The GFZ real-time GNSS precise positioning service system and its adaption for COMPASS
Section snippets
Introduction and motivation
Precise point positioning (PPP) (Zumberge et al., 1997) can provide mm-cm positioning accuracy with single GNSS receiver. The global real-time precise positioning service based on PPP is proved being very promising because of its cost-efficiency, global coverage and its accuracy meeting the requirements of most applications (Agrotis et al., 2010, Bar-Sever et al., 2003, Bar-Sever, 2010; Dixon, 2006; Mireault et al., 2008, Ge et al., 2009, Melgard et al., 2009). In the global real-time PPP
Uniform positioning scheme
A uniform positioning scheme is introduced in this section to satisfy the requirements of various applications including standard PPP, PPP with ambiguity fixing, single-frequency PPP and regional augmented PPP. In the new algorithm, un-differenced raw observations are employed, the ionospheric and tropospheric delays are estimated as parameters with proper spatial and temporal constraints and real-time derived atmospheric model or atmospheric corrections as well. The positioning performance in
Real-time service system
The EPOS-RT software (server-part) is running at the GFZ IGS real-time data analysis centre for providing orbits, clocks, UPD (uncalibrated phase delay), GIM (global ionospheric map), RAC (regional augmentation correction) in real-time. Recently, new software module “iPPP” (client-part) in C/C++ was developed to implement the proposed uniform positioning algorithm. Now the system is running operationally to provide standard float PPP, ambiguity-fixed PPP, single-frequency PPP (SF-PPP) and
Positioning performance
We process the stream data of about 80 IGS stations in real-time for providing orbits and clocks at 5 s sampling interval. From the IGS real-time combination, the user range accuracy of the orbits and clocks is about 0.1 ns or 3 cm. UPDs are also determined in real-time using the same network. About 150 streams are employed for GIMs generation. Orbits, clocks, GIMs and UPDs are broadcasted through the same caster via INTERNET.
For assessing the performance of the proposed algorithm, about 60
Adaption for COMPASS
We have adapted the service system to accept the COMPASS data for this study. As the COMPASS signal is very similar to GPS and GALLIEO’s, the adaption is very straight forward. The only difference is recently there are only GEOs and IGSOs in the COMPASS system instead of MEOs. The tracking network for GEOs and IGSOs can only be a regional one and the observation geometry for precise orbit determination and as well as positioning are somehow different from current GPS and special attention might
Conclusions and outlooks
A global real-time precise positioning service system is operational running at the GFZ IGS real-time data analysis centre. Based on the real-time data streams from IGS, EUREF and SAPOS reference networks, various products are generated in real-time by EPOS-RT software and broadcasted to users by NTRIP. The system structure and data flow at both server side and client side are carefully illustrated. The real-time processing at the server-end includes precise orbit determination, clock
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