Our real-time clock product is named as SGG-CLK and can be downloaded at the IGS NTRIP caster.

The processing flowchart of real-time clock estimation is summarized in Fig. 1. At the beginning, real-time observation data, broadcast ephemeris and ultra-rapid satellite orbit are updated and stored. After that, quality control is carried out to detect the gross error and cycle slips in the raw observations. Before the computation, the earth tides, ocean tide loading, relativistic delays, phase wind-up as well as phase center offsets (PCOs) and variations (PCVs) are corrected according to the existing models. Then, it goes to the core processing part, where the real-time clock estimation is carried out to generate real-time clock products. At last, clock corrections are encoded to SSR information according to the RTCM standards and broadcasted based on the NTRIP protocol, to support multi-GNSS RTPPP at the user side.

Observations at frequencies L1 and L2 for GPS and GLONASS, B1 and B2 for BDS, E1 and E5a for Galileo are used to compose the Ionosphere-free (IF) observations to eliminate the first-order ionospheric delays. The elevation dependent weight for observations is applied and the elevation cut-off angle is set to 7°. The sampling interval is set to 5 s. Receiver clocks are epoch-wise estimated as white noise. Specifications of the processing strategy are summarized in Table 1.