Near real time precise orbit and clock determination for GLONASS

We present a near real-time precise orbit and clock determination system for the GLONASS constellation. The system utilizes tracking data from a global network of GPS+GLONASS receivers and a hybrid GPS/GLONASS estimation strategy to produce GLONASS spacecraft orbit and clock estimates with a latency of about 1.5 hours. This paper provides a detailed overview of our processing system and estimation strategy, and describes challenges unique to the GLONASS system. We assess orbit and clock solution accuracy via internal and external metrics. The near real-time orbit solutions are shown to be accurate to better than 15 cm (1D) in the RMS sense, while the clock solutions are shown to be accurate at the 30-40 cm level (RMS). We further assess the near real-time products by performing GLONASS-only static and kinematic precise point positioning for 20 globally distributed sites over a period of 4 weeks. The 3D median position estimate accuracy is 4.7 cm and 7.4 cm for the static and kinematic test, respectively.