea level heights their changes can be determined in an absolute sense in a global reference frame and the impact of climate change on sea level can be quantified (e.g. by ice sheet and glacier melting, water inflow, global warming). The paper presents the main scientific questions to be addressed by the project, introduces the idea of using SAR transponders for this application and describes the observation network implemented for this feasibility study.

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.