Precise Orbit Determinating Method And Application Of Bds Enhanced By LEO Satellites

For the construction and development of the Beidou Satellite Navigation System(BDS)in China,the problem of tracking stations regionally distributed is a great limitation for development.The rise of large-scale low earth orbit(LEO)satellite constellations is another opportunity in addition to the satellite inter-link,which can effectively solve the problem of improving the accuracy of orbit determination for BDS satellites with regional stations distributed.Based on the background,the article conducts research on enhanced BDS orbit determination by LEO satellites and focuses on quality control of satellite-borne observation data from LEO.The optimal selection of LEO satellites from the constellations and the enhancement of parameters and products in joint orbit determination were discussed and analyzed in depth,and some new algorithms were proposed.The main innovations and summary are as follows.1.In view of the characteristics of large ionospheric changes and instability in satellite-borne observation data,a dual-frequency combined variable of second-order ionospheric residual for cycle slips detection is proposed,which can eliminate the influence of both the first-order ionospheric term and the second-order term.While eliminating the ionospheric influence as much as possible,it can limit the noise of the combined detection variable to 0.259 weeks.Compare the new detection variable with the MW(Melbourne-Wubbena)wide lane cycle slip detection variable,it shows that the stability for intense ionospheric changes has stronger applicability.2.Based on the Satellite Positon Dilution of Precision(SPDOP),a time-weight SPDOP for LEO satellites selection algorithm is proposed for the large-scale LEO constellation enhancing BDS satellite orbit determination.The SPDOP value of the navigation constellation corresponding to the LEO satellite is extracted from the sum of the SPDOP values for the whole navigation satellites,and the observable arc length is converted into a weight value and then synthesized.After sorting,it is used as a reference for preferential selection of LEO satellites.Simulation experiments show that the SPDOP value of BDS constellation calculated by data from staions in region scheme is obviously improved.The smaller the distributing region,the more significant the improvement effect.The SPDOP value of the BDS constellation dropped the fastest during the addition of the first 10 LEO satellites.After adding about 20 LEO satellites,the SPDOP decline rate slowed down and gradually flattened.Taking the Walker constellation as an example,for the LEO satellites enhancing BDS satellite orbit determination,it is better for the selected LEO satellites to have a dense sub-satellite points trajectory distribution outward along the longitude line with the center of Chinese region.3.For the large-scale LEO constellation,in order to improve the efficiency of BDS satellite orbit determination enhanced by LEO and reduce the unnecessary memory and time consumption,it is proposed to add the step of selecting the best LEO satellites which have a great impact on the BDS satellite orbit determination result in the enhanced orbit determination revolution process.The simulation results show that the LEO satellite has a significant effect on improving the orbit accuracy of BDS satellite.By adding the satellite selection step of LEO satellites,the enhanced orbit determination time can be reduced exponentially on the premise that the accuracy level of BDS satellite orbit resolution is basically the same.At the same time,with the increase number of LEO satellites,the accuracy of BDS satellite orbit and clock difference is improved.However,the improvement of its accuracy will not increase indefinitely with the number increasing of LEO satellites,but when the number reaches 20 or more,the accuracy of BDS satellite orbit determination will be basically maintained at the same level.With the orbit revolution enhanced by FY-3C LEO satellite for the regional or global ground distributed monitoring stations determined,the accuracy of GEO satellite orbit can be improved by 47% and 50% respectively,the accuracy of IGSO satellite orbit can be improved by 36% and 23% respectively,the accuracy of MEO satellite orbit can be improved by 50% and 29% respectively.The specific accuracy improvement ratio has a great relationship with the number and distribution of ground monitoring stations.4.It discusses and analyzes the influence of orbit enhancement of LEO satellite on the orbit deviation of GEO satellite.Compared with simply introducing GEO satellite orbit deviation correction model,using LEO satellite to enhance the orbit determination of BDS can reduce the systematic deviation in GEO satellite orbit products to a greater extent.For the small amount of LEO satellites cannot completely eliminate the deviation of GEO satellite orbit,LEO satellites and correction model are put forward at the same time for the GEO satellite orbit deviation elimination strategy.The measured data experiment shows that the new strategy can further reduce the system error in GEO orbit products compared with only using model correction strategy,and orbit accuracy in tangential,normal and radial can improve by 39%,11% and 54%,respectively.5.The influence of LEO satellite enhancement on the solar radiation pressure(SRP)model and fixation of ambiguity parameters in the process of BDS satellite orbit determination was analyzed firstly.Compared the LEO satellite enhancement effect on ECOM-5 and Adjustable box-wing SRP model parameters,the measured data experiments show that the enhancement effect has relation to the type of BDS satellite and SRP model selected.Compared with the ground monitoring stations used only for orbit determination,the difference of SRP acceleration component caused by the enhancement of LEO satellite will cause a cumulative error in the centimeter to decimeter of the BDS satellite orbits.6.The influence of LEO satellite on earth rotation parameters(ERP)in orbit determination of BDS satellite is studied.On the basis of the simulation experiment,it is proposed that the LEO satellite has more influence on the ERP parameter revolution under the condition of regional distributed stations than the global.The improvement ratio of ERP parameter precision in LEO satellite enhancement solution increases with the number of LEO satellites,but the gap between the improvement ratio decreases.When the number of LEO satellites increases to a certain number,its effect on the improvement of ERP parameter solution accuracy will reach the maximum limit.Compared with the ground monitoring stations only,the enhanced ERP accuracy revolved by data added with a measured LEO satellite can be improved by 15%,9% and 9% respectively on the pole shift X,Y and length of day.7.The influence of LEO satellite enhancement on the calculation of GEO satellite PCO parameters is analyzed and discussed.By simulation and measured data experiments,it is proposed that under the condition of only ground monitoring stations used,it is usually impossible to accurately calculate the GEO satellite PCO parameters.The improvement effect of LEO satellite enhancement on the calculation accuracy of GEO satellite PCO parameters is stronger than that of the same number of ground monitoring stations.When the number of LEO satellites increases to a certain value,the PCO parameters can be revolved with the same precision level by stations of either regional or global distribution.