Real‑time service performances of BDS‑3 and Galileo constellations with a linear satellite clock correction models

In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigation satellite system(Galileo)have provided real-time satellite clock correction,which is updated at a high-frequency.However,the frequent updates pose the challenges of increasing the computational burden and compromising the timeliness of these correction parameters.To address this issue,an improved Real-Time Service(RTS)method is developed using an extrapolation algorithm and a linear model.The results indicate that a 1 h arc length of the satellite clock correction series is optimal for fitting a linear model of the RTS.With this approach,the 1 h extrapolation results for BDS-3 and Galileo are superior to 0.09 ns.Moreover,when these model coefficients are transmitted and updated at the intervals of 1,2,5,and 10 min,the corresponding PPP can converge at the centimeter-level.It is evident that these improved RTS methods outperform the current approach with high-frequency interval transmission,as they effectively mitigate the challenges associated with maintaining the timeliness of correction parameters.

Glacial Isostasy:Regional—Not Global

The load of the continental ice caps of the Ice Ages deformed the bedrock, and when the ice melted in postglacial time, land rose. This process is known as glacial isostasy. The deformations are compensated either regionally or globally. Fennoscandian data indicate a regional compensation. Global sea level data support a regional, not global, compensation. Subtracting GIA corrections from satellite altimetry records brings—for the first time—different sea level indications into harmony of a present mean global sea level rise of 0.0 to 1.0 mm/yr.

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

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 tile combined GPS/GLONASS pro- cessing. At present, a large number of IGS Analysis Centers （AC） provide clock corrections in 5-rain 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-rain 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 1GS. Allan deviation also gives the same conclusion. Further validation of the SHAO 30-s clock product is performed in kine- matic 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.