PPP using NRCan Ultra Rapid products (EMU): Near real-time comparison and monitoring of time scales generated in time and frequency laboratories

Abstract

The Precise Point Positioning (PPP) time-transfer technique requires the availability of precise estimates of GNSS satellite orbits and clock offsets. Several such products are available from the International GNSS Service (IGS), each having their own characteristics: robustness, update rate, latency and satellite clock offset time interval. The most frequently updated IGS products are the Ultra Rapid products, which are generated four times a day with a latency of three hours. Natural Resources Canada (NRCan) contributes its own Ultra Rapid GPS product to the IGS for combination. However, the underlying processes running at NRCan generate products much more frequently - 24 times a day - with a latency of 90 minutes, offering an opportunity for more timely time-transfer results when used in PPP. INRIM and NRCan hereby assess the potential of using the PPP with the NRCan Ultra Rapid GPS products to serve as a short latency time-transfer tool. A specific experiment has been set up, where the NRCan Ultra Rapid GPS products, as well as all currently available IGS products, are used in PPP time transfer between selected IGS stations collocated in timing laboratories. Results and relative merits are compared in light of their respective delivery and frequency stability characteristic, in view of designing an automated near real-time monitoring system to assist timing laboratories in operational maintenance of frequency standards and time scales dissemination to external users.