利用Bernese5.0软件实现LEO卫星精密定轨

越来越多的LEO卫星装载了高精度的星载GPS接收机,星载GPS定轨已成为LEO卫星精密定轨的重要手段之一。星载GPS精密定轨精度依赖于GPS星历及钟差精度,采用CODE(Center for Orbit Determination in Europe)官方网站提供的GPS精密星历及钟差数据,基于瑞士伯尼尔大学开发的Bernese 5.0软件,采用非差减缩动力学定轨方法,解算了60天的CHAMP卫星和SAC-C卫星轨道,并将所得轨道与JPL和GFZ事后科学轨道比较,得出的轨道位置三维精度优于20 cm量级,速度三维精度约为0.20 mm/s。     

抗差估计在星载GPS卫星非差运动学定轨中的应用

针对星载GPS卫星非差运动学定轨的特点,提出将抗差估计应用于星载GPS卫星运动学定轨,一方面尽量保留来自每颗GPS卫星的观测值,保持较强的卫星几何强度,避免轨道求解出现奇异;另一方面,采用等价权思想,有效地降低质量较差的观测值对定轨结果的影响,保证定轨精度．还采用CHAMP卫星的实测GPS数据验证了新方案的可行性和有效性．     

星载GPS相位观测值非差运动学定轨探讨

在几何法、动力学法和减缩动力学法定轨基础上，探讨了星载GPS相位观测值非差运动学定轨方法及其实现程序。该方法无需复杂的力学模型和地面资料，只需LEO(Low Earth Orbit)卫星上的GPS数据和IGS的GPS精密星历产品，它计算简单、方便，能快速、高精度地确定轨道，同时，还能确定一些动力学参数，但没有轨道预报功能；针对法方程系数矩阵比较庞大，提出了矩阵分块、上三角化的参数解算方法，并用CHAMP卫星资料分析了上述方法的定轨精度。     

LP估计在星载GPS运动学定轨中的应用及精度分析

为得到高精度的星载GPS运动学定轨,必须利用观测精度高的相位观测值,但是相位观测值预处理后,仍然存在残余小周跳．在残差服从正态分布情况下LS法是最佳参数解算方法,但该方法不能解决资料的系统误差消除问题,LP估计是处理资料残差分布含有系统误差的有效方法之一．基于LS、LP方法的有效条件和GPS数据预处理的特性,将LP估计方法引入星载GPS运动学定轨数据处理中,以CHAMP卫星资料为例,研究了LP估计在星载GPS运动学定轨中的应用及其精度分析．实践表明:在处理含有残余小周跳的相位观测值时,LP估计比LS更有效,提高了星载GPS运动学定轨精度,但随着残余周跳的进一步修复,LP估计相对于LS估计的优越性越来越弱,在资料完全没有系统误差,残差服从正态分布的情况下,LP估计不能很好地体现其优越性,精度反而低于LS估计．     

小倾角LEO多星天基平台光学跟踪GEO精密定轨

针对地基卫星测控系统(Tracking Telemetry and Command, TT&C)系统对地球静止轨道(Geostation-\lk ary Earth Orbit, GEO)卫星在空间和时间覆盖上的局限性, 提出小倾角低地球轨道(Low Earth Orbit, LEO)多星组网天基平台对GEO卫星进行跟踪定轨的方法. 根据空间环境和光学可视条件对仿真数据进行筛选以模拟真实的观测场景, 利用光学测角数据, 使用数值方法对GEO卫星的轨道进行确定. 结果与参考轨道进行重叠对比, 在平台轨道精度5 m、测量精度5rq\rq、 定轨弧长12 h的情况下, 两颗LEO卫星对GEO卫星进行跟踪定轨的精度可达到千米量级, 4颗LEO卫星对GEO目标进行跟踪定轨的精度可达到百米量级. 随着LEO组网卫星数量的增加, 定轨精度得到了较大的提高.     

星载单频GPS接收机低轨卫星几何法定轨研究

讨论星载ＧＰＳ接收机为单频情形的低轨卫星几何法定轨,包括绝对定轨法,相对定轨法和动态网定轨法,并利用ＴＯＰＥＸ／ＰＯＳＥＩＤＯＮ卫星星载ＧＰＳ实现Ｌ１观测值进行验证。结果表明,绝对定轨法三维轨道位置精度可达２０ｍ左右,适用于低轨卫星实时导航;相对定轨和动态网定轨精度均比绝对定轨精度高,伪距相对定轨三维轨道位置精度可达米级,载波相位相对定轨精度可达分米级;动态网定轨相当于在各基准站相对定轨之间加权均     

GPS星历对LEO星载GPS精密定轨精度的影响

目前,越来越多的低轨卫星上都搭载了用于精密定轨的星载GPs接收机,星载GPS已成为低轨卫星精密定轨的主要手段之一.星载GPS精密定轨精度依赖于GPS星历及钟差精度.基于SHORDE-Ⅲ非差动力学定轨功能,以2005年8月1日至8月7日一周的GRACE卫星实测数据为例,采用事后精密轨道(igs)、快速轨道(igr)和超快速轨道(igu)三种GPS星历在同等条件下定轨,估计GPS星历精度对低轨卫星定轨精度的影响,实际计算结果表明igs和igr两类GPS星历定轨精度相当,约为9.5 cm,igu星历定轨精度略低于igs和igr星历,约为10.5cm:高频GPS卫星钟差数据对定轨精度会产生1-6cm影响.     

基于双频星载GPS数据的LEO卫星运动学定轨研究

运动学定轨是星载GPS特有的定轨方法,该方法不依赖于任何力学模型(地球重力场、大气阻力及太阳辐射压等),尤其适用于受大气阻力影响严重的低轨卫星定轨.基于双频星载GPS数据,研究了运动学定轨原理,讨论了数据预处理方法,建立了一套非差运动学定轨算法.并以GRACE (Gravity Recovery And Climate Experiment)-A、B卫星2008年2月实测数据作为试算验证了本研究方法的有效性和可靠性.GRACE 卫星实测数据计算结果表明:运动学定轨能达到5 cm精度(相对于SLR (Satellite Laser Ranging)),与动力学和简化动力学定轨精度相当.     

静态测量型GPS接收机的研制及其性能

静态测量型GPS接收机系统由8通道、单频ST-1接收机和静态后处理软件两部分组成,通过跟踪测量卫星载波信号、测距码信号及数据码(包含有星历数据)信号,获得伪距和载波相位观测值,采用差分(主要是双差)处理方法,达到精确测定两接收机天线间相对位置的目的.基线测量精度为10mm+2ppm×D.     

用非差分方法确定单颗导航卫星的轨道

在导航系统中有时需要对单颗导航卫星进行定轨.此时由于无法组成常用的同历元单差或双差以消除卫星钟差或接收机钟差,有必要发展新的定轨策略和精度分析.该文以GPS为例,讨论在不依赖于星站间时间同步的情况下,对单颗导航卫星进行精密定轨.首先分析了GPS卫星钟差以及GPS接收机钟差的特性,发现在一定间隔内钟差主要表现为线性变化,而在去除这一线性项后,非线性钟差在3 m以内.利用GPS的伪距对单颗卫星定轨,在将钟差的主要部分作为测距的偏差和偏差变化率后,伪距测量量等价于常见的测距测量量.在利用等价的测距测量量定轨时可同时解算出偏差和偏差变化率参数.为验证该方案的可行性及其定轨精度,利用实测GPS观测数据进行了试验.结果表明,此种定轨方案定轨的径向精度优于4 m.考虑到GPS接收机的频率信号是由普通的晶振产生的,如果地面接收机采用原子钟提供的频率标准,其钟差的非线性部分将更小.模拟计算表明,采用本方案可以期望得到更高的定轨精度.     

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

With the precise GPS ephemeris and clock error available, the iono- spheric delay is left as the dominant error source in the single-frequency GPS data. Thus, the removal of ionospheric effects is a ma jor prerequisite for an improved orbit reconstruction of LEO satellites based on the single-frequency GPS data. In this paper, the use of Global Ionospheric Maps (GIM) in kine- matic and dynamic orbit determinations for LEO satellites with single-frequency GPS pseudorange measurements is discussed first, and then, estimating the iono- spheric scale factor to remove the ionospheric effects from the C/A-code pseu- dorange measurements for both kinematic and dynamic orbit determinations is addressed. As it is known that the ionospheric delay of space-borne GPS sig- nals is strongly dependent on the orbit altitudes of LEO satellites, we select the real C/A-code pseudorange measurement data of the 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 to eliminating ionospheric effects in C/A-code pseudorange measurements by estimating the ionospheric scale factor is highly effective. Employing this approach, the accu- racy 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 improvements in orbit accuracy, which are 55.6% and 47.6% for kine- matic and dynamic orbits, respectively. SAC-C with the highest orbit altitude has the least improvements in orbit accuracy accordingly, which are 47.8% and 38.2%, respectively.     

Kinematic Precise Orbit Determination for LEO Satellites Using Space-borne Dual-frequency GPS Measurements

As a special approach to orbit determination for satellites with spaceborne GPS receivers, the kinematic Precise Orbit Determination (POD) is independent of any mechanical model (e.g., the Earth gravity ?eld, atmospheric drag, solar radiation pressure, etc.), and thus especially suitable for the orbit determination of Low Earth Orbiting (LEO)satellites perturbed strongly bythe atmosphere. In this paper, based on the space-borne dual-frequency GPS data, we study the kinematic POD, discuss the pre-processing of the data, and construct an algorithm of zero-difference kinematic POD. Using the observational data from GRACE (Gravity Recovery And Climate Experiment) satellites covering the whole month of February 2008, we verify the effectiveness and reliability of this algorithm. The results show that the kinematic POD may attain an accuracy of about 5 cm (with respect to satellite laser ranging data), which is at the same level as the dynamic and reduced-dynamic PODs     

Evaluation of LEO based GPS slant TEC using a simulation technique

With the increased number of low Earth orbit (LEO) satellites equipped with Global Positioning System (GPS) receiver, the LEO based GPS slant total electron content (STEC) data play a more important role in ionospheric research due to better global coverage. The accuracy of LEO TEC is hardly evaluated by comparison with the independent TEC measurement simultaneously. We propose an approach based on the simulated data to verify the accuracy of TEC determination. The simulated data (i.e., the pseudorange and carrier phase observations) was generated based on the consideration of the effect of the ionosphere, the so-called differential code bias (DCB) and observational noise. The errors of carrier phase to code leveling process and DCB estimation are analyzed quantitatively. Also, the effect of observational noise, solar activity and LEO orbit altitude on the accuracy of TEC determination will be discussed in detail. The accuracy of TEC determination is relative to solar activity and LEO orbit altitude, the higher LEO orbit and lower F10.7 index, the higher accuracy of TEC determination. It is found by the first time that, with the amplification of the pseudorange noise, the accuracy of leveling process and TEC determination declines almost linearly. With the LEO missions in the near future, it is hoped that the GPS satellite DCBs estimated based on LEO observations would be better than those based on ground-based observations.     

GPS掩星技术低轨卫星计划的现状及进展

主要介绍了几个国际上已经实施的GPS掩星计划（GPS／MET，Φrsted,Sunsat,SAC-C,CHAMP)和在研的（COSMIC，ACE）低轨卫星计划的现状及取得的进展。通过总结可知，下一代GPS掩星接收器应具有体积小、质量轻（几百克）、低功耗的特点；能提供实时的卫星物理状态参数；飞行器上的自主计算和控制；星上数据通信和命令解释；所有跟踪数据应符合厘米级精密定轨的要求；能提供掩星和海洋反射实验的测量。     

The Effect of GPS Ephemeris on the Accuracy of Precise Orbit Determination of LEO Satellite-borne GPS

The satellite-borne GPS receivers dedicated to precise orbit determination are now being carried by more and more low earth orbit (LEO) satellites and the satellite-borne GPS has become one of the main means for the precise orbit determination of low earth orbit satellites. The accuracy of satellite-borne GPS precise orbit determination depends on the accuracies of the GPS ephemeris and the clock error. Based on the orbit determination function of SHORDEIII zero-difference dynamics and using the observational data obtained by the GRACE satellites for the week from 2005 August 1 to 7 as an example, three versions of GPS ephemerides (igs, igr and igu) are used to carry out orbit determination under the same conditions and to estimate the effect of the GPS ephemeris accuracy on the accuracy of orbit determination of low earth orbit satellites. Our calculated results show that the two ephemerides, igs and igr, are equivalent to each other in orbit determination accuracy (about 9.5 cm), while igu is slightly less accurate, at about 10.5 cm. The effect produced by the data of the high frequency GPS satellite clock error on the accuracy of orbit determination is 1–6 cm.