Session G2.3

G2.3 | Global Geodetic Observing System: The Reference for Earth System Monitoring and featuring VLBI component

Global Geodetic Observing System: The Reference for Earth System Monitoring and featuring VLBI component

Convener: Kosuke Heki | Co-conveners: Martin Sehnal, Allison Craddock, Esther AzcueECSECS, Anastasiia WalentaECSECS, Minghui Xu, Aletha de Witt

Orals

| Mon, 15 Apr, 14:00–15:45 (CEST)

Room G2

Posters on site

| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00

Hall X2

Posters virtual

| Attendance Tue, 16 Apr, 14:00–15:45 (CEST) | Display Tue, 16 Apr, 08:30–18:00

vHall X2

High precision modern geodetic observations enable comprehensive monitoring of multiple spheres of the Earth. They record fingerprints of changes within the Earth System, providing crucial information to address major scientific issues, e.g., natural hazards, climate changes, global water cycles. Interpreting geodetic observations requires implementation of reference frames, analysis techniques and models with accuracy comparable to or exceeding the observations. Consequently, geodesy expanded its scope from just measuring geometry, gravity, and rotation of the Earth to understanding fingerprints recorded there and has become a key science to understand the Earth System for functioning and sustainability of our society. The Global Geodetic Observing System (GGOS) realizes the metrological basis for monitoring the Earth System. It is designed to unite individual geodetic observations and model them into one consistent frame with the highest precision available. We welcome contributions relevant to GGOS, particularly its scientific and social aspects, infrastructure, products, and activities of geodetic services.

Very Long Baseline Interferometry (VLBI) is a key contributor to the GGOS, primarily through the development and role-out of the VLBI Global Observing System (VGOS) by the International VLBI Service for Geodesy and Astronomy (IVS). VLBI stands apart as the sole method with the capability to establish and sustain the International Celestial Reference Frame (ICRF). The ICRF3 was constructed using VLBI data at the standard S/X frequencies, along with observations at K-band and X/Ka-band, making it the first multi-frequency frame. The backward compatibility with the running legacy VLBI network is to be considered as a tool to bridge nearly 40 years of legacy and last 4 years of VGOS observations. VGOS antennas were designed with two aims: to increase the measurement precision, from a cm-level to the GGOS goal of 1 mm; to increase the observational cadence, from 2-3 sessions per week to continuous observations. In this session we explicitly seek contributions to revisit the original goals and map the future VLBI contribution to GGOS. Besides this, we welcome the contributions dedicated to the satellite tracking with the fast VGOS antennas, an approach that promises to enhance and homogenize the reference frame determination.

Orals: Mon, 15 Apr | Room G2

Chairpersons: Martin Sehnal, Anastasiia Walenta, Allison Craddock

14:00–14:05

Introduction

GGOS-General

14:05–14:15

EGU24-11678

On-site presentation

GGOS: Ensuring a Coherent Earth Observation System

Laura Sanchez, Michael Pearlman, Detlef Angermann, Martin Sehnal, Thomas Gruber, Benedikt Soja, Anna Riddell, Kirsten Elger, Richard Gross, Kosuke Heki, Jose M. Ferrandiz, Michael Schmidt, Timothy Melbourne, Allison Craddock, and Basara Miyahara

The Global Geodetic Observing System (GGOS) is the response of the international geodetic community, organised under the umbrella of the International Association of Geodesy (IAG), to the need to monitor changes in the Earth system continuously. GGOS is Geodesy’s contribution to the Global Earth Observation System of Systems (GEOSS) by providing the reference frames needed for all position-dependent observations, thus the foundation for most Earth observations, and measuring changes in the Earth's shape, size, gravity field and rotation over time and space. GGOS is built on the Scientific Services of the IAG (IGS, IVS, ILRS, IDS, IERS, IGFS, ISG, PSMSL, IGETS, IDEMS, ICGEM, BGI) and the products they derive on an operational basis for Earth monitoring using space- and ground-based geodetic techniques. A key objective of GGOS is to realise an integrating framework that moves from the provision of technique-specific products to a level of combined, integrated products as the basis for a consistent modelling and interpretation of Earth system processes and interactions. This is necessary to ensure a coherent Earth monitoring system that contributes significantly to a better understanding of global change and its impacts on the environment and society. This is being achieved through strong international and multidisciplinary cooperation, focusing on (1) bringing together different geodetic observing techniques, services and analysis methods to guarantee that the same standards, conventions, models and parameters are used in all data analysis and modelling of Earth system processes; (2) combining geometric, gravimetric, and Earth rotation observations in data analysis and data assimilation to jointly estimate and model all necessary parameters representing the different elements of the Earth system; (3) identifying science and societal needs that can be addressed by (new) geodetic products and define the requirements for accuracy, time resolution, and consistency of these products; (4) identifying service gaps and developing strategies to fill them; and (5) promoting and enhancing the visibility of Geodesy by improving the accessibility of geodetic observations, information and products to the widest range of users and their attribution. This contribution summarises recent achievements, ongoing activities, and main challenges for the near future.

How to cite: Sanchez, L., Pearlman, M., Angermann, D., Sehnal, M., Gruber, T., Soja, B., Riddell, A., Elger, K., Gross, R., Heki, K., Ferrandiz, J. M., Schmidt, M., Melbourne, T., Craddock, A., and Miyahara, B.: GGOS: Ensuring a Coherent Earth Observation System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11678, https://doi.org/10.5194/egusphere-egu24-11678, 2024.

14:15–14:25

EGU24-5776

On-site presentation

The Absolute Gravity Reference Network of Italy

Riccardo Barzaghi, Federica Riguzzi, Filippo Greco, Giovanna Berrino, Alessandro Germak, and Augusto Mazzoni

The project for realizing the reference network for absolute gravity in the Italian area is presented. This fundamental infrastructure is the general frame for all the scientific and technological activities related to the gravity field in Italy. The project is in line with the actions promoted by the International Association of Geodesy that during its 2015 General Assembly approved a resolution on the establishment of the new global gravity network the so-called International Terrestrial Gravity Reference System/Frame that will replace IGSN71.

The selection of the absolute gravity station sites in Italy has been performed either taking into account the existing absolute gravity stations and to have a homogeneous distribution of points. An initial set of 30 stations has been defined over the peninsular part of Italy and the two islands of Sicily and Sardinia. Particularly, the GGOS core station of Matera (the Agenzia Spaziale Italiana Center for Space Geodesy “Bepi” Colombo) is one of the network points as required in the documents of the GGOS-Bureau of Networks and Observations. Thus, this station will provide one link between the Italian national absolute gravity network and the GGOS observation system of IAG.

The project is now ongoing and will close at the beginning of 2025.

As required by the international standards on gravity measurements (https://www.bipm.org/documents/20126/41442296/CCM++IAG+Strategy+for+Metrology+in+Absolute+Gravimetry/7f9bc651-a2b6-08cc-7bba-f63b0a7e9765), the absolute gravimeters used in the measurements have been compared with absolute gravimeters that participated into international comparison campaigns in order to ensure the measurements traceability.

Furthermore, absolute gravity measurements have been supplemented with direct measurements of the local value of the vertical gravity gradient, in order to reduce to the ground reference level the absolute values measured by different instruments at different heights. The gravity field campaigns will be assisted by topographic survey campaigns. This will allow a precise georeferencing (of the order of 12 cm) of the gravity stations that will be so framed to the current ITRF.

The collected data will be then validated and reduced following the internationally accepted standards and finally published through a dedicate web page of the project. These data will also be sent for storage to the absolute gravity database maintained by the Bureau Gravimétrique International/Bundesamt fuer Kartographie und Geodaesie where the absolute gravity data that will contribute to the new global absolute gravity reference system are collected.

How to cite: Barzaghi, R., Riguzzi, F., Greco, F., Berrino, G., Germak, A., and Mazzoni, A.: The Absolute Gravity Reference Network of Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5776, https://doi.org/10.5194/egusphere-egu24-5776, 2024.

14:25–14:35

EGU24-14602

Highlight

On-site presentation

IHRF Coordination Center, a newly established IAG/IGFS component to ensure the sustainability of the IHRS/IHRF

Georgios S. Vergos, Laura Sánchez, and Riccardo Barzaghi

The International Association of Geodesy (IAG) introduced the International Height Reference System (IHRS) in 2015 as the international standard for the accurate determination of physical heights worldwide. The primary vertical coordinates are geopotential numbers referenced to a conventional W_o value. The realization of the IHRS is the International Height Reference Frame (IHRF), which corresponds to a global network of reference stations with precise reference coordinates, geopotential numbers specified in the IHRS and (X, Y, Z) coordinates in the International Terrestrial Reference Frame (ITRF). In the framework of the IAG and after a strong international collaboration the scientific foundations of the IHRS have been outlined and a first realization of the IHRF has been computed. In that frame, it has been deemed necessary to ensure the long-term sustainability of the IHRF by establishing a new dedicated component within the IAG gravity field related services. Recently (December 2023), the IAG has accepted the establishment of the IHRF Computation Center (IHRF-CC) as a central coordinating body under the responsibility of the International Gravity Field Service (IGFS) with direct adherence to the IGFS Central Bureau (IGFS CB), composed of individual modules taking care of the main components of the IHRF. These modules are the IHRF Reference Network Coordination, the IHRF Conventions’ Coordination, the IHRF Associate Analysis Centers, and the IHRF Combination Coordination. In this work we outline the main components of the IHRF-CC, the objectives and goals foreseen, the main responsibilities of its component as well as their planned interrelation, complementarity and synergies in order to deliver its main products. The latter refer to the IHRS standards and conventions and their update; the update of the IHRF network and status; the IHRF computation cookbook; computation of offsets to national and regional vertical datums; and finally, IHRF station coordinates for the global core network and contributions to regional and national densifications. Finaly, we outline the first steps taken to formulate the IHRF-CC components and initiatives to begin normal operation.

How to cite: Vergos, G. S., Sánchez, L., and Barzaghi, R.: IHRF Coordination Center, a newly established IAG/IGFS component to ensure the sustainability of the IHRS/IHRF, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14602, https://doi.org/10.5194/egusphere-egu24-14602, 2024.

14:35–14:45

EGU24-10584

On-site presentation

Modelling Global Crustal Deformations Induced by Geophysical Fluid Loading for Space-Geodetic Applications

Henryk Dobslaw, Jungang Wang, Robert Dill, and Kyriakos Balidakis

With planet Earth being a deformable body, any geodetic marker attached to its crust exhibts slight motions in response to various geophysical forces. Prominent examples are the diurnal and semi-diurnal tides of the solid Earth, but also other periodic and non-periodic forces induced by mass transport divergence in atmosphere, oceans and the terrestrially stored water are deforming the Earth's surface and therefore displace any geodetic instrument attached to it. Based on a suite of different numerical model data-sets, the Earth System Modelling group at GFZ is routinely calculating both tidal and non-tidal surface deformations that can be readily applied as a priori information for the processing of space geodetic data. The model data-sets are publicly available as global grids with 3-hourly temporal sampling covering almost five decades from 1975 until present time.

We present results from dedicated geodetic analysis experiments in order to demonstrate potential impact of such prior information on the GNSS-based coordinate estimates. We utilize data from 220 globally distributed IGS stations from 2005 until 2019 and apply the IGS repro3 strategies for the GPS daily precise orbit determination strategy. We apply non-tidal atmospheric and oceanic loading corrections from the ESMGFZ products on the (i) observation, (ii) normal equation, and (iii) parameter levels, and study the impact of such background models on the coordinate time-series of GNSS permanent stations and other associated parameters.

How to cite: Dobslaw, H., Wang, J., Dill, R., and Balidakis, K.: Modelling Global Crustal Deformations Induced by Geophysical Fluid Loading for Space-Geodetic Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10584, https://doi.org/10.5194/egusphere-egu24-10584, 2024.

14:45–14:55

EGU24-15590

On-site presentation

The International DORIS Service: new challenges

Laurent Soudarin, Frank Lemoine, Claude Boniface, Guilhem Moreaux, and Jérôme Saunier

The International DORIS Service (IDS) had its 20^th anniversary in 2023 and is now looking forward to new challenges.

Over a 30-year period, between 1990 and 2020, the DORIS constellation contributing to the IDS has totaled nine satellites with lifetimes ranging from 3 to 19 years (with the lifetime of SPOT-2, at 19 years, being a record). Since the launch of the SWOT mission in December 2022, nine satellites have been in simultaneous operation and are supplying DORIS data to the IDS. This large number of missions is a challenge for the Analysis Centers, which must integrate them into their processing, taking into account each mission’s special characteristics (w.r.t shape, altitude, attitude law). New missions are expected from 2025 including Sentinel-3C & 3D, Sentinel-6B & 6C, HY-2E & 2F, GENESIS. In addition, the DORIS system continues to evolve. The ground network is growing while providing a high level of service, 4G beacons are gradually replacing those of the previous generation, and a new more powerful DORIS instrument is under study.

New groups have approached IDS in recent years, bringing new processing capabilities, or wishing to become involved in DORIS processing in the medium term. These new strengths are also opening up new applications. Since 2021, DORIS data from the Jason-3 mission have been made available to IDS with a delay of less than three hours. This has enabled the IDS Working Group “NRT data” to demonstrate the value of these data for validating existing GNSS-based ionosphere models. In 2024, NRT DORIS data will be made available for additional missions (Sentinel-3A, Sentinel-3B, Sentinel-6A, Saral…). A new established IDS Working Group will focus on using these data for further ionospheric modelling applications.

In this presentation, we provide information on DORIS system developments and upcoming missions. We also present the recent achievements made by IDS and its components, and the future plans for the service.

How to cite: Soudarin, L., Lemoine, F., Boniface, C., Moreaux, G., and Saunier, J.: The International DORIS Service: new challenges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15590, https://doi.org/10.5194/egusphere-egu24-15590, 2024.

14:55–15:05

EGU24-19106

Highlight

On-site presentation

Metadata recommendations for geodetic data

Kirsten Elger and the GGOS Committee on DOIs for Geodetic Data Sets

The geodetic services of the International Association for Geodesy (IAG) are international key players in the provision and distribution of geodetic data. Their operating institutions and funding agencies increasingly require the provision of tangible statistics on data use and access. In addition to the classical provision of data download statistics, data use can also be provided through citations in scholarly literature. Credit through citations, together with the desire for a coordinated approach across the geodetic services, was the motivation for the IAG’s Global Geodetic Observing System (GGOS) to establish a “Working Group on using DOI (digital object identifier) for Geodetic Data Sets” in 2019. The “GGOS Committee on DOIs for Geodetic Data Sets” is continuing the work since 2023 for the longer term.

Challenges for applying DOIs to geodetic data and products include the fact that they are mostly dynamic, often provided as real-time data streams (with hundreds of files per day) where the “classical” assignment (and citation) of DOIs to individual (daily) files provided in different product levels is not a practicable solution. In addition, many geodetic data products are based on contributions from hundreds of researchers and institutions that need to be acknowledged following “rules for good scientific practice”. Today, DOI-referenced research outputs are fully citable in scholarly literature and scientific journals are increasingly demanding that all sources underlying scientific results (data, code, models, samples) are made available/ published along with the article. Initial data citation metrics allows data providers to demonstrate the value of the data collected by institutes and individual scientists.

An additional benefit of using DOIs for geodetic data is the associated standardised (e.g. DataCite) and machine-readable metadata for data discovery. DataCite is a DOI registration agency specialised for data, code and other publications beyond scholarly literature. Their constantly further-developed metadata schema is supporting the implementation of the FAIR Principles (to make data findable, accessible, interoperable and reusable for humans and machines) and complements discipline-specific metadata standards, like GeodesyML for GNSS station information.

Here we present the first version of our metadata recommendations for geodetic data, developed for the GNSS data use case. The recommendations guide through the DataCite metadata schema, identify recommended and optional properties and how they can be used for geodetic data supporting data discovery. Initial guidelines were: (1) to include persistent identifier, like ORCID, ROR, DOI for uniquely identifying persons, institutions in the DOI metadata and cross reference with related data/articles/code whenever possible. (2) to have a maximum alignment with existing metadata, like GeodesyML or Sitelogs for GNSS station data with automated processes for mapping DOI metadata generation from existing GNSS metadata bases to DataCite metadata.

How to cite: Elger, K. and the GGOS Committee on DOIs for Geodetic Data Sets: Metadata recommendations for geodetic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19106, https://doi.org/10.5194/egusphere-egu24-19106, 2024.

GGOS-Very long baseline interferometry

15:05–15:15

EGU24-3287

ECS

On-site presentation

Optimal observing strategy of GENESIS in geodetic VLBI experiments

David Schunck, Lucia McCallum, and Guifré Molera Calvés

One of the major deficiencies in the realization of the International Terrestrial Reference Frame (ITRF) stems from the combination of the four space-geodetic techniques, that are contributing: Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellites (DORIS). The GENESIS satellite mission, a component of the European Space Agency’s (ESA) FutureNAV program, will address this problem. Scheduled for launch in 2027, the GENESIS satellite embodies a dynamic space-geodetic observatory, equipped with instruments encompassing all four space-geodetic techniques. The mission’s objective is to facilitate the in-orbit combination and co-location of these techniques in space, known as space ties. It is not yet known how GENESIS will be implemented in geodetic VLBI operations. In this talk, we will present a dedicated simulation study of VLBI observations to the GENESIS satellite. We look at the realistic observability given current and foreseeable antenna networks and session cadence. We schedule and simulate VLBI observations to the GENESIS satellite to investigate the accuracy with which VLBI antenna positions of a global network can be derived. In addition to the most common VLBI error sources, troposperic delays, clock inaccuracies, and white noise, we simulate satellite orbital errors. The observations to the GENESIS satellite are scheduled within regular, geodetic experiments. We compare different schedules varying the amount of time that is dedicated to observe the satellite. We analyse how incorporating these observations reduces the amount of time quasar sources are observed and, consequently, how fundamental geodetic VLBI observables, i.e. Earth Orientation Parameters (EOPs), are affected. We try to answer the question whether it would be necessary to include observations to the GENESIS satellite outside of regular geodetic experiments in the form of dedicated GENESIS sessions. The fact that VLBI is organized in sessions instead of continuous observing further raises the question to assess a minimal mission lifetime to achieve desired accuracies.

How to cite: Schunck, D., McCallum, L., and Molera Calvés, G.: Optimal observing strategy of GENESIS in geodetic VLBI experiments , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3287, https://doi.org/10.5194/egusphere-egu24-3287, 2024.

15:15–15:25

EGU24-7362

On-site presentation

VGOS – current status, challenges, and prospects

Rüdiger Haas

During the last decade, the next generation VLBI system, called the VLBI Global Observing System (VGOS), has been developed. It involves new, fast moving radio telescopes, that are equipped with dual-polarization broad-band receivers covering a broad frequency range from upper S-band to lower Ku-band. VGOS is planned to become the major VLBI contribution to the Global Geodetic Observing System (GGOS), surpassing the legacy S/X VLBI contribution by about one order of magnitude in terms of precision and accuracy of the geodetic products. While still being in its roll-out phase, VGOS started to become operational in 2020. The International VLBI Service for Geodesy and Astrometry (IVS) is now operating two VLBI networks in parallel, the legacy S/X VLBI network, and the new VGOS network. In early 2024, up to 13 VGOS stations are observing together in 24 h network sessions three times per month. These sessions are meant for the determination of the terrestrial reference frame (TRF), the earth orientation parameters (EOP), and the celestial reference frame (CRF). Additionally, several short (1 h) VGOS sessions are performed on several days each week, involving two or three VGOS stations only and focussing on the determination on earth rotation, i.e. the UT1-UTC parameter. There are several ongoing projects worldwide to establish further VGOS stations. It is expected that several of these will become operational in the near future, some even already in 2024, thus improving the geographical distribution of the VGOS network. In conjunction to an improved and densified VGOS network it is also planned to intensify the observation plan. In this presentation, the current status, challenges, and prospects of VGOS are reviewed and discussed. This includes a review of the expectations and obtained results of the geodetic parameters derived from the analysis of VGOS sessions.

How to cite: Haas, R.: VGOS – current status, challenges, and prospects, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7362, https://doi.org/10.5194/egusphere-egu24-7362, 2024.

15:25–15:35

EGU24-9519

ECS

On-site presentation

Rethinking operational VGOS observations

Matthias Schartner, Bill Petrachenko, Patrick Charlot, Minghui Xu, Arnaud Collioud, Hana Krasna, and Soja Benedikt

The VLBI Global Observing System (VGOS) was created to meet the ambitious requirements set by the Global Geodetic Observing System (GGOS). Its primary objective is achieving millimeter-level precision while maintaining continuous 24/7 observations. Currently, both aims remain unfulfilled. Simultaneously, new requirements, such as the development of a dedicated VGOS Celestial Reference Frame (CRF), have emerged. Thus, a reevaluation of our current VGOS observational framework is necessary to reach the VGOS goals.

This study addresses three pivotal challenges within VGOS: attaining millimeter precision, providing observations for a CRF, and achieving uninterrupted 24/7 observations. Each of these topics demand a readjustment of our current observation scheduling methodology.

Based on insight from VGOS R&D sessions, this work discusses potential approaches to meet the requisite precision through shorter, signal-to-noise-driven observations. Additionally, it explores the combination of this methodology with source-based scheduling to facilitate the creation of essential observations for establishing a dedicated VGOS CRF. Finally, it addresses the issue of reaching 24/7 observations, currently limited by data transfer and correlation capacities. To overcome this, a potential solution involves a significant reduction in the recorded data volume per session by temporarily thinning out the schedule. Thus, it comes with a trade-off in precision. This concept might be seen as a paradigm shift in VLBI observations, traditionally striving for the highest precision possible, which we believe is worth being discussed. Based on observation statistics and Monte-Carlo simulations, we will elaborate on the expected impact of this approach.

How to cite: Schartner, M., Petrachenko, B., Charlot, P., Xu, M., Collioud, A., Krasna, H., and Benedikt, S.: Rethinking operational VGOS observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9519, https://doi.org/10.5194/egusphere-egu24-9519, 2024.

15:35–15:45

EGU24-15350

ECS

On-site presentation

Long-term geodetic product assessment derived from a VLBI transmitter on Next-Generation GNSS

Shrishail Raut, Susanne Glaser, Patrick Schreiner, Karl Hans Neumayer, Nijat Mammadaliyev, and Harald Schuh

Classical Very Long Baseline Interferometry (VLBI) observations are unique for the estimation of UT1-UTC and Celestial Intermediate Poles (CIPs). The innovative feature of placing a VLBI transmitter on a satellite provides additional information about Earth’s origin, the geocenter. It also enables the VLBI technique to be combined with other satellite-based techniques such as GNSS via a space tie on the common satellite. This research aims to evaluate the long-term geodetic products estimated by VLBI observations to a next-generation Global Navigation Satellite System (NextGNSS) satellite. We simulate a VLBI network comprising 20 stations including 18 current and future VLBI Global Observing System (VGOS) stations that simultaneously observed a single VLBI transmitter on a Galileo-like satellite, in conjunction with extra-galactic radio sources. Terrestrial Reference Frame (TRF) including station positions and velocities, geocenter coordinates, and the full set of Earth Orientation Parameters (EOPs) are estimated for a long-term period of three years. Subsequently, we impose no-net rotation (NNR) and no-net translation (NNT) conditions, resulting in a minimum constraint solution. Satellite observations were assumed at a ratio of 30% of the total observations. The results show that the estimated corrections in the X and Y geocenter coordinates are on the mm-level and the Z coordinate on the cm-level.

How to cite: Raut, S., Glaser, S., Schreiner, P., Neumayer, K. H., Mammadaliyev, N., and Schuh, H.: Long-term geodetic product assessment derived from a VLBI transmitter on Next-Generation GNSS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15350, https://doi.org/10.5194/egusphere-egu24-15350, 2024.

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

Display time: Tue, 16 Apr, 14:00–Tue, 16 Apr, 18:00

Chairpersons: Martin Sehnal, Anastasiia Walenta, Esther Azcue

X2.13

EGU24-10339

The International Association of Geodesy

Richard Gross

2024 marks the 162^nd anniversary of the founding of the International Association of Geodesy. In 1862, 15 States agreed to cooperate in a "Central European Arc Measurement" project to observe the shape of the Earth. Besides leading to an improved knowledge of the shape of the Earth, the measurements taken during this project also led to an improved reference frame and geoid for Central Europe. In the course of taking these measurements scientific issues were encountered that also had to be addressed. The spirit of cooperation in both taking operational measurements and conducting scientific research that exists today within the IAG has been a hallmark of the IAG ever since it was founded in 1862.

The dual nature of the IAG, in advancing both observations and science, is reflected in the organizational structure of the IAG. Services are responsible for advancing geodetic observations in their area of expertise; Commissions and Inter-commission Committees are responsible for advancing geodetic science; Projects are incubators for new initiatives; the Communications and Outreach Branch, together with GGOS, is responsible for promoting geodesy to the other sciences and to society at large; and GGOS, the Global Geodetic Observing System, is meant to integrate the diverse geodetic observations into a coherent geodetic imaging system of the Earth as a whole.

One of the strengths of geodesy is its interdisciplinary nature. Geodetic observations contribute to improving our understanding of many different Earth processes, from space weather to core dynamics. This affords the opportunity for geodesists to collaborate with scientists from many different disciplines. Besides the value to science, geodetic data and products are also of great value to society. The International Terrestrial Reference Frame (ITRF) provided by the International Earth Rotation and Reference Systems Service (IERS), one of the 12 Services of the IAG, underpins location-based services like navigation aids on cell phones. By forging collaborations with other organizations, the IAG can ensure that its data and products continue to meet the needs of both its scientific and societal customers.

How to cite: Gross, R.: The International Association of Geodesy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10339, https://doi.org/10.5194/egusphere-egu24-10339, 2024.

X2.14

EGU24-1314

Highlight

GGOS Portal - The future Metadata Platform for Geodetic Data - Feasibility Study and Perspectives

Martin Sehnal and Lena Steiner

The services of the International Association of Geodesy (IAG) provide very important and valuable geodetic data, information, and data products that are increasingly relevant for Earth system research, including monitoring of global change phenomena and a wide range of diverse applications such as satellite navigation, surveying, mapping, engineering, geospatial information systems, and so on.

Currently, it is difficult for many people to obtain an overview of all available geodetic products and data. The Global Geodetic Observing System (GGOS) of the IAG aims to fill this gap by developing the GGOS-Portal (ggos.org/portal), which will serve as a unique search and access point (one-stop shop) for geodetic data and products. Data and products will be described by rich metadata and remain physically located at their originating data centers of each contributing IAG service and other data providers. With this future platform, GGOS will contribute to increase the visibility of geodetic data for scientific research and to make other disciplines and the society aware of geodesy and its beneficial products.

Several software packages are available for the realization of such a metadata platform. Two of them are particularly suitable for this purpose: GeoNetwork and CKAN. Based on the community survey conducted in spring 2023, a requirements profile for the GGOS portal was drawn up as part of a feasibility study and compared with the tested functionalities of the two software packages. A particular focus was on testing the metadata harvesting function.

How to cite: Sehnal, M. and Steiner, L.: GGOS Portal - The future Metadata Platform for Geodetic Data - Feasibility Study and Perspectives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1314, https://doi.org/10.5194/egusphere-egu24-1314, 2024.

X2.15

EGU24-22454

The CDDIS – Updates and Future Developments

Justine Woo and Taylor Yates

X2.16

EGU24-10228

GGOS Bureau of Products and Standards: Recent activities and future plans

Detlef Angermann, Thomas Gruber, Gerstl Michael, Heinkelmann Robert, Hugentobler Urs, Sanchez Laura, and Steigenberger Peter

The GGOS Bureau of Products and Standards (BPS) supports the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) in its goal to provide highly accurate, consistent, and long-term stable geodetic products needed to monitor, map, and understand changes in the Earth’s shape, rotation, and gravity field. A key objective of the BPS is to keep track and to foster homogenization of adopted geodetic standards and conventions across all IAG components for the generation of geodetic products. This includes the interaction with the IAG Services and other entities that deal with standards and conventions, such as the Conventions Center of the IERS (International Earth Rotation and Reference Systems Service), the Commission A3 ”Fundamental Standards” of the International Astronomical Union (IAU) and the Technical Committee 211 of the International Organization for Standardization (ISO/TC 211).

This contribution presents the structure and role of the BPS. It highlights some of the recent activities, which are focused on the updating the BPS inventory of standards and conventions used for the generation of IAG products, the revision of the IERS Conventions, mainly related to Chapter 1 ”General definitions and numerical standards” as well as the description and promotion of geodetic products published at the GGOS website (www.ggos.org). The BPS also contributes to the generation of GGOS outreach material, such as videos, brochures, social media posts, etc. to make other disciplines and society aware of geodesy and its beneficial products. Finally, planned activities of the BPS according to the new GGOS Strategic Plan 2024-2034 are provided.

How to cite: Angermann, D., Gruber, T., Michael, G., Robert, H., Urs, H., Laura, S., and Peter, S.: GGOS Bureau of Products and Standards: Recent activities and future plans, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10228, https://doi.org/10.5194/egusphere-egu24-10228, 2024.

X2.17

EGU24-584

ECS

Estimation of the potential value of given sea segments for certain time periods

Kamilla Cziraki and Gábor Timár

Since Gauss (1828), the theoretical shape of the Earth has been defined as a distinct potential surface of the gravity field that best fits the sea level at rest. The gravity field is described as a sum of spherical function series whose coefficients are calculated from satellite and in situ gravity measurements. Sea levels have been measured in harbours since the 18th century using mareographs, and are now often supplemented by data from nearby GNSS stations.

In our work, we developed a program to determine the potential value for a given height from mareograph data. This allows us to use the data available from the stations to determine what this value was in an earlier period as well. Furthermore, if more than one dataset is available for a particular sea segment, the average value for that sea over a certain period can be given.

We tested the method in the Japanese Sea, where we had data from 9 stations. These were averaged every 5 years and the resulting data were used to calculate the potential values, as well as the average value for the sea segment for the latest period 2016-2020. In the future, we plan to use this method to perform such calculations for more sites, which would also provide information on the effects of tectonics and global sea level change.

Gauss, C. F. (1828) Bestimmung des Breitenunterschiedes zwischen den Sternwarten von Göttingen und Altona. Vandenhoeck und Ruprecht, Göttingen, 84 p.

Supported by the ÚNKP-23-1 New National Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund.

How to cite: Cziraki, K. and Timár, G.: Estimation of the potential value of given sea segments for certain time periods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-584, https://doi.org/10.5194/egusphere-egu24-584, 2024.

X2.18

EGU24-12665

ECS

Investigation of sea level variations and trends in the Baltic Sea from geometric and gravimetric observations

Fenghe Qiu, Thomas Gruber, and Roland Pail

Geometric and gravimetric measurements both have proven to be robust approaches to analyzing sea level changes. The relationship between them is also worth exploring. In this research, the geometric signal and gravimetric signal as well as volume variations in Baltic Sea are compared during the period from 2002.4 to 2016.12. Ideally, the geometric signal should be the sum of gravimetric signal and volume variations, which is so-called sea-level budget. Here, the geometric signal is selected as altimetric data from multi missions combined with in-situ observations from tide gauges. The Mascon solutions are used as gravimetric signals while the volume variations are represented by steric height derived from Baltic Sea Physics Reanalysis model. The Baltic Sea is divided into four regions and the sea level budget equation is applied in each region. The results reveal the gravimetric and volume components exhibit satisfying correlations with geometric signals, which are larger than 0.85 in all four regions. The north region has the least correlation due to the sea ice problem. Furthermore, the comparison underscores the dominance of the gravimetric signal, contributing to approximately 90% of the total sea level change. On the other hand, the sea level trend is estimated by both geometric signal and the sum of gravimetric and volume components. The difference between the two trends in each region is mainly caused by ocean bottom deformation, primarily influenced by glacier isostatic adjustment (GIA). In the processing of mason, the GIA effect is already removed but the geometric signal contains ocean bottom deformation. Therefore, it is necessary to consider the land deformation during the trend comparison. However, because of the sea level equation, the sea level does not change as much as ocean bottom changes, but much smaller. Here we employ the geoid change from NKG2016LU as a trend correction in ocean bottom deformation. The findings contribute valuable insights for predicting sea level changes in the Baltic Sea, emphasizing the significance of accounting for gravitational and volumetric factors along with ocean bottom deformation in sea-level research.

How to cite: Qiu, F., Gruber, T., and Pail, R.: Investigation of sea level variations and trends in the Baltic Sea from geometric and gravimetric observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12665, https://doi.org/10.5194/egusphere-egu24-12665, 2024.

X2.19

EGU24-8196

ECS

Highlight

20 years of the ICGEM Service and the new developments

E. Sinem Ince, Sven Reißland, Christoph Förste, and Frank Flechtner

ICGEM is one of the five services coordinated by the International Gravity Field Service (IGFS) of the International Association of Geodesy (IAG). The service has been actively responding to the needs of the scientific community for the last two decades with an archive of static, temporal, and topographic global gravity field models of the Earth in a standardized format with the possibility to assign DOIs. Furthermore, ICGEM provides interactive calculation and visualisation services of gravity field functionals. Maintenance of such a service and development of new “demand-based” tools are of utmost importance to provide state-of-the-art products.

In 2016, the ICGEM portal has been renewed to guarantee a smooth transition to future needs. Since then, the last remaining component of the previous ICGEM portal, the G3 Browser, has been upgraded and integrated into the present ICGEM portal. The G3 Browser (http://icgem.gfz-potsdam.de/g3) aims to compute time series of equivalent water height interactively and gives users the opportunity to compare different gravity model time series as well as impacts of corrections (e.g., GIA, C20) or filters. The G3 Browser is complementary to existing services such as GFZ’s GravIS portal which provides ready-to-use products based on GFZ and COST-G solutions with already applied corrections and filters. On the other hand, the ICGEM G3 Browser includes time series from further processing centres and institutions and different filtering options.

Recently, ICGEM has included simulated models (http://icgem.gfz-potsdam.de/sl/simulated) in its archive that are relevant to future gravity mission studies. Currently available simulated Level 2a models are from the ESA’s MAGIC simulation studies and they are the first of their kind on the ICGEM Service. Monthly and weekly series of different scenarios have been made available on the relevant pages together with the links to the publications provided by the authors.

As demanded by the users, ICGEM plans to include some practical tools in the service, such as comparison of the functionals computed based on two different models and interactive evaluation tools n spatial and spectral domains. Finally, a new project called SAMDAT (Service and Archive for Mass Distribution And mass Transport data) that is funded by the German Research Foundation will be realized during the next three years which aims to expand the ICGEM service based on FAIR (Findable, Accessible, Interoperable, Reusable) data and a sustainable data archive principles.

How to cite: Ince, E. S., Reißland, S., Förste, C., and Flechtner, F.: 20 years of the ICGEM Service and the new developments , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8196, https://doi.org/10.5194/egusphere-egu24-8196, 2024.

X2.20

EGU24-6267

ECS

Investigating the independently derived tropospheric parameters at GNSS-VLBI co-located sites

Anastasiia Walenta, Claudia Flohrer, Rolf Dach, Daniela Thaller, and Gerald Engelhardt

This paper presents the next step of the recently undertaken comparison of the tropospheric parameters independently derived from the analysis of Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS) data. We established a concept of cross-validation of the tropospheric parameters which allows us to focus now on the investigation of the discrepancies detected in the cross-validation. In particular, the dataset and its parameterization are examined in view of their impact on the obtained biases. The most recent 5 years of observations are considered, during which the sufficiently dense time series of observations are available for the legacy VLBI stations as well as for the new generation antennas following the VLBI Global Observing System (VGOS) specifications. In our study the co-location sites are limited to those observatories, where the legacy VLBI antenna, VGOS antenna and GNSS receiver are present. Furthermore, the tropospheric parameters are compared only at the common epochs, which are chosen to include the independently conducted observations of the legacy VLBI antenna, VGOS antenna and GNSS receiver during a defined time span. The corresponding solution parametrization is varied between intervals of VGOS, legacy and GNSS solution parametrizations in order to identify the most optimal duration. While the parameterization of the GNSS solution considers the tropospheric variations stable over 2 hours, the parameterization of VLBI solutions for legacy antennas is known to be reliable over a shorter 1-hour interval. The highly dense VGOS observations allow us to reach up to 20-minute duration without losing performance.

How to cite: Walenta, A., Flohrer, C., Dach, R., Thaller, D., and Engelhardt, G.: Investigating the independently derived tropospheric parameters at GNSS-VLBI co-located sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6267, https://doi.org/10.5194/egusphere-egu24-6267, 2024.

X2.21

EGU24-17390

Velocity field estimated from HEPOS permanent GNSS network in Greece, preliminary results.

Dimitrios Anastasiou, Xanthos Papanikolaou, Georgios Serelis, and Maria Tsakiri

The analysis of data from permanent Global Navigation Satellite System (GNSS) stations plays a pivotal role in the assessment of ground motion within a given region. Greece, situated at the convergence zone of various tectonic plates, experiences heightened seismic activity and other geotectonic phenomena. The Hellenic Positioning System (HEPOS) constitutes a network of 98 permanent GNSS sites strategically installed across the entire Greek territory, serving as a critical infrastructure for data provision within the country. In the framework of this study, daily data collected at a sampling rate of 30 seconds for four individual years, ranging from 2011 to 2022, were analyzed. The data was processed via the Bernese GNSS Software v5.2. For the realization of IGb14 reference frame, 19 permanent stations of the IGS network were used, additionally incorporating final products (satellite orbits, clocks, and antenna calibration parameters). Comprehensive analysis was conducted on position time series for all stations, resulting in the estimation of tectonic velocities, harmonic signals, and permanent displacements attributed to seismic events in proximity to each site. Subsequently, preliminary results of the deformation field for the entire Greek region are presented, employing diverse algorithms for the estimation of strain and rotational rates.

This study was funded by the "Hellenic Cadastre", which also provided access to the data of the HEPOS network.

How to cite: Anastasiou, D., Papanikolaou, X., Serelis, G., and Tsakiri, M.: Velocity field estimated from HEPOS permanent GNSS network in Greece, preliminary results., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17390, https://doi.org/10.5194/egusphere-egu24-17390, 2024.

X2.22

EGU24-19907

Crust deformation in the Northern Adria plate from twenty years of geodetic monitoring

Lavinia Tunini, Andrea Magrin, Giuliana Rossi, and David Zuliani

In the complex geodynamic context of the central Mediterranean, squeezed between the two major tectonic plates of Africa and Eurasia, the Adria microplate plays a key role in modulating the deformation and seismicity of the region. The northern sector of Adria is of particular interest as it exhibits moderate seismicity despite low deformation rates.

The crustal deformation is monitored thanks to the various geodetic networks in the area, which can provide continuous and highly accurate daily data. The geodetic network with the most stations is the Friuli Regional Deformation Network - FReDNet (https://frednet.crs.ogs.it), set up by the National Institute of Oceanography and Applied Geophysics – OGS, to monitor the distribution of crustal deformation and provide complementary information for regional seismic hazard assessment (Zuliani et al., 2018). FReDNet currently counts 22 permanent GNSS stations homogeneously covering the Eastern Alps, the alluvial plain, and the coastal areas of northeastern Italy. Most of the time series are longer than 15 years. In addition to FReDNet, another geodetic network in northeastern Italy, the Marussi GNSS network, comprises ten stations and is managed by the Friuli Venezia Giulia (FVG) region. The geodetic network of the Veneto region in the west and the permanent GNSS networks of Austria and Slovenia in the North and East respectively, complete the puzzling northern border of the Adria microplate opposite the southern front of Eurasia.

We processed daily GNSS data from the different permanent geodetic networks using the GAMIT/GLOBK software package version 10.71 (Herring et al., 2018). Data processing was performed on the HPC cluster GALILEO100 of CINECA, which uses the SLURM system for job scheduling and workload management (Tunini et al., 2023).

This study shows the processing results, in the form of time-series and velocity field, as well as the different aspects taken into account to check the reliability of the processing procedure applied and the results obtained, such as the consideration or avoidance of tidal or non-tidal loads or the change of the reference stations, the influence of the type of GNSS monuments, or the location of the geodetic antenna on a roof or in an open field.

OGS and CINECA supported this research under the HPC-TRES program. We acknowledge the CINECA award under the ISCRA initiative for the availability of high performance computing resources and support (IscraC IsC96_GPSIT-2 and IsCa7_GPS-MAST).

References

Herring, T.A. and King, R., Floyd, M.A. and McClusky, S. C.; 2018: GAMIT Reference Manual: GPS Analysis at MIT, Release 10.7. Department of Earth. Tech. rep., Massachusetts Institute of Technology, Cambridge, Mass. URL: <http://geoweb.mit.edu/gg/Intro_GG.pdf>

Tunini, L., Magrin, A., Rossi, G., and Zuliani, D.; 2023: GNSS time series and velocities about a slow convergent margin processed on HPC clusters: products and robustness evaluation, Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2023-131, in review.

Zuliani, D., Fabris, P., Rossi, G.; 2018: FReDNet: Evolution of permanent GNSS receiver system. In: New Advanced GNSS and 3D Spatial Techniques Applications to Civil and Environmental Engineering, Geophysics, Architecture, Archeology and Cultural Heritage, Lecture Notes in Geoinformation and Cartography; Cefalo, R., Zielinski, J., Barbarella, M., Eds.; Springer: Cham, Switzerland, pp.123–137.

How to cite: Tunini, L., Magrin, A., Rossi, G., and Zuliani, D.: Crust deformation in the Northern Adria plate from twenty years of geodetic monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19907, https://doi.org/10.5194/egusphere-egu24-19907, 2024.

X2.23

EGU24-2949

High-cadence VLBI in Australia for an improved TRF in the southern hemisphere

Lucia McCallum

The accuracy and robustness of the International Terrestrial Reference Frame lies in the combination of the four space-geodetic techniques. Network imbalances, partly caused by geography and land coverage strongly favour the northern hemisphere in the number of observations and, to a less clear extent, in accuracies. This is evident in large tie discrepancies, for example in Katherine and Yarragadee in Australia, where results from the various techniques differ to a significant degree.

In this contribution we investigate the hypothesis that those discrepancies stem from deficiencies in the global combination of the various techniques, rather than from the individual observations. Specifically, we show that a regionally processed VLBI dataset is superior in its local station coordinate repeatabilities than when processed as part of the global network.

The Australian AuScope VLBI network has been operating for over 10 years, delivering higher cadence and partly more precise observations than the regular global IVS observations. It is our aim here to investigate whether a local comparison between VLBI and GNSS data in Australia can shed light into the mystery of significant tie discrepancies that are currently present in the ITRF for this region.

How to cite: McCallum, L.: High-cadence VLBI in Australia for an improved TRF in the southern hemisphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2949, https://doi.org/10.5194/egusphere-egu24-2949, 2024.

X2.24

EGU24-10637

VLBI signal transmitter onboard Earth orbiting satellites

Özgür Karatekin, Hakan Sert, Hugues Vasseur, Veronique Dehant, Birgit Ritter, Urs Hugentobler, Jan Kodet, Željko Jelić, Karel Paternoster, Gerhard Kronschnabl, Christian Ploetz, Akhil Gunessee, Graciela Lopez Rosson, and Ananya Krishnan

Creating an absolute space-tie where all the geodetic methods are onboard is the key for an improved and stable terrestrial reference frame as well as with various scientific applications. Such satellite concepts have already been proposed to achieve an accurate and stable terrestrial reference frame. Next generation Galileo satellites can provide a single well-calibrated platform for the colocation of the space-based geodetic techniques establishing precise and stable ties between the key geodetic techniques. One of the most crucial and novel aspect of such concepts is the VLBI transmitter (VT) which will emit quasar-like signals from the space to be observed by the VLBI ground stations. VT can directly link the terrestrial and celestial reference frames and bring the unique features of VLBI technique to an Earth orbiting satellite. In the context of call for future Galileo payloads a novel VT has been under development. VT shall be compatible both with the legacy and VGOS antennas. Here, we present the progress on ongoing ESA study for VT for Galileo as well as for other future missions.

How to cite: Karatekin, Ö., Sert, H., Vasseur, H., Dehant, V., Ritter, B., Hugentobler, U., Kodet, J., Jelić, Ž., Paternoster, K., Kronschnabl, G., Ploetz, C., Gunessee, A., Lopez Rosson, G., and Krishnan, A.: VLBI signal transmitter onboard Earth orbiting satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10637, https://doi.org/10.5194/egusphere-egu24-10637, 2024.

X2.25

EGU24-7935

VLBI processing in FocusPOD

Carlos Fernández, Marc Fernández, and Jaime Fernández

GMV is developing FocusPOD, a suite of tools for POD and geodesy, powered by GMV MAORI, a new GMV in-house Flight Dynamics & Geodesy library, written from scratch in modern C++ and python. FocusPOD supports several projects led by GMV, including the operational provision of Precise Orbit Determination (POD) products of the Copernicus Sentinel satellites in the frame of the CPOD Service, the simulation of tracking data for Galileo 2^nd Generation (G2G) System Test Bed, and other space debris and flight dynamics activities.

FocusPOD is currently capable of processing GNSS data, with a focus on on-board receivers to support POD, and Satellite Laser Ranging (SLR), mostly used in CPOD as an external orbit validation source. Capabilities to process DORIS have been recently added, also targeting POD applications as a first step. GMV’s roadmap for FocusPOD include processing VLBI in addition to these 3 techniques, with the target of becoming a reference software for the geodesy community.

This contribution intends to present FocusPOD roadmap to incorporate VLBI processing capabilities, describing the modelling challenges that have been identified and the various steps that will be taken to finally be able to process VLBI and provide VLBI-based ITRF products. As part of this roadmap, other parallel activities to tie together the rest of the techniques will also be undertaken and described, mostly related to the ground-based processing of GNSS, SLR and DORIS data.

How to cite: Fernández, C., Fernández, M., and Fernández, J.: VLBI processing in FocusPOD, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7935, https://doi.org/10.5194/egusphere-egu24-7935, 2024.

Posters virtual: Tue, 16 Apr, 14:00–15:45 | vHall X2

Display time: Tue, 16 Apr, 08:30–Tue, 16 Apr, 18:00

Chairpersons: Martin Sehnal, Kosuke Heki, Esther Azcue

vX2.1

EGU24-6362

ECS

Estimation of the Length of Day (LOD) from DORIS observations

Vikash Kumar, Petr Stepanek, Vratislav Filler, Onkar Dikshit, and Nagarajan Balasubramanian

We estimated the true Length of Day (LOD) from DORIS observations. The DORIS RINEX data has been processed by the DORIS development version of the Bernese GPS Software 5.2. We performed single satellite and multisatellite (Sentinel-6A, Sentinel-3A, Sentinel-3B, Jason-3, HY-2C, HY-2D, SARAL, and Cryosat-2), and pre-eliminated solutions. The DORIS data has been processed separately for each satellite on the basis of daily arcs. The troposphere, frequency offset, and orbit parameters were pre-eliminated from the normal equation systems and the finalized matrices were combined on a weekly basis. Hence, individual satellite solutions as well as multi-satellite combined solutions were created. From this solution, we calculated the transformation parameters w.r.t. ITRF 2020 (more precisely w.r.t. the DORIS extension DPOD 2020,) and after applying the 7-parameter Helmert transformation we calculated the RMS w.r.t. DPOD 2020.

We performed solutions with different settings, in particular with different handling of cross-track once-per-revolution harmonic parameters (adjusted with different constraints or not adjusted), since the amplitude of the sine term correlates with LOD. For a comparison of our results, we used the IERS 20 C04 model as a reference.

How to cite: Kumar, V., Stepanek, P., Filler, V., Dikshit, O., and Balasubramanian, N.: Estimation of the Length of Day (LOD) from DORIS observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6362, https://doi.org/10.5194/egusphere-egu24-6362, 2024.

vX2.2

EGU24-13228

ECS

Device and angle dependent waveform and a new representation of ocean sound speed structure in GNSS-A

Koya Nagae, Tadashi Ishikawa, Shun-ichi Watanabe, Yuto Nakamura, and Yusuke Yokota

For more than 20 years, Japan Coast Guard has been developing various technologies to improve the observation accuracy of GNSS-Acoustic ranging. In this presentation, I will introduce two topics that we have been paying attention to in recent years in GNSS-A observations.

The first is about instrument errors and angular characteristics that depend on the shape of the transducer (sea surface station) or transponder (seafloor station). In the long-term observations conducted by JCG, multiple types of oscillators are used on both transducers and transponders. It has become clear that this instrumental error has a non-negligible effect on the positioning accuracy of GNSS-A, so we develop a new method to read a received signal considering the instrumental and angle dependence.

The second is about a representation method of ocean structure. When we estimate positioning of seafloor station, it is very important to consider sound speed structure (SSS). We use the open-source software GARPOS which can estimate transponder position with SSS. Yokota et al., (in prep) introduce a new representation method of SSS with G-ellipse in GNSS-A analysis. I will talk about the meaning of G-ellipse and some applications of this method.

How to cite: Nagae, K., Ishikawa, T., Watanabe, S., Nakamura, Y., and Yokota, Y.: Device and angle dependent waveform and a new representation of ocean sound speed structure in GNSS-A, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13228, https://doi.org/10.5194/egusphere-egu24-13228, 2024.

vX2.3

EGU24-15420

ECS

Overview of Japan Coast Guard’s GNSS-A seafloor geodetic observation and data management

Yuto Nakamura, Tadashi Ishikawa, Shun-ichi Watanabe, Koya Nagae, and Yusuke Yokota

The Japanese Archipelago lies along subduction zones, where megathrust earthquakes are known to occur repeatedly (e.g., M_w 9.0 2011 Tohoku-oki Earthquake). The source regions of such megathrust earthquakes mainly lie beneath the seafloor, making it necessary to monitor the crustal deformation not only on land but also on the seafloor. The Japan Coast Guard (JCG) has been conducting seafloor geodetic observation using the GNSS-Acoustic ranging combination technique (GNSS-A) since the early 2000s. By combining GNSS and underwater acoustic ranging, GNSS-A measures the absolute position of a seafloor benchmark in the precision of centimeters, which provides us fruitful information on the crustal deformation under ocean. JCG currently deploys 27 seafloor sites along the Japan Trench and the Nankai Trough named the Seafloor Geodetic Observation Array (SGO-A).

JCG and the Univ. Tokyo group has been working on open data of GNSS-A. In the past, we have published the position time series data (Yokota et al. 2018), and the GARPOS software (Watanabe et al. 2020) which is used in our current routine analysis. Recently, we have been discussing on a standardized data format for GNSS-A in the task force of the Inter-Commission Committee on Marine Geodesy (ICCM) in the International Association of Geodesy. Currently, we are releasing the latest position time series data of each SGO-A site, and the GNSS-A observation dataset in the GARPOS data format (https://www1.kaiho.mlit.go.jp/chikaku/kaitei/sgs/datalist_e.html).

How to cite: Nakamura, Y., Ishikawa, T., Watanabe, S., Nagae, K., and Yokota, Y.: Overview of Japan Coast Guard’s GNSS-A seafloor geodetic observation and data management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15420, https://doi.org/10.5194/egusphere-egu24-15420, 2024.