GNSS clock corrections densification at SHAO: from 5 min to 30 s

Abstract

High frequency multi-GNSS zero-difference applications like Precise Orbit Determination (POD) for Low Earth Orbiters (LEO) and high frequency kinematic positioning require corresponding high-rate GNSS clock corrections. The determination of the GNSS clocks in the orbit determination process is time consuming, especially in the combined GPS/GLONASS processing. At present, a large number of IGS Analysis Centers (AC) provide clock corrections in 5-min sampling and only a few ACs provide clocks in 30-s sampling for both GPS and GLONASS. In this paper, an efficient epoch-difference GNSS clock determination algorithm is adopted based on the algorithm used by the Center for Orbit Determination in Europe (CODE). The clock determination procedure of the GNSS Analysis Center at Shanghai Astronomical Observatory (SHAO) and the algorithm is described in detail. It is shown that the approach greatly speeds up the processing, and the densified 30-s clocks have the same quality as the 5-min clocks estimated based on a zero-difference solution. Comparing the densified 30-s GNSS clocks provided by SHAO with that of IGS and its ACs, results show that our 30-s GNSS clocks are of the same quality as that of IGS. Allan deviation also gives the same conclusion. Further validation of the SHAO 30-s clock product is performed in kinematic PPP and LEO POD. Results indicate that the positions have the same accuracy when using SHAO 30-s GNSS clocks or IGS (and its AC) finals. The robustness of the algorithm and processing approach ensure its extension to provide clocks in 5-s or even higher frequencies. The implementation of the new approach is simple and it could be delivered as a black-box to the current scientific software packages.