GPS PPP-AR frequency transfer and its application for comparing atomic fountain primary frequency standards between NRC and PTB

We report on the first characterization of the frequency transfer performance of the GPS precise point positioning with carrier-phase integer ambiguity resolution (PPP-AR) implemented by the Natural Resources Canada (NRCan) online service CSRS-PPP. We show that continuous PPP-AR links of multiple days can be formed by carefully fixing the day boundary phase discontinuity. The stability of the links can reach 7 × 10 − 16 and 1 × 10 − 16 (Allan deviation) at 1 d and 7 d averaging times, respectively, and mid to low 10−17 at 20 d–30 d. We compared the atomic fountain primary frequency standards (PFS) between NRC in Ottawa, Canada and PTB in Braunschweig, Germany for 135 d via GPS PPP-AR and precise point positioning links. The NRC and PTB PFS agree within a few parts in 1016, which is well below the combined systematic uncertainty. It is expected that with uncertainty at 10−17, the PPP-AR links will become a powerful tool for remote comparisons of atomic optical clocks, essential for the future redefinition of the SI second.