The 14th General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS GM2026)

Apr 12, 2026, 8:00 AM → Apr 17, 2026, 9:00 PM Europe/Berlin

Richard-Strauss Konzertsaal (Kongresshaus Garmisch-Partenkirchen)

Alexander Neidhardt (FESG - Technical University of Munich)

The 14th General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS GM2026)

Linking the Celestial and Terrestrial Realms

April 12-17, 2026

 

Download of the Group Foto

We are pleased to announce that the fourteenth General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS GM2026) will be held during the week of April 12-17, 2026, in Garmisch-Partenkirchen in the Bavarian Alps. All IVS Associate Members and individuals who have interests in the application of VLBI in the fields of geodesy, Earth sciences, astrometry, and other astronomical applications in geodesy are invited to attend the meeting.

The International VLBI Service for Geodesy and Astrometry (IVS) holds a General Meeting every two years. The purpose of the General Meeting is to assemble representatives from all IVS components to share information, hear reports, and plan future activities. The meeting also provides a forum for interaction with other members of the VLBI and Earth science communities.

In addition to the General Meeting, an IVS Analysis Workshop and an IVS Directing Board meeting will be held.

Download of the Analysis Workshop Group Photo

Download of the Directing Board Group Foto

Hosting institutions

Research Facility Satellite Geodesy at the Technical University of Munich (TUM) in cooperation with the Chair of Astronomy and the Earth Observation Research Cluster of the Julius- Maximilians-Universität Würzburg

Important dates

•   First Announcement: August 31, 2025
•   Second Announcement: November 19, 2025
•   Abstract submission deadline: January 30, 2026 extended to February 10, 2026
•   Early-bird deadline: February 1, 2026 extended to February 10, 2026
•   Registration deadline: March 1, 2026 extended to April 1, 2026

Contact information

LOC: Alexander Neidhardt (Chair), Stefanie Daurer, Chanye Fu, Urs Hugentobler, Matthias Kadler, Florian Kroner, Simon Seidl, Martin Brandl, Till Rehm, Theresa Lohbinger (with kind personnel support from Federal Agency for Cartography and Geodesy (BKG) to represent the Geodetic Observatory Wettzell)

PC: IVS-gm-pc <ivs-gm-pc@lists.nasa.gov>

Dirk Behrend, Chris Dieck, Rüdiger Haas, Masafumi Ishigaki, Chris Jacobs, Matthias Kadler, Pepe Lopez-Perez, Lucia McCallum, Alexander Neidhardt, Fengchun Shu, Benedikt Soja, Chet Ruszczyk, Tobias Ullmann, Alet de Witt

 

GM2026_booklet.pdf

GroupFoto_AnalysisWorkshop.jpg

GroupFoto_DirectingBoard.jpg

IVSGM2026_GroupPhoto.jpg

RequestForExemptionFromTheSpaFee.pdf

Photos

• Behrend.zip
• Bolotin.zip
• Neidhardt.zip

Proceedings

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Sun, April 12

5:00 PM → 8:00 PM Icebreaker, reception

Mon, April 13

7:30 AM → 8:30 AM IVS GM Registration: Welcome and Registration

8:30 AM → 9:30 AM IVS GM: Opening

8:30 AM Welcome address

Speakers: Alexander Neidhardt (FESG - Technical University of Munich), Urs Hugentobler (Technical University of Munich), Matthias Kadler (Uni Würzburg)

8:42 AM The importance of VLBI to satellite services and critical infrastructure (online)

The importance of VLBI to satellite services and critical infrastructure

Speaker: Nicholas James Brown (UN-GGCE)

8:54 AM Science at the Environmental Research Station Schneefernerhaus / Zugspitze

The Environmental Research Station Schneefernerhaus is situated on the south face of Mt. Zugspitze at an elevation of 2650m asl. It is a center for high altitude and climate research and an observatory for long-term environmental monitoring. The station is home to many different institutes and research facilities that use the infrastructure, rent lab-space and operate their instruments. Both long-term partners as well as temporary users are welcome, creating a unique scientific environment and interdisciplinary exchange.

Permanent staff at the station supports the scientists, maintains the facility, takes care of safety issues and ensures that high quality data can be collected in the harsh alpine environment.

Speaker: Till Rehm (Betriebsgesellschaft Umweltforschungsstation Schneefernerhaus GmbH)

9:06 AM High-Altitude Logistics for Extending ngVLA to the Zugspitze

The realization of the Wetterstein Millimeter Telescope (WMT) on the Zugspitze represents a high-altitude extension of the ngVLA and poses significant technical and logistical challenges.

Therefore, mtex antenna technology conducted a feasibility study assessing the requirements for deploying and operating a next-generation radio antenna in an extreme alpine environment. Methods include site evaluation, structural design adaptations, and detailed transport and installation analyses under the constraints of limited accessibility.

Key aspects comprise the segmentation and airlift of major components, rail transport compatibility, and the development of a construction and assembly concept, including foundation design and heavy-lift operations.

The results demonstrate that, with targeted engineering modifications and environmental control systems, as well as a coordinated logistics strategy, implementation is technically feasible.

Speakers: Lutz Stenvers, Prof. Matthias Kadler

9:18 AM Chair’s Report

9:30 AM → 10:20 AM IVS GM: Session 1 (Components) - Slot 1

9:30 AM Coordinating Center Report 2024-2026

We summarize the major activities of the IVS Coordinating Center over the past two years. This includes, but is not limited to, observing program coordination, communications and information (e.g., meetings, publications, mailing lists), and support of committees and VLBI component types. We briefly address recent personnel changes and provide an outlook into the future.

Speaker: Dirk Behrend (NVI, Inc./NASA GSFC)

9:45 AM The Wetterstein Millimeter Telescope

The Wetterstein Millimeter Telescope (WMT) is a planned radio telescope associated with the Environmental Research Station (UFS) Schneefernerhaus at the Zugspitze in the Bavarian Wetterstein mountains. It is planned to operate the WMT at radio frequencies between 1.2GHz and 120GHz with the possibility to extend further towards shorter millimeter wavelengths. The WMT is envisioned as an interdisciplinary research platform for astronomy, geo- and environmental research as well as for data and technology development. The WMT shall be integrated into international astronomical VLBI networks such as the European VLBI Network, the Global mm-VLBI Array, and provide long baselines to the upcoming next-generation Very Large Array (ngVLA) and Square Kilometre Array (SKA VLBI). It can further provide key contributions to satellite technology and operation, to space-situational awareness, to solar-system research, and to worldwide geodetic-VLBI services. In this talk, we will present a summary of recent developments within the WMT project and prospects for the WMT to support the goals of the IVS.

Speaker: Kadler Matthias (Julius-Maximilians-Universität Würzburg)

10:05 AM Astrometry, Geodesy, and the ngVLA

The Very Long Baseline Array (VLBA) has been a prolific data provider for both astrometric and geodetic studies for over three decades. The National Radio Astronomy Observatory (NRAO) has been designing and developing a replacement for the VLBA, known as the ngVLA. The ngVLA will consist of 30 18-meter antennas spread across 10 sites in the United States. These 10 sites, referred to as ngVLA LONG, will be part of a larger array of 244 identical antennas that aim to also replace the Very Large Array (VLA). The entire array will be equipped with a modern receiver package that covers frequencies ranging from 1.2 to 116 GHz. In this presentation, I will describe the current design of the ngVLA, and more specifically ngVLA LONG, and cover some of the scientific use cases for ngVLA LONG. I will also discuss how the ngVLA can continue NRAO’s legacy of contributions to the astrometric and geodetic communities.

Speaker: Lucas Hunt (National Radio Astronomy Observatory)

10:20 AM → 10:50 AM Coffee break

10:50 AM → 11:35 AM IVS GM: Session 1 (Components) - Slot 2

10:50 AM Updates on the RAEGE project

The RAEGE Project (Atlantic Network of Geodynamic and Space Stations) is a Spanish-Portuguese scientific initiative to build and operate a network of four advanced space geodesy observatories designed to study the Earth and contribute to global reference systems. The project was launched through a memorandum of understanding signed in 2010 by the Spanish National Geographic Institute (IGN) and the Regional Government of the Azores (GRA, Portugal).

This talk will provide an update on the current status of the project and its components. The latest hardware and software upgrades in the VGOS antennas at Yebes and Santa María as well as their operational status, the progress in constructing the antenna in Gran Canaria, the status of the Yebes correlator, and a brief overview of the SLR station in Yebes. In addition, the latest technical developments implemented for these instruments, as well as associated activities, will be presented.

Speaker: Javier González-García (Yebes Observatory / IGN)

11:05 AM Advancing the AuScope VLBI Array

Geoscience Australia (GA), in partnership with the University of Tasmania (UTAS), continues to strengthen the performance, reliability, and output of the AuScope VLBI array—Australia’s national geodetic VLBI infrastructure and a key contributor to the IVS. The array is undergoing significant modernisation as part of the ongoing transition towards full VGOS capability. Recent collaborative efforts include investment in correlation and data‑processing capability through high‑performance computing resources, enabling more timely delivery of geodetic products and a future Australian IVS correlation centre.

A major advancement is the completion of high‑speed AARNet fibre connectivity to all AuScope stations, dramatically improving data transport efficiency and positioning the network for higher‑cadence observing. Current joint work also includes the development of improved performance monitoring systems, enhancements to VGOS processing workflows, and targeted RFI‑mitigation initiatives.

Looking forward, GA and UTAS are prioritising reliable VGOS operations, deeper automation of station and correlation workflows, and the establishment of a sustainable long‑term operational model aligned with Australia's on-going support for the global geodesy supply chain and global IVS requirements. Together, GA and UTAS are building a modern, resilient, and globally integrated southern hemisphere VLBI capability that will underpin Australia’s geodetic infrastructure for the coming decades.

Speaker: Craig Harrison (Geoscience Australia)

11:20 AM China's Next-Generation VLBI Network: Progress and Prospects

China currently operates geodetic VLBI observations at three stations: Shanghai, Urumqi, and Kunming. To significantly strengthen the national and global geodetic infrastructure, two new candidate sites in Shigatse and Changbai Mountain have been identified as future core stations for the Global Geodetic Observing System (GGOS).
In addition to the existing Shanghai and Urumqi 13-m VGOS telescopes, a major new project has been funded to establish a next-generation VLBI network. This project will deploy seven new 18-m antennas: twin telescopes at each of the three core stations (Urumqi, Shigatse, and Changbai Mountain) and a single antenna at Kunming. All new telescopes will be fully compatible with the standard VGOS frequency bands while offering enhanced continuous coverage from 8 to 36 GHz. Integrating this network nationally and internationally will enable key scientific objectives, including contributions to a multi-band celestial reference frame (CRF) and the determination of high-resolution Earth Orientation Parameters (EOP). Currently, the first two antennas at the Urumqi site are under construction and are expected to be completed by the end of 2026.
This presentation will introduce the status and prospects of the project, with an emphasis on the planned observing strategy, simulation results of its measurement accuracy, and expected system performance analysis.

Speaker: Fengchun Shu (Shanghai Astronomical Observatory)

11:35 AM → 11:50 AM Stretch-your-legs break

11:50 AM → 12:35 PM IVS GM: Session 1 (Components) - Slot 3

11:50 AM Monitoring and modeling thermal deformation of VGOS telescope at Metsähovi

Thermal deformation of the telescope structure affects the position of the telescope reference point and, if not properly modeled, leads to systematic errors in geodetic VLBI data. This deformation is not uniform across the structure, as it depends on uneven heat distribution influenced by the Sun’s position relative to the telescope.
We present a monitoring procedure implemented at the Metsähovi Geodetic Research Station with an external stationary tachymeter measuring the position and angles to reflective of prisms mounted on the back of the VGOS telescope dish and its counterweights. These measurements are analyzed together with comprehensive temperature and solar heating data, including both outdoor and indoor readings.
Based on these observations, we developed a thermal expansion model that accounts for temperature variations across different parts of the telescope. We compare the results of this model with those from a standard thermal expansion approach that uses only outdoor temperature. In our model, we calculate the thermal expansion of different telescope components using their corresponding temperature data and expansion coefficients. We find that the new model provides better agreement with changes in reference point coordinates calculated from robot tachymeter measurements. Precise modeling of thermal deformation is crucial for reliable reference point determination in geodetic VLBI analysis and local tie measurements.

Speaker: Nataliya Zubko (Finnish Geospatial Research Institute, National Land Survey of Finland)

12:05 PM Status of the VLBI Radio Telescopes and Correlator at Wettzell

The radio telescope Wettzell-South (Ws) has been an integral part of the IVS VGOS network since 2016 and is equipped with an eleven-feed broadband receiving system. In contrast, the radio telescope Wettzell-North (Wn) was originally operated with an S/X/Ka-band tri-band feed system and was upgraded in November 2023 with a fully VGOS-compliant quad-ridge feed horn (QRFH) feed. Consequently, both Wettzell VGOS radio telescopes are now routinely participating in IVS VGOS observing sessions. Moreover, the 20 m Wettzell radio telescope Wettzell (Wz) has been a core component of the IVS S/X VLBI network since 1983. The frontend of Wz is scheduled to undergo an upgrade of its cryogenically cooled S/X-band Dewar frontend in June and July 2026, aiming for operational robustness and ease of maintenance. Furthermore, the operational tasks of the VLBI correlator at Wettzell are briefly described, with a focus on IVS VGOS session correlation. This presentation presents the current technical configurations at the Wettzell site, summarizes recent VGOS-related upgrades, and outlines planned component developments, including the VLBI correlator.

Speaker: Mr Christian Plötz (Bundesamt für Kartographie und Geodäsie)

12:20 PM Status of the Bonn Correlator

We will present the status of the Bonn Correlation Center for the years 2024 and 2025 mainly focusing on geodesy. We summarize our duties as one of the IVS correlators and the experience we have gained in the correlation of intensive sessions (Int3, Int-M), S/X Legacy (R1, T2 and OHG) and VGOS observations (VO and R3).

Speaker: Yoon Kyung Choi (Reichert GmbH, BKG, MPIfR)

12:35 PM → 2:05 PM Lunch break (please choose your own catering option from the offerings in the city)

2:05 PM → 2:20 PM IVS GM: Session 1 (Components) - Slot 4

2:05 PM NASA's Crustal Dynamics Data Information System (CDDIS): Current State, Challenges, and Future Outlook

NASA's Crustal Dynamics Data Information System (CDDIS) has served the space geodesy and geodynamics communities for over forty-five years, experiencing numerous transformations including technological advances, budget constraints, and evolving national and international strategies. Today, CDDIS faces unique challenges including cloud infrastructure proliferation, heightened IT security and cyber awareness requirements, reduced budgets, expanding applications of space geodesy data and products, and uncertain strategic guidance at national and international levels. These pressures can create uncertainty about the future of one of the largest and most critical repositories of space geodesy and geodynamical data.
Despite these challenges, the future of CDDIS is bright and promising. This presentation will address the current state of CDDIS operations and key challenges, while emphasizing the robust long-term strategy and strong viability of the system. The talk will highlight exciting upcoming changes and improvements that will enhance CDDIS capabilities and ensure its continued leadership in space geodesy data archiving. Through strategic planning and innovative solutions, CDDIS is well-positioned to continue its vital mission for decades to come. The presentation will also provide an overview of current CDDIS services and its ongoing support of the IVS community.

Speaker: Benjamin Michael (NASA - Crustal Dynamics Data Information System)

2:20 PM → 2:45 PM Additional break

2:45 PM → 3:15 PM IVS GM: Session 2 (Products) - Slot 1

2:45 PM New Developments in the DBBC4 and DBBC3 Backend Systems

We present two recent developments with immediate application to VGOS in the context of digital backends for VLBI.
The first is the DiFrEnd4T module, a new element developed within the DBBC4 project, designed to enhance flexibility and performance in digital signal processing and data formatting for next-generation VLBI backends. DiFrEnd4T introduces a modular and scalable approach that improves system configurability and facilitates the integration of advanced processing features required by modern VLBI experiments.
The development includes a shielding box that allows installation of the DiFrEnd4T component in the frontend area of the telescope.

The second development is a direct consequence of this work and concerns the DBBC3 system. Concepts and design choices introduced with DiFrEnd4T have been adapted and applied to the DBBC3, extending its capabilities and enabling improved interoperability and functionality without major hardware changes. This demonstrates how innovations developed for DBBC4 can be effectively transferred to existing VLBI backends, providing a practical upgrade path for current infrastructures. The boards can be used also as a platform for the linear-circular polarization conversion together with the already existing functionalities.

These developments contribute to an increased flexibility, longevity, and performance of DBBC-based systems in current and future VLBI observations.

Speakers: Gino Tuccari (HatLab), Helge Rottmann (Max-Planck-Institut for Radioastronomy)

3:00 PM Reconfigurable digital back-end with VLBI capabilities for the China-Argentina Radio Telescope

The China-Argentina Radio Telescope (CART) is a 40-meter single-dish radio telescope currently under construction in San Juan, Argentina. In this work, we present the development of a new digital back-end for CART based on the RFSoC 4×2 platform, designed to support geodetic, astronomical, and future Very Long Baseline Interferometry (VLBI) observations.
The system performs signal acquisition on the RFSoC and streams the data via a 100 GbE link to a dedicated server, where GPU-based processing is utilized for real-time analysis and data storage. This architecture enables high data-rate operations while maintaining hardware reconfigurability and processing flexibility for different observational modes.
We report test observations of the Vela pulsar conducted with the Argentina Institute of Radio Astronomy (IAR) antenna. The successful detection of pulsed emission validates the complete signal chain under real observing conditions. Additionally, simulations were performed to evaluate CART's contribution as a future station in the global VLBI network. The results indicate that CART significantly improves reference coverage in the Southern Hemisphere and that the current back-end architecture is compatible with VLBI data rates and recording requirements.

Speaker: Ms Carolina del Valle Garay (Observatorio Astronómico Félix Aguilar - Universidad Nacional de San Juan - Argentina)

3:15 PM → 3:45 PM IVS GM: Session 2 (Products) - Slot 2

3:15 PM Proposal for future VGOS observation channels

The ongoing and constantly increasing demand for wireless communication is leading to high demand for electromagnetic spectrum. This demand is met through allocations by the ITU following decisions made at the World Radiocommunications Conference. As a result, interference-free access to natural cosmic radio sources is becoming increasingly difficult and may, in the long term, call VLBI into question. For this reason, the IVS must engage in the spectrum on its own behalf. Together with the European Committee of Experts for Radio Astronomy Frequencies (CRAF), a proposal for future frequencies for VGOS is being made, which shall be introduced as an agenda item at WRC-2031 and is intended to secure geodetic observation frequencies for VGOS in the Radio Regulations. The presentation explains the new observation frequencies.

Speaker: Hayo Hase (BKG)

3:30 PM VGOS-protect test observations

During recent months, a new VGOS frequency setup has been developed to avoid current and anticipated disturbance from active radio services. Provided that the proposed frequency setup performs satisfactorily, it is intended to serve as the basis for efforts to achieve international protection for VGOS. The goal is to bring this topic onto the agenda of the World Radiocommunication Conference 2031 of the International Telecommunication Union (ITU).

To assess and evaluate the proposed frequency setup, two one-hour test sessions were conducted in January and February 2026. The first so-called VGOS-protect (vp) session involved Onsala and Wettzell, while the second vp session additionally included Ny-Ålesund, Ishioka, and Hartebeesthoek. We present initial results from these two vp sessions.

Speaker: Dr Lim Chin Chuan (Onsala Space Observatory)

3:45 PM → 3:55 PM Stretch-your-legs break

3:55 PM → 4:35 PM IVS GM: Session 3 (Operations) - Slot 1

3:55 PM Routine Analysis and Automation at the GSFC VLBI Analysis Center

VLBI Intensive (INT) sessions provide dUT1 corrections required for GNSS
applications and precise navigation, where low latency is a key requirement. At the NASA GSFC VLBI Analysis Center, these sessions are currently processed in a fully automated operational mode. This end-to-end pipeline integrates ADAP/APS for data management, nuSolve for preliminary analysis, and SOLVE for final dUT1 estimation, ensuring a seamless data flow from the correlator's database release to the final product submission. This talk describes the technical architecture of the current system and evaluates its performance in delivering rapid, reliable dUT1 products. Beyond current operations, we examine the scalability of this framework in the context of future 24/7 VGOS (VLBI Global Observing System) operations.

Speaker: Sergei Bolotin (NVI, Inc. / NASA GSFC)

4:15 PM The VGOS Observing Strategy for 2026

The VLBI Global Observing System (VGOS) network is undergoing rapid expansion and currently comprises around 20 operational stations worldwide. While this growth is an exciting development, the VGOS infrastructure faces challenges in keeping pace with increasing data volumes associated with a growing global network.

While the original goal of VGOS was to provide continuous observations, in practice, VGOS observing has been limited to approximately three to four 24-hour sessions per month due to limitations in data transport, storage, and correlator capacity. With the continued expansion of the network, even this limited cadence has become increasingly difficult to sustain. To address this challenge, a data volume limit of 200 TB per session was introduced. In addition, two new session types, VGOS-R3 and VGOS-CRF, are introduced to support rapid-turnaround products and celestial reference frame maintenance, respectively. Together, these changes enable the VGOS observing plan for 2026 to achieve weekly observations for the first time.

In this contribution, details of the implementation of these changes in the scheduling of VGOS sessions are provided. A special focus is placed on the additional data volume constraint introduced for VGOS-OPS sessions. Based on comparisons between recent VGOS-OPS sessions and earlier observing programs, the expected characteristics of the new sessions are discussed.

Speaker: Matthias Schartner (ETH Zurich)

4:35 PM → 6:00 PM Coffee, refreshments

4:45 PM → 6:00 PM IVS GM: Poster session 1

4:45 PM Antenna Telemetry Processing for Monitoring Antenna Health

In an effort to improve on the analysis of geodetic data at IVS observing
stations, we have developed infrastructure for processing antenna
telemetry. The telemetry data we use are the system temperature, phase
calibration phases and amplitudes, system equivalent flux density, the
differences between formatter clock and GPS clock, the meteorological data,
and the total power integration. The processing consolidates data from
both VLBI observing sessions and so called single dish experiments. This
process assess baseline telemetry at each antenna, along with the levels
of natural variability of the monitored parameters when the antennas are
performing normally. Examples of abnormalities we are able to detect,
include, anomalously high system temperature, unstable phase calibration
phases, jumps in the GPS and formatter clock differences, and others.

Speaker: Nlingi Habana

4:45 PM Construction Progress of a VLBI Radio Telescope at Bosscha Observatory

A new VLBI Global Observing System (VGOS)-compatible radio telescope, namely ITB-Bosscha VLBI Station is currently in phase of completion at Bosscha Observatory, thanks to the partnership between ITB and the SHAO - CAS. The construction of the telescope tower has been finalized, accompanied by a supporting building to facilitate telescope operations. The main reflector disk was successfully hoisted during the Big Lift operation in July 2025, representing a pivotal achievement in the structural assembly of the telescope. Subsequently, integration and installation of the signal chain components were completed successfully, initiating the next stage of RF and backend instrumentation deployment in the VGOS system. This achievement was validated by a successful fringe test conducted between Sheshan and ITB-Bosscha Stations on 28 December 2025. The telescope is expected to join upcoming international VLBI observing campaigns, including those organized by the International VLBI Service for Geodesy and Astrometry (IVS), thereby supporting the maintenance of global geodetic and astrometric reference frames. Located at geodetic coordinates 6° 49′ 29.85316″ S and 107° 37′ 03.09318″ E, with an ellipsoidal altitude of 1324.1265 m, the newly commissioned VGOS telescope is strategically positioned to enhance VLBI baseline coverage in the equatorial region and contribute to the densification of the International Celestial Reference Frame (ICRF) in the Southern Hemisphere.

Speaker: Prof. Taufiq Hidayat (Department of Astronomy and Bosscha Observatory, Institut Teknologi Bandung, Indonesia)

4:45 PM CVN e-VLBI Network Updates

Chinese VLBI network(CVN) stations has been expanding recently, including new big telescopes and VGOS antennae’s, providing new capability for astronomical, geodesy and space science researches. With the addition of new observatories along with existing ones, network links and data transmission path and data transfer flow becoming more and more important because of huge volume data movement and real-time application needs. In CVN, real-time e-VLBI already has been applied in the field of lunar and deep space probe orbit determination. For VGOS filed, international e-VLBI data transfer has been running for decade. To meet increasingly large data transmission requirements, e-VLBI network is under upgrading to connect these new stations and telescopes. CVN e-VLBI latest statuses is represented.

Speaker: Zhong Chen (Shanghai Astronomical Observatory,CAS)

4:45 PM Designing for Discovery: Educational Buildings Inspired by Space Science. The Development of VGOS at Bosscha Observatory.

Established in 1923 and centered around a large refractor telescope designed by C.P. Wolff Schoemaker, Bosscha Observatory represents Indonesia’s longest-standing engagement with modern astronomy. Closely tied to the founding of Institut Teknologi Bandung (ITB) in 1920, it has significantly shaped the country’s scientific, cultural, and educational development. Its national importance was recognized through its designation as a Cultural Heritage Monument (2004) and a Vital National Object (2008).

In the mid-2000s, efforts to expand Bosscha’s role in global geodetic science led to Indonesia’s integration into the VLBI network. A key milestone came in 2022 with a Memorandum of Understanding between ITB and the Shanghai Astronomical Observatory (SHAO), supported by the Belt and Road Initiative and Indonesia’s Global Maritime Fulcrum. This led to the rapid completion of a VGOS (VLBI Global Observing System) station in under two years.

Celebrating its centennial in 2023, Bosscha entered a new era with VGOS Bosscha—now the closest VLBI station to the equator in the Eastern Hemisphere. This project addresses the architectural and infrastructural challenges of embedding a high-precision scientific facility within a protected heritage site, positioning architecture as a bridge between scientific innovation, conservation, and public engagement. Bosscha stands as a rare example of century-long continuity in scientific mission, architecture, and institutional growth.

Speakers: Mr Firman Irmansyah (Department of Astronomy and Bosscha Observatory, ITB, Indonesia), Prof. Taufiq Hidayat (University Center of Excellence for Space Science, Technology, and Innovation, ITB, Indonesia), Widjaja Martokusumo (School of Architecture, Planning, and Policy Development, Institut Teknologi Bandung)

4:45 PM FGO 12m VGOS Development and Integration

Abstract: We will provide an update for the Fortaleza Geophysical Observatory (FGO) 12m VLBI Global Observing System (VGOS) development and integration. We will discuss NASA’s objective to build a new 12m VGOS antenna at the FGO VLBI station located in Eusébio, Ceara, Brazil. The newly built 12m antenna will be the same design as the 12m antennas deployed at NASA’s Kokee Park and McDonald VGOS stations and will include a MIT designed signal chain. We will discuss the FGO station facility infrastructure modification, which allows for the capacity to continue operating the active 14.2m Legacy VLBI antenna while simultaneously establishing new VGOS baselines using the new 12m VGOS antenna. We will present additional upgrades to the FGO station over the last 2 years including: GNSS, MHM-2020 maser and timing infrastructure, weather sensors, and monitoring and control system (MAS). We will discuss how the improvement of these subsystems will work concurrently with the MIT signal chain to advance the overall VGOS observing technique.

Speakers: Katie Pazamickas (Peraton / NASA GSFC), Sean Gilliams (Peraton/NASA GSFC)

4:45 PM Improvement of VGOS-INT-A Scheduling through Source Flux Catalog Improvement

Improvement of VGOS-INT-A scheduling is currently focused on the sources used for scheduling. Until May 2023, the IVS GSFC Technology Development Center, which updates the source flux catalogs used in VGOS-INT-A scheduling, had a policy of using four to eight weeks of input data for each flux catalog update. Then the IVS GSFC Analysis Center began testing the use of four, five, six, seven, and eight weeks of input data, to see if one of these five ranges of input data is preferable. Here we present results.

Source flux catalog quality also depends on the frequency at which the sources' flux information is updated. Here we also assess whether the fluxes for the sources used in VGOS-INT-A scheduling are being updated sufficiently frequently.

Speaker: Sergei Bolotin (NVI, Inc. / NASA GSFC)

4:45 PM Improving VLBI stations performance: Insights from the Pilot Project on Station Feedback

Healthy and well performing VLBI stations are essential for the quality and reliability of all IVS products. However, station performance issues are often identified only months after data acquisition, and current feedback mechanisms remain unstructured and inconsistent across the network. At the same time, many stations must report performance metrics to their funders, developing its own local procedures to diagnose issues and track performance, but there is no unified or standardized IVS level feedback system to support them.
To address these challenges, the IVS Pilot Project on Station Feedback aims to develop an automated system that collects publicly available IVS data (logs, schedules, correlation and analysis reports, spool files, etc.), derives station level statistics, and provides regular standardized reports to participating stations.
This contribution presents the goals, structure, and current progress of the pilot project. Because this initiative is still under development, feedback from the community is both essential and actively encouraged. We invite VLBI stations and IVS stakeholders to share their perspectives on the needs, usefulness, and potential extensions of this system. Stations interested in contributing or joining the project after the initial pilot phase are especially welcome.
By collaboratively defining meaningful performance indicators and enabling timely, structured feedback loops, this pilot project aims to strengthen station operations.

Speaker: Esther Azcue (National Geographic Institute of Spain)

4:45 PM Initial Results Obtained from VGOS Observations Using CHIANGMAI 13-m Radio Telescope

The CHIANGMAI 13-m radio telescope (CHANGM13) operates as a VLBI Global Observing System (VGOS) station, equipped with two receivers: a broadband receiver (3–14 GHz) and a dual-band X/Ka receiver covering 7–9.5 GHz and 28–34 GHz. First fringes have been detected during three one-hour VGOS-mode tests in 2024. Subsequently, two 24-hour VGOS observing sessions were completed in April 2025. All sessions were correlated and analyzed, enabling precise estimation of CHANGM13’s initial station coordinates. The station has been formally registered with a CDP/DOMES number through the IVS, establishing its readiness for future international geodetic VLBI observations.

Speakers: Fengchun Shu ((1)Shanghai Astronomical Observatory, Chinese Academy of Sciences (SHAO, CAS) (2)University of Chinese Academy of Sciences), Xuan He (Shanghai Astronomical Observatory, Chinese Academy of Sciences)

4:45 PM Introducing the USNO-INT-P VLBI Intensive Series

In May 2020, the United States Naval Observatory (USNO) commenced observing geodetic VLBA "Intensive" sessions using the Mauna Kea and Hancock stations of the Very Long Baseline Array (VLBA). Within the IVS, this series of sessions is dubbed the "USNO-INT-P" series. Herein, the frequency setup, developed to minimize the loss of channels due to radio frequency interference (RFI), the duration, and the semi-automated approach to session scheduling in the dynamic VLBA utilization schedule are described. The USNO VLBI Analysis Center's analysis of these sessions is also presented and discussed.

Speaker: Christopher Dieck (US Naval Observatory)

4:45 PM Investigation of Unwanted Electromagnetic Radiation at Onsala Space Observatory

The VLBI Global Observing System (VGOS) was originally designed to operate in two linear polarisations over the frequency range from 2 to 14 GHz, observing four bands of 1 GHz bandwidth each, distributed in this range. During the last years, VGOS has been operated using linear polarised observations in four bands of 480 MHz bandwidth, each synthesised by eight 32 MHz-wide channels, in the range of 3−10.7 GHz. Virtually all VGOS frequency channels overlap with licensed radio frequency services coordinated by the International Telecommunication Union (ITU). These services include both ground-based transmitters and space-borne systems, whose artificial radio emissions can be orders of magnitude stronger than the signals received from quasars.
We investigated the responses of the system temperature (Tsys) and
the spectrum analyser to characterise the directions, magnitudes, and
frequencies of disturbing electromagnetic radiation detected by the Onsala Twin Telescopes (OTT). In this work, we present updates from our most recent studies.

Speaker: Lim Chin Chuan (Onsala Space Observatory)

4:45 PM MIT Haystack Technology Development

MIT Haystack technology developments will focus on the advancements of the VGOS compliant signal chain recently deployed to the Fortaleza station. We will present the technology advancements from the frontend to the backend subsystems, along with the calibration and monitor and control modifications.

Speaker: Chester Ruszczyk (MIT)

4:45 PM NASA Kokee Park Geophysical Observatory Site Update

Site updates to include 2024-2025 IVS contributions, site challenges, site observation metrics, staffing and organization, technical improvements, and future plans being coordinated for the site.

Speaker: Christopher Coughlin (NASA Kokee Park Geophysical Observatory)

4:45 PM NASA VLBI Network Sustaining Engineering Developments

A. Gerrety, S. Gilliams

Abstract: We will discuss sustainment engineering lessons learned in the NASA VLBI network, broken into sections. These sections will discuss:

Challenges of cryogenic system sustainment of legacy systems

M125A compressors at WF, GS, and FGO 14m

Ebox issues with M700 compressors at KPGO/MGOstrong text

Lightning protection challenges encountered during construction of the new Fortaleza Geophysical Observatory (FGO) 12m VLBI Global Observing System

Component obsolescence and the integration of modern replacements

GS motor obsolesce and costly control system upgrade

Can verbally mention the GGAO 12m getting stuck and needing a lift assist (probably not worth writing on the poster)

Incident reporting and classification

Problem reports

Station start/stop messages to communicate with the IVS (specifically correlators)

Communicate downtime with IVS schedulers

We will address the challenges of maintaining legacy equipment, focusing on common age-related failures in electric motors, feedback devices, switches, and encoders. We will examine the integration of non-standard cryogenic compressors into the FGO 14m and GGAO 12m VGOS antennas following the discontinuation of the M125 model. Additionally, we highlight how systematic documentation and classification of station issues are vital for long-term system sustainment.

Speakers: Austin Gerretty (NASA Goddard Geophysical and Astronomical Observatory (Peraton)), Sean Gilliams (NASA Goddard Geophysical and Astronomical Observatory (Peraton))

4:45 PM New Agenda Item for WRC-2031: Protect Geodetic VLBI—Preserve Time Keeping

This poster is based on a flyer that explains to non-scientists the crucial nature of geodetic VLBI and the essential contributions of this service to global time-keeping, navigation, and other applications, as well as how VLBI science is negatively affected by the commercial usage of space and the rapid expansion of mobile telecommunication networks. It is designed for sharing with United Nations and other laypeople to explain geodesy and VLBI in a condensed handout.

Speakers: Dr Hayo Hase, Nancy Kotary (MIT Haystack Observatory), Rüdiger HAAS (Chalmers tekniska högskola)

4:45 PM NIGERIA BULDS 1ST GEODETIC VLBI IN COLLABORATION WITH CHINA.

Nigeria made history as the National Space Research and Development Agency (NASRDA) in collaboration with the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Science completed and hoisted the main antenna of the country's 1st Very Long Baseline Interferometry Global Observing System (VGOS) at the Centre for Geodesy and Geodynamics (CGG), Toro in Bauchi state Nigeria. It is also the 1st VGOS in West Africa and 2nd in Africa. The project was initiated in 2019. Construction work began in November 2024. The station which is at its completion stage is completion is a 13-m radio telescope characterized by high slew rate as 12 deg/s in azimuth and 6 deg/s in elevation, broad-band receiving by covering 2 GHz to 14 GHz as well as dual-band coverage X/Ka-band, which is designed especially for geodetic and astrometric studies in accordance with the international technical specifications. After successful commissioning the telescope will take part in the observation experiments of the international VLBI network and work together with the China VLBI network, to precisely determine the station coordinates and velocities, observation target coordinates as well as the EOP. This paper is aimed at presenting the progress made so far in the building and operating the new VGOS in Nigeria.

Speaker: JOSEPH DODO (CENTRE FOR GEODESY AND GEODYNAMICS, NATIONAL SPACE RESEARCH AND DEVELOPMENT AGENCY, NIGERIA)

4:45 PM Observing Program Committee (OPC): Who we are and what we do

The Observing Program Committee (OPC) is a standing body in the IVS that reviews and approves the observing programs that are being coordinated by the Coordinating Center. The currently fourteen, Board-confirmed members meet monthly to review and approve the IVS annual observing program, to review proposals for observing time that use IVS resources, to monitor observing program performance and resource usage, and to provide advice and recommendations to the Coordinating Center as needed. The observing program is based on the final report of Working Group 2 on “Product Specification and Observing Programs”, whose recommendations have been applied since 2002.
We give an overview of the work of the OPC in the last couple of years. We explain the role of the OPC and lay out how regular IVS members can engage and contribute to improving IVS observing programs. For the 2026 VGOS observing plan, we outline the general features and address the rationale and decision-making processes behind it. The plan includes the allocation of resources for research and development (R&D), which can be tapped into following an open call for proposals (for VGOS-RD sessions).

Speaker: Lucia McCallum (University of Tasmania)

4:45 PM On the evaluation of the efficiency of the source-centric scheduling approach for VGOS-OPS sessions

In the second half of 2025, IVS observed VGOS-OPS sessions using two alternating scheduling approaches, switching between the standard SNR-based approach (called “VO” sessions) and a source-centric approach (called “VS” sessions). The SNR-based scheduling method determines the scan length based on predicted signal strength rather than a fixed duration to maximize the number of observations. The source-based approach focuses on balanced observations of core and good sources, as well as test sources, which are evenly distributed across the sky. In this study, we will research the geodetic products obtained from both “VO” and “VS” sessions and evaluate the efficiency of each scheduling method. The research should contribute toward having a better understanding of the standard SNR-based vs. the new source-centric approach and chart a viable path for future VGOS-OPS sessions.

Speaker: Dirk Behrend (NVI, Inc./NASA GSFC)

4:45 PM On the Path to Reliable Geodetic Correlation: Verifying New DiFX Versions at the Bonn Correlator

Like any other software, DiFX (Distributed FX)1 undergoes frequent updates to enhance performance, add new features, and ensure compatibility. Major releases introduce significant new functionality, architectural changes, or performance improvements.

Before transitioning to a new DiFX version, the software output (fringe visibility measurements) must be carefully compared with results from earlier versions. This comparison is performed using several tools, which are described in detail in this poster.

1A. T. Deller, W. F. Brisken, C. J. Phillips, J. Morgan, . Alef, R. Cappallo, E. Middelberg, J. D. Romney, H. Rottmann, S. J. Tingay & R. Wayth, “DiFX-2: A More Flexible, Efficient, Robust, and Powerful Software Correlator”, PASP, 2011, 123, 275–287

Speaker: Simone Bernhart (Reichert GmbH / BKG / MPIfR)

4:45 PM Onsala Space Observatory Status Report

We report the status updates of the Onsala Space Observatory (OSO) for 2024/2025, including the operation and support of the VGOS and S/X VLBI components.
This report also includes preliminary effort to enhance VGOS results using collocated geodetic facilities, such as the water vapour radiometer and GNSS. Furthermore, we report on an ongoing flux density monitoring program using the VGOS antennas.
In addition, a longer time series from the invar systems installed on the VGOS antennas has improved our understanding of antenna motion during observations.
We also investigated the phasecal stability and its relation to room temperature in the backend room.

Speakers: Lim Chin Chuan (Onsala Space Observatory), Rüdiger HAAS (Chalmers tekniska högskola)

4:45 PM Operational Status and Technical Enhancements of the Sejong VLBI Station

This poster presentation introduces on the recent operational status and technical updates of the Sejong VLBI station. The key developments include: 1) The implementation of an in-house Field System (FS) developed to automate observations and improve operational efficiency. 2) The upgrade of the antenna servo system, which has enhanced tracking precision and overall observing efficiency. 3) Monitoring results and operational countermeasures regarding Radio Frequency Interference (RFI) in the 2 GHz and 8 GHz bands. 4) Cumulative results of local tie surveys, including updated antenna axis offset values and the analysis methodologies used to derive the Invariant Point (IVP) for high-precision geodesy.

Speaker: YI Sang-Oh (National Geographic Information Institute, Republic of Korea)

4:45 PM Operational status of the BKG Data Center

VLBI data centers are a fundamental component of the global VLBI supply chain, ensuring reliable long-term archiving, distribution, and accessibility of observational data and derived products for the geodetic community. As part of the IVS infrastructure, data centers provide redundancy, data integrity, and continuity, which are essential for reproducible analysis and the generation of high-quality geodetic products.
The BKG VLBI Data Center is one of the primary IVS data centers. During the past two years, the BKG data center was operated in a limited mode and used mainly for internal processing and testing. In Q1 2026, we plan to reactivate the system and return to full external operation. This contribution presents the current status of the BKG VLBI Data Center and summarizes recent technical and organizational updates. An overview of available services, including data ingestion, archiving, and user access to VLBI session data, is provided.

Speaker: Sadegh Modiri (Federal Agency for Cartography and Geodesy BKG)

4:45 PM Processing VLBI observations with the Bernese GNSS Software – current state of development

The Geodesy Group of the BKG (Federal Agency for Cartography and Geodesy) uses different software packages for the analysis of the different space-geodetic techniques VLBI (Calc/Solve), SLR and GNSS (Bernese) as well as for the combination of the individual technique contributions at normal equation level (DOGS CS) to derive improved reference frame and Earth rotation parameters.

Currently, we are working towards combining the different techniques consistently on the observation level within a single software package, namely the Bernese GNSS Software. It is developed by AIUB (Astronomical Institute of the University of Bern) and capable of GNSS and SLR processing. AIUB started adding VLBI processing capabilities to the Bernese a few years ago. We present the latest status of the on-going software implementations and show VLBI processing results derived from the current software version. We will discuss the next steps towards automated VLBI processing, in particular for residual screening and detection of outliers and clock jumps.

Speaker: Claudia Flohrer (Federal Agency for Cartography and Geodesy)

4:45 PM Progress on a new genetic algorithm for VLBI network optimization

The Observatory Coordinate Estimation & Long-baseline Optimization Tool (OCELOT) is a new optimization software in development that utilizes a genetic algorithm with the existing simulation software, VieSched++, to identify an optimal network geometry for VLBI arrays. OCELOT determines the optimal network geometry for new VLBI arrays or new stations being added to existing arrays. OCELOT’s genetic algorithm uses VieSched++ to simulate many different network configurations, iteratively building on candidate networks until a global minimum has been found. OCELOT is currently able to optimize for geodetic sessions; future work will include an option for astrometric optimization.

Speaker: Sara Hardin (U.S. Naval Observatory)

4:45 PM The potential of the Hellenic participation to IVS - The THERMOpYlae radio telescope

We introduce THERMOpYlae to the VLBI community. The forthcoming Hellenic radio telescope is a 32-m professional instrument located at the southeastern border of Europe, offering valuable geographic coverage for international VLBI observations. THERMOpYlae is already recognized within the EVN/VLBI framework as an observing station (two-letter code: Th) and is included in the EVN calculator and the JIVE planobs system.

The facility is currently being equipped with an S/X receiver, an Ettus USRP E320 backend, a mid-range processing server, and a rubidium frequency standard to support initial testing and commissioning. In parallel, installation of a dark-fiber link connecting THERMOpYlae to the GEANT network is planned, enabling high-rate data transfer and future real-time VLBI participation.
Located in the seismically active eastern Mediterranean region, THERMOpYlae has the potential to support future geodetic and astrometric VLBI applications and to strengthen southeastern European participation in global VLBI activities. The development of this new infrastructure aims to expand observational capabilities and foster international scientific collaboration.

Speaker: Prof. Nectaria Gizani (Hellenic Open University)

4:45 PM Upgrading the Fortaleza Geodetic Observatory (FGO) for Next Generation VGOS Observations

Infrastructure upgrades were carried out at the Fortaleza Geodetic Observatory (FGO), part of the Northeast Space Radio Observatory (ROEN), to support the installation and operation of a new VGOS-compliant 12 m antenna system, while maintaining uninterrupted operation of the legacy 14 m VLBI antenna. The project involved coordinated civil, electrical, logical, and operational reforms to establish FGO as a modern and reliable VGOS station

Civil works included the construction of a dedicated foundation and complete logical-electrical infrastructure for the new VGOS antenna. The control room was updated for new equipment racks for antenna control, data acquisition, recording, and high-speed data transmission systems

A new electrical system was designed and installed, comprising a 350 kVA diesel generator and a 175 kW uninterruptible power supply (UPS). This configuration provides sufficient capacity to supply both antennas and supports continuous operation for up to 48 hours without refueling. All electrical panels are fully monitored, with continuous logging of key electrical parameters accessible through a graphical interface to assist preventive and corrective maintenance.

The new antenna is fully VGOS-compatible with a maximum angular speed of 12 deg/s. The receiving system includes an ultra-wideband cryogenic receiver covering 2–18 GHz. In addition, a new hydrogen maser frequency standard (Microchip MHM-2020) was installed in a dedicated, environmentally controlled room.

Speaker: Adeildo Sombra da Silva (CRAAM - Center for Radio Astronomy and Astrophysics Mackenzie)

4:45 PM VGOS Radio Telescopes Wettzell - Radio Frequency Interference (RFI) Monitoring at Frontend Level

This poster presents site-specific constraints at the Wettzell Geodetic Observatory caused by both local environmental factors and the increasing global occupation of the radio spectrum by terrestrial and space-based transmitters - a trend that increasingly affects broadband geodetic VLBI systems. At Wettzell, these conditions challenge the broadband VGOS frontend signal chain operating from 2 to 14 GHz, with potential sensitivity extending below 1 GHz. Reliable VGOS operation therefore requires careful engineering of the frontend architecture to balance high sensitivity with robustness against radio frequency interference (RFI). A key prerequisite for this process is the systematic characterization and continuous monitoring of the surrounding RFI horizon. The poster describes the technical implementation of an RFI horizon monitoring system at Wettzell and presents representative measurement results. The observed interference characteristics provide essential input for frontend optimization, operational risk assessment, and long-term performance evaluation of the VGOS station.

Speaker: Mr Daniel Amberger (Bundesamt für Kartographie und Geodäsie)

4:45 PM VLBI applications of Canberra Deep Space Network stations

Canberra Deep Space Communication Complex (CDSCC), Tidbinbilla, is part of the NASA Deep Space Network (DSN). Because of the Southern Hemisphere location and large apertures, the radio telescopes at CDSCC have been used for VLBI over the last half century for imaging, astrometry, and space navigation. At Tidbinbilla there are one 70-m dish (DSS-43) and three 34-m dishes (DSS-34, 35, and 36) that support deep space communication and radio astronomy. JPL developed and deployed in 2022 a modernised VLBI backend VRA for DSN stations that is compatible with multiple recording modes. DSS-43 is equipped with a K-band receiver and is in high demand as the largest steerable single dish radio telescope in the Southern Hemisphere for VLBI projects such as Long Baseline Array (LBA), East Asian VLBI Network (EAVN), and K-band Celestial Reference Frame (K-CRF). DSN installed a CSIRO developed wide band L-band receiver at DSS-43 in 2025 along with the Jimble digital backend. We discuss the strength of the VLBI arrays including DSS-43 and recent highlights.

Speaker: Shinji Horiuchi (Canberra Deep Space Communication Complex)

4:45 PM What’s New in VieSched++?

The VLBI scheduling and simulation software VieSched++ continues to gain popularity within the geodetic VLBI community. In 2026 alone, roughly 100 global 24-hour sessions and about 900 Intensive sessions are expected to be generated using VieSched++. Alongside this growing operational use, the software itself has undergone further development.

In this contribution, we present several new key features of VieSched++ and its automated operational frameworks. These include support for tabular source datasets, enabling tracking of arbitrary objects such as lunar landers (e.g., NovaMoon); enhanced flexibility and configuration options for calibration scans; clearer distinction between sites and stations in scan constraints; and support for VGOS antenna catalogs, among other improvements. Furthermore, groundwork has been laid for a revised support of twin-telescope sites, which will be tested in an upcoming VGOS R&D session later this year. We invite the community to discuss these developments and to outline additional requests and improvements for upcoming releases.

In addition, we report on the migration of the software stack from Qt5, QMake, and C++14 to Qt6, CMake, and C++17. While admittedly a rather "nerdy" endeavor, this transition is essential to improving the installation experience on Linux, Windows, and macOS and to ensuring the long-term maintainability and support of VieSched++.

Speaker: Matthias Schartner (ETH Zurich)

6:00 PM → 7:00 PM Splinter Meetings: VTC Splinter Meeting (López Pérez José Antonio)

Convener: López Pérez José Antonio

7:00 PM → 8:00 PM Splinter Meetings: SC 1.4: Interaction of Celestial and Terrestrial Reference Frames (Maria Karbon)

Tue, April 14

8:30 AM → 9:15 AM IVS GM: Session 3 (Operations) - Slot 2

8:30 AM A Web-based approach to register and manage antenna data with a workflow

Often, content on official websites is outdated. Catalog data and other files on numerous servers are not up-to-date and must be maintained manually. Registering new antennas and undergoing onboarding requires many manual steps. As part of a Network Coordinator project, initial plans and test implementations were developed to implement these processes in a web-based workflow. Approaches are being explored to describe the new, complex antenna receiver chains. Furthermore, initial direct, graphical feedback for sessions is being tested.

Speaker: Alexander Neidhardt (FESG - Technical University of Munich)

8:45 AM VLBI Communications Center

One of the goals of the VGOS framework is to achieve continuous observing of earth orientation parameters. In order to achieve this ambitious goal, various components of the IVS need to be in communication with each other on a continuous basis. Yet, most of the operational communication takes place via E-Mails and IVS exploder lists, which require personnel to read, interpret and respond. The VLBI Communications Center (VCC) aims to streamline the correspondence between the Operations Center, Coordinating Center and the network stations. In this talk, I will present the vision of the VCC, which is achieving machine-to-machine, traceable, near real-time and secure communication, as well as how this vision is implemented in practice.

Speaker: Gonenc Mogol (NVI Inc. (NASA contractor))

9:00 AM A Report on Experience: Taking a VLBI Station from a University to a Commercial Environment

In July 2024, Space Operations New Zealand Ltd. (SpaceOps NZ) acquired the Auckland University of Technology’s Warkworth VLBI station, prompting fundamental questions regarding the station’s capabilities, operational purpose and the standards required for continued participation in the International VLBI Service for Geodesy and Astrometry (IVS). This paper outlines SpaceOps NZ’s progress in integrating academic expertise with commercial operational practices to ensure the consistent delivery of high quality VLBI data. We describe the steps taken to assess the station’s existing performance, develop internal competency and evaluate system readiness, thereby addressing the initial questions of what had been acquired and how effectively it could be operated. We then examine the more challenging question of defining “how good is good enough” within the context of IVS requirements, a determination that is essential for guiding future capital investment and carries broader implications for the IVS community. Our findings highlight both the progress achieved to date and the inherent complexities involved in bringing rigour, reliability and long term sustainability to VLBI operations.

Speaker: Robin McNeill (Space Operations New Zealand Ltd)

9:15 AM → 9:30 AM Stretch-your-legs break

9:30 AM → 10:15 AM IVS GM: Session 3 (Operations) - Slot 3

9:30 AM Assessing and Modelling Tsys for Complete Amplitude Calibration in VGOS Networks

Accurate system temperature (Tsys) measurements are essential for robust amplitude calibration in VGOS observations. The temporal and elevation-dependent behaviour of Tsys (1) can reveal potential instrumental issues at a station upon inspection, and (2) allows us to investigate and validate a parametric model of Tsys for each station and IF. In this report, we assess the quality of Tsys measurements as a rapid diagnostic of station performance during an experiment, and aim to obtain a consistent, smooth description of Tsys evolution across an observing session.

Additionally, as amplitude calibration depends directly on reliable Tsys values, a complete set of Tsys measurements from all stations is crucial for full-network calibration. However, not all VGOS stations routinely provide Tsys data, limiting amplitude calibration and forcing data analysis and imaging to rely more heavily on closure quantities. Therefore, our investigation of Tsys behaviour also supports closure imaging, as improved Tsys understanding helps in recovering total flux densities. Furthermore, using closure-based imaging results, we evaluate existing Tsys measurements and derive parametric Tsys models for stations lacking such data. This approach highlights the necessity of routinely measured Tsys at all VGOS stations, as real measurements remain fundamental for accurate calibration and modelling across the network.

Speaker: Ezequiel Albentosa-Ruiz (GFZ Helmholtz Centre for Geosciences)

IVS_GM2026_TSYS.pdf

9:45 AM Improving VLBI Observation Data Merging and Transfer at the Ishioka Station

At the Ishioka station, observation data is merged and copied from FlexBuff to a storage server and then transferred to a correlator. For 24-hour observations, long merge time and limited transfer speed had been major bottlenecks.
To address this, we changed our merge tool and introduced parallel processing, greatly reducing the merge time. In addition, parallel e-transfer improved the data transfer performance. This presentation reports on the implementation and results of these improvements.

Speaker: Kayako Hori (Geospatial Information Authority of Japan)

10:00 AM Recent Status of VGOS intensive observing program using Shanghai-Urumqi baseline

We conducted the VLBI Intensive program using the Shanghai and Urumqi VGOS antennas to rapidly determine the Earth's rotation angle. The program began in May 2022 and run three times per week from March 2023, with a series of one-hour-long observing sessions were performed using two (or three) VGOS antennas. The VGOS data were correlated, post-correlation processed, and analyzed at the Shanghai Astronomical Observatory, CAS.
We present the implementation of UT1 observations from 2025 to 2026, the status of the VGOS stations, and the resulting UT1 estimates. In May 2025, a superconducting filter was installed at the Seshan13 station to mitigate Radio Frequency Interference (RFI), thereby reducing the number of data channels that required deletion during processing. Persistent repairs at the Urumqi13 station enabled the use of its phase-cal system for phase calibration in UT1 processing. In August 2025, an automated data correlation pipeline was implemented, significantly improving processing efficiency. Statistics indicate a marked reduction in both correlation time and data processing queuing delays.
Our analysis includes dUT1 estimates compared with the IERS C04 series, along with their formal errors and the weighted root-mean-square (WRMS) of delay residuals. Furthermore, we evaluate the VGOS Intensive sessions by comparing results from the TIANMA13-URUMQI13 and SESHAN13-URUMQI13 baselines.

Speaker: Dr Jiangying Gan (Shanghai Astronomical Observatory, CAS)

10:15 AM → 10:45 AM Coffee break

10:45 AM → 11:00 AM IVS GM: Session 3 (Operations) - Slot 4

10:45 AM VLBI operations at AGGO

The geodetic observatory AGGO (La Plata, Argentina) operates a 6 m S/X offset radio telescope and plans to install a VGOS telescope in the coming years. We present AGGO’s performance within the IVS network since the start of its VLBI observations and discuss findings relevant for schedule optimization.

Local radio-frequency interference (RFI) has not significantly affected S/X observations so far; however, we identify substantial S-band interference from both terrestrial and space-borne sources. In preparation for the upcoming VGOS system, we also present results from broadband electromagnetic spectrum measurements at the site.

Speaker: Mr Christian Kristukat (BKG)

11:00 AM → 11:35 AM IVS GM: Session 4 (Products) - Slot 1

11:00 AM Progress Towards ICRF4 at X/S and K Bands

VLBI observations at X/S (8.6/2.3 GHz) and K bands (24 GHz) have continued since the third realization of the International Celestial Reference Frame (ICRF3) in order to expand and improve the upcoming ICRF4. At X/S band, we are adding sessions from monthly VLBA astrometry sessions, monthly RDV sessions, and IVS legacy sessions. The current pre-ICRF4-SX catalog now contains 5807 sources, 28% more than ICRF3-SX. The VLBA astrometry and RDV sessions are currently concentrating on a list of 920 ICRF3 sources that show small offsets from Gaia positions. At K band, we are making monthly VLBA astrometry sessions, approximately monthly Korea VLBI Network (KVN) sessions, and several global EVN/VLBA/KVN sessions. The current pre-ICRF4-K catalog now has 1317 sources, 60% more than ICRF3-K. We have also revisited the K band noise floor and will present new estimates that are somewhat larger than those used for ICRF3, particularly south of -35° declination. We will present median and average scaled uncertainties and will present and discuss the rotations and distortions with respect to ICRF3 and Gaia DR3, as indicated by vector spherical harmonic (VSH) analysis for both X/S and K bands.

Speaker: Dr David Gordon (United States Naval Observatory)

11:20 AM MAORI – A new VLBI processing library

GMV has developed VLBI processing within its new flight dynamics and geodesy software, GMV MAORI. MAORI is a modern, modular C++/Python library providing state-of-the-art modelling and estimation capabilities. This contribution presents ongoing work on VGOS DB processing, with emphasis on the simultaneous estimation of EOPs, station coordinates, troposphere and clock models. Initial results for selected sessions are shown, providing an early validation of the modelling and estimation chain.

Speaker: Mr Miguel Ángel Muñoz de la Torre (GMV Aerospace & Defence)

11:35 AM → 11:50 AM Stretch-your-legs break

11:50 AM → 12:35 PM IVS GM: Session 4 (Products) - Slot 2

11:50 AM Ambiguity Resolution with Multiband-Singleband Delay Differences

A new ambiguity resolution method for X/S-band VLBI group delays—estimated routinely by the correlation centers with fringe fitting program HOPS/fourfit—is introduced. The method is based primarily on multiband minus singleband delay differences (MBD-SBD). It exploits the fact that SBDs are unambiguous, whereas MBDs may contain ambiguity jumps. Their difference can therefore isolate the ambiguity structure on each baseline. However, due to differing effects on SBD and MBD, in conjunction with the implementation of phase calibration exclusively on legacy MBD, the precision of SBD reaches several nanoseconds and SBD cannot be utilized to anchor the MBD directly at each baseline, as demonstrated by Nothnagel et al. (2025, IVSGM2024 Proceedings). Therefore, median MBD-SBD differences are computed per baseline to obtain robust values unaffected by outliers, and these median values are combined in modified triangle closure relations to estimate consistent ambiguity corrections across the full station network. The approach was tested on all X/S CONT17-L1 sessions and demonstrated that ambiguities can be resolved automatically. We identified, that further development of the method is needed for challenging sessions with specific clock breaks. Our results show that MBD-SBD delay differences provide a highly effective, computationally efficient basis for autonomous ambiguity resolution and offer a promising path toward fully integrated pre-processing within VieVS.

Speaker: Peter Urban (TU Wien)

IVSGM2026_Presentation_Peter_Urban.pdf

12:05 PM Microwave radiometer observations for VGOS data processing

The Onsala Space Observatory is operating a new modern microwave radiometer, called Greta, since 2023. Greta is a commercial product of type HATPRO-G5. It is co-located with the other microwave radiometer, called Konrad, which has been developed and built at Onsala. Konrad has been in operation since 2000 and is usually operated in so-called sky-mapping mode. The data of complete sky-scanning sequences are then analyzed together, providing zenith wet delay and wet horizontal gradient results with a temporal resolution of 5 minutes. This type of data are available for this study from the beginning of 2023 to July 2024. In addition to operating in a similar sky-mapping mode, the new radiometer Greta has been operated synchronised with VGOS observations during several VGOS 24 h sessions from the year 2023 to 2024. This means that Greta was performing measurements of the local atmosphere in the same direction as the VGOS telescopes at Onsala, thus providing slant wet delay measurements for each individual VGOS observation. Together with the slant hydrostatic delays, calculated from ground pressure measurements, the possibility to avoid estimating the delays due to the neutral atmosphere exists and are evaluated. We present an update of using these slant delays as external a priori information in the VGOS data analysis.

Speaker: Rüdiger HAAS (Chalmers tekniska högskola)

12:20 PM VGOS operational sessions scheduled with source-centric approach in 2025

Very Long Baseline Interferometry Global Observing System (VGOS) has been in its operational phase since 2019. In our previous studies (Krásná et al., 2025, A&A 693; Krásná et al., EVGA2025) we demonstrate the high potential of VGOS sessions for geodetic and astrometric products. At the same time, possibilities for improvement in the scheduling and analysis strategies of the sessions have been identified, keeping in mind the unique VLBI characteristics as a bridge between geodesy, astrometry and astronomy. Based on our proposal, the International VLBI Service for Geodesy and Astrometry (IVS) has been testing an updated source-centric scheduling approach (Schartner et al., 2023, JGeod 97) in operational 24-h VGOS sessions once per month since July 2025.
In this contribution, we assess the performance of available source-centric VGOS sessions (VS) and compare the precision and accuracy of derived geodetic parameters against those from established operational VGOS sessions (VO). Furthermore, we provide an overview of the performance and characteristics of VS versus VO sessions with a focus on the anticipated benefits for the maintenance of the celestial reference frame. In addition, we approach the sensitivity of VGOS solutions to critical analysis parameters such as observation cut-off elevation angle, elevation-dependent weighting schemes, and the temporal resolution for zenith wet delay and tropospheric gradient estimates.

Speaker: Hana Krasna (TU Wien)

12:35 PM → 2:00 PM Lunch break

2:00 PM → 3:15 PM IVS GM: Session 4 (Products) - Slot 3

2:00 PM UT1 Comparison between c5++ and nuSolve

Tsukuba Correlator/Analysis Center at GSI has developed a fully automated correlation system for the 1-hour S/X session, INT-2, and the 1-hour VGOS sessions, VGOS-INT-B and C. After the correlation, UT1 values for these sessions are estimated by the analysis software C5++. This presentation will summarize the estimated UT1 values calculated by C5++ for VGOS-INT-B and C, and provide a comparison with those calculated and submitted to the IVS by the NASA Analysis Center using nuSolve.

Speaker: Haruna Furui (Geospatial Information Authority of Japan)

2:15 PM Impact of IVS Solutions on Ultra-Short-Term UT1-UTC predictions

The availability of precise UT1-UTC measurements is limited by latencies of several days to weeks, which can be compensated for by prediction. Existing UT1-UTC prediction approaches utilise post-processed IERS UT1-UTC series because they are provided at regular epochs. However, the most direct UT1-UTC observations are produced by the IVS, whose solutions are not used as inputs for prediction models due to their irregular temporal sampling.

This study focuses on incorporating both IERS and IVS UT1-UTC series into ultra-short-term (10-day) prediction. A hybrid prediction framework is developed, combining a local linear trend model with a non-linear DL method, Coupled Oscillatory Recurrent Neural Network (coRNN). The model uses UT1-UTC estimates from the IERS 20 C04 and IVS solutions, together with Earth’s effective angular momentum data from GFZ, covering the period from 2000 onward. The evaluation is conducted over the Second EOP Prediction Comparison Campaign test interval (September 2021-December 2022).

When only IERS data are used, the model shows an improvement of 30% at a 10-day lead time compared to the IERS prediction centre. The inclusion of additional IVS epochs leads to a small reduction in prediction accuracy, which is equivalent to the root-mean-square difference between the IERS and IVS series. These results indicate that the benefit of incorporating IVS solutions is primarily controlled by their consistency and precision relative to the IERS reference series.

Speaker: Arnab Laha (Indian Institute of Technology Kanpur)

2:30 PM Improving the Regularity and Accuracy of VLBI-Based UT1-UTC Estimates

This study presents the development of a daily VLBI time series of UT1-UTC with improved accuracy and temporal regularity by combining inputs from different VLBI session types at the normal equation level. The approach addresses the limitations of the current IVS EOP products, in particular the EOP-S and EOP-I series, which are estimated independently from 24-hour geodetic and 1-hour Intensive sessions.
While UT1-UTC estimates from EOP-S benefit from high accuracy due to 24-hour observation periods and globally distributed networks, their temporal resolution is irregular and not available on a daily basis. In contrast, the EOP-I series provides daily UT1-UTC estimates but at irregular mid-session-epochs and with reduced accuracy due to the short observation duration of one hour and the network of two to three stations. By combining both session types, the approach exploits the complementary strengths of 24-hour and Intensive VLBI sessions to generate a more consistent daily UT1-UTC time series with improved accuracy.
The presentation describes the combination strategy, including session selection and the normal equation handling. Challenges such as data gaps, inconsistencies between session types, and systematic effects are addressed. The results demonstrate a significant improvement in both the temporal regularity and the accuracy of the combined UT1-UTC estimates compared to the IVS products. The resulting time series represents a more robust input for UT1-UTC prediction.

Speaker: Claudia Flohrer

2:45 PM Comparison of VLBI-derived radio source positions and EOP from three frequency bands as part of GFZ’s contribution to ICRF4

In the ongoing preparations for the next realization of International Celestial Reference System, ICRF4, we have submitted radio source position solutions analyzed at the GFZ VLBI Analysis Center with the software package PORT (Potsdam Open-source Radio interferometry Tool). The radio source positions are derived from VLBI observations provided by the IVS at S/X-bands (8.4 and 2.3 GHz) and VGOS broad bands (3-12 GHz) and by the K-band Astro2Geo VLBI Project at K-band (24 GHz). Radio source and station positions, as well as EOP were determined independently at each frequency to preserve the original content of the measurements. We focus on the statistical assessment of positional adjustments and their uncertainties for 5,780 S/X, 583 VGOS, and 1,321 K-band radio source positions present in our solutions. The estimated radio source positions are obtained with respect to a priori positions taken from ICRF3-SX for S/X and VGOS, and from ICRF3-K for K-band data. The obtained VGOS adjustments suggest the introduction of an own catalog for VGOS a priori positions. We compare the individual positions of common sources measured at different frequency bands and the EOP obtained from the different frequency-band solutions for identical epochs to assess inconsistencies. With this overview presentation, we provide a comprehensive assessment of the consistency of VLBI-derived radio source positions and EOP across frequency bands highlighting insights into the astrometric performance.

Speaker: Sujata Dhar (Technische Universität Berlin, Berlin, Germany)

3:00 PM The JPL X/Ka Reference Frame: transition to ITRF-2020-u2023

The JPL X/Ka-band (8.4/32 GHz) reference frame is based upon data collected from 2005 to the present from a sparse network of five deep space tracking sites. This data set presents several challenges for creating an accurate reference frame. The data set is comprised solely of single baseline of Very Long Baseline Interferometry (VLBI) data due to the extreme length of the baselines as well as scheduling constraints. The lack of multi-baseline data presents some unique challenges to forming a terrestrial frame. Another feature of the X/Ka frame is the existence of up to four X/Ka antennas per site.
Additionally, three of the five sites are seismically active with events which have created discontinuities in station locations followed by non-linear post-seismic motion. Because the X/Ka reference frame is used for spacecraft navigation, changing to a new ITRF system requires coordination with both JPL operational earth orientation products and spacecraft tracking data analysis. This paper will discuss our approach to dealing with all of the above challenges.

Speaker: Mr Christopher Jacobs (Jet Propulsion Laboratory, California Institute of Technology)

3:15 PM → 3:30 PM Stretch-your-legs break

3:30 PM → 4:30 PM IVS GM: Session 4 (Products) - Slot 4

3:30 PM The effect of different modelling options on reference frames estimated with VLBI

In VLBI data analysis several different models are applied to correct for geophysical effects, like atmospheric refraction and geophysical loading. Errors in these models can affect the VLBI results, for example the estimated terrestrial and celestial reference frames (TRF and CRF) and the Earth Orientation Parameters (EOP). Furthermore, if different models are used when estimating the TRF and the CRF, it can lead to inconsistencies between these frames.
In this work, the impact of different geophysical models on the reference frames estimated from VLBI are investigated. Several different global VLBI solutions are made, using geodetic VLBI data between 1990 and 2025. This includes both legacy S/X and VGOS observations. In each solution, one model is varied and the impacts on the estimated TRF, CRF and EOP are studied. Examples of models investigated are those used for atmospheric refraction, thermal and gravitational deformation of VLBI telescopes, and non-tidal atmospheric, oceanic, and hydrological loading. The results provide information on the impact of different models on the references frames and EOP estimated from VLBI and how these models affect the consistency between the TRF and the CRF.

Speaker: Tobias Nilsson (Lantmäteriet)

3:45 PM VLBI Scale: Where Do We Stand in Solving the “Needle in the Haystack” Problem?

In the VLBI contribution to ITRF2020, a significant scale drift appeared after epoch 2013.75. The IVS has coordinated a focused effort to resolve the issue. A dedicated Task Force, now IVS Working Group 9, has investigated modeling, instrumental, and analysis-related causes. This contribution summarizes progress across the ITRF2020 updates (u2023, u2024).

A key issue identified was inconsistent station velocity modeling at Ny-Ålesund between GNSS and VLBI. This problem has now been resolved and is treated consistently in the ITRF2020-u2023 discontinuity files, reducing the post-2013.75 scale drift by ~50% over 2013.75–2021.0 and highlighting the need for coordinated handling of co-located techniques.

However, the scale factors from the four additional years included in u2023 and u2024 show that, while Ny-Ålesund and known station events explain the VLBI scale behavior during 2013.75–2021.0, they fail to account for the scale behavior over 2021.0–2025.0. IVS WG9 therefore recommended a complete reprocessing for ITRF2020-u2025. Issues with potential scale impact include a new axis offset for Sejong, erroneous vgosDB ionospheric corrections, and modeling differences between solution generations.

Using the OSO analysis center solution, we evaluate the separate and combined effects of consistent modeling, the Sejong axis offset, and corrected ionospheric modeling on the VLBI scale, helping to constrain the remaining sources of the discrepancy.

Speaker: Karine Le Bail (Onsala Space Observatory / Chalmers University of Technology)

4:00 PM Operational activities of the BKG/DGFI-TUM IVS Combination Centre

VLBI is the only space-geodetic technique sensitive to the full set of Earth Orientation Parameters (EOP), i.e., polar motion offsets and rates, UT1–UTC, length-of-day (LOD) and nutation offsets. The BKG/DGFI-TUM IVS Combination Centre (IVS-CC) provides the IVS contribution to the official EOP product of the International Earth Rotation and Reference Systems Service, namely the IERS 20 C04 series. The IVS-CC-combined EOP time series is aligned to the 2024 update of the International Terrestrial Reference Frame (ITRF2020-u2024) since November 1, 2025. Classically, the Rapid (R1/R4) sessions, scheduled twice a week, are generated to determine the full set of EOP, complemented by VGOS sessions, scheduled thrice a month, since end of 2024.

This presentation outlines recent developments at the IVS-CC and investigates the consistency between the operational EOP products. Moreover, it puts a focus on additional VLBI session types suitable for EOP combination. These sessions include, but are not limited to, 24-hour sessions with globally well-distributed networks which were initially scheduled for other purposes like the determination of the Terrestrial Reference Frame (TRF) but are also sensitive to EOP.

Speaker: Alexander Kehm (BKG Federal Agency for Cartography and Geodesy)

4:15 PM Developments at the BKG/DGFI-TUM IVS Combination Centre within the framework of the IVS Contribution to ITRF2020-u2025

The BKG/DGFI-TUM IVS Combination Centre (IVS-CC) provides the official IVS contribution to realisations of the International Terrestrial Reference System (ITRF) by combining the contributions of the IVS Analysis Centres (ACs).
For the 2025 update of the ITRF 2020 (ITRF2020-u2025), the IVS initiated a reprocessing of the full VLBI observation history since 1979. Besides S/X-band and VGOS sessions, for the first time, K-band VLBI sessions are included into the ITRF contribution. Moreover, on an experimental basis, the IVS-CC provides combined normal equations including radio source positions as parameters to allow for joint and consistent computation of terrestrial and celestial reference frames, and EOPs as the link between them.
This presentation focuses on the developments in the framework of the IVS-CC combination setup for the IVS contribution to ITRF2020-u2025. Starting with an outline of the combination setup, we present the validation of input data provided by the contributing ACs and the combined IVS contribution to ITRF2020-u2025. A special focus is put on characteristics of the session types from different frequency bands.

Speaker: Shrishail Raut (BKG Federal Agency for Cartography and Geodesy)

4:30 PM → 6:00 PM Coffee, refreshments

4:45 PM → 6:00 PM IVS GM: Poster session 2

4:45 PM A New ITRF Solution Based on Long-Term VLBI Observations (1979-2025)

The International Terrestrial Reference Frame (ITRF) serves as the fundamental reference system in the field of space geodesy. Following the release of ITRF2020, an updated version is planned to be issued in 2026, incorporating new observational data. Using 24-hour VLBI data from conventional S/X and VGOS observations spanning from 1979 to 2025, we have derived a new set of parameters for the Earth reference frame. In this study, we computed both single-session solutions and combined multi-session solutions. This presentation will report on the updates to the reference frame results and provide a comparative analysis of the Earth Orientation Parameters (EOP) and radio source positions obtained from traditional S/X data and VGOS data, respectively.

Speaker: Li Guo ((1)Shanghai Astronomical Observatory, Chinese Academy of Sciences (SHAO, CAS) (2)University of Chinese Academy of Sciences)

4:45 PM Comparison of near-field delay models

Classical VLBI delay models assume plane-wave propagation, which is valid for distant radio sources but inadequate for Earth-orbiting satellites, where wavefront curvature and relativistic effects cannot be neglected. Near-field VLBI therefore requires dedicated delay formulations with consistent treatment of space-time reference systems and time scales. In this work, we compare four established near-field VLBI delay models within a fully relativistic and internally consistent framework. The models are evaluated under a range of orbital geometries relevant to satellite-based VLBI applications for future missions.

Speaker: Hakan Sert (Royal Observatory of Belgium)

4:45 PM Core-shifts and Faraday rotation measurements from VGOS observations.

The wide bandwidth and polarimetry capabilities of VGOS, together with the high cadence of observations and large source sample, makes it a very interesting instrument for the astronomical community.

We have developed a set of algorithms that allow us to retrive wide-band and full-polarization images of AGNi from VGOS observations. These tools include the conversion of VGOS visibilities into a circular-polarization basis and a Global Fringe-Fitting with dispersive corrections.

The first results, focused on one VGOS epoch, allowed us to determine the core-shift of source 1803+784 across the whole VGOS band and spatially resolve the inhomogeneous Faraday screen along the jet. Our results suggest that the parsec-scale jet of 1803+784 is out of energy equipartition.

Although our analysis is of interest to the astronomical community, it may also have its impact in geodesy and astrometry, especially when using the broad-band group delay as the main observable. We will show our results on 1803+784, together with preliminary results on other sources observed in the same VGOS epoch.

Speaker: Dr Ivan Marti-Vidal (Departament d'Astronomia i Astrofísica)

4:45 PM DTRF2020 updates – VLBI specific aspects

DTRF2020 as a realization of the ITRS, was calculated from consistently reprocessed VLBI, SLR, GNSS and DORIS data provided by the international technique services. Its updates, DTRF2020-u2023 and DTRF2020-u2024, incorporate extended input series covering 2021–2023 and 2024, respectively.
These extension series are computed as consistent as possible to the DTRF2020 input data but consider also new models if appropriate. Specifically for VLBI gravitational deformation models for six more telescopes are considered. But, the main aspect in view of VLBI is the increasing number of VGOS sessions contributing to the DTRF2020 updates. While in DTRF2020 35 VGOS sessions are included, for DTRF2020-u2024 163 VGOS sessions are available.
We discuss the DTRF2020 updates with a focus on the VLBI contribution, in particular the integration of legacy and VGOS networks and the VLBI scale, applied to realize the DTRF2020 scale together with GNSS. We compare the DTRF2020 and its updates and draw conclusions on the accuracy and consistency of the DTRF2020 update series.

Speaker: Manuela Seitz (TUM)

4:45 PM ENHANCING EARTH ORIENTATION PARAMETER PREDICTION USING MACHINE LEARNING, VLBI OBSERVATIONS, AND WEB-BASED DISSEMINATION

Accurate prediction of the Earth Orientation Parameters (EOP) is of great importance for geodesy and astrometry, as well as for their associated applications. Consequently, our research group has explored the combined application of machine learning techniques and VLBI data with the aim of further improving EOP prediction accuracy. The results obtained demonstrate that machine learning algorithms enhance model performance by capturing complex and non-linear behaviours present in EOP time series.

In particular, VLBI observations have been exploited to estimate and predict precise Celestial Pole Offsets (CPO), with special emphasis on modelling the contribution of the Free Core Nutation (FCN). The incorporation of FCN-related signals derived from VLBI data leads to a significant improvement in CPO prediction accuracy, especially at short- and medium-term prediction intervals.

Beyond the development of different prediction models, we consider the dissemination of EOP predictions and methodologies to the scientific community to be essential for achieving shared objectives in this field. To this end, our group has developed a publicly accessible web platform that provides regularly updated EOP predictions, including CPO estimates, in both numerical format and interactive graphical representations to facilitate interpretation and practical use. This initiative aims to promote open access to EOP predictions for the geodetic and astrometric community.

Speaker: Lucía Daniela Del Nido Herranz (UAVAC, Applied Mathematics Dept., Universidad de Alicante)

4:45 PM Extending VLBI Station Capabilities for Delta-DOR and Navigation via Open-Source RDEF Software Compliant with CCSDS Standards

Wideband open-loop recordings from VLBI stations are increasingly relevant beyond geodesy and astrometry, including deep-space exploration, spacecraft navigation, and Delta-DOR. While VDIF is the standard for VLBI recording and correlation, navigation and inter-agency mission support requires CCSDS compliance, particularly the Delta-DOR Raw Data Exchange Format (RDEF). For many stations, the software complexity of CCSDS compliance remains limiting, despite suitable wideband receivers and high-precision timing infrastructure.
This contribution presents RDEFpy, the first open-source, standards-compliant Python library for reading, validating, and analyzing CCSDS RDEF products. RDEFpy provides efficient binary I/O, metadata inspection, precise time-tag reconstruction, multi-record streaming, and spectral and radiometric analysis tools for large datasets typical of modern VLBI observations. The library has been validated using operational RDEF products, demonstrating accurate reproduction of reference metadata, timing, and spectral content with numerically stable and memory-efficient performance across multi-gigabyte recordings.
By lowering the barriers to CCSDS compliance, RDEFpy enables VLBI stations to extend VDIF-based workflows toward CCSDS-compliant navigation and Delta-DOR deliverables without modifying core pipelines, supporting VLBI expansion toward new applications and providing a community-maintained foundation for integrating VLBI into future exploration activities.

Speaker: Andrea Togni (Morehead State University)

4:45 PM Inconsistencies between correlator metadata and vgosDB ionospheric parameters.

The computation of ionospheric corrections for S/X observations has been
straight forward for many years. The necessary parameters are normally carried over from observation and correlation setups to vgosDB entries in standardized pipelines. Unfortunately, recent investigations revealed that in some cases important information is not transferred correctly. In this presentation, we depict the current pipeline for the transfer of the necessary parameters for ionospheric corrections in the Mark V analysis environment where the majority of vgosDB files stems from. We provide a comprehensive analysis of the identified data discrepancies, their underlying causes and the resulting magnitude of error in the final geodetic solutions. Finally, describe the methodology used to conduct the software updates and data correction procedures implemented to mitigate these effects.

Speaker: Sergei Bolotin (NVI, Inc. / NASA GSFC)

4:45 PM Operational dUT1 Estimates from VLBI Intensive Sessions at the IVS Analysis Center of BKG

Accurate and low-latency estimates of dUT1 (UT1–UTC) are essential for satellite navigation, space operations, and geodetic applications. Very Long Baseline Interferometry (VLBI) is the only technique capable of determining dUT1, with Intensive sessions providing daily, near-real-time updates. The recent transition from legacy S/X observations to broadband VGOS has introduced a variety of Intensive session types and observing strategies, raising key questions: Are dUT1 estimates consistent and reliable across different Intensive configurations over the long term, and how well do they agree with dUT1 derived from 24-hour VLBI solutions?
To address these questions, we analyse ten years of dUT1 estimates from VLBI Intensive sessions, comparing S/X- and VGOS-based observations and evaluating their agreement with IERS Bulletin A reference values using standard statistical measures. We further assess the sensitivity of dUT1 precision to the choice of terrestrial reference frame.
Our results show that updated reference frames with improved station coordinates reduce errors and enhance consistency across all session types. Several VGOS configurations perform particularly well, confirming the advantages of broadband observations. This study supports optimized VLBI observation planning, improved analysis strategies, and robust operational dUT1 monitoring, and builds on the automated Intensive processing at the BKG VLBI Analysis Center aimed at reducing product latency.

Speaker: Dr Sadegh Modiri (Federal Agency for Cartography and Geodesy BKG)

4:45 PM Optimizing IVP Determination for Spatially Restricted VLBI Stations: A Case Study of KVN Yonsei

Accurate determination of the IVP is fundamental for defining the geodetic reference of VLBI antennas and realizing the ITRF. However, operational stations often face environmental limitations that prevent ideal geometric network configurations for local tie surveys. The KVN Yonsei station is a prime example, where spatial restrictions limit the accessible azimuth range for optical targets. This partial coverage poses a risk of introducing systematic geometric biases into the estimated reference point.
Our previous work proposed a refined IVP determination method based on constrained optimization. By enforcing rigorous physical and geometric constraints—such as axis orthogonality and constant radii—this method significantly reduced the RMSE of IVP estimation in numerical simulations.
This study extends that methodology to address the challenges of spatially restricted sites. To identify the optimal survey strategy for KVN Yonsei, we conducted comparative simulations between two approaches: (1) a traditional Total Station survey providing high single-point precision but limited to a partial arc, and (2) a Terrestrial Laser Scanner survey offering full 360-degree coverage but with lower point precision.
We present a statistical analysis quantifying the trade-off between measurement precision and geometric coverage. Based on these results, we identify the superior strategy for the KVN Yonsei environment and report the final determined IVP coordinates.

Speaker: Sung-Moon Yoo (Korea Astronomy & Space Science Institute)

4:45 PM Performance Assessment of Zhufeng and Changbai 40-m Radio Telescopes for VLBI Astrometry

China has expanded its Very Long Baseline Interferometry (VLBI) capabilities with the addition of the Zhufeng station in Xizang and the Changbai station in Jilin Province. Equipped with 40-m radio telescopes, both stations have been operational since February 2025. Several geodetic observing sessions were carried out using domestic VLBI networks or in IVS follow-on observing modes. Raw data were transferred to the Shanghai VLBI Data Processing Center for correlation and subsequent analysis.
The system equivalent flux densities (SEFDs) of the two new stations were estimated from baseline signal-to-noise ratios and compared with those of established VLBI stations to assess their sensitivity performance. In addition, radio source flux densities were estimated from the same observations, and the results show good correlation with the corresponding values provided by IVS analyses, serving as an external validation of the estimation procedure. Station coordinates were independently determined for each observing session, with repeatability at the level of a few millimeters.
Based on these observational results, we will further discuss the potential roles of the Zhufeng and Changbai stations in future VLBI astrometry, particularly in terms of network geometry, sensitivity contribution, and their impact on source flux density estimation and astrometric performance in domestic and international observing networks.

Speaker: Tian Jiang (Shanghai Astronomical Observatory, Chinese Academy of Sciences)

4:45 PM Preliminary Assessment of Ionospheric VTEC from 24-hour VGOS Sessions at Chinese Stations

This study presents a preliminary investigation of ionospheric Vertical Total Electron Content (VTEC) over China by utilizing observations from the VLBI Global Observing System (VGOS) observations. The derived VTEC time series from three Chinese VGOS telescopes (TIANMA13, SESHAN13, URUMQI13) are compared with Global Ionospheric Maps (GIM). The data were derived from 24 hour vgosDb sessions in 2025 with a standard least-squares estimation method. Initial comparisons with co-located GIM data show a consistent diurnal variation pattern, with correlation coefficients typically above 0.95. However, a systematic offset is identified, with VGOS-derived VTEC values lower than GIM estimates. The offset magnitude varies with station, local time, and geophysical conditions. Among the stations, URUMQI13 exhibits the smallest data scatter. Furthermore, the formal errors of the VGOS-derived VTEC remain relatively stable across the sampled periods. These early results demonstrate the potential of VGOS as a complementary ground-based data source for ionospheric monitoring, warranting further investigation with extended datasets.

Speaker: Yidan Huang

4:45 PM Preparing for VLBI with signals of ESA’s Genesis satellite

The European Space Agency (ESA) currently prepares its Genesis mission, a co-location satellite that will contribute to the improvement of the International Terrestrial Reference Frame (ITRF). The idea is to combine the four space geodetic techniques Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR) and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS) on one single spacecraft that is orbiting Earth.

In order to work on the Genesis mission goals, ESA set up a Genesis Science Exploitation Team (GSET). GSET involves four technique-specific working groups (WGs), as well as one WG for the ITRF and combinations. The technique-specific WGs advise and support ESA for all aspects of the Genesis mission, including assistance in calibration, processing and validation of Genesis data, and the exchange information with the international science community.

Working Group 3 (WG-3) focusses on the VLBI aspects of Genesis. Currently discussed topics are the VLBI transmitter and transmitting antenna, compatability with normal operations of the International VLBI Service for Geodesy and Astrometry (IVS), and the IVS product generation. Other important aspects for WG-3 are optimal scheduling, end-to-end simulations, and eventually also test observations of Genesis.

This presentation is on behalf of ESA GSET WG-3 and gives an overview on the current status of the work performed in the working group.

Speaker: Rüdiger HAAS (Chalmers tekniska högskola)

4:45 PM Probing atmospheric turbulence from VGOS residuals: implications for stochastic modeling

Atmospheric water vapor turbulence introduces stochastic delay fluctuations that limit the precision of geodetic VLBI. Current analysis strategies rely on simplified stochastic models that do not fully capture the temporal correlation structure of tropospheric delays. Exploiting the high data rates and sensitivity of VGOS, we analyze post-fit residuals from 31 VGOS-OPS sessions (2024) on two baselines of contrasting length (Oe-Ws, 920 km; Mg-Wf, 3138 km) to directly characterize turbulence-induced variability. Power spectral density analysis reveals a clear two-slope spectrum consistent with the -2/3 and -8/3 power laws predicted by Kolmogorov-Obukhov theory, including a sinusoidal modulation at high frequencies. A Matérn-based spectral model fitted via debiased Whittle maximum likelihood estimation yields two key turbulence parameters - the cutoff frequency λ, related to the outer scale length, and variance σ² - which exhibit pronounced seasonal variability. Higher λ values in winter reflect stable stratification, while lower values in summer indicate enhanced buoyancy-driven turbulence. Cross-validation using co-located Onsala telescopes confirms the physical consistency of the estimates (r > 0.82). These results demonstrate that routine VGOS observations can resolve atmospheric turbulence signatures at short time scales, laying the groundwork for refined stochastic models in geodetic VLBI and new climatological applications.

Speaker: Gaël Kermarrec (Institute of Meteorology and Climatology, Leibniz Universität Hannover)

4:45 PM Satellites and Beyond

In the coming years, several exciting opportunities will emerge to extend VLBI observations into new observing regimes. Satellite missions equipped with VLBI transmitters, such as Genesis, are expected to play an important role in the future of space geodesy. In parallel, the European Space Agency is planning the launch of a new lunar lander (NovaMoon/Argonaut), which will also feature a VLBI transmitter to enable a range of novel scientific applications. These forthcoming missions necessitate advances in VLBI observing strategies, signal processing and data analysis techniques.

In this work, we investigate VLBI observations of satellites and other artificial targets. Beyond assessing basic visibility and dedicated satellite orbital configurations, we aim to provide a comprehensive perspective that incorporates additional factors, such as signal strength and its impact on observation requirements. Addressing these effects introduces new challenges and requires the development of dedicated models to be integrated into existing VLBI software frameworks.

Speaker: Matthias Schartner (ETH Zurich)

4:45 PM Status of the IERS Conventions Updates

The International Earth Rotation and Reference Systems Service (IERS) Conventions describes the reference systems realized by the IERS, in addition to developing and maintaining the models and procedures used to support this endeavor. The IERS Conventions Centre has been preparing to release a major update to the conventions from the current Conventions (2010). This poster will discuss the proposed changes to the chapters and their technical content as well as the changes in the associated experts and editors. A timeline for the proposed release of the updated conventions will also be discussed. Additionally, we will give a general overview of the procedure and criteria for requesting and releasing minor and moderate updates to the conventions that happen in between major releases.

Speaker: Sharyl Byram (USNO)

4:45 PM Towards the Integration of Earth Satellites into Global VLBI Operations for Establishing Inter‐Technique Ties: Activities of the IVS Working Group on Satellite Observations with VLBI (WG7)

Co‐location in space has been discussed within the geodetic community for several years. Space ties offer an opportunity to establish inter‐technique ties and to provide an independent validation of local ties, which remain one of the main deficiencies of the current International Terrestrial Reference Frame (ITRF). After multiple attempts to realise a dedicated satellite mission, the European Space Agency (ESA) selected the Genesis mission, with a planned launch in 2028. ESA presents Genesis as a contribution to the geodetic community and invites the components of the International Association of Geodesy (IAG), in particular its services, to participate actively.

For the International VLBI Service for Geodesy and Astrometry (IVS), the Working Group on Satellite Observations with VLBI (WG7) has taken the lead in coordinating efforts by IVS components related to the Genesis mission. The needs for concerted activities are manifold and address observational capabilities of the IVS telescopes, peculiarities of processing steps as well as their integration into IVS observing plans.

This poster presents an overview of recent activities of IVS WG7, highlighting current developments, scientific potential and unresolved issues. The presented efforts aim to support the future integration of Earth‐orbiting satellites into global IVS VLBI operations, with a primary focus on the Genesis mission.

Speaker: Lucia McCallum (University of Tasmania)

4:45 PM Validation of new Earth rotation models as part of the IERS conventions update

A global initiative is currently underway to revise geodetic reference systems, with the objective of achieving the millisecond-of-arc accuracy required by GGOS for Earth System Monitoring. Our working group is divided into two sections: Theory and Observations.

While the theoretical team is developing an extended Earth rotation model, which includes re-computing the precession-nutation solution and refining the separation of nutation and polar motion for improved Free Core Nutation (FCN) modelling, this presentation focuses on the results of the observational validation.
The observational analysis systematically fits the new models to VLBI data, with complementary checks using SLR and GNSS orbit determination. This multi-technique evaluation quantifies residual errors, verifies theoretical consistency, and confirms that the new formulations are accurately represented in operational analysis packages.

These results are a vital input to the evaluation and acceptance of the revised models for the next IERS Conventions update, ensuring that future geodetic standards are both theoretically consistent and empirically validated.
We would like to express our sincere gratitude to all contributors whose efforts have made this progress possible.

Speaker: Maria Karbon (UAVAC-Universidad de Alicante)

4:45 PM VGOS-INT-G Sessions: UT1-UTC Performance and Perspectives for Higher-Frequency Operation

Radio Frequency Interference (RFI) has become a significant limitation for VGOS observations, particularly affecting several key VLBI stations due to increasing use of radar, communication systems, and fixed radio services. Consequently, the traditional 2–3 GHz observing range is largely unusable, and even the VGOS A-band (3–3.5 GHz) is increasingly compromised by 5G interference. To mitigate these issues, the VGOS-INT-G initiative was proposed to assess alternative network configurations and higher observing frequencies, while maintaining or improving UT1 determination accuracy.

This study presents the motivation, implementation, and current results of VGOS-INT-G, with a focus on Phase 1. UT1 estimates from the RAEGSMAR, RAEGYEB, SESHAN13 and ISHIOKA network are compared with regular VGOS-INT-A sessions using the same frequency setup. Observations began in February 2024 and were conducted on a weekly basis. In April 2024, a schedule optimization was introduced to enhance sensitivity to UT1-UTC. Further refinement of SESHAN13 station coordinates and velocities led to increased consistency of the UT1-UTC estimates, reducing residuals and minimizing the need for station downweighting.

Phase 2, currently on hold, aims to evaluate UT1-UTC performance using an alternative 4–14 GHz frequency plan to avoid RFI, This effort is planned to be coordinated with ongoing studies within the IVS VGOS Technical Committee studies on bandwidth expansion and higher-frequency operation.

Speaker: Ms Mariana Moreira (UAVAC, Applied Mathematics Dept., University of Alicante)

4:45 PM VLBI data analysis at ESA/ESOC

This contribution presents the latest developments in the VLBI analysis activities by the Navigation Support Office at ESA/ESOC. These focus on further developing the ESA Precise Navigation System (EPNS), and on setting up an operational environment for the processing of different VLBI sessions. Since EPNS is already used for generating GNSS, SLR, and DORIS products, the integration of VLBI represents a major expansion of ESA’s geodetic capabilities, strengthening the agency’s contribution to the ITRF and supporting the preparation for the GENESIS mission.
The presentation outlines the status of the VLBI module within EPNS, and provides an overview of the VLBI sessions routinely supported in the processing pipeline. The fully automated processing strategy yields reliable results for most sessions, though it can lead to increased noise when station performance is degraded. The accuracy of the ESOC R1/R4 solutions is generally consistent with that of other IVS Analysis Centers.
The EPNS-based processing chain routinely analyses R1/R4 and VGOS-OPS sessions, as well as S/X and VGOS intensives. These solutions are regularly fed to a test branch of the ESA Earth Rotation Parameter estimation and prediction service built exclusively on ESA geodetic solutions. A roadmap towards the submission of ESOC’s VLBI result to IVS will be also presented. A major milestone has been the submission of 25 years of reprocessed VLBI data as a test contribution for the latest IVS ITRF combination.

Speaker: sara bruni (PosiTim UG for ESA/ESOC)

7:00 PM → 10:00 PM Workshop Dinner

Wed, April 15

8:30 AM → 9:10 AM IVS GM: Session 5 (Forefront) - Slot 1

8:30 AM NovaMoon and Lunar VLBI: Extending IVS Concepts to the Moon

Sustained lunar exploration requires the establishment of a stable lunar reference frame and timing infrastructure to support interoperable navigation, communication, and scientific operations on and around the Moon. ESA’s NovaMoon station, to be deployed on the lunar south pole by ESA’s Argonaut lander, is conceived as a multi-technique selenodetic station. It combines a lunar VLBI transmitter, a Lunar Laser Ranging (LLR) retroreflector, Moonlight and GNSS navigation receivers, and direct-to-Earth radiometric tracking.
The co-location of these complementary techniques enables improved separation of systematic effects, strengthening the realization of the lunar reference frame and its ties to terrestrial and celestial frames. Within this architecture, lunar VLBI observations are expected to provide complementary plane-of-sky constraints, increase NovaMoon positioning accuracy, and improve the determination of lunar tidal response and interior properties,
This presentation provides an overview of NovaMoon, with focus on the role of VLBI, addressing interactions with IVS. Particular emphasis is placed on signal compatibility between the lunar VLBI transmitter and existing ground infrastructure (VGOS), including waveform, bandwidth, and frequency considerations, as well as early coordination with the VLBI community to define realistic scheduling and processing strategies and to maximize the scientific and geodetic return of lunar surface VLBI.

Speaker: Serena Molli (ESA)

8:50 AM Science objectives of ESA's Genesis mission: a flying geodetic observatory to improve ITRF accuracy and stability

Genesis is an ESA mission in preparation within the Navigation Directorate under the FutureNAV Programme, dedicated to advancing space geodetic science and the International Terrestrial Reference Frame (ITRF). It co-locates GNSS, SLR, DORIS, and a pioneering VLBI transmitter on a single satellite in near-polar orbit (~6000 km), creating a dynamic space geodetic observatory that delivers well-calibrated space ties between all techniques.

These co-located measurements enable rigorous integration of space-geodetic techniques, revealing and mitigating inter-technique biases that currently limit ITRF scale, origin, and orientation. The Genesis objectives demand a stable and well-characterised platform as well as rigorous calibration of instruments and antennas, including phase/group delays and phase center offsets. The mission's novelty and methodology at mm-level demand also the careful preparation of observation strategies and adoption of data analysis and combination techniques for Genesis data exploitation.

Here, we present an overview of the ongoing activities relevant to the science community and ITRF realisation, including the scientific objectives and the status and plans of science instruments and calibrations. The scientific datasets and expected data products, along with their planned availability to the scientific community, will also be discussed.

Speaker: Özgür Karatekin (Royal Observatory of Belgium)

9:10 AM → 9:25 AM Stretch-your-legs break

9:25 AM → 10:15 AM IVS GM: Session 5 (Forefront) - Slot 2

9:25 AM Geodetic Reference Instrument Transponder for Small Satellites

The local ties between the different geodetic techniques are an important component of the realization of the International Terrestrial Reference Frame but the survey accuracies are limited due to the inaccessibility of the instrument reference points. The NASA Geodetic Reference Instrument Transponder for Small Satellites (GRITSS) technology demonstration mission is designed to overcome this limitation by using a small satellite as a space-based reference point for tying together the measurement points of collocated geodetic stations. The GRITSS instrument takes the Global Positioning System (GPS) signals received at the satellite, upconverts them in real-time to S and X band, and transmits them to a VLBI Global Observing System (VGOS) antenna ground station. The instrument can also transmit a pseudorandom code that can also be used as a delay observable by the VGOS stations. The measurement concept does not require the satellite to be in view of more than one VLBI station at a time. The GRITSS demonstration mission is being implemented using a 12U-XL CubeSat in a Low Earth, Sun Synchronous orbit to broadcast the signals to the NASA VGOS stations in Maryland, Hawaii, and Texas. Expanding to include other international VGOS stations is also being planned for the second half of the mission. An overview of the GRITSS mission and measurement concept will be presented.

Speaker: Stephen Merkowitz (NASA)

9:45 AM Phase-center correction for VLBI observations of the Genesis satellite

The ESA Genesis satellite mission, planned for launch in 2028, aims to establish ties between all four global geodetic observing techniques in space. The challenge for VLBI is that the broadband signal will be emitted by multiple antennas with different frequency ranges and phase-center variations. Without correction, VLBI observations would lack a reference point. We present a method for Level-1 phase-center correction that solves the issue by referencing all antenna signals to a common point.

Speaker: Frederic Jaron (TU Wien)

10:00 AM Evaluating Simulated VGOS Sessions to Support Genesis Simulations

In geodetic Very Long Baseline Interferometry (VLBI), simulations are used in scheduling and analysis software to optimise observing schedules and evaluate future session performance. This includes simulations related to the observation of the upcoming Genesis satellite of the European Space Agency (ESA) with the VLBI Global Observing System (VGOS).

In simulations, VLBI observations are commonly generated by computing the geometric time delay on a baseline observing a radio source and adding error contributions from measurement noise, tropospheric turbulence, and clock drift. Because the outputs of the simulations depend strongly on these inputs, the error sources should be modelled as realistically as possible for meaningful performance assessments. Although these error sources are generally well understood and recent studies continue to improve their modelling, simulated VLBI sessions often remain overly optimistic compared to real ones.

To improve the realism of simulated VGOS sessions, we evaluate different error source modelling approaches by comparing the resulting simulated sessions with real VGOS sessions. In particular, we investigate the modelling of the troposphere using parameters estimated from machine learning models trained on observational data, as well as a method that directly uses error source contributions taken from real VGOS sessions. The results support more realistic VGOS simulations, which are relevant for the Genesis mission.

Speaker: Rimsky Wolfs (Chalmers University of Technology)

10:15 AM → 10:45 AM Coffee break

10:45 AM → 11:15 AM IVS GM: Session 5 (Forefront) - Slot 3

10:45 AM Analysis of VLBI terrestrial reference frames based on quasar and satellite observations

A distinctive feature of the European Space Agency’s (ESA) Genesis mission is its dedicated Very Long Baseline Interferometry (VLBI) transmitter, which enables observations to the satellite using the existing VGOS antennas and infrastructure. The mission aims to significantly enhance the accuracy and stability of Terrestrial Reference Frames (TRFs).

In this study, weekly 24-hour VLBI sessions over a five-year period are scheduled and simulated, comprising observations to both quasars and the Genesis satellite. This allows us to (i) derive a single TRF by jointly estimating station positions and velocities from the combined observation set, and (ii) derive two separate TRFs simultaneously by treating the quasar and satellite observations quasi-independently.

This allows for a comparative analysis of the satellite- and quasar-based TRFs (ii) against the combined frame (i), and for assessing the potential to reveal frame biases.

Speaker: Lisa Maria Kern (TU Wien)

11:00 AM Assessing the potential of VLBI for satellite orbit determination using simulated observations

The ESA Genesis mission, planned for launch in 2028/29, will carry a dedicated VLBI (Very Long Baseline Interferometry) transmitter, enabling direct VLBI observations to a satellite. This represents a major step forward, as it opens new possibilities for satellite orbit modelling based on VLBI data and may improve the accuracy and consistency of orbit determination across space-geodetic techniques.

In this study, the capability of VLBI to estimate the six orbital elements together with nine solar radiation pressure (SRP)–related dynamical parameters is assessed using simulated VLBI observations to Galileo satellites. Partial derivatives of the orbital and dynamical parameters are obtained from the ORBGEN module of the Bernese GNSS Software. The SRP accelerations are decomposed into three orthogonal directions: along the satellite–Sun direction, along the solar panel axis, and along the direction completing the right-handed coordinate system. In each of these three directions, constant and periodic empirical parameters are estimated.

The results provide insight into the sensitivity of VLBI observations to orbital and SRP parameters and demonstrate the potential of VLBI for satellite orbit determination.

Speaker: Helene Wolf (TU Wien)

11:15 AM → 11:35 AM IVS GM: Session 6 (Crossroads) - Slot 1

11:15 AM Imaging ICRF Sources for the Fundamental Reference Image Data Archive

Imaging ICRF sources to reveal the underlying source structure is a critical component to any monitoring effort. Not only can structure on VLBI scales degrade the accuracy of the astrometry of ICRF sources, in extreme cases it can cause large jumps on the order of tens of milliarcseconds in the positions of sources. The United States Naval Observatory, serving as an IVS Analysis Center for Source Structure, has been producing images of ICRF sources for 30 years. These data are made available to the community via the Fundamental Reference Image Data Archive (FRIDA), which currently contains over 38,000 images of 5344 sources. FRIDA has recently undergone a major overhaul to offer more value to the astrometric, geodetic, and astronomical communities through an improved web interface and data products. A new catalog of source fluxes, the FRIDA Flux and Time-series Catalog (FaTCat) has also been produced by combining traditional image-domain source fitting with a novel Bayesian search algorithm which statistically identifies real emission to help reject false source fits. I will discuss new features offered by the overhauled FRIDA website and recent improvements to our automated imaging pipeline.

Speaker: Christopher DiLullo (United States Naval Observatory)

11:35 AM → 11:50 AM Stretch-your-legs break

11:50 AM → 12:35 PM IVS GM: Session 6 (Crossroads) - Slot 2

11:50 AM Investigating quasar spectral index as a probe for quasar position stability

Source structure is regarded as one of the major error sources of geodetic VLBI. Substantial effort has been made in the last few years to image geodetic sources in order to understand and mitigate this effect. However, source structure on scales smaller than the synthesized beam, which is invisible in images, has been found to affect the observed source positions significantly. Structure changes in active galactic nuclei are often caused by the emergence of new jet components from the core. A potential way to detect such changes early is to monitor source flux density at multiple frequencies. The formation of a new jet component could be indicated by a flare and a change of spectral index. At Onsala Space Observatory, a flux density monitoring program has been ongoing since 2023. The targets of this monitoring program are ICRF3 defining sources in the four operationally used frequency bands for the VLBI Global Observing System (VGOS). Observations are performed with a cadence of once a month. This dataset allows tracking of both flux density and spectral index variation. In parallel, source position time series have been obtained by analysis of VGOS-operational and VGOS research and development sessions. We investigate the correlation between spectral index variability and source position variability. Such a correlation could provide an alternate metric to evaluate if a source is suitable for VGOS experiments.

Speaker: Alva Kinman (Chalmers University of Technology)

12:05 PM Beyond S/X: Source Variability Metrics from K-band Time Series

The long-term stability of celestial radio sources is a cornerstone of high-precision geodesy and astrometry. The growing availability of K-band data provides an independent window into source behavior, complementing and expanding beyond the traditional S/X foundation. Comparing positions at both bands probes frequency-dependent effects such as core shift, varying emission structure, and ionospheric contributions, and understanding source variability across the spectrum is important for maintaining a robust multi-frequency CRF. Building on our 2024 work on S/X variability metrics, we extend this framework to K-band source position time series. We will discuss the resulting variability metrics for a comprehensive list of celestial sources observed at K-band. We will present K-band variability statistics and compare to S/X results for the overall source catalogs, and highlight some individual sources of interest.

Speaker: Phil Cigan (USNO)

12:20 PM The U.S. Naval Observatory VLBI Light curve Catalog (UVLC) and its Applications

We introduce the U.S. Naval Observatory VLBI Light curve Catalog (UVLC). Leveraging the latest data from photometric surveys such as Gaia, the Zwicky Transient Facility, the Wide-field Infrared Survey Explorer, and the Catalina Real-time Transient Survey, we retrieve light curves for a sample of 21,950 sources previously detected via very long baseline interferometry (VLBI) observations. The UVLC aims to maximize the variability information available for these sources, as well as to identify sources in the catalog that exhibit the high levels of variability typical of bona fide blazars. This variability information is not only key for work involving the optimal selection of defining sources for the International Celestial Reference Frame (ICRF), but it is also important generally for studies of blazars and radio-loud AGN. Moreover, recent work has shown that variability can be used to optimally weight sources in CRFs such that the tie between frames defined at different wavelengths (e.g., S/X, K, X/Ka, and Gaia) is stronger. Therefore, the UVLC should play an important role in ongoing and future CRF work, as well as the pursuit of a wavelength-independent frame. The methods used to create the UVLC are also applicable to most time-series data, making them useful for studying the population of AGN and blazars in forthcoming surveys (e.g., LSST).

Speaker: Kyle Corcoran (U.S. Naval Observatory)

12:35 PM → 2:00 PM Lunch break

2:00 PM → 3:05 PM IVS GM: Session 6 (Crossroads) - Slot 3

2:00 PM VLBI astrometry of radio stars to link radio and optical CRFs at the optical bright end

A multi-wavelength celestial reference frame is crucial for both astronomical research and astrometric/geodetic applications. The Gaia Celestial Reference Frame 3 (Gaia-CRF3) is the optical realization of the International Celestial Reference System (ICRS), and is aligned to the radio realization, the International Celestial Reference Frame 3 (ICRF3) using common quasars at the optical faint end (G magnitude > 13). However, calibration-related inconsistencies have been identified between the Gaia bright (G < 13) and faint ends, manifesting as a systematic rotation. Estimating this effect is challenging due to the scarcity of optically bright quasars.
Very Long Baseline Interferometry (VLBI) astrometry of radio stars provides a unique and independent means to estimate this systematic rotation through a comparison between optical and radio astrometric parameters (positions and proper motions). In this talk, I present C-band Very Long Baseline Array (VLBA) astrometric results for 11 radio stars, achieving median parallax and proper motion uncertainties better than 0.1 mas and 0.1 mas/yr, respectively. With these new measurements, an updated estimation of the systematic rotation between the Gaia bright and faint ends is derived.
In addition, the multi-epoch self-calibrated images of the 44 quasars used as calibrators have been produced, which are valuable for both astrometric and astrophysical studies, and I'll also present the preliminary analysis results.

Speaker: Jingdong Zhang (Finnish Geospatial Research Institute)

2:15 PM The European VLBI Network (EVN), JIVE, and geodetic VLBI approach the SKA era

This presentation will trace developments at JIVE that enabled output of totals in a format native to geodetic post-processing software as well as other technical developments of mutual benefit to geodetic VLBI (data transport protocols, linear-to-circular polarization conversion, fringe-fitting including dispersive-delay terms). JIVE's expertise in near-field VLBI offers common ground for VLBI co-location of GNSS satellites within the ICRF.

We will discuss more ambitious technical/operational challenges arising in the near future. Tri-band (K/Q/W) receivers will significantly boost data rates. Phased-array MeerKAT joined EVN observing in 2025, and recent tests with uGMRT have shown encouraging results. These stations offer the opportunity to investigate multi-beam VLBI and calibration procedures directly using local interferometer data. We will cover areas of mutual interest to the two communities within current and potentially new JIVE-coordinated EU projects.

Looking farther over the horizon, it is vital to incorporate VLBI with SKA. There will be a need for more unified coordination among existing VLBI networks -- in operational, technical, and policy domains -- in order to achieve this. The Global VLBI Alliance (GVA) is pursuing such enhanced coordination among VLBI arrays; participation of the IVS would help address the shared challenges an opportunities linking the two communities, where each depends critically on the other to reach their ultimate goals.

Speaker: Bob Campbell (Joint Institute for VLBI ERIC)

2:35 PM The Origins of Astro2Geo

In this presentation, I cover the history of working as part of the Astro2Geo team to develop the Astro2Geo program: a combined astronomy and geodesy project in order to optimize telescope time and get win-win outcomes. I briefly cover some of the astronomical science that has come out the collaboration including the quest to measure Dark Energy and an interesting correlation between astrometric positions and Gamma-ray brightness in AGN.

Speaker: Jeff Hodgson (Sejong University)

2:50 PM Astro2Geo K-band VLBI: At the Crossroads of Astrometry, Geodesy, and Astronomy

K-band (24 GHz) VLBI has provided a powerful bridge between astrometry, geodesy, and astrophysics for more than a decade, offering improved angular resolution, enabling observations closer to the Sun and the Galactic plane, and reducing susceptibility to radio-frequency interference compared to lower-frequency bands. The Astro2Geo K-band VLBI project was established to explicitly exploit these advantages through coordinated global observations designed to serve multiple scientific domains simultaneously. In this contribution, we present an overview of the Astro2Geo project, highlighting recent progress in astrometric and geodetic analysis, high-resolution imaging, network expansion, and scheduling optimisation. We discuss how K-band imaging informs the characterisation of stable geodetic reference sources and enables a broad range of astrophysical studies, while astrometric, geodetic, and imaging requirements jointly drive observing strategies that enhance long-baseline sensitivity and effective uv-plane sampling without compromising any science case. The results demonstrate the benefits of truly integrated observations and highlight the opportunity to optimise telescope resources, improve operational efficiency, and accelerate scientific progress across astrometry, geodesy, and astronomy.

Speaker: Dr Aletha de Witt (Department of Science, Technology and Innovation (DSTI) and South African Radio Astronomy Observatory (SARAO))

deWitt_IVS2026.pdf

3:05 PM → 3:20 PM Stretch-your-legs break

3:20 PM → 4:05 PM IVS GM: Session 6 (Crossroads) - Slot 4

3:20 PM Activities in K-band and High-Frequency Geodetic VLBI in South Korea

South Korea has steadily expanded its capabilities in VLBI, integrating astronomical, astrometric, and geodetic applications. Key components are the Korean VLBI Network (KVN) and the Sejong Space Geodetic Observatory. In 2025, the commissioning of the KVN Pyeongchang radio telescope further strengthened national VLBI capabilities. While the KVN antennas are equipped with a unique simultaneous multi-frequency receiving system (22/43/86/129 GHz), the Pyeongchang telescope additionally hosts X/Ka-band receivers.

K-band geodetic VLBI observations using Korean antennas are being actively pursued to improve astrometric accuracy, mitigate source structure effects, and enhance the realization of celestial reference frames. The Sejong Space Geodetic Observatory plays a central role in Korea’s geodetic infrastructure through VLBI observations and co-location with other space geodetic techniques. Together with KVN, it provides a foundation for domestic and international collaboration. Recent activities include EAVN K-band and GMVA W-band experiments.

Korea is also exploring optical clock comparison for the redefinition of time, optical fiber–based time-frequency dissemination to VLBI stations, and photonic phase calibration systems. This highlights VLBI’s role as a bridge between geodesy, fundamental metrology, and astrophysics. This presentation summarizes current observational status, technical developments, and scientific outcomes, and discusses future perspectives.

Speaker: Taehyun Jung (Korea Astronomy and Space Science Institute)

3:35 PM VLBI 2030 at the Geodetic Observatory Wettzell: Transitioning to a Multi-Purpose Future

The Geodetic Observatory Wettzell (GOW) is a key site in the global VLBI network, currently operating a triple-telescope setup: the legacy 20-m RTW (operational since 1983) and the Twin Telescope Wettzell (TTW), consisting of two 13.2-m antennas. To meet future demands for geodetic precision and multi-technique integration, GOW is planning a new, modular telescope system designed for diverse applications.

This next-generation infrastructure is intended to serve three primary roles:

Geodetic VLBI: Maintaining VGOS-compatibility by observing quasars in the 3–14 GHz range.

GNSS Monitoring: Tracking the Galileo constellation in the L-band to enhance orbit determination.

Solar Science: Performing solar radio flux measurements (F10.7) for space weather monitoring.

Furthermore, our VLBI telescope concept is expanding internationally. A second VGOS telescope is currently being planned for the Argentine-German Geodetic Observatory (AGGO), our sister site near Buenos Aires, to strengthen the Southern Hemisphere’s VLBI geometry.

This presentation provides an overview of the current operational status at Wettzell and details the planning phase for the new multi-purpose system and the AGGO expansion. These developments represent a strategic evolution toward a more versatile and robust contribution to the IVS and the global geodetic community.

Speaker: Torben Schüler

3:50 PM From Jets to Reference Frames: AGN Physics, Astrometry, and Geodesy with the ngVLA

Very Long Baseline Interferometry (VLBI) uniquely links active galactic nucleus (AGN) physics, geodesy, and astrometry by relying on the same distant, compact radio sources to probe both relativistic jets and the Earth’s orientation and reference frames. However, the accuracy and long-term stability of these fundamental measurements are degraded by our incomplete understanding of radio AGN jet physics. Flux density variability, spectral evolution, opacity effects, and structural changes associated with jet formation and propagation introduce systematic errors that directly impact astrometric and geodetic observables. The Next Generation Very Large Array (ngVLA) will address these limitations by enabling sensitive, high-resolution observations of compact AGN jets across 1–116 GHz. I will present ngVLA imaging simulations based on the new revision F configuration that demonstrate its power to resolve parsec-scale jet structure and to track frequency-dependent source evolution relevant to reference frame stability. I will also present forecasts of the expected geodetic and astrometric performance of the long baseline array of the ngVLA. These results highlight the scientific and technical synergy between AGN physics and VLBI geodesy, and illustrate how next-generation facilities can improve both our physical understanding of radio jets and the robustness of future celestial and terrestrial reference frames.

Speaker: Kristina Nyland (CPI/USNO)

4:05 PM → 4:35 PM Coffee break

4:35 PM → 5:20 PM IVS GM: Session 6 (Crossroads) - Slot 5

4:35 PM Implementing source structure correction in VGOS data: Progress of Astrogeodesy project

The new generation VLBI system, the VLBI Global Observing System (VGOS), is being developed with the ambitious goal of achieving, on global scales, the accuracy of 1 mm in station position and 0.1 mm/yr in station velocity. It has become clear that the true potential of VGOS can never be reached without understanding and correcting for the effects caused by the angular structure of the AGNs (i.e. distribution of the radio emission on the sky). The Astrogeodesy project, funded by the ERC, is progressing to (1) study and monitor the frequency- and time-dependent structure of the AGNs through full calibration of VGOS data and (2) develop approaches to model them as point-like fiducial anchors on the sky. In this talk, we will report the intermediate progress of the project by highlighting the technical development of imaging, such as handling multi-IF data, automatic flagging, combining closures and self-calibrated visibility as input, and formatting the image output compatible with difmap. We will also report the investigation of source structure modeling with the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) observations as the testbed for VGOS to gain knowledge and prepare for the processing chain. For this purpose, we processed 150 MOJAVE experiments from 2012 till now in the geodetic mode in the Astrogeodesy project, and use the high-quality images at 15 GHz, aligned over time and provided by the MOJAVE team.

Speaker: Minghui Xu (GFZ)

4:50 PM Implementing source structure correction in VGOS data: data reduction and jet kinematics

It has been shown that the structure and variability of active galactic nuclei (AGN) is a significant limiting factor to the desired accuracy of geodetic products. In order to improve the accuracy of these measurements, we are aiming to quantify temporal and frequency-dependent changes in AGN, by implementing a pipeline for astronomical calibration, imaging, and analysis of VGOS data. In this talk, I detail our efforts regarding the data reduction, and show first results from our kinematic analysis of AGN with extended jets during a 12-month period, as this is crucial to align the source structure model consistently across time to improve the astrometry.

Speaker: Petra Benke (GFZ)

5:05 PM AGN Structure Evolution and Core-Shift Measurements from CONT17 Observations

We analyze multi-epoch, multi-frequency Very Long Baseline Interferometry (VLBI) observations from the CONT17 campaign, which combines data from both VLBA and IVS antennas. The dataset consists of continuous 15-day observations at two frequencies—2.3 GHz (S band) and 8.6 GHz (X band) with approximately 80 extragalactic radio sources observed. For this study, we select a subset of sources with sufficient spatial resolution and temporal UV-coverage to enable reliable imaging and variability analyses. One of the key objectives of the Astrogeodesy project is to understand and quantify the structural evolution and core-shift variability of AGN jets on short timescales relevant to geodetic VLBI. In this work, we focus on measuring the frequency-dependent core shift between the S and X bands in sources with extended jet emission. We investigate core-shift properties in a sample of ten AGNs. Based on null-hypothesis testing applied to multi-epoch measurements, we identify significant temporal variability of the core-shift position in two blazars over the 15-day observing period with statistically significant variations detected across epochs. We explore whether the observed variability is source-specific and correlated with source activity or influenced network geometry, scan lengths, UV-coverage, calibration uncertainties, and methodological effects related to 2D Gaussian model fitting of visibilities and 2D cross-correlation of optically thin jet regions for the entire sample.

Speaker: Wara Chamani (GFZ Helmholtz Centre for Geosciences)

5:20 PM → 5:35 PM IVS GM: Closing

6:00 PM → 8:00 PM Splinter Meetings: K-band meeting - Closed event (Alet de Witt)

Thu, April 16

7:40 AM → 9:00 AM Travel to/from Zugspitze Mountain with train: Train from Garmisch-Partenkirchen to Research Station Schneefernerhaus (for Analysis Workshop and Social Event)

9:00 AM → 10:15 AM IVS Analysis Workshop (limit of 70 participants): Slot 1

9:00 AM → 9:30 AM Travel to/from Zugspitze Mountain with train: Cable car to Zugspitzplatt (Social Event only)

9:30 AM → 10:30 AM Social event: Zugspitzplatt

10:15 AM → 10:45 AM Coffee break

10:30 AM → 12:00 PM Lunch time

10:45 AM → 12:00 PM IVS Analysis Workshop (limit of 70 participants): Slot 2

12:00 PM → 2:30 PM Guided Glacier and Climate Excursion as a snowshoe hike to the Schneeferner glacier

12:00 PM → 1:00 PM Lunch break

1:00 PM → 2:30 PM IVS Analysis Workshop (limit of 70 participants): Slot 3

2:30 PM → 3:00 PM Coffee break

2:30 PM → 6:30 PM Travel to/from Zugspitze Mountain with train: Self-organized travel back with train to Garmisch-Partenkirchen (Latest departure: 16:25 o'clock)

3:00 PM → 5:00 PM IVS Analysis Workshop (limit of 70 participants): Slot 4 and Free time

5:00 PM → 6:30 PM Travel to/from Zugspitze Mountain with train: Travel back from Research Station Schneefernerhaus with train to Garmisch-Partenkirchen

Fri, April 17

9:00 AM → 10:30 AM IVS Directing Board Meeting (for invited guests and DB members): Slot 1

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM IVS Directing Board Meeting (for invited guests and DB members): Slot 2

12:30 PM → 2:00 PM Lunch break

2:00 PM → 3:30 PM IVS Directing Board Meeting (for invited guests and DB members): Slot 3

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM IVS Directing Board Meeting (for invited guests and DB members): Slot 4

7:00 PM → 9:00 PM Board Dinner (for invited guests and DB members): Directing Board Dinner