星间单差模糊度固定的低轨卫星精密定轨精度分析

Accuracy Assessment for LEO Precise Orbit Determination with Single‑Difference Ambiguity Resolution

高精度、高可靠性的卫星轨道是实现低轨卫星精密应用的重要前提,而模糊度固定技术是提高卫星定轨精度的关键途径。研究了基于整数钟的星间单差模糊度固定原理和方法,并利用2019年4月—5月的两颗GRACE⁃FO(gravity recovery and climate experiment follow on)卫星数据(GRACE⁃C/D)系统评估了固定解对低轨卫星简化动力学和运动学定轨的精度提升效果。结果表明,两颗卫星简化动力学和运动学定轨的宽巷模糊度固定率均达到99%,而窄巷模糊度固定率在95%左右。对于简化动力学定轨,GRACE⁃C/D固定解轨道的重叠轨道的3D均方根误差(root mean square error,RMSE)分别从7.1 mm和7.4 mm减小到了4.2 mm和3.6 mm;卫星激光测距(satellite laser ranging,SLR)残差标准差(standard deviation,STD)分别从15.9 mm和14.4 mm降低到了10.8 mm和11.0 mm,精度提升了32%和24%;K波段测距残差RMSE从8.0 mm减小到2.9 mm,进一步表明固定解还能有效提升低轨卫星间相对位置精度。对于运动学定轨,与精密科学轨道产品互差3D RMSE,浮点解分别为37.5 mm和36.4 mm,固定解分别为27.7 mm和25.5 mm,精度提升约28%,SLR残差STD也减小了约20%。

Objectives:High⁃accuracy and high⁃reliability satellite orbit is the fundamental requirement for precise applications of low earth orbit(LEO)satellites.Due to the uncalibrated phase delay(UPD)origi⁃nated from receivers and satellites,the phase ambiguity cannot be estimated as integer values.Fixing phase ambiguity to proper integer number is one of the key issues to improve the precise orbit determination(POD)accuracy.The algorithms and methods of single⁃difference(SD)ambiguity resolution(AR)based on integer clocks are demonstrated.The reduced dynamic POD and kinematic POD with SD AR are imple⁃mented and the performance is analyzed.Methods:Integer clock is the precise clock product that absorbs satellite UPD.By applying integer clock products,the receiver UPD can be eliminated by forming SD am⁃biguities between two global navigation satellite system(GNSS)satellites.And the SD ambiguity recover its integer nature and can be fixed to integer value by a rounding strategy.The onboard gravity recovery and climate experiment follow on(GRACE⁃FO)data(GRACE⁃C/D)and integer clocks from Centre National d’Etudes Spatiales/Collecte Localisation Satellites(CNES/CLS)of April and May 2019 was employed to evaluate the improvement of reduced dynamic POD and kinematic POD accuracy with SD AR.Results:The wide⁃lane ambiguity fixing rates of both reduced dynamic and kinematic POD reach 99%and the narrow⁃lane fixing rates are about 95%.For reduced dynamic POD,the 3D root mean square error(RMSE)values of overlapping orbit difference reduced from 7.1 mm and 7.4 mm to 4.2 mm and 3.6 mm for GRACE⁃C/D,respectively.The standard deviation values of satellite laser ranging(SLR)residuals de⁃crease from 15.9 mm and 14.4 mm to 10.8 mm and 11.0 mm,with improvements of 32%and 24%.Be⁃sides,the RMSE values of K⁃band ranging residuals reduced from 8.0 mm to 2.9 mm,demonstrating that SD AR can also improve the relative position accuracy of LEO satellites.As for kinematic POD,the 3D RMSE values for orbit difference with precise science orbit(PSO)of ambiguity⁃float solution are 37.5 mm and 36.4 mm,while those of ambiguity⁃fixed solution are 27.7 mm and 25.5 mm,with improvements of about 28%.Moreover,the SLR residuals results also improved by 20%.Conclusions:With the integer clock products,SD AR can be achieved using onboard observations of a single LEO satellite.The SD AR can significantly improve both the reduced dynamic and kinematic POD accuracy of LEO satellites.