VLBI Global Observing System (VGOS)

To improve VLBI data to meet increasingly demanding requirements, an end-to-end redesign called the VLBI Global Observing System (VGOS, formerly VLBI2010) is in progress. The key concepts are a broadband signal acquisition chain (2-14 GHz) with digital electronics and fast, small antennas. By placing up to four carefully chosen RF bands in the 2–14 GHz range, Radio Frequency Interference (RFI) should be ameliorated and the requisite observation precision achieved. Fast antennas will provide many more observations. More observations support higher temporal and spatial resolution in estimating the effect of the troposphere at each station. Simulations show tropospheric effects as the largest noise source. High recording bandwidths are required to achieve the necessary sensitivity.

VGOS is being developed to be minimally staffed, remotely controllable, broadband, RFI avoiding, fully digital, fast slewing, and capable of producing VLBI delays with precision of 4 picoseconds (in 4 picoseconds light travels 1 millimeter.) The system is designed to observe continuously.

The VGOS vs Legacy systems are compared in Table 1:

Table 1: VGOS vs. Legacy systems: Comparison of Characteristics.

 

Legacy S/X System

VGOS System

Benefit

Antenna size

5- 100 m dish

12-13 m dish

Reduced cost

Slew Speed

~20-200 deg/min

≥ 360 deg/min

More observations for troposphere

Sensitivity

200-15,000 SEFD

≤ 2,500 SEFD

More homogeneous

Frequency Range

S/X band             (two bands)

~ 2-14 GHz         (four bands)

Increased sensitivity & data precision

Recording Rate

128, 256, 512 Mbps

8, 16, 32 Gps

Increased sensitivity

Data Transfer

usually e-transfer, some ship disks

e-transfer, ship disk when required

 

Signal Processing

analog/digital

digital

Stable instrumentation

SEFD: “System Equivalent Flux Density”, is used to measure overall antenna performance. Units are Jy (Janskys).

 

NASA’s contribution to VGOS, which is managed under the auspices of the Space Geodesy Project in NASA GSFC Code 61A,  includes the construction of a 12-m antenna at the Goddard Geophysical and Astronomical Observatory (GGAO) in Greenbelt, Maryland (Figure 1), support for the development of the VGOS antenna at Kokee Park Geophysical Observatory (Hawaii) provided by the U.S. Navy (Figure 2), the construction of a 12-m antenna at the McDonald Observatory (Texas), and the installation of a 12-m VGOS antenna in Tahiti in cooperation with France.  

The International VLBI Service for Geodesy and Astrometry (IVS) anticipates a gradual introduction of VGOS systems into the new broadband network as they become available. A number of new and existing telescopes already have accomplished successul VGOS observations: GGAO, Westford, Kokee Park (USA); Ishioka (Japan); Wettzell (Germany); and Yebes (Spain).  Several new telescopes are working on the installation of a VGOS signal chain of their new telescopes; these include the Onsala Twin Telescopes (Sweden), the Spanish/Portuguese RAEGE telescope at Santa Maria (Azores, Portugal), and the AuScope antennas at Hobart, Katherine, and Yarragadee (Austrailia).  Other sites are in an advanced stage of their telescope construction; e.g., Hartebeesthoek (South Africa); Ny-Alesund (Spitsbergen, Norway), Sheshan (China), and Metsahovi (Finland).  The eventual future IVS network, equipped with VGOS stations, is shown as it is expected to appear in 2020 (see Figure 3); currently operative stations are indicated by blue triangles.

 

 

 Figure 1:VGOS 12-m antenna at NASA’s Goddard Geophysical and Astronomical Observatory

 


Figure 2: Kokee Park (Hawaii) VGOS antenna. “First light” for this telescope occurred in February 2016.

 

 

Figure 3: Projected IVS Network in 2020 with VGOS stations.

 

For more information please contact:
Frank Lemoine Frank.G.Lemoine@nasa.gov
Stephen Merkowitz Stephen.M.Merkowitz@nasa.gov
Dirk Behrend Dirk.Behrend-1@nasa.gov

References:

Gomez-Gonzalez, J., J.A. Lopez-Fernandez, F. Colomer, L.R.Santos, "An Atlantic Network of Geodynamical and Space Stations: The RAEGE Project", International VLBI Service for Geodesy and Astrometry, 2014 General Meeting Proceedings.

Lopez-Fernandez, J.A., B.Vaquero Jimenez, J.M. Serna Puente, "Yebes Observatory: Future core site and laser ranging station status", 20th International Workshop on laser Ranging, Potsdam, Germany, October 9-14, 2016.

Nickola, M., R. Botha, L. Combrinck, A. de Witt, P. Mey, P. Stronkhorst, J. Quick, C. Jacobs, "New developments at the Hartebeesthoek radio astronomy observatory" (poster), 5th International VLBI Technology Workshop, MIT Haystack Observatory, Westford, Massachusetts, Oct 12-14, 2016.

Nothnagel, A., T. Artz, D. Behrend, Z. Malkin (2017), "International VLBI Service for Geodesy and Astrometry: Delivering high-quality products and embarking on observations of the next generation", J. Geodesy, 91(7), 711-721,doi: 10.1007/s00190-016-0950-5.

Petrachenko, W.T., A.E. Niell, B.E. Corey, D. Behrend, H. Schuh, J. Wresnik (2012), "VLBI2010: Next Generation VLBI System for Geodesy and Astrometry" in GEODESY FOR PLANET EARTH: PROCEEDINGS OF THE 2009 IAG SYMPOSIUM, International Association of Geodesy Symposia, Vol. 136, pp. 999-1005, Springer-Verlag, Berlin (Germany), ISBN: 978-3-642-20338-1; 978-3-642-20337-4, doi: 10.1007/978-3-642-20338-1_125

Schuh, H. and D. Behrend (2012), "VLBI: A fascinating technique for geodesy and astrometry", J. Geodynamics, 61(68-80), doi: 10.1016/j.jog.2012.07.007.

Schüler, T., G. Kronschnabl, G. Plotz, A. Neidhardt, A. Bertarini, S. Bernhart, L. la Porta, S. Halsig and A. Nothnagel, "Initial results obtained with the first Twin VLBI radio telescope at the Geodetic Observatory Wettzell", Sensors, 15(8), 18767-18800, 2015, doi:10.3390/s150818767.

Wakasugi, T., M. Umei, T. Toyota, M. Ishimoto, R. Kawabata, B. Miyahara, "VGOS Development for Ishioka 13-m antenna", The 23rd EVGA (European VLBI Group for Geodesy and Astrometry) Working Meeting, Gothenburg, Sweden, May 15-19, 2017.

International VLBI Service for Geodesy and Astrometry 2016 General Meeting Proceedings “New Horizons with VGOS ”, edited by D. Behrend, K.D. Baver, K.L Armstrong, NASA/CP-2016-219016, NASA Goddard Space Flight Center, October 2016.