GNSS Real Time Precise Satellite Clock Error Estimation Based On Single Difference Between Satellites

The GNSS real time precise satellite clocks are the key to realize the technology of real time precise point positioning(RT-PPP).The Ultra-Rapid satellite clock products provided by International GNSS Services(IGS)have the lower precision and can't satisfy the demand of RT-PPP.At present,IGS can only provide the afterwards satellites' clock of BDS and can't provide the real-time ones.Therefore,the theory and algorithm of GNSS precise satellite clock is researched based on the area GNSS reference stations network in this article.Then,the GNSS real time precise satellite clocks are estimated to realize the RT-PPP within certain areas and has important application value.In this article,using the observation model of single difference between satellites(SDBS)and the method of sequential least square,the relative satellites' clocks of GPS and BDS are estimated based on GNSS regional reference stations network.Firstly,the algorithm of GNSS real time precise satellite clock error estimation based on single difference between satellites is researched.Then,the algorithm is realized with the language of Fortran based on the data of State Oceanic Administration GPS business observatory in the region surrounded by the Bohai sea and the MGEX data in Australia.Finally,the estimated satellite clocks are applied in GNSS RT-PPP of two experiment schemes and the results are compared and analyzed.The zenith troposphere delay parameters between different stations in the regional reference station network are nearly correlated due to the closer distance.And these parameters will be correlations if they are estimated together.In this article,the relative satellite clocks are estimated based on single stations and the final satellite clocks are required by weighting in all of these stations.The precision of the relative satellite clocks of GPS and BDS is analyzed compared to the final satellite clock products of IGS and MGEX respectively.The result shows that the error standard deviations(STD)of all GPS relative satellite clocks are all less than 0.16 ns and the values of BDS are within 0.07 ns.In this article,the IGU ephemeris and the afterwards ephemeris of MGEX are applied to fix the satellites' coordinates in GPS and BDS satellite clock estimation respectively.Because of the precision of IGU ephemeris is lower than the afterwards ephemeris of MGEX,the estimated GPS satellite clocks have the lower precision than the BDS ones.To verify the feasibility of the estimated real time satellite clocks applied in RT-PPP within areas,the real time satellite clocks are estimated by using the data of State Oceanic Administration GPS business observatories in the region surrounded by the Bohai sea.Then,two experiment schemes are designed.In the first experiment scheme,the RT-PPP is realized using the observation data of IGS station and other two business observatories by applying the estimated satellite clocks in this article.Finally,the precision is evaluated by compared the known coordinates of these stations.The results shows that the errors of all observation station are within 5 centimeters and 10 centimeters in the horizontal and vertical directions respectively after the initial integer ambiguity convergence.The results illustrate that the real time satellite clocks estimated by the method in this article can satisfy the application demand of real time precise point positioning with higher precision.In the second experiment scheme,the RT-PPP of stations far away from the regional reference stations network is realized by applying the estimated satellite clocks.And the precision of the results is analyzed and compared with the first experiment scheme.Then,the feasibility of PPP in different regions by applying the estimated satellite clocks is discussed.The results shows that the increasing distance between the stations and the regional reference stations network will reduce the numbers of the common view satellites to make the spatial geometry of satellites worse so that the precision of PPP will be decreased.The distance between the stations and the regional reference stations network should be concerned sufficiently to establish the suitable regional reference stations network to satisfy the need of actual production.