THE USE OF PRECISE EPHEMERIDES, IONOSPHERIC DATA AND CORRECTED ANTENNA COORDINATES IN A LONG-DISTANCE GPS TIME TRANSFER

W. Lewandowski, G. Petit, C. Thomas, M.A. Weiss

Abstract:	Over intercontinental distances the accuracy of GPS time transfers ranges from 18 to 20 ns. The principal error sources are the broadcast ionospheric model, the broadcast ephemerides and the local antenna coordinates. Previous work has already shown the impact of correcting each of these error sources individually, using either measured ionospheric delays, precise GPS satellite ephemerides, or improved antenna coordinates. Ionospheric delay measurements can be provided by dual frequency codeless ionospheric calibrators. Precise GPS satellite ephemerides are now available from the U.S. Defense Mapping Agency (DMA), and others. GPS receiver antenna coordinates should be accurately linked to stations of the IERS Terrestrial Reference Frame. If such a link is not available from geodetic methods, accurate differential positioning, between GPS antennas, can be realized over short distances, using the BIPM method. For the first time, the three major error sources for GPS time transfer can be reduced simultaneously for a particular time link. Ionospheric measurement systems of the NIST type are now operating on a regular basis at the National Institute of Standards and Technology in Boulder (Colorado, USA) and at the Paris Observatory in Paris (France), Broadcast ephemerides are currently recorded for time-transfer tracks between these sites, this being necessary for using precise ephemerides. At last, corrected local GPS antenna coordinates are now introduced in GPS receivers at both sites. This paper shows the improvement in precision for this long-distance time comparison resulting from the reduction of these three error sources.
Published in:	Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting December 4 - 6, 1990 Sheraton Premiere Hotel Vienna, Virginia
Pages:	547 - 558
Cite this article:	Lewandowski, W., Petit, G., Thomas, C., Weiss, M.A., "THE USE OF PRECISE EPHEMERIDES, IONOSPHERIC DATA AND CORRECTED ANTENNA COORDINATES IN A LONG-DISTANCE GPS TIME TRANSFER," Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting, Vienna, Virginia, December 1990, pp. 547-558.
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