Westford VLBI to GPS Vertical Tie and Implications for the TRF
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.
KeywordsHeight Difference Terrestrial Reference Frame Minimum Elevation Elevation Cutoff Apparent Height
Unable to display preview. Download preview PDF.
- Carpenter Troy V., Vaughn E. Nelson: “Westford-Haystack Check Survey”, AlliedSignal Technical Services Corporation note, Feb 1997.Google Scholar
- 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