Westford VLBI to GPS Vertical Tie and Implications for the TRF

  • Arthur E. Niell
Part of the International Association of Geodesy Symposia book series (IAG SYMPOSIA, volume 120)


The difference between the heights of the VLBI and GPS antennas at Westford as found in ITRF96 differs from the optical survey value by approximately 3 cm. The height of the GPS antenna is, however, a function of the minimum elevation angle cutoff with a sensitivity of approximately -3 mm/°. A sample of other Dorne Margolin choke ring antennas of the global GPS network shows similar sensitivity, while two Trimble antennas have more severe sensitivities which are of the opposite sign. Until the elevation dependent phase error can be measured in situ there is no way to determine the absolute height of the current GPS antennas. As a consequence, the scale of the Terrestrial Reference Frame cannot be determined by GPS to better than several parts per billion, and the heights of individual sites are uncertain at the several centimeter level.


Height Difference Terrestrial Reference Frame Minimum Elevation Elevation Cutoff Apparent Height 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Carpenter Troy V., Vaughn E. Nelson: “Westford-Haystack Check Survey”, AlliedSignal Technical Services Corporation note, Feb 1997.Google Scholar
  2. Carter W. E., Rogers A. E. E., Counselman C. C. III, Shapiro I. I.,: “Comparison of Geodetic and Radio Interferometric Measuerements of the Haystack-Westford Base Line Vector”, JGR, Vol 85, No B5,2685-2687, May 10, 1980.CrossRefGoogle Scholar
  3. Elósegui P., Davis J.L., Jaldehag R.T.K., Johansson J.M., Niell A.E., Shapiro I.I.: “Geodesy Using the Global Positioning System: The Effects of Signal Scattering on Estimates of Site Position”, JGR, Vol. 100, No. B7,9921–9934, June 10, 1995.CrossRefGoogle Scholar
  4. Jaldehag R.T.K., Johansson J.M., Rönnäng, Elósegui P., Davis J.L., Shapiro I.I., Niell A.E.: “Geodesy Using the Swedish Permanent GPS Network: Effects of Signal Scattering on Estimates of Relative Site Positions”, JGR Vol 101, No. B8, 17,841–17,860, August 1996.CrossRefGoogle Scholar
  5. Niell A.E.: “Near-field Problems for GPS Antennas”, in The Global Positioning System for the Geosciences, National Academy Press, Washington, D.C. 1997.Google Scholar

Copyright information

© Springer-Verlag Berlin · Heidelberg 1997

Authors and Affiliations

  • Arthur E. Niell
    • 1
  1. 1.MIT Haystack ObservatoryWestfordUSA

Personalised recommendations