G2.3

The “GGOS Working Group on Digital Object Identifiers (DOIs) for Geodetic Data Sets” is entering its third year of regular meetings and discussions to develop best practices, recommendations and advocate for improved global coordination for using DOI to geodetic data and products. The group was established by the International Association of Geodesy’s (IAG) Global Geodetic Observing System (GGOS) and includes international representatives of IAG Services and geodetic data centres and associated members.

Data publications with digital object identifiers (DOI) are best practice for FAIR sharing data. They are fully citable in scholarly literature and many journals require the data underlying a publication to be available. Initial metrics for data citation allows data providers to demonstrate the value of the data collected by institutes and individual scientists. This possibility to get credit for providing data products and running data services has been identified in the group as key requirement for the motivation to implement DOIs to geodetic data.

Our group activities include the collection of data products and discussions on already existing and planned DOI activities for IAG services and geodetic data centres, including for recent projects, like FAIR GNSS. Whenever possible, we recommend that DOIs shall be included in standard data formats (e.g. Rinex) and cited when using the data. This presentation will give an update of the group activities.

How to cite: Elger, K. and the GGOS DOI Working Group: News from the GGOS DOI Working Group, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10982, https://doi.org/10.5194/egusphere-egu22-10982, 2022.

Measuring, studying, and understanding global change effects demand unified geodetic reference frames with (i) an order of accuracy higher than the magnitude of the effects to be observed, (ii) consistency and reliability worldwide, and (iii) long-term stability. The development of the International Terrestrial Reference System (ITRS) and its realisation, the International Terrestrial Reference Frame (ITRF), enable the precise description of the Earth’s geometry by means of geocentric Cartesian coordinates with an accuracy at the cm-level and with global consistency. An equivalent high-precise global physical reference system that provides the basis for the consistent determination of gravity field-related coordinates worldwide, in particular geopotential differences or physical heights is missing. Without a conventional global height system, most countries are using local height systems, which have been implemented individually, applying in general non-standardised procedures. It is proven that their combination in a global frame presents discrepancies at the metre level. Therefore, a core objective of the international geodetic community is to establish an international standard for the precise determination of physical heights. This standard is known as the International Height Reference System (IHRS). Its realisation has been a main topic of research during the last years. Recent achievements concentrate on (1) compiling detailed standards, conventions, and guidelines for the IHRS realisation, (2) evaluating computational approaches for the consistent determination of potential differences, and (3) designing an operational infrastructure that ensures the maintenance and long-term stability of the IHRS and its realization. This contribution summarises advances and current challenges in the establishment, realization and sustainability of the IHRS.

How to cite: Sanchez, L., Huang, J., Barzaghi, R., and Vergos, G. S.: Towards an international standard for the precise determination of physical heights, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2523, https://doi.org/10.5194/egusphere-egu22-2523, 2022.

Geodetic observations on Earth accurate to better than a part per billion require a common reference for the same precision as described in the goals of the Global Geodetic Observing System. The International Gravity Reference System (IGRS) is proposed as a new reference for terrestrial gravity observations (Wziontek et al. 2021).

The International Gravity Reference Frame (IGRF) as the realization of IGRS is represented by absolute gravity measurements traceable to the SI. Due to the lack of a natural reference, absolute gravimeters need to be compared and the gravity reference is realized based on a set of measurements by a group of absolute gravimeters and the functional model for their processing.

We present the international comparison of absolute gravimeters WET-CAG2021 hosted at the Geodetic Observatory Wettzell in autumn 2021. This comparison is classified as an additional comparison following the strategy paper of the Consultative Committee for Mass and related quantities (CCM) and IAG. Seven FG5/X absolute gravimeters and two AQG quantum gravimeters have observed up to four individual piers over a period of twelve weeks. The individual observation epochs are connected by recordings of the continuously operating superconducting gravimeter GWR OSG 030 in the same laboratory.

We show the procedure of data analysis following Pálinkáš et al. (2021) and discuss the results also with respect to the latest regional metrological EURAMET comparison 2018 at the same location.

Marti, U., Richard, P., Germak, A., Vitushkin, L., Pálinkáš, V., Wilmes, H.: CCM-IAG Strategy for Metrology in Absolute Gravimetry, 11 March 2014

Pálinkáš, V., Wziontek, H., Vaľko, M. et al.: Evaluation of comparisons of absolute gravimeters using correlated quantities: reprocessing and analyses of recent comparisons. J Geod 95, 21 (2021). https://doi.org/10.1007/s00190-020-01435-y

Wziontek, H., Bonvalot, S., Falk, R. et al.: Status of the International Gravity Reference System and Frame. J Geod 95, 7 (2021). https://doi.org/10.1007/s00190-020-01438-9

How to cite: Rülke, A., Falk, R., Engfeldt, A., Glässel, J., Hellerschmied, A., Iacovone, D., Kostelecký, J., Pálinkáš, V., Reich, M., Timmen, L., Ullrich, C., Valluzzi, A., Wziontek, H., and Zehetmaier, B.: WET-CAG2021: An international comparison of absolute gravimeters for the realization of the International Gravity Reference System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2964, https://doi.org/10.5194/egusphere-egu22-2964, 2022.

The GGOS Bureau of Networks and Observations works with the IAG Services (IVS, ILRS, IGS, IDS, IGFS, IERS, and PSMSL) to advocate for the expansion and modernization of space geodetic networks for the maintenance and improvement of the reference frame and other applications, as well as for the integration of the techniques.  Of particular interest is the integration of gravimetric and tide gauge networks in view of the forthcoming establishment of a new absolute gravity reference frame and of the International Height Reference System/Frame. New sites are being established following the GGOS concept of “core” and co-location sites, and new technologies are being implemented to enhance performance in data yield as well as accuracy. 

The IAG Committees and Joint Working Groups play an essential role in the Bureau activity. The Standing Committee on Performance Simulations and Architectural Trade-offs (PLATO) uses simulation and analysis techniques to project future network capability and to examine trade-off options. The Committee on Data and Information is working on a strategy for a GGOS metadata system for data products and a more comprehensive long-term plan for an all-inclusive system. The Committee on Satellite Missions is working to enhance communication with the space missions, to advocate for missions that support GGOS goals and to enhance ground systems support. The IERS Working Group on Site Survey and Co-location (also participating in the Bureau) is working to enhance standardization in procedures, outreach and to encourage new survey groups to participate and improve procedures to determine systems’ reference points, a crucial aid in the detection of technique-specific systematic errors.

We will give a brief update on the status and projection of the network infrastructure for the next several years, and the progress and plans of the Committees/Working Groups in their critical role in enhancing data product quality and accessibility to the users, scientists and the general community.   

How to cite: Pearlman, M., Behrend, D., Craddock, A., Pavlis, E., Saunier, J., Barzaghi, R., Bradshaw, E., Carabajal, C., Thaller, D., Maennel, B., Hippenstiel, R., Pail, R., Shum, C., Brown, N., Blevins, S., and Sanchez, L.: An Update on the GGOS Bureau of Networks and Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2070, https://doi.org/10.5194/egusphere-egu22-2070, 2022.

Improving and homogenizing time and space references on Earth and, more directly, realizing the terrestrial reference system with an accuracy of 1 mm and a long-term stability of 0.1 mm/yr are relevant for many scientific and societal endeavours. The knowledge of the terrestrial reference frame (TRF) is fundamental for Earth system monitoring and related applications. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the position of continental or island reference stations, such as those located at tide gauges, as well as the ground stations of the tracking networks. Also, numerous applications in geophysics require absolute millimetre precision from the reference frame, as for example monitoring tectonic motion or crustal deformation for predicting natural hazards. The TRF accuracy to be achieved (mentioned above) represents the consensus of various authorities, including the International Association of Geodesy, which has enunciated geodesy requirements for Earth science (see GGOS-2020). Moreover, as stated in the A/RES/69/266 United Nations Resolution: “A global geodetic reference frame for sustainable development”, the UN recognizes the importance of “the investments of Member States in developing satellite missions for positioning and remote sensing of the Earth, supporting a range of scientific endeavours that improve our understanding of the Earth system and underpin decision-making, and… that the full societal benefits of these investments are realized only if they are referenced to a common global geodetic reference frame at the national, regional and global levels”. These strong statements by international bodies underline that a dedicated mission is highly needed and timely. Today we are still far away from this ambitious goal. It can be achieved by combining and co-locating, on one satellite platform, the full set of fundamental space-time geodetic systems, namely GNSS and DORIS radio satellite tracking systems, the satellite laser ranging (SLR) technique, and the very long baseline interferometry (VLBI) technique, that currently operates by recording the signals from quasars. This platform can then be considered as a dynamic space geodetic observatory carrying all these geodetic instruments referenced to one another on a unique well-calibrated platform through carefully measured space ties and a very precise atomic clock. It is necessary to set up a co-location of the techniques in space to resolve the inconsistencies and biases between them. Such a mission will be proposed as the first one of a series of missions in the GNSS/NAV Science Programme. The purpose of this abstract/talk is to revive the support of the scientific community for this mission.

How to cite: Karatekin, Ö., Dehant, V., Ventura-Traveset, J., Rothacher, M., Delva, P., Hugentobler, U., Altamimi, Z., Boehm, J., Couhert, A., Flechtner, F., Glaser, S., Haas, R., Jaeggi, A., Maennel, B., Perosanz, F., Schuh, H., and Sert, H.: GENESIS-1 mission for improved reference frames and Earth science applications., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10616, https://doi.org/10.5194/egusphere-egu22-10616, 2022.

Very Long Baseline Interferometry (VLBI) technique was developed in the 1960s by astronomers, for high angular resolution observations of celestial radio sources. In the late 1970s, it was adopted for high-precision geodetic applications, in a reverse manner. In this application, VLBI is used to monitor the kinematics of individual points on the Earth, and also of the Earth as a body in the space using the precisely known astronomical positions of radio sources. Despite differences between astronomical and geodetic applications, the instrumentation and analysis techniques employed in VLBI are broadly similar, allowing for antennas designed for VLBI to be usable for either application. In this presentation, we describe a proposal for upgradation of three existing communication antennas with 18-m, 30-m and 32-m diameter, located at Arvi, Pune, India, for astronomical and geodetic VLBI purposes. The main objective is to retrofit the antenna with new gearboxes and modern servo control systems to make them compatible for use in VLBI observations, as well as with suitable L, S, and C band receivers and digital recorders, in a short period of time. Each motor will be driven by a drive with close loop precision pointing system, making it suitable to point to and track celestial sources. The antennas will be fitted with suitable antenna feeds and receiver systems, after the analysis of the dish parameters and its mounting possibilities. A development of cooled S-band feed will also be initiated simultaneously. Further, the three antennas will be fitted with new front-end electronics, baseband converter and digital recorders. The observed bandpass with different feeds (S and C band) will be down converted to L-band. This signal will be transported over optical fibre to the Giant Meterwave Radio Telescope (GMRT) facility, which is located nearby, for data recording and correlation activities. The retrofitted instrument will provide a test bed for instrumentation, tuning analysis pipelines and software, while providing the capability to carry out both astronomical and geodetic VLBI experiments with other international facilities.

How to cite: Laha, A., Tiwari, A., Srivastava, S., Singh, S., Joshi, B. C., Balasubramanian, N., Kumar, A., Gupta, Y., and Dikshit, O.: Retrofitting communication antennas for astronomical and geodetic VLBI applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13321, https://doi.org/10.5194/egusphere-egu22-13321, 2022.

Satellite Laser Ranging (SLR) is the only one space geodetic technique in which troposphere correction is calculated based on in situ measurements (pressure, temperature, and humidity) and used in the least square adjustment process as a fixed value measured at the epoch of observation.  In the past few years, we observe that the use of malfunctioning barometers for some of the SLR stations significantly affects the SLR-based global geodetic parameter estimates, such as station coordinates, geocenter coordinates, and terrestrial reference frame scale. Thus, we examine different handling of the SLR range tropospheric delay to LAGEOS by analysing the a priori zenith total delay from the standard Mendes and Pavlis (2004) model with a corresponding mapping function, the estimated tropospheric correction, and the range bias parameter. Moreover, we conduct a simulation study of artificial pressure bias, investigating the capability of tested approaches to properly reconstruct the tropospheric error. The new approach based on the estimation of the troposphere delay correction for SLR solutions, which is also widely used in microwave techniques, explicitly demonstrates more suitable handling of errors affecting the SLR station than solutions based on estimation of range biases.

The progress in precise orbit determination of low Earth orbiter (LEO) satellites using GPS demands improvements of the SLR procedures considering their orbit validation, determination of station coordinates, and global geodetic parameters from SLR to LEOs solutions. Within this study, we also consider including the proper handling of range errors in SLR to LEOs. We test solutions incorporating the estimation of tropospheric biases with and without horizontal gradients, range biases, and station coordinate corrections in an example of the SLR observations to LEO Swarm satellites. We discuss the values of estimated corrections and their impact on the solution quality, and dependency of residuals to different measurement conditions, such as elevation angle, azimuth angle, station-satellite distance, or satellite view from a station. Estimating tropospheric biases once-per-day and horizontal gradients, absorbs elevation- and azimuth-dependent errors, provides a reduction of solution statistics, and dependency of SLR residuals for almost all used SLR stations.

How to cite: Strugarek, D., Drożdżewski, M., Sośnica, K., Zajdel, R., and Bury, G.: Estimation of tropospheric biases in SLR to Swarm, and LAGEOS satellites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9834, https://doi.org/10.5194/egusphere-egu22-9834, 2022.