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Guilhem Moreaux (CLS) made a presentation at the 2017 Fall AGU meeting: "Analysis of the DORIS, GNSS, SLR, VLBI and gravimetric time series at the GGOS core sites", by Guilhem Moreaux (CLS), Frank Lemoine (GSFC 61A), Vincenza Luceri (E-GEOS), Erricos Pavlis (UMBC), Dan MacMillan (GSFC 61A/NVI), Sylvain Bonvalot (IRD) and Jerome Saunier (IGN). The presentation discussed initial analysis of time series from different geodetic techniques at co-located GGOS sites. The goals were to evaluate the level of agreement between the techniques and physical tie vectors and to compare their spectral content. Horizontal site velocities showed good agreement. Common annual signals are seen for several sites.

John Gipson gave a poster presentation at the 2017 Fall AGU meeting on the "Ad Hoc Working Group on Diurnal and Semi-diurnal Earth Orientation Variation". The working group is tasked with evaluating different models of EOP variation and making recommendations to the IERS. The current IERS model is over 20 years old, and much has changed since then.

On December 14, 2017 John Gipson attended a workshop on the Terrestrial Reference Frame Error Budget, and he gave a presentation on the error sources in VLBI. A large error source is gravitational deformation of VLBI antennas. This deformation changes the path length of the radio signal and results in a change in the estimated up position. The magnitude of the effect can be up to 20 mm. Fortunately this deformation effect can be measured by a one-time antenna survey that costs ~$25K. These surveys should be done to achieve 1 mm accuracy.

John Gipson attended the IERS directing board meeting in New Orleans on December 10, 2017 as the IVS representative. He gave a presentation on the activities of the IVS. He also discussed the work of the IERS working group on sub-daily EOP variation, of which he is a chair. Gipson also attended a meeting of the Bureau for Networks and Operations on December 14 and gave a summary of IVS activities.

The paper "Star Scheduling Mode-A New Observing Strategy for Monitoring Weak Southern Radio Sources with the AuScope VLBI Array" by L. McCallum, K. Le Bail (61A/NVI), D. Mayer, M. Schartner, J. McCallum, J. Lovell, O. Titov, F. Shu, and S. Gulyaev was published in Publications of the Astronomical Society of Australia, 34. This paper discusses a new VLBI observing strategy, the star scheduling mode.

Hana Krásná (TU Wien) made a presentation at the IAG meeting in Kobe, Japan: ''Correlated Atmosphere Noise in VLBI Analysis'', by Hana Krásná and John Gipson. She demonstrated that modeling station dependent measurement noise in the VieVs VLBI analysis software improves the repeatability of station positions and the agreement between VLBI and GPS determinations of Polar Motion. John Gipson had demonstrated the same effect in Solve, the Goddard VLBI software, in 2007, but the new study provides the first independent verification.



Welcome to the home page of the GSFC VLBI Group--the NASA Goddard Space Flight Center's Very Long Baseline Interferometry group.

Why is VLBI Important?

VLBI is the only space geodetic technique that can accurately measure the Earth's rotation. As such, it is a critical factor for GPS.

A partial list of our VLBI applications includes:

  • Providing accurate Earth rotation measurements to GPS
  • Spacecraft navigation support to the Jet Propulsion Laboratory
  • Measurement of the Earth's crustal motion
  • VLBI contribution to the U.S. Naval Observatory Earth orientation combination series. This in turn has many applications including:
    • the navigation system used by the FAA for civil aviation (Wide Area Augmentation System)
    • spacecraft instrument pointing
    • satellite orbit prediction

General Information

The VLBI technique uses radio signals from quasars to measure positions of VLBI antennas, the Earth's crustal motion, and the Earth's orientation, including its rotation (UT1). Our group performs research to improve the VLBI technique, and supports current VLBI operations through: data analysis, software development and other activities.

We are part of the NASA Space Geodesy Project (SGP), which encompasses the development, operation, and maintenance of a global network of space geodetic technique instruments including Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite System (GNSS), and the Doppler Orbitography and Radio-positioning by Integrated Satellite (DORIS) system.

Quick Links
Our Stations GGAO Antenna in stow, or resting, position (pointing straight up)
GGAO (Maryland)
Gilcreek Antenna on a cloudy day
Gilcreek (Alaska) (inactive)
close up of Kokee Antenna
Kokee Park (Hawaii)

New VGOS Antenna at GGAO
Photo of antenna pointing up and left, with a person in the foreground to show scale.
In September 2003, the International VLBI Service for Geodesy and Astrometry (IVS) recognized the need to implement the next generation of VLBI, VGOS (VLBI2010 Global Observing System), in order to meet increasing demands on the VLBI technique. Since then many IVS components have been developing aspects of VGOS ranging from hardware to analysis.
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