Local augmentation to wide area PPP systems: a case study in Victoria, Australia

Precise GNSS positioning services and infrastructure are becoming increasingly important to support precise positioning applications for machine control in mining, civil construction, agriculture, and transport. Currently these applications are serviced by Real-time Kinematic (RTK) services relying on dense GNSS tracking networks. These services are impractical to deploy over wide areas or for applications in remote areas such as hydrographic surveying. Precise Point Positioning (PPP) have demonstrated potential to deliver centimetre-level accuracy without the onerous requirement of ground GNSS network. However PPP requires solution convergence times in the order of tens of minutes compared to the few seconds with RTK. A wide area (national or regional level) GNSS positioning infrastructure should consist of a sparse wide area reference network for PPP and complemented by dense local networks supporting RTK-like systems where practical. The wide area infrastructure is used for computation of precise satellite orbits, clocks and signal biases while the local network is used to derive atmospheric corrections required for rapid convergence. This paper presents the results this type of PPP-RTK system which uses existing global correction streams, i.e., JAXA's MADOCA and CNES's CLK91, and local ionospheric corrections derived from these streams using Victoria's GPSnet network stations. Observables from individual stations and the global corrections were used to estimate tropospheric and ionospheric delays. The computed ionospheric delays were then used to generate local ionospheric correction maps for each GPS satellite. Real-time tests using GPS and GLONASS satellites were performed at 5 GPSnet CORS stations. Results show that PPP-RTK type system using local ionospheric corrections can significantly reduce the solution convergence times and positioning errors in PPP.