Precise Orbit Determination And Geodetic Parameter Calculation By Combining GNSS And SLR Data From Multiple Satellites

Space geodesy techniques mainly consist of the Very Long Baseline Interferometry(VLBI),the Satellite Laser Ranging(SLR),the Laser Lunar Ranging(LLR),the Global Navigation Satellite System(GNSS),and the Doppler Orbitography by Radio-positioning Integrated on Satellite(DORIS),etc.In the current space geodesy techniques,SLR is the unique observation technique that can provide the station-satellite distance with the observation values of sub-centimeter-level and without ambiguity,while GNSS has been deeply integrated into the daily life of human society,with the advantage of all-weather high-precision positioning and timing,not being constrained by weather conditions,as well as simple and efficient observation,etc.Both SLR and GNSS techniques play an important role in the satellite precise orbit determination(POD),the accurate measurement of Earth Rotation Parameter(ERP),the establishment and maintenance of high precision Earth reference frame,the measurement and refinement of Earth gravity field model,as well as another scientific research.In this paper,the author mainly studies the theory and method of precise orbit determination and geodetic parameter calculation based on GNSS and SLR data of multiple satellites,including most of Multi-GNSS satellites and four geodynamic satellites.The main contents are as follows.1.Based on the modified Bernese GNSS Software Version 5.2,the SLR data processing module of are expanded for the Galileo,BDS-2 and BDS-3 satellites.The SLR validation function are realized steadily and reliably for multi-GNSS long-time series precision orbit products,regardless of which GNSS Analysis Center(AC)these products come from.Moreover,the SLR validation residual screening strategies are designed according to different types of GNSS satellites.2.The multi-GNSS precise orbit products with long-term series derived from multiple GNSS ACs are validated by using SLR data.The results show that,the overall accuracy of these precise orbit products is in the range of 4?7 cm for Galileo satellites,20?50 cm for BDS-2 GEO satellites,5?8 cm for BDS-2 IGSO satellites,3?5 cm for BDS-2 MEO and 3-6 cm for BDS-3 MEO satellites.Moreover,the precise orbit products of many GNSS ACs are also continuously improved with the continuous up dates and refinements in their Multi-GNSS precise orbit determination strategies.3.With regard to Chinese BDS-2 GEO,IGSO and MEO,four kinds of precise orbit products derived from four GNSS ACs are validated by using SLR from 2013 to 2018.These SLR validation residuals are analyzed by dividing them into the non-eclipse period,eclipse period,as well as yaw maneuver(YM)period.In addition,the author compares and discusses the dependency of these SLR validation residuals derived from four GNSS ACs on the satellite nadir angle,the SLR station observation characteristics,as well as between the Sun elevation angle ? and the satellite latitude argument ??.The periodic error signals can be detected clearly among the SLR residuals,the ?-angle and the ??-angle,owing to the inaccurate dynamic model parameters estimation of BDS-2precise orbit during eclipse period for all four GNSS ACs.Among the four ACs,the ISC integrated products derived from iGMAS always have the highest overall performance in precision.4.By stacking multiple SLR-only single-day normal equation(NEQ),the author realizes the multi-day solutions of the Multi-GNSS SLR-only POD.including the 3-,5-,7-,and 9-day solutions.The accuracy of these orbits is evaluated and compared,to finding the rule of the accuracy improvement with the multi-day arc extension.The necessary conditions of GNSS SLR-only high-precision orbits are explored in detail.The overall optimal 3D-RMS values of GNSS SLR-only multi-day solution are about 25 cm for GLONASS,50 cm for Galileo,577 cm for BDS-2 GEO,189 cm for BDS-2 IGSO,17 cm for BDS-2 MEO and 50 cm for BDS-3 MEO by comparing the orbital overlap arcs.And the overall accuracy can reach 1?2 cm in the R direction of GNSS MEO satellites.5.The SLR-only multi-day solution orbits of Chinese BDS-2 and BDS-3 satellites are analyzed in the first half year of 2019,to explore the dependence of the SLR-only orbital accuracy on the number of SLR observations and the number of SLR stations in detail.When the multi-day arc satisfies both more than 50?80 SLR observations and including 5?7 evenly distributed SLR stations around the world,the accuracy of SLR-only multi-day solution precise orbit is well and stable.6.In a view of nearly full constellation SLR observation capability of GLONASS,seven kinds of strategies are designed for GLONASS SLR-only multi-day orbits in September 2019.These results are compared and analyzed to explore the dependency of the accuracy of SLR-only orbits on the prior orbits,on the solar radiation pressure(SRP)model parameters,and on the SLR range bias(RGB).Owing to the influence of eclipse period or YM mode,the estimation of dynamic model parameters is getting more and more inaccurate,which leads to the accuracy of SLR-only orbits decreases sharply with the length of multi-day arcs.7.The combined GNSS L-band/SLR multi-day solution POD is realized by stacking of SLR-only and L-band NEQs,and the geodetic parameters are also computed synchronously,including the individual GLONASS,the individual Galileo,the individual BDS-2 IGSO/MEO satellites.Compared with the GNSS L-band orbits,the accuracy of the combined L-band/SLR multi-day solution is always getting improved in the orbital RTN direction.The improved accuracy is on the millimeter scale for individual GLONASS and individual BDS-2 IGSO/MEO satellites.Interestingly,the overall orbital external coincidence has been improved to 2-9 cm for individual Galileo multi-day solution.8.The accuracy contribution of SLR data to the combined GNSS L-Band/SLR multi-day solution are discussed.It is strongly correlated with the estimated accuracy of satellite dynamic model parameter,the distribution of GNSS stations on the ground,and the quality of SLR data in the combined arc.Taking CODE ERP as a reference,the calculated ERP parameters are compared and analyzed between GNSS L-band and combined GNSS L-band/SLR multi-day solution,including the X-,Y-pole coordination,and the UT1-UTC values.At present,the addition of SLR data does not contribute significantly to the improvement of ERP accuracy.9.The 7-day solution of the high-precision POD and geodetic parameter calculation are extended with a one-day interval of moving window mode to four geodynamic satellites,namely Lageos-1,Lageos-2,Etalon-1,and Etalon-2 satellites.Seven kinds of modes are designed,including the individual mode of four satellites,the combined mode of two Lageos satellites,the combined mode of two Etalon satellites,and the combined mode of all four satellites.The synchronously estimated orbital and geodetic parameters of seven modes are compared and analyzed with each other in detail,including the accuracy of orbits,the X-,Y-pole coordination and the UT1-UTC values of ERPs,the N-,E-,U-coordination of station coordinates,the X-,Y-,Z-coordination of geocentric variation,and the SLR range biases.The difference among them is mainly due to the comprehensive influence of the SLR observation data quality,the SLR station core stand prior sigma constraints,etc.10.The monthly low-degree time-varying gravity field of Earth are recovery are preliminarily realized based on Lageos-1 satellite.Compared with the ILRS-B precise orbit products,the overall accuracy of Lageos-1 monthly arc solution is 1-2 cm in the R direction,and 3-5 cm in the T direction and N direction.Taking EGM2008 as a reference,the 6×6 order time-varying coefficient of Earth gravity field are compared and analyzed,including their monthly variation values of the coefficient of zonal harmonic,the coefficient of tesseral harmonic and the coefficient of sectorial harmonics,as well as the spectral analysis of their corresponding sequence.The results show that,the accuracy of recovered monthly low-degree time-varying gravity field of Earth is good and stable,accompanied by obvious seasonal,semiannual,and annual signals in spectral analysis.