Formation of a GPS-linked global ensemble of hydrogen masers, and comparison to JPL's linear ion trap

This paper describes the use of precision GPS time transfer to form an ensemble of hydrogen maser clocks. The performance of this ensemble, including the GPS time transfer system, was measured relative to a stable linear ion trap standard. Very high-precision techniques have recently been developed in support of efforts to achieve cm-level accuracy in the use of GPS for geodesy. A global network of tracking stations, equipped with precision dual-frequency GPS receivers, has been in operation for several years. The post-processing software developed for cm-level geodesy has been used to demonstrate sub-nanosecond (ns) time synchronization, as reported in the PTTI conferences of 1991 and 1993. The global network of GPS stations includes 25 which are run coherently from hydrogen masers. This paper explores the use of high precision GPS estimation techniques to transfer time globally in conjunction with ensembles of atomic time standards, which in principle should be superior in performance to a single clock. Together, these techniques have potential to provide a means of directly assessing performance of individual clocks for which statistical information about stability is desired.