Low Earth Orbiter Satellite Enhancing Navstar Orbit Determination Experiments And Data Processing Methodology Research

This paper in view of the problem of BeiDou satellite navigation system(BDS)uneven ground station layout and the bad orbit accuracy of the geostationary orbit satellite,surrounding the enhancement experiment of using satellite-borne GNSS receiver data combined with the ground station data to improve the orbit accuracy of navigation star.The contents involve space-borne observation data quality analysis,BDS satellite differential code bias(DCB)correction,cycle slip detection and repair,precise orbit determination(POD)enhancement.The main contents and work summarized as follows:1.The basic theory of satellite POD and related contents of GNSS data preprocessing are discussed in detail.We focus on the deduction of satellite motion equations and variational equations,and we propose forward two kinds of geometry-free and ionosphere-free(GFIF)combination with triple-frequency observations.Then the performance of differenced combination observations between epochs is validated by real data.Besides,the quality of spaceborne BDS observations is assessed.2.Considering the frequency of observations is inconsistent to the frequency of reference satellite clock products,the BDS DCB correction formula in stand point position(SPP)and precise point position(PPP)is deduced and summarized.Besides,considering that there is the closure error among the values of BDS DCB in B1B2,B2B3 and B1B3,the different expressions of DCB correction formula are derived.The influence of the DCB on positioning accuracy is analyzed by using the real data.Results show that in SPP the dual-frequency positioning will have an effect on dm-m magnitude,in static PPP on mm-cm magnitude,in kinematic PPP on cm-dm.The pseudorange positioning accuracy of using dual-frequency data is even worse than using single frequency data.The closure error is validated by SPP and PPP,and it is pointed out that the error should be taken into account in kinematic PPP.3.A new real-time cycle slip repair algorithm for BDS triple-frequency undifferenced observations with low-frequency rate and ionospheric disturbance is developed.The key innovation is two GFIF combinations are selected in real number field.Then the pseudo-phase combination only containing B3 phase data are jointly used to repair cycle slip by only rounding the two GFIF combinations in the search range.The algorithm is optimized as following: the combinations values are updated by estimating the ionospheric variation of previous epoch time difference.In the case of the least sensitive cycles ±(1,1,1)occurring the repair process is validated secondary.The proposed algorithm is tested on the real observations with the simulated different magnitude cycle slips and insensitive cycle groups,results show that the developed method can fix all cycle slips of triple-frequency data.4.The results of navstar orbit determination enhanced with spaceborne observations are carefully analyzed.The POD precision of three LEO satellites,HY2 A,GRACE-A and JASON-2 is evaluated by using the “two-step method”.Then the influence of the number of LEO,the LEO orbital height and inclination angle on enhanced results is evaluated.Results show the LEO orbital height and inclination angle should be considered when the ground station distribution is regional,and with 6 China's ground station the difference of different LEO in the case of one LEO is dm magnitude,in two LEOs is 6cm.Then the enhanced experiments are processed by using the 3 LEOs observations and 150 global ground stations with 14 different ground station layouts.The items of “Asia-Sea”,“Asia-Pacific” ground station layout are proposed.The POD enhanced results of global well-distribution and regional distribution,among different regional distribution are compared comprehensively.Finally,the enhanced effects under regional ground station distribution are evaluated.5.The enhanced results of BDS satellite orbit precision are analyzed.Based on the observations of Fengyun3 C carried GPS/BDS receivers,the enhancement experiments in the case of global and regional ground observation stations layout are processed with the POD schemes of BDS single system and GPS/BDS double system.Results show that the along directional precision of BDS GEO satellite has he improvement percentage above 50%.The precision of cross direction and the along direction of remaining satellites shows the second biggest improvement.The root mean square(RMS)of overlapping clock difference of visible arcs is improved in sub-nanosecond level.Besides,three POD strategies with different parameter models are evaluated.Results show that the POD strategy by using CODE 5 parameters combing to add along,cross constant experience force can get the optimal POD results.