Satellite Positioning and Orbit Determination System(SPODS):Introduction and Evaluation

The Satellite Positioning and Orbit Determination System(SPODS)is a software package for GNSS positioning/orbit determination,developed by the Xi’an Research Institute of Surveying and Mapping.So far it has been able to analyse GPS data and has the capability of high precision GPS positioning and orbit determination.The underlying theory and the performance evaluation are briefly addressed in this paper.The experiments are carried out with GPS data collected from about 127 IGS stations during 4~10 January 2009.The results show that the RMS 1D difference is 1.1 cm between SPODS orbits and final IGS combined orbits,and that the repeatability of daily solutions of station coordinates is 1.5 mm for horizontal components,and 4.5 mm for vertical component,and that the consistency of ERP solutions with IGS final products is 0.025 mas,0.093 mas and 0.013 ms/d respectively for pole coordinates and LOD.

Orbit determination and time synchronization for BDS-3 satellites with raw inter-satellite link ranging observations

To provide competitive global positioning and timing services under the condition that monitoring stations are confined to Chinese territory,inter-satellite link(ISL)technology is used by the third-generation BeiDou Navigation Satellite System(BDS-3).The ISL,together with the dual one-way links between satellites and anchor stations,may enable autonomous navigation for BDS-3.In this paper,we propose a general observation model for orbit determination(OD)and time synchronization(TS)directly using non-simultaneous observations,such as raw ISL pseudoranges.With the proposed model,satellite orbits,clocks,and hardware delay biases of ISL equipment can be determined simultaneously by jointly processing inter-satellite one-way pseudorange data and observation data from ground monitoring stations.Moreover,autonomous OD and TS are also achievable with one-way pseudorange data from anchor stations and satellites.Data from eight BDS-3 satellites,two anchor stations,and seven monitoring stations located in China were collected to validate the proposed method.It is shown that by jointly processing data from the ISL and seven monitoring stations,the RMS of overlap orbit differences in radial direction is 0.019 m,the overlap clock difference(95%)is 0.185 ns,and the stability of the estimated hardware delay biases for each satellite is greater than 0.5 ns.Compared with the results obtained with the seven stations,the improvements of orbits in radial direction and clocks are 95.7%and 90.5%,respectively.When the hardware delay biases are fixed to predetermined values,the accuracies of orbits and clocks are further improved.By jointly processing pseudoranges from the satellites and the two anchor stations,the RMS of overlap orbit differences is 0.017 m in the radial direction,and the overlap clock difference(95%)is 0.037 ns.It has also been demonstrated that under the condition of one-way ranging links,the accuracies of orbits and clocks obtained by the above two modes are still significantly better than those obtained by using the data from the monitoring stations alone.

Uncombined precise orbit and clock determination of GPS and BDS-3

There is increasing concern about the uncombined(UC)observation model in the field of global navigation satellite system(GNSS).Based on the global positioning system(GPS)and the third-generation BeiDou navigation satellite system(BDS-3),this study processed the UC precision orbit determination(POD)for single and dual systems.First,a UC observation model suitable for multi-GNSS POD was derived,and the ionospheric-free(IF)combination observation model was presented.Although the ambiguity parameters of UC and IF strategies were different after reparameterization,the difference could be removed when processing ambiguity resolution,and the equivalence was proved theoretically.To demonstrate the accuracy of BDS-3 orbits fully,the observation data of approximately 1 month were selected for determining the precise orbit for global positioning system(GPS)only,BDS-3 only,and GPS/BDS-3 systems based on the UC and IF models.The orbit precision of BDS-3 satellites was validated by using metrics,including comparison with precision products released by Wuhan University,orbit boundary discontinuity,and satellite laser ranging(SLR)residuals.The results show that the orbit accuracies of the IF and UC models are almost the same,the difference in orbits is approximately several millimeters,and the clock difference is within 0.01 ns.The GPS/BDS-3 combined solution shows better accuracy compared to other solutions.The average accuracies in the R and 3D directions are approximately 4 and 15 cm,and the clock standard deviation is approximately 0.2 ns compared to external orbit product.The root mean square of SLR residuals is approximately 4 cm.