固定模糊度的精密单点定位几何定轨方法及结果分析

Kinematic Precise Orbit Determination Based on Ambiguity-Fixed PPP

传统的基于PPP(precise point positioning)模式的定轨方法采用浮点解,导致其定轨精度及可靠性较双差固定解稍差。为了进一步提高PPP模式事后定轨的精度和可靠性,利用2012年1月2～7日全球IGS跟踪站数据计算出当天所有卫星的宽巷和窄巷FCB产品,实现了GRACE卫星固定PPP整数模糊度的精密定轨。并将定轨结果分别与GFZ事后精密轨道、K波段测距结果进行比较,分析其内外符合精度。实验结果表明:与GFZ提供的事后精密轨道相比,GRACE-A卫星单天轨道固定解的精度为R方向2～3cm,T方向大部分优于2cm,N方向优于2cm,较之浮点解的定轨结果3个方向分别改善了约19%、30%、50%;GRACE-B卫星3个方向精度分别为2～3cm、2cm左右、1～2cm,较之浮点解各方向也有同等程度的改善。与K波段测距结果相比,浮点解的KBR残差STD均值为22.6mm,固定解为16.4mm,比浮点解提高了约28%。可见,PPP模糊度固定解明显改善了低轨卫星的定轨精度,能提供更可靠的轨道服务。

With the development of space-borne GPS technologies and IGS precise orbit and clock products, precise orbit determination （POD） of Low Earth Orbiters （LEOs） based on PPP technology has become a hot issue. At present, an accuracy of 3~5 cm in Radial（R）, Along-track（T）, Cross-track（N） components can be achieved with conventional PPP. How- ever, the results are less precise or reliable than the double-differenced fixed solution due to the ambiguity-float solution in traditional PPP. In order to further improve the precision and reliability of POD with PPP, daily observations from all IGS tracking stations through day 2 to 7 in 2012 were used to estimate the wide and narrow-lane fractional cycle bias （FCB） of all satellites for PPP integer ambiguity resolution. The POD of the two GRACE satellites were respectively compared with GFZ^s post precise orbit and K-band measurements for the analy- sis of the inner and external conformities. As compared to GFZ, the daily orbital accuracy of the ambiguity-fixed solution in this work is about 2~3 cm in R direction, better than 2 cm in T direction and better than 2 cm in N direction for GRACE-A, an improvement of 19%, 30% and 50% respectively when compared with that of the float solution. The POD preci- sion for GRACE-B are 2-3 cm, 2 cm and 1-2 cm in R, N, T directions for the fixed solution, respectively. The accuracy improvement in the fixed solution for GARCE-B is nearly equiva- lent with that for GRACE-A. For K-band cases, the mean STD error of KBR residual is a- bout 16.4 mm for the fixed solution, and 22.6 mm for the float solution. These results show that PPP with ambiguity-fixed can greatly improve POD precision of LEO satellites and pro- vide more reliable orbital service.