The importance of VLBI to satellite services and critical infrastructure
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...
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...
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.
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...
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...
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...
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...
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...
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...
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,...
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).
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...
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...
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...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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,...
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...
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...
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,...
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...
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.
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.
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...
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...
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...
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...
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....
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...
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...
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)...
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...
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,...
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...
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...
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...
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...
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)...
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...
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...
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...
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...
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...
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...
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...
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...
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%...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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 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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
The VGOS Technical Committee proposed to test new VGOS frequency mode sessions to assess alternative frequency configurations aimed at increasing synthesized bandwidth and extending frequency coverage in VGOS, while addressing potential radio frequency interference. Two sets of sessions were conducted in 2024 and 2025 and analyzed, each including the standard VGOS configuration and four...
