LEO Satellites Precise Orbit Determination Based On Space-borne BDS/GPS Data And Research On DCB And Antenna PCV Of Navigation Satellite Enhanced By LEO

Low Earth Orbit(LEO)satellites play an important role in the successful completion of various Earth observation missions.Especially,the continuous and all-weather precise orbit determination of the onboard GNSS receiver is the basis for the satellite to complete various tasks.BeiDou satellite system(BDS)is an independent satellite navigation system developed in China.The research on LEO satellite precise orbit determination(POD)and navigation enhancement based on BDS/GPS is of great significance for the construction of integrated PNT system in China,and the research on LEO navigation enhancement is still in its infancy.For LEO satellite POD based on BDS/GPS onboard data,this paper discusses the relationship between the Jason-3 satellite attitude and its phase center of antenna correction and its influence on orbit determination.The orbit determination of the onboard BDS/GPS single and dual systems for FY3C and FY3D satellites are sutdied and analyzed,also including their corresponding orbit prediction studies.In terms of LEO navigation enhancement,taking LEO satellites as the space-based monitoring stations,this paper studies an enhanced estimation of navigation satellite DCB using LEO measured data,and makes the enhanced estimation of BDS-2 satellite antenna PCV model based on LEO onboard BDS/GPS observations,which provides reference for some research on the LEO navigation enhancement of integrated PNT in China.The main contents of this paper are as follows:1.The theory of LEO satellite attitude and antenna phase center correction are studied.Taking Jason-3 satellite as an example,a combined attitude model is designed and validity of the model is verified,the relationship between the Jason-3 satellite attitude and antenna PCO/PCV is studied,and the influence of the two on precise orbit determination is analyzed.In the current LEO satellites,Jason series satellite attitude is more complex.Taking Jason-3 as an example,a combination attitude model based on experimental analysis is designed in the absence of measured attitude or attitude data has time delay.It can provide an alternative or correction of event files without the measured attitude data or near real-time POD.In order to verify the validity of the designed attitude model,the effects of different attitude modes on PCO geometric correction and POD are analyzed.The results of Jason-3 POD show that the orbit accuracy using the combined attitude model is higher than that of the attitude event file.Satellite attitude is related to antenna PCO,and antenna PCO and PCV constitute the correction of antenna phase center.There is a certain relationship between the three directly or indirectly.After the PCO estimation and PCV modeling of Jason-3 satellite,the average value of 3D-RMS of Jason-3 satellite POD is improved by 5.7 mm by introducing the reciever PCV model,and the equivalent distance error accuracy of SLR verification is improved by 4.1 mm.The final results of Jason-3 POD show that the orbital radial RMS mean is close to 1 cm,and the 3D-RMS is within 3 cm.which meets the needs of its scientific mission2.The LEO precise orbit determination platform based on onboard BDS/GPS data are adapted and developed independently.The single system POD and dual system joint orbit determination based on onboard BDS/GPS data are realized,which is initially formed a more mature orbit determination platform.On this basis,FY3C and FY3D POD are carried out,and POD results of two satellites are compared.In addition,the related research on LEO orbit prediction is carried out.The self-adapted onboard BDS/GPS LEO POD platform are used for a single and dual system POD research.Firstly,the number of visible satellites and the total number of epoch observations of GPS and BDS for FY3C and FY3D satellites are analyzed and compared.It is found that the number of visibe satellites and the total number of epoch observations of FY3D are more than those of FY3C in the selected period.Then,the antenna PCV models of two LEO satellites are estimated respectively,and the POD accurcy is improved after the introduction of reeiver PCV models.Finally,the POD of two LEOs with single and dual system are carried out respectively.The average 3D-RMS values of orbit overlapping arcs of FY3C and FY3D satellites are 0.0234 and 0.0161 m respectively.The 3D-RMS and 1D-RMS of FY3C and FY3D satellite onborad BDS POD results are 0.1831,0.1057 m and 0.1516,0.0875 m,respectively,compared with their onboard GPS orbits.The average values of 3D-RMS of the orbital overlapping arcs of FY3C and FY3D space-borne BDS/GPS joint orbit determination are 0.0357 m and 0.0194 m,respectively.Overall,the orbital accuracy and stability of FY3D POD are better than those of FY3C.The orbit prediction of two LEO satellites is studied.The accuracy of 2 h orbital prediction is centimeter level,and the RMS mean value of 6 h,12 h and 24 h prediction is decimeter level.With the increase of the forecast time,the orbit prediction accuracy RMS gradually decreasesIn addition,the experimental results of POD based on onboard GPS/BDS-2/BDS-3 data show that the 3D-RMS of POD results of onboard BDS-2,BDS-2/BDS-3 and GPS/BDS-2/BDS-3 data are 0.0886 m,0.0573 m and 0.0296 m,respectively.Due to the limited number of BDS signal channels on the onborad receiver,the POD results of FY3C and FY3D satellites are not as good as the above results.With LEO satellites generally equipped with BDS-3 onboard receiver in the future,the POD accuracy of onboard BDS-3 observations may be better than GPS,or at least comparable to GPS.3.A topside ionosphere processing method is proposed for LEO observation data at different orbital altitudes,which can process onboard data at different altitudes,and estimate navigation satellite DCB,receiver DCB and corresponding topside ionospheric electron content at the same time.Based on the LEO onboard data at different orbital altitudes,we first select and use the iterative data preprocessing method to obtain relatively clean code and phase observation data.In this paper,a method can be proposed to simultaneous estimate DCB using different altitudes onboard GPS observation data,that is,by introducing LEO-based topside ionosphere or plasmasphere model to eliminate its effects in advance,and the topside ionosphere mdoels are derived from the modeling results of LEO data at the same orbital altitude.The conclusions are as follows:For LEO onboard data at different altitudes,the more LEO satellites,the higher the monthly stability of the estimated results;the monthly stability and accuracy of GPS satellite DCB estimated by multiple LEOs data at different altitudes are higher than those estimated by LEO data at the same altitude or single LEO onboard data.Compared with the estimated results of single LEO solution,the monthly stability and accuracy of multi-LEO solution at different heights are improved by 25%～35%.In all test schemes,the monthly stability of DCB estimated by LEO data at different altitudes is 0.064 ns,and the optimal accuracy of GPS DCB is approximately 0.146 ns.The stability and accuracy of the LEO-based DCB estimates are similar to those obtained by using ground-based observation data.4.The antenna PCV estimation of BDS-2 satellite based on onboard BDS/GPS data is proposed and implemented.The PCV model of BDS-2 satellite is solved by using FY3D satellite space-borne BDS/GPS joint orbit determination residuals,and its effects on POD is analyzed.At present,BeiDou satellite navigation system does not have available antenna PCV products,affecting its competitiveness in high-precision applications.The zenith angle of LEO satellite corresponding to GNSS navigation satellite is larger than that of ground station,and the common PCV model estimated based on ground station data is not fully suitable for LEO POD and related research.This paper proposes and implements an estimation method of BDS-2 antenna PCV based joint orbit determination residuals.The BDS-2 antenna PCVmdoel is estimated based on FY3D onboard BDS/GPS joint orbit determination residuals,and the nadir angles of BDS-2 IGSO and MEO satellites are extended to 10° and 15° successfully.The results show that the accuracy of joint orbit determination of onboard BDS/GPS data with BDS-2 antenna PCV model is slightly improved,and the R-RMS,T-RMS and 3D-RMS of space-borne BDS orbit are improved by 1.53 cm,0.35 cm and 0.96 cm,respectively.This method can provide a feasible scheme to enhance the antenna PCV estimation of BDS-3 satellte using onboard BDS-3 data,and provide a useful reference for the in-orbit calibration of the BeiDou satellite antenna phase center in China.