Precise GPS Time Transfer to a Moving Vehicle

Bernard Thomas, Tor Egil Melgtid and David Last

Abstract:	GPS time transfers normally employ the common- view method and take place between pairs of etationary receiver8 at precisely-known locations. This paper focuses on techniques for time transfer to a GPS navigation receiver on a moving ship, a land vehicle or aircraft. The accuracy requirement is 20 ns (1~) and, preferably, the system should work anywhere on earth. Single point precise orbit and clock positioning emerges as a the beet way of achieving extremely high timing accuracy when computation is performed post-mission. Its key advantage is its global coverage without reference stations or communications links. DGPS time transfer using a calibrated time standard at the reference station is a viable alternative. It may be employed in real time, although its performance may also benefit from postmission processing using precise orbit data. Both these technique8 will be presented in detail and their performance evaluated. The context of this study is the measurement on a moving ship, a land vehicle or aircraft of the arrival times of Loran-C pulses. The arrival times are required in order to calibrate the Additional Secondary Factors (ASFs) caused by the propagation of the signal over land paths. In this application all processing may be carried out post-mission. Our experiments show that both timing methods can meet the 20 ne accuracy requirement. The paper compares the two with one another and with more conventional timing techniques, including time transfer via a common-view satellite and geodetic positioning. The specifications of the GPS receivers required to implement the methods are set out. The technique8 presented are, of course, also applicable to GPS time transfers between stationary locations.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	1229 - 1236
Cite this article:	Thomas, Bernard, Melgtid, Tor Egil, Last, David, "Precise GPS Time Transfer to a Moving Vehicle," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 1229-1236.
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