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David Horsley gave a presentation to members of the international VLBI community gathered at the MIT Haystack Observatory in Westford, Massachusetts, USA. The presentation demonstrated the current state of new operations monitoring software being developed and tested at the GGAO VLBI station. The talk resulted in stations from Australia and Spain offering their support of the project.

Dirk Behrend is a co-author of a paper that has been accepted by the Journal of Geodesy: "International VLBI Service for Geodesy and Astrometry---Delivering High-Quality Products and Embarking on Observations of the Next Generation". Axel Nothnagel (University of Bonn) is the paper's first author, and Thomas Artz (University of Bonn) and Zinovy Malkin (Pulkovo University) are the other co-authors. The paper discusses the current operations of the International VLBI Service (IVS), as well as the service's outlook for realizing the VLBI Global Observing System. The paper places an emphasis on the IVS polar motion product because this product can be independently validated, and the paper compares IVS polar motion results to results from the International GNSS Service.

A paper written by David Gordon, "Impact of the VLBA on Reference Frames and Earth Orientation Studies", has been accepted by the Journal of Geodesy. The paper examines how usage of the VLBA has improved the celestial reference frame, the terrestrial reference frame, and Earth orientation parameters.

On Thursday, June 9, successful fringes were detected between the GGAO12m (Maryland), Westford (Massachusetts), Wettzell (Germany), and Yebes (Spain) VGOS stations for all four VGOS bands. This is the first observation of a transatlantic, four band VGOS baseline. People who contributed to this major accomplishment include Ed Himwich (NASA GSFC), Katie Pazamickas and Jay Redmond (GGAO), Mike Titus, Brian Corey, and Chet Ruszczyk (Haystack), Mike Poirier and Alex Burns (Westford), Alexander Neidhardt, Christian Ploetz, and Gerhard Kronschnabl (Wettzell), and Pablo de Vicente and Laura Barbas Calvo (Yebes).

"Second Epoch VLBA Calibrator Survey Observations --- VCS-II" has been published in the Astronomical Journal (doi:10.3847/0004-6256/151/6/154).. David Gordon is the first author, and Chopo Ma is a co-author. The other authors are Christopher Jacobs (JPL), Anthony Beasley (NRAO), Alison Peck (NRAO), Ralph Gaume (USNO), Patrick Charlot (Laboratoire d'Astrophysique de Bordeaux, University of Bordeaux and CNRS) Alan Fey (USNO), Oleg Titov (Geosciences Australia), and David Boboltz (NSF).

"Second Epoch VLBA Calibrator Survey Observations --- VCS-II" has been accepted for publication in the Astronomical Journal. David Gordon is the first author. The other authors are Christopher Jacobs (JPL), Anthony Beasley (NRAO), Alison Peck (NRAO), Ralph Gaume (USNO), Patrick Charlot (Laboratoire d'Astrophysique de Bordeaux, University of Bordeaux and CNRS) Alan Fey (USNO), Chopo Ma, Oleg Titov (Geosciences Australia), and David Boboltz (NSF).

The GSFC VLBI group participated in the 9th IVS General Meeting, which was held in mid-March in Johannesburg, South Africa. The group gave the following five oral presentations. John Gipson presented "El Niño; and VLBI Measured LOD". David Gordon and Karine Le Bail presented "Status of the X/S Source Catalog". Le Bail, Gordon, and Chopo Ma presented "Selecting Sources that Define a Stable Celestial Reference Frame with the Allan Variance". Ma, Dan MacMillan, Gordon, and Le Bail presented "Aspects of ICRF-3". MacMillan presented "Next Generation Global Geodetic Networks for GGOS" along with Erricos Pavlis, Magda Kuzmicz-Cieslak, and Daniel Koenig (all from UMBC).



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

The VLBI technique uses radio signals from quasars to measure movements of the Earth's crust and the rotation of the Earth. The GSFC VLBI group:

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)
Quick Links Click here for baseline and site evolution series and other data from our latest nuvel solution, 2011an.

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. Under the direction of Arthur Niell of the MIT Haystack Observatory, the Goddard Geophysical and Astronomical Observatory, GGAO, has contributed by serving as the test bed for NASA's VGOS Network Station development activities, including the development of NASA's first 12-meter VGOS antenna. The relatively small size of the antenna will allow it to move rapidly but will also reduce its sensitivity. Increased bandwidth will compensate for this loss of sensitivity. The combination of a small, fast antenna observing over a large bandwidth should allow the antenna to meet the VGOS goal of achieving 1-mm position accuracy over a 24 hour observing session.

Milestones achieved by GGAO:
October 8, 2010: Mounted the antenna's main reflector on its pedestal.
March 21, 2011: Detected first X-band fringes with Eleven feed.
June 7, 2011: Detected first X-band fringes with QRFH feed, one polarization.
January 19, 2012: Observed five hours on source 3C345 with four bands placed contiguously.
May 16, 2012: Observed a six-hour geodetic schedule with four bands at 3.2, 5.3, 6.3, and 9.4 GHz.
July 27, 2012: Estimated the antenna position from fully coherent ionosphere-corrected full-polarization delays using all four RF bands. The position uncertainties were ~8 mm in vertical and 2.5 mm in horizontal from 100 scans over six hours.
October 4 and 5, 2012: Observed two six-hour sessions at 34 scans per hour with and without a mask in the south for the NGSLR radar. The geodetic agreement between the sessions was better than 5 mm.
January 29, 2013: Observed a 24-hour R&D; session to test mixed S/X and broadband recording.
April 25, 2013: Observed a test session for flux density calibration. The session consisted of observing six sources twice, and it showed amplitude and SNR agreement of better than 3%.
May 21, 2013: Observed a 24-hr session with the antenna, RDBEs, and Mark5Cs under Field System control. With a minimum scan length of 30 seconds and the minimum SNR set to 15 per band-polarization, the schedule achieved 48 scans per hour.
December 8, 2014: Completed the first 24-hour VGOS geodetic VLBI session with the MIT Haystack Observatory 18.7-m antenna at Westford, Massachusetts, as the partner station. The uncertainty in the baseline length for this session was less than 1 millimeter.
December 2014 through February 2016: Completed thirteen geodetic VLBI sessions with the Westford 18.7-m antenna. The majority of the sessions were of one-hour duration with the primary goal of developing the VGOS operational procedures. The longest session spanned a full 24 hours. The length repeatability was 1.9 mm.
February 2016 through May 2016: Participated in the commissioning sessions for the Kokee 12-m antenna VGOS system. These were the first global baseline observations for the new VGOS geodetic VLBI technique, developed by MIT Haystack Observatory and NASA.
June 20, 2016: Detected the first transatlantic, four band VGOS fringes with Westford (Massachusetts), Wettzell (Germany), and Yebes (Spain). GGAO used the RDBE-G/Mark6.
July 2016 through October 2016: Participated with the other NASA antennas at Westford (Massachusetts, USA) and Kokee (12m) (Hawaii, USA) in a series of regular VGOS trial sessions to evaluate compatibility of technologies and to help bring into operation the new antennas at Wettzell (Germany), Yebes (Spain), and Ishioka (Japan). These sessions are the seed of the emerging VGOS network.
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