应用天文研究组知识库

利用载波相位偏差产品对卫星端硬件偏差进行改正,采用星间单差消除接收机端偏差;结合对应的GPS精密轨道和钟差产品,依次固定宽巷和窄巷模糊度,然后得到基于整数解的无电离层组合模糊度,再利用虚拟观测值对非差无电离层模糊度进行约束,最终得到固定解轨道。同时,利用载波相位残差值开展星载天线相位中心变化（PCV）在轨估计,以进一步提升定轨精度。分别利用欧洲定轨中心（CODE）、法国空间研究中心（CNES）和武汉大学（WHU）发布的GPS精密轨道、钟差和相位偏差产品,对GRACE-FO卫星进行模糊度固定和精密定轨,评估不同机构产品的性能。结果表明:天线PCV改正能够有效减小载波相位残差,提升定轨精度;采用不同机构产品的GRACE-FO卫星宽巷模糊度固定率均优于99%,窄巷模糊度固定率优于95%;对基于CODE, CNES和WHU产品的GRACE-FO卫星精密定轨结果进行评估,与JPL精密轨道相比,固定解轨道三轴平均精度优于7.0 mm;SLR测距残差RMS值分别优于9.6, 10.7和9.1 mm;与KBR星间测距值相比,利用固定解轨道计算的星间距离精度分别优于1.8, 2.3和2.1 mm。利用不同机构产品解算的GRACE-FO卫星轨道整体差异小于2 mm。 

Single receiver ambiguity resolution can significantly improve the accuracy of orbit determination for low earth orbit (LEO) satellites. Carrier phase bias product is employed to calibrate the satellite phase delay, and single difference (SD) observation between satellites is applied to remove the phase delay of receiver. Combined with related GPS precision orbit and clock products, wide lane and narrow lane ambiguities are fixed to integer. Ionosphere free (IF) ambiguity is recovered with the fixed wide lane and narrow lane ambiguities. The resolved SD ionosphere free ambiguities are taken as pseudo observations to constrain the undifferenced IF ambiguity parameters and derive the orbit of LEO satellite. Antenna phase center variation (PCV) is estimated with carrier phase residuals of IF combination. GPS precise orbits, clock and phase bias products provided by Center for Orbit Determination in Europe (CODE), Centre National d’Etudes Spatiales (CNES) and Wuhan University (WHU) are used to perform the single receiver ambiguity resolution and precise orbit determination. The performance of ambiguity resolution and orbit accuracy related to the different products is analyzed. In-flight antenna PCV correction can effectively reduce the carrier phase residuals and improve the orbit accuracy, especially the along-track orbit accuracy. With products from different institutions, the fixing rates of wide-lane and narrowlane ambiguities are better than 99% and 95%. Compared with the precise orbit generated by Jet Propulsion Laboratory (JPL), the one dimensional accuracy of GRACE-FO’s orbit determined with single receiver ambiguity resolution is better than 7. 0 mm. RMSs of SLR residuals for GRACE-FO orbits generated with CODE, CNES and WHU’s products are 9. 6, 10. 7 and 9. 1 mm. Standard deviations (STDs) of the independent K-band range (KBR) residuals for the three kinds of orbits are 1. 8, 2. 3 and 2. 1 mm respectively. The overall difference of GRACE-FO orbits calculated with different products is less than 2 mm.