GIM在LEO卫星单频GPS定轨中的应用

电离层延迟误差是单频GPS(Global Positioning System)数据最主要的误差源,为提高基于单频GPS数据的LEO(Low Earth Orbiting)卫星定轨精度,必须消除/减弱GPS观测数据中电离层延迟影响.研究了全球电离层模型GIM(Global IonosphericMaps)在基于单频GPS伪距数据的低轨卫星运动学和动力学定轨中的应用,并通过估算电离层尺度因子的方法消除C/A码伪距观测量中电离层延迟影响.由于LEO卫星星载GPS信号受电离层延迟影响与卫星轨道高度相关,选取了轨道高度在300～800 km的CHAMP(CHAllenging Mini-satellite Payload)、GRACE(Gravity Recovery AndClimate Experiment)、TerraSAR-X及SAC-C等LEO卫星C/A码伪距观测量作为试算数据.CHAMP等卫星实测数据计算结果表明:以JPL(Jet Propulsion Laboratory)发布的GIM模型作为背景模型,通过电离层比例因子法能很好地消除C/A码伪距观测量中电离层延迟影响,提高LEO卫星运动学和动力学定轨精度,其中,CHAMP卫星轨道最低,受电离层延迟影响最严重,定轨精度提高最显著,分别为55.6%和47.6%;SAC-C卫星轨道高度最高,受电离层延迟影响最小,相应的定轨精度提高幅度也最低,分别为47.8%和38.2%.

The Application of GIM in Precise Orbit Determination for LEO Satellites with Single-frequency GPS Measurements

With the availability of precise GPS ephemeris and clock solution,the ionospheric range delay is left as the dominant error sources in the post-processing of space-borne GPS data from single-frequency receivers.Thus,the removal of ionospheric effects is a major prerequisite for an improved orbit reconstruction of LEO satellites equipped with low cost single-frequency GPS receivers.In this paper,the use of Global Ionospheric Maps(GIM) in kinematic and dynamic orbit determination for LEO satellites with single-frequency GPS measurements is discussed first,and then,estimating the scale factor of ionosphere to remove the ionospheric effects in C/A code pseudo-range measurements in both kinematic and adynamia orbit defemination approaches is addressed.As it is known the ionospheric path delay of space-borne GPS signals is strongly dependent on the orbit altitudes of LEO satellites,we selected real space-borne GPS data from CHAMP,GRACE,TerraSAR-X and SAC-C satellites with altitudes between 300 km and 800 km as sample data in this paper. It is demonstrated that the approach of eliminating ionospheric effects in space-borne C/A code pseudo-range by estimating the scale factor of ionosphere is highly effective.Employing this approach,the accuracy of both kinematic and dynamic orbits can be improved notably.Among those five LEO satellites,CHAMP with the lowest orbit altitude has the most remarkable orbit accuracy improvements,which are 55.6%and 47.6%for kinematic and dynamic approaches,respectively.SAC-C with the highest orbit altitude has the least orbit accuracy improvements accordingly,which are 47.8%and 38.2%,respectively.