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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. place where home page more vgos ggao pointer points

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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