Report of the GGOS Days 2025

Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) 1 GGOS Days 2025 framed at the IAG2025 Scientific Assembly 3-5 September 2025 | Rimini, Italy Meeting Summary In 2025, the GGOS Days event was held in the frame of the 2025 Scientific Assembly of the International Association of Geodesy (IAG2025) in Rimini, Italy (1–5 September; https://eventi.unibo.it/iag2025) to inform a broader audience about ongoing GGOS activities and challenges. The IAG2025 Scientific Assembly attracted around 700 participants from 68 countries and featured 300 oral presentations and 395 posters, reflecting strong engagement across geodetic topics. GGOS Days 2025 consisted of five dedicated symposia and a highlight session with 83 oral presentations and 92 poster presentations. During the IAG2025 Assembly, a business meeting of the GGOS Governing Board and GGOS Science Panel was also held. GGOS Symposia at the IAG2025 Throughout the assembly, several symposia and sessions highlighted GGOS initiatives. These sessions provided a platform for presenting advances and fostering discussions on the role of geodesy in addressing current challenges. Symposium G06: Global Geodetic Observing System ▪ G06-1: Contribution of geodesy to Earth observation Conveners: Laura Sánchez, Richard Gross, Hansjörg Kutterer ▪ G06-2: Global geodetic infrastructure for Earth System Monitoring Conveners: José Rodriguez, Martin Lidberg, Lucia McCallum, Cornelia Eschelbach ▪ G06-3: Standardisation, integration and optimisation of geodetic products Conveners: Detlef Angermann, Robert Heinkelmann, Nicholas Stamatakos, George Vergos ▪ G06-4: Enhancement of GGOS collaboration at regional level Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) 2 Conveners: Claudia Tocho, Esther Azcue Infanzón, Aletha de Witt Symposium G11: Geodesy for Society: Data Management, Policy Networking and Public Engagement ▪ G11-1: Data Management, Dissemination of Results, and Stakeholder Networking Conveners: Anna Riddell, Roger Fraser, Markus Bradke, Taylor Yates ▪ G11-2: Geodesy at the Intersection of Science and Policy Conveners: Allison Craddock, Basara Miyahara ▪ G11-3: Communication, Education and Outreach in Geodesy Conveners: Martin Sehnal, Szabolcs Rózsa, Öykü Koç, Sujata Dhar Symposium J01: Geodetic Space Weather Research Conveners: Michael Schmidt, Ehsan Forootan, Fabricio Dos Santos Prol, Ningbo Wang, Andrés Calabia Aibar Symposium J02: Artificial Intelligence and Machine Learning in Geodesy ▪ J02-1: Geodetic Machine Learning: Theoretical Challenges and Opportunities for Geodesy Conveners: Lotfi Massarweh, Mostafa Kiani Shahvandi, Alireza Amiri-Simkooei ▪ J02-2: AI for Deformation Analysis and GNSS Remote Sensing: Earth, Atmosphere and Natural Hazards Conveners: Milad Asgarimehr, Ashutosh Tiwari, Monique Kuglitsch ▪ J02-3: Decoding Earth's Dynamics: Machine Learning Frontiers in EOP and Gravity Field Assessment Conveners: Sadegh Modiri, Santiago Belda, Fupeng Li, Justyna Śliwińska-Bronowicz, Zhangli Sun Symposium J03: Geohazard Monitoring through Geodesy Conveners: Tim Melbourne, Susanna Ebmeier, Jean-Mathieu Nocquet, Masayuki Kano, Michaela Ravanelli Highlight Session H03: Geodetic Monitoring for Geohazards Conveners: Tim Melbourne, Laura Sanchez, Jean-Mathieu Nocquet The GGOS Governing Board and Science Panel Meeting took place on 4 September in a hybrid format with 51 participants in total. This meeting focused on status of the GGOS Implementation Plan, with active discussions on updating the GGOS2020 book, developing outreach materials, and current capacity-building activities offered by the different IAG components. Participants provided feedback both in-person and via online forms, resulting in lively exchanges and constructive recommendations. During this meeting, Allison Craddock announced her engagement to the United Nations Global Geodetic Centre of Excellence (UN-GGCE), which will see her leave GGOS. We would like to thank her for her active contributions to GGOS and wish her every success in this new chapter. We also took the opportunity to take a group photo with the last four GGOS presidents, who were all present at IAG2025 Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) 3 and contributed to the success of GGOS Days: Laura Sánchez (current president, since 2023), Basara Miyahara (2019-2023), Richard Gross (2017-2019) and Hansjörg Kutterer (2011-2017). The integration of GGOS Days into the IAG Scientific Assembly was met with positive feedback, highlighting increased participation and enhanced interdisciplinary collaboration. For the next year it was announced that GGOS Days 2026 will return to its traditional standalone format, scheduled from 5–7 October 2026 in Gävle, Sweden. This event will be held in conjunction with the IAG Commission 3 Symposium (TIGER: Tracking and Investigating Geodynamics and Earth Rotation) and a GGOS Topical Meeting on Geohazards, offering a comprehensive platform for discussing geodetic science and its applications. More info: https://geodesy.science/event/ggos-days-2026-topical-meeting Selected GGOS presentations at the IAG2025 Scientific Assembly are available at https://zenodo.org/communities/ggosdays2025. Highlights of Symposium G06: Global Geodetic Observing System by Laura Sánchez and Detlef Angermann Symposium G06 was dedicated to key aspects of GGOS, in particular (1) to highlight the contribution of geodesy to Earth observation, (2) the standardisation, integration and optimisation of geodetic products, and (3) the improvement of the geodetic infrastructure at global and regional scales. The symposium brought together 60 contributions (26 oral presentations and 34 posters), distributed in four oral slots and one poster session. All sessions were well attended, with an average of about 100 to 130 participants. A main current initiative of GGOS is the compilation of a catalogue of Essential Geodetic Variables (EGVs) to highlight the contribution of geodesy to Earth observation using the same language as other global observing systems such as the Global Climate Observing System (GCOS) or the Global Ocean Observing System (GOOS). This will increase the visibility of geodesy and the usability of its products for the benefit of other sciences and society. During the G06 symposium, details about the concept, classification, definition and requirements of the EGVs were presented. Additionally, a representative of GCOS summarised the ongoing rationalisation of the Essential Climate Variables (ECVs) to ensure the long-term availability and consistency of quantities that support climate system monitoring. Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) 4 Another presentation explained how geodetic parameters can greatly affect the reliability of key climate change signals, such as sea-level rise, ice mass loss and hydrological cycle. The session also provided an update on the progress in establishing an International Altimetry Service (IAS) under the auspices of the IAG to contribute to GGOS, GCOS and GOOS. Further presentations provided insights into the operational activities of various GGOS components, including the GGOS Bureau of Products and Standards, the GGOS Bureau of Networks and Observations, the GGOS Coordinating Office and the GGOS Focus Areas on Geohazards, Geodetic Space Weather Research and Artificial Intelligence for Geodesy, in order to achieve the strategic goals of GGOS. Regarding the session devoted to standards and products, main contributions focused on developing unified standards and improved geophysical models, integrating different observation techniques and generating consistent geodetic products. Key contributions included advances in ISO standards (Geodetic Register and observation station (DOMES) numbering standards), updates to the IERS Conventions, improvements to IAU and IERS standards relating to Earth's rotation, and progress towards defining a new reference ellipsoid. Other highlights included the ICGEM Service's recent developments in gravity field-related products and their applications, improvements in generating consistent potential values for the International Height Reference System (IHRS/IHRF), and recommendations on data formats and procedures. Concerning geodetic space infrastructure, two interesting presentations described, firstly, the challenges posed by the upcoming ESA Genesis mission to the data analysis performed by the IAG Services, especially with the precise and consistent determination of the satellite orbit using the four different space techniques (GNSS, SLR, VLBI, DORIS). The second presentation covered the development of the Japanese Omni-SLR, a compact, low-cost, multi-purpose satellite laser ranging (SLR) system that promises to significantly expand the global geodetic network by improving spatial coverage and temporal resolution. Additional contributions focused on the global geodetic infrastructure centred on the proceedings of the GGOS Committee on Performance Simulations and Architectural Trade-Offs (GGOS-PLATO). This committee is compiling various simulation studies to optimise the distribution of geodetic core stations worldwide, thereby improving the quality and longterm stability of the terrestrial reference frame. Other presentations summarised recent achievements of the different IAG Services, updates at many geodetic core sites, extension of the ground networks for VLBI, SLR and DORIS, and new developments for integrating local ties into the terrestrial reference frame determination. As a complement to the global efforts on geodetic infrastructure, the G06 symposium offered the opportunity to learn about regional initiatives that promote GGOS activities, providing an umbrella for regional collaboration on geodetic topics to improve infrastructure, research, and operational products. Presentations were given on the well-established GGOS Affiliates GGOS Japan, GGOS D-ACH (Germany, Austria and Switzerland) and GGOS IberAtlantic (Spain and Portugal). A highlight was the overview of the objectives and progress of establishing GGOS Africa. The session also featured reports on the construction of a regional millimetre-level non-linear epoch reference frame in China, recent advances in Australia, India, South Africa and the SIRGAS region, as well as recent progress in improving the accessibility and quality of GNSS data and products through EPOS (the European Plate Observing System). Highlights of Symposium G11: Geodesy for Society: Data Management, Policy Networking and Public Engagement by Martin Sehnal Symposium G11 aimed to highlight the societal relevance of geodesy by focusing on three main areas: effective data management, the interface between geodesy and policy, and communication, Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) 5 education, and outreach. Across the three sessions, a total of 9 oral presentations and 11 posters were presented, engaging participants in discussions about technical data management challenges, the promotion of geodetic science to broader audiences, and strategies for fostering collaboration across other disciplines. The session Data Management, Dissemination of Results, and Stakeholder Networking addressed the importance of managing geodetic data effectively, emphasizing FAIR principles (Findable, Accessible, Interoperable, Reusable), the use of open-source tools, and the integration of multiple data sources to support research, operational applications, and decision-making. The session Geodesy at the Intersection of Science and Policy explored the role of geodesy in policy-making, showcasing how stronger connections with stakeholders and advocacy efforts can enhance the visibility of geodesy in decision-making processes, while the session Communication, Education and Outreach in Geodesy focused on education and outreach, highlighting approaches to communicate geodesy effectively to both scientific and non-specialist audiences. Key outcomes of this symposium underscored the importance of open, accessible geodetic data for reproducible research, operational applications, and evidence-based decision-making across scientific and societal domains. The discussions highlighted the critical role of global collaborations and coordinated initiatives in fostering transparency, stakeholder engagement, and increased visibility of geodesy within and beyond the scientific community. Outreach and communication efforts, both at regional and international levels, were recognized as essential for inspiring early career scientists and students, while also promoting a broader understanding of geodesy’s societal relevance. Educational activities were emphasized as most effective when linked to tangible, real-world applications, such as environmental monitoring, disaster risk reduction, and everyday geospatial services. Overall, the G11 Symposium successfully combined scientific exchange with strategic discussions on policy engagement, education, and outreach, offering a dynamic platform for knowledge transfer, networking, and capacity building. By integrating these elements, the symposium reinforced the role of geodesy not only as a rigorous scientific discipline but also as a practical contributor to societal wellbeing, sustainable development, and informed decision-making across multiple sectors. Highlights of Symposium J01: Geodetic Space Weather Research by Ningbo Wang Symposium J01 aimed to advance the geodetic Earth system monitoring through the integration of available space geodetic observation methods, solar observations, real-time modelling and forecasting techniques. This symposium attracted ~50 participants and featured 27 oral and poster presentations. Contributions reflected the rapid progress in upper-atmosphere modelling and forecasting, with growing emphasis on machine learning and data assimilation approaches. A central topic was the May 2024 geomagnetic storm, whose ionospheric and thermospheric responses were comprehensively investigated using SAR-based ionospheric imaging, GNSS-derived non-gravitational accelerations from commercial LEO constellations, and GRACE-FO observation data. Further studies demonstrated the potential of shipborne multi-GNSS and GEO-based measurements for detecting ionospheric irregularities. The combined use of GNSS, LEO, and RO data was shown to markedly improve the reconstruction of ionospheric electron densities. In the Q&A part of the symposium, participants highlighted the key contribution of geodetic observations to space weather research and their importance for operational monitoring and earlywarning systems. Two main directions for future work were identified: 1) strengthening interdisciplinary collaboration between the geodetic and atmospheric science communities, and 2) developing robust, AI-driven methodologies for real-time space weather monitoring and forecasting. Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) 6 Highlights of Symposium J02: Artificial Intelligence and Machine Learning in Geodesy by Benedikt Soja Symposium J02 explored the growing impact of artificial intelligence (AI) and machine learning (ML) on geodesy. The symposium was structured into three sessions: Geodetic Machine Learning: Theoretical Challenges and Opportunities for Geodesy, AI for Deformation Analysis and GNSS Remote Sensing: Earth, Atmosphere and Natural Hazards, and Decoding Earth's Dynamics: Machine Learning Frontiers in EOP and Gravity Field Assessment. The symposium featured 17 oral presentations and 22 posters and was well attended, reflecting the strong and growing interest in AI/ML across the geodetic community. Contributions demonstrated the breadth of AI/ML applications across geodesy, including positioning, gravity field modelling, GNSS remote sensing, and environmental monitoring. A wide range of methodological approaches were presented, from spatial modelling and temporal forecasting to classification and anomaly detection. Several notable advances were highlighted: hybrid approaches that integrate geophysical knowledge into data-driven models; new strategies for realistic uncertainty quantification; the first applications of AI foundation models in geodesy; the use of ML to emulate complex environmental models at greatly reduced computational cost; and novel applications in fundamental geodetic data processing. Lively discussions surrounding the Symposium underscored the challenges and opportunities for the near future. Key themes included the rapid increase in data volumes and the question of how to best exploit them; strategies for balancing physics-based and data-driven approaches; and the importance of education and training to increase ML literacy within the geodetic community. Overall, Symposium J02 demonstrated both the diversity and maturity of AI/ML applications in geodesy and the strong momentum for further development. The sessions provided a valuable forum for scientific exchange and highlighted opportunities for future research at the intersection of geodesy, data science, and Earth system science. Highlights of the Symposium J03: Geohazard Monitoring through Geodesy by Laura Sánchez At Symposium J03, the focus was on integrating geodetic methods to improve our understanding of dynamic processes on the Earth's surface, ranging from plate motion to natural hazard monitoring. Many of the contributions demonstrated the effectiveness of using GNSS and SAR techniques to link changes in microplate motion to the seismic cycle, model the interaction between geodetic strain rates and seismicity rates, and analyse afterslip deformation following earthquake sequences. In particular, contributions to seismic hazard assessment and the quantitative assessment of geological hazard susceptibility zones using integrated, multi-parameter ground observations were presented, with case studies from Japan. New developments focused on probabilistic flood monitoring using normalised SAR time series data for dynamic inundation mapping and on L-band SAR-based, nationwide land deformation monitoring in Japan using ALOS-2/4 satellites. Evidence of land subsidence induced by aquifer compaction was presented using geodetic data, which is a powerful tool for assessing the risk of infrastructure damage due to land subsidence. This can be achieved using advanced MT-InSAR remote sensing techniques and GNSS interferometric imaging in coal mining areas. The importance of large-scale GNSS data analysis for ground deformation measurement, and the essential role of geodesy in monitoring, understanding and warning of natural hazards using GNSS, was also emphasised. Additional key presentations demonstrated how submarine volcanic unrest can be detected using data from the NGGM/MAGIC gravity mission and emphasised the importance of international efforts such as the GNSS-enhanced Earthquake and Tsunami Early Warning Tonga Pilot Project, coordinated by the GGOS Focus Area Geohazards Monitoring, in supporting rapid hazard response in vulnerable island Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) 7 regions. Another central topic of Symposium J03 was the analysis of GNSS-derived ionospheric total electron content (TEC) data to enhance tsunami early warning systems, as this provides real-time insights into ocean-atmosphere coupling following major seismic events, and can be used to identify subtle pre-seismic ionospheric changes as potential earthquake precursors and to detect and model co-seismic ionospheric disturbances. Highlight Session H03: Geodetic Monitoring for Geohazards by Laura Sánchez Plenary thematic sessions were organised for the first time during the IAG2025 Scientific Assembly to showcase innovative case studies using geodetic data and methods in multidisciplinary areas. One of these plenary sessions was devoted to geodetic monitoring for geohazards. Three presentations covered the main areas of geodetic contribution o geohazard monitoring: vulcanogeodesy, seismogeodesy, and tsunami early warning systems. In seismogeodesy: Strain localisation and inelastic deformation of inland Japan and their implications for seismic hazard, by Tekeshi Sagiya and colleagues. In vulcanogeodesy: Synergy of GNSS, InSAR and seismic data for monitoring of the Santorini volcano (Greece): Insights from past and ongoing volcanic unrest, by Stylianos Bitharis and colleagues. In tsunami early warning systems: Exploring ALTRUIST: Harnessing GNSS towards the enhancement of tsunami early warning systems, by Michela Ravanelli and colleagues.