(return
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home)The satellite-based augmentation system (SBAS) includes the US-American WAAS, the European GEGNOS, and the MSAS etc. The primary correction data streams of these systems include satellite orbit, clock, and ionosphere correction data specified regions. The main objectives of these systems are providing integrity positioning with a safety-of-life quality and providing a better accuracy than stand-alone GNSS. They are expected to be used with single-frequency code observations. For more precise applications we could use the SBAS orbit and clock corrections together with dual frequency code and carrier phase observations to compute precise point positioning (PPP) solution.
Current reported user positioning accuracy of WASS could reach sub-meter. It is a big improvement over the legacy PNT service. Its applications in real-time positioning with accuracy of 0.1-0.2 meter are limited. The bottleneck of the WAAS accuracy improvement lies in the accuracy of the correction information it broadcasts.
We propose a new type of SBAS correction information: zone-correction. It is defined to augment to the existing SBAS long-term and fast corrections, and applies to regions covering up to one million square kilometers. Protype results show that convergence time of PPP using the new augmentation information is shorter than 2 minutes and positioning accuracy is around 0.1 and 0.15 meter in horizontal and vertical directions.
The GPS and GLONASS are the most used GNSS systems providing positioning navigation and timing (PNT) services to global users. The two systems are in the status of modernization with new generations of satellites launched and new signals added. In addition, the Galileo Compass/BeiDou and QZSS systems provide users with additional signals and may deliver better accuracy, reliability and availability of PNT services. To achieve this goal, unique analysis of data from multi-GNSS system is of vital importance. Unique analysis of multi-GNSS data provides users with consistent satellite orbits, clocks, station coordinates and other products. On the user side, more satellites may improve the observing geometry especially in mountain area and city canyon environments. Key issue of multi-GNSS data analysis is the handling of system differences and biases. In addition, multi-GNSS data analysis need to process more satellites and stations, thus new algorithms and strategies need to be developed.
With the development of the satellite constellation and ground tracking network, multi-GNSS data analysis may encounter the era of processing more than 100 satellites and 300 stations. Multi-GNSS analysis brings many benefits in performance, however it increase the requirement on computation efficiency with higher resolution and precision but lower latency. As reported in Ge et al. (2006), parameter elimination method could help in solving this problem. However, there are many practical issues need to be considered and discussed, especially in case of Multi-GNSS data analysis. In our own GNSS data analysis activities we have used around ~100 globally distributed IGS stations plus ~250 CMONOC stations, which is still quite resource-commanding even when parameter elimination strategy was implemented.
Ambiguity fixing (AR) is another important issues in huge network analysis. In huge network processing, efficiency should also be considered together with AR success rates. Blewitt (2008) present an effective AR strategy, which could be implemented and tested in different software packages.
Starting from the year 2007 the IGS operates the Real-time Pilot Project (IGS-RTPP). IGS-RTPP aims to gather and distribute real-time data and products associated with GNSS satellite constellations. The primary products envisioned for the project are multi-frequency observation data and precise satellite clocks made available in real-time. Following the availability of real-time precise GPS satellite orbit and clock products from the IGS-RTPP, the interest to apply PPP to real-time kinematic positioning is currently strong as a next generation RTK methodology. It overcomes the distance limits of RTK and therefore has valuable applications in remote area and ocean. Applying PPP positioning technique, the accuracy of orbits and clocks is the main issues to guarantee required positioning precision.
In practice, real-time orbits are retrieved from the IGS predicted orbit file. However, there are issues about real-time orbits quality, reliability of real-time tracking network and efficiency of real-time analysis strategy. In addition, the robustness and reliability of analyzing system are other topics to be addressed.
Real-time PPP, PPP-AR and PPP-RTK are our most interested topics which has huge potential applications. Main tasks are the issues of shortening convergence-time and improving performance reliability etc.
The output of the GNSS data analysis of the CMONOC network contains time series of atmosphere and coordinates of all stations. These information provides us a resource looking into the dynamic process embodied. We aim at the inversion of the strain rate fields from the continental geodetic velocity field in China to analyze their geophysical mechanism in the crust movements and deformations of Chinese continent.
We could also to study the dynamic mechanisms, which drive atmosphere variations, through the reconstruction of the 3-D ionospheric tomography through the inversion of electron density from ionospheric delay and inversion of water vapor content from tropospheric delay (Refer to the latest SHAtrop model ).
30 Mar. 2019,
originator Prof.
Junping Chen
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