Research On Multi-GNSS Precise Point Positioning Technology Surveying And Mapping Engineering

At present,the coexistence of the four global navigation satellite systems(GPS,GLONASS,BDS,Galileo)has been formed.Precise Point Positioning(PPP)technology integrates the advantages of standard point positioning and relative positioning,thus,Multi-GNSS precise point positioning has become a hot research topic at home and abroad.In this paper,the Multi-GNSS precise point positioning theory,key technologies and applications are studied.The main research contents and results are as follows:(1)The transformation and unification of GNSS space-time reference frame are summarized.The error sources involved in Multi-GNSS precise point positioning and its correction strategy are analyzed in detail.The function model and stochastic model of Multi-GNSS precise point positioning are systematically stu,died.(2)The Multi-GNSS PPP data preprocessing problem is studied.The consistency of precise orbit and clock products provided by GFZ,CODE and Wuhan University is evaluated.The results show that the GPS,GLONASS and Galileo satellite orbits provided by the three analysis centers have a good consistency,the orbit 3D error,is basically maintained within 15cm,BDS MEO is second,and maintained within 25cm.The GPS and Galileo satellite clock error provided by the three analysis centers have a good consistency,and the clock error quadratic difference sequence is better than 2ns and 0.5ns.(3)The extended Kalman filter(EKF)model is studied,and the filter recursive process and the determination of the initial value is explained.Based on the precise orbit and clock error products provided by GFZ,four stochastic model of GNSS PPP ISB(time constant,piecewise constant,random walk,white noise process)are compared.The results of the random walk or white noise process to estimate the ISB,the positioning results are better than the constant estimation.At the same time,the positioning results of different GLONASS pseudo-IFB schemes are carried out.The results show that the estimation of a pseudo-distance IFB parameter for each GLONASS satellite can significantly improve the convergence time of the combined PPP,but the accuracy of the PPP single-day solution is not significant,within 10%.(4)The static and static simulated dynamic PPP performance of different satellite navigation system combinations are analyzed from satellite availability,convergence time and positioning accuracy.The results show that the number of visible satellites increases and the convergence speed increases after multi-system combination.The GRCE combined static PPP can obtain a reliable solution for 30 minutes.The GRCE combined dynamic PPP can keep the visible number of satellites at more than 10 at 30 degree elevation angle,and can acquire high-precision positioning solution,while single-GPS dynamic PPP cannot achieve continuous positioning.(5)Considering that the PPP positioning solution is related to the framework of the precise ephemeris,the author has carried out research on the calculation of CGCS2000 coordinates from PPP technology from ITRF2008 and ITRF2014.The results show that for the ITRF2008 framework,compared with the real CGCS2000 coordinates after the epoch and frame transform,the coordinate component difference is within 4cm.,and for the ITRF2014 framework,the coordinate component difference is within 5cm.Based on the PPP technology,the application of time transfer is studied.The results show that the single GPS PPP can reach the sub-nanosecond time transfer accuracy,combined PPP has a slight improvement in single GPS PPP time transfer accuracy,within 10%,when the single GPS system has fewer view satellites,multi-system fusion can improve time transfer accuracy.