Real-time Precise Orbit Determination For GNSS Satellites And Maneuver Detection

GNSS aims to provide precise and stable positioning service and real-time precise orbit is the prerequisite for real-time precise positioning service.However,maneuvers happen occasionally and severly degrade the precision of real-time orbit.The thesis studied on real-time precise orbit determination for GNSS satellites and a real-time maneuver detection strategy is disgussed.Main conclusions are listed as follows:1.The thesis introduced a real-time precise orbit determination method using the sqare root information filter(SRIF)and developed a software to realise realtime orbit determination for GNSS satellites based on GREAT software.The thesis optimized the ambiguity handling method by adding and removing ambiguities according to the real-time obsevations.While a method introduced in other papers is to preset all ambiguities between all satellites and all sites regardless of the existence of the ambiguities in current epoch,which is much more time-wasting.Besides,because the precision of the broadcast ephemeris for GPS,Galileo and BDS3 are somewhat precise,the thesis studied a strategy which updates orbit reference epoch every 24 hours to improve the efficiency of the real-time orbit determination algorithm.2.The real-time orbit and clock products for GPS,Galileo and BDS satellites solved from the software introduced in 1 are analyzed by comparing to IGS and MGEX orbit and clock products.The 1D RMS of orbit difference for GPS,Galileo and BDS satellites are 5.7cm,6.1cm and 8.0cm.The mean STD of clock difference for GPS,Galileo and BDS satellites are 0.27 ns,0.26 ns and 0.39 ns.The dynamic precise point positioning(PPP)results show that positioning accuracies of 7.6cm,6.4cm and 13.6cm can be achieved using the real-time orbit and clock products for GPS,Galileo and BDS satellites solved from the software introduced in 1,respectively.3.A maneuver detection algorithm was realized and a maneuver for G21 was detected at 9:20 am on DOY 323,2020,while it was announced by NANU that a maneuver was performed during 7:16-14:49 on DOY 323,2020.