风云三号C卫星星载GPS/BDS分米级实时定轨模型研究

Decimeter-Level Orbit Determination for FY3C Satellite Based on Space-Borne GPS/BDS Measurements

风云三号C(Fengyun 3C,FY3C)卫星于2013年发射,搭载了全球导航卫星掩星探测仪(GNSS occultation sounder,GNOS),是国际首台兼容GPS和北斗卫星导航系统(BeiDou navigation satellite system,BDS)的掩星探测仪,可同时提供GPS和BDS双频观测数据,为研究星载GPS/BDS组合定轨提供了机会。为了实现分米级精度的星载GPS/BDS组合实时定轨,首先推导了基于载波相位观测值的星载GPS/BDS实时定轨数学模型;然后重点分析了GPS与BDS广播星历误差的变化特性,对不同类型轨道的BDS广播星历误差在信号传播路径(location of signal,LOS)方向的投影进行统计,并以此为依据,建立载波相位观测值的伪模糊度待估参数及其随机模型,用来吸收LOS方向的广播星历误差,从而实现分米级精度的实时定轨。采用自主研制的实时定轨软件SATODS对FY3C卫星GPS/BDS实测数据模拟在轨实时处理,结果表明,在使用广播星历的条件下,基于星载GPS/BDS载波相位实时定轨,可以达到30 cm的位置精度以及0.3 mm/s的速度精度。加入BDS观测数据后,虽然BDS卫星的广播星历整体精度低于GPS,但是通过合理设置伪模糊度参数的随机模型,实时定轨结果相对于单GPS有了一定的提高,当FY3C卫星经过亚太地区上空时,实时定轨精度可提高10%以上。

The satellite Fengyun 3 C(FY3 C)launched in 2013 and carried a global navigation satellite system(GNSS)occultation sounder,which is the first BDS/GPS compatible radio occultation sounder in the world and records both GPS and BDS measurements.It provides an opportunity for investigating the precision realtime orbit determination based on space-borne GPS/BDS measurements.In order to realize the real-time orbit determination based on space-borne GPS/BDS measurements with decimeter-level accuracy,this paper carries out in-depth research in the following aspects.Firstly,the real-time orbit determination mathematical model based on the space-borne GPS/BDS carrier phase observations is introduced.Then the properties of the errors in the signal’s propagation path that originates from GPS/BDS broadcast ephemeris are analyzed,and the signal-in-propagation path error(SIPPE)statistics of different kinds of GPS/BDS satellites are also presented.Based on the analysis,a pseudo-ambiguity is modeled as a stochastic process and estimated in the real-time orbit determmination(RTOD)filter to absorb the SIPPE error,and then the decimeter-level accuracy can be realized.The space-borne GPS/BDS data from China’s FY3 C satellite are employed for the simulative RTOD test using the SATODS software.Results have demonstrated that the position and velocity accuracy of 30 cm and 0.3 mm/s,respectively,are achieved when using GPS/BDS carrierphase data and broadcast ephemeris.Although the accuracy of BDS broadcast ephemeris is obviously worse than that of GPS,orbit results of the GPS/BDS fusion solution with reasonable stochastic models for pseudo-ambiguities will be slightly superior to that using single GPS data.For example,when the FY3 C satellite flew over Asia/Pacific region where more BDS satellites can be tracked,the orbit accuracy can be improved by 10%with the GPS/BDS fusion solution.