Precise orbit determination of Haiyang-2 using satellite laser ranging

With the successful launch and official commissioning of China’s first dynamic ocean environment satellite Haiyang-2(HY-2),China’s capabilities for oceanic environment monitoring and oceanic resource detecting have been further improved and enhanced.Precise tracking and orbit determination are not only key technical concerns in the ocean dynamic environment satellite project but also necessary conditions for carrying out related oceanic science research using observational data obtained using spaceborne instruments including radar altimeter.In this study,the current available status of international satellite laser ranging(SLR) monitoring on HY-2 was introduced.Six-months of SLR data from HY-2 were processed to obtain precise satellite orbit information using the dynamic orbit determination method.We carried out a detailed assessment of the SLR orbit accuracy by internal evaluation,comparisons with the orbit derived by the French Doppler orbitography and radio-positioning integrated by satellite(DORIS) system,and station-satellite distance validation.These assessments indicate that the three-dimensional orbital accuracy of HY-2 is about 12.5 cm,and the radial accuracy is better than 3 cm.It provides a good example of the application of international SLR monitoring and precise orbit determination in China’s earth observation satellite project.     

Precise orbit determination for Jason-1 satellite using on-board GPS data with cm-level accuracy

The joint US/French Jason-1 satellite altimeter mission, launched from the Vandenberg Air Force Base on December 7, 2001, continues the time series of centimeter-level ocean topography observations as the follow-on to the highly successful T/P radar altimeter satellite. Orbit error especially the radial orbit error is a major component in the overall budget of all altimeter satellite missions, in order to continue the T/P standard of observations. Jason-1 has a radial orbit error budget requirement of 2.5 cm. In this work, two cycles (December 19, 2002 to January 7, 2003) of the Jason-1 on-board GPS data were processed using the zero-difference (ZD) dynamic precise orbit determination (POD) technique. The resulting Jason-1 orbit accuracy was assessed by comparison with the precise orbit ephemeris (POE) produced by JPL, orbit overlaps and SLR residuals. These evaluations indicate that the RMS radial accuracy is in the range of 1－2 cm.     

JASON-2卫星精密轨道确定：GPS，SLR和DORIS分析

本文针对GPS,SLR和DORIS3种观测手段的定轨问题进行了研究．以JASON-2卫星为例,讨论了GPS,SLR和DORIS的定轨策略、轨道精度评价和轨道叠加问题．并基于2009-01-21—25日实测数据进行了试验．试验结果表明,DORIS定轨结果要优于GPS和SLR;不同的轨道验证方法得到的GPS和SLR轨道的相对精度不同;基于SLR验证和轨道重叠验证的结果定权,综合GPS,SLR和DORIS进行轨道叠加,其叠加轨道的精度是一致的,通过与JPL轨道比较,其径向精度为2cm．     

Satellite SAR interferometric observations of displacements associated with urban subsidence in Suzhou, Eastern China

SAR interferometry (InSAR) has a high potential for surface displacement mapping in the range from millimeter to meter. In this paper the potential of ERS-1/2 SAR interferometry for mapping subtle land subsidence has been investigated. A time series of ERS-1/2 SAR data from February 1993 to February 2000 is collected from measurements taken in Suzhou city, Jiangsu Province, China, eight ERS-1/2 SAR images are used to create seven interferograms, and three differential interferograms are produced using the three-pass method, which clearly show the spatial extent of land subsidence. The deformation maps are validated by leveling surveys, the correlation coefficient and standard deviation between them are 0.943 and 0.1706 respectively. Based on seven benchmarks, the subsidence rates are estimated, the overall trends are in close agreement with InSAR results. The results of study show that for the mapping of land subsidence in urban environments InSAR has a strong potential due to its cost-saving, high resolution and accuracy.     

Zero-difference and single-difference precise orbit determination for LEO using GPS

Various methods for precise orbit determination (POD) of low earth orbiters (LEO) are briefly intro-duced in this paper. Based on the software named SHORD-Ⅲ developed by our institute,sin-gle-difference (SD) and zero-difference (ZD) dynamic POD based on LEO carrying an on-board GPS receiver is mainly discussed. The approaches are tested using real GRACE data (November 5―25,2002) and independently validated with Satellite Laser Ranging (SLR) measurements over the same 21 days. Comparisons with the scientific orbits provided by GFZ indicate that the SD POD RMS accuracy can achieve 5,10 and 6 cm in radial,along and cross the track,and the ZD POD RMS accuracy can achieve 4,8 and 4 cm in radial,along and cross the track. SLR validation shows that SD POD accuracy is better than 8 cm in distance,and ZD POD accuracy is better than 6 cm.     

Earthquake monitoring in australia using satellite radar interferometry

Are there any earthquakes in Australia? Although most Australians are not as familiar with earthquakes as citizens in countries such as Japan, there are some quakes on the Australian continent every year. Differential Synthetic Aperture Radar Interferometry (DInSAR) has been widely used in recent years for monitoring crustal deformation due to earthquakes, volcanoes, underground mining, oil extraction, and so on. Hence the follow-on question is, can repeat-pass satellite DInSAR be used in Australian regions to monitor earthquakes? Nine ERS-1 and ERS-2 radar images of the Burakin region in Western Australia were used to form the InSAR pairs. Twenty-two InSAR pairs were formed and were used to study the temporal decorrelation characteristics in the Burakin area. It was found that good coherence could be maintained all over the full scene for a pair spanning 211 d. The repeat cycles of RADARSAT and ERS (all C-band SAR missions) are 24 and 35 d respectively, Furthermore it is easier to maintain good coherence in L-band SAR images (e.g. the JERS-1 mission has a 44 d repeat cycle). Therefore the authors are confident that repeat-pass differential InSAR can be used to monitor ground deformation due to earthquakes in the Burakin region.     

卫星姿态对JASON-2卫星精密定轨影响分析

针对因姿态不稳定性对轨道的影响而难以评估的问题, 详细讨论了卫星的姿态模型, 推导了卫星姿态变化对观测值影响的解析表达式。模拟试验结果表明, 随着姿态不稳定性加剧, 轨道精度随之急剧下降, 另一方面姿态不稳定会随坐标轴不同而对轨道精度产生不同影响。为获得高精度的卫星轨道, 需要卫星姿态稳定性满足一定的要求, 尤其是相位中心偏大的坐标轴方向, 以JASON-2为例, 姿态在轴向变化必须稳定在2°内。基于JASON-2实测姿态计算表明, 该卫星姿态稳定性处在1°左右, 对轨道精度影响为0.036 m。该模拟实验方法为评估姿态稳定性对卫星精密轨道的影响提供了有效的方法。     

PANDA software and its preliminary result of positioning and orbit determination

PANDA (Position And Navigation Data Analyst) software is designed for data analysis of different satellite positioning and navigation systems, such as SLR, GPS and the future GALIEO.The software has being developed since 2000 at GPS Research Center of Wuhan University. A brief introduction of the software and its developing progress are given at first, and then the results of static positioning and GPS satellite orbit determination archived with PANDA are presented in this paper.     

卫星轨道完备性监测研究

为了解决高精度定位中的卫星轨道粗差判别问题,采用轨道积分方法和轨道拟合方法,重点分析了卫星精密星历SP3文件的轨道积分精度,利用对卫星轨道加入不同粗差的计算方案,讨论了轨道积分的精度以及其对定位的影响,研究了利用卫星轨道积分精度实现完备性监测的方法。结果表明:通过卫星轨道积分精度的方法,可以反映卫星的粗差信息并予以将粗差卫星剔除;当剔除粗差卫星后,精密单点定位精度提高;当对正常卫星加入粗差,且随着加入粗差的增大,卫星轨道积分精度越来越差。该成果对完备性监测的研究具有一定的参考价值和指导意义。     

基于导星电子星图模拟器的卫星控制系统半物理试验方法

为了实现卫星的高精度高稳定度控制,中法天文卫星建立了卫星姿轨控半物理仿真试验系统.对该系统采用导星电子星图模拟器引入仿真闭环进行研究.首先,将导星敏感器作为高精度姿态测量部件引入控制系统,地面动力学为其提供输入信息.接着,高精度测量单机和高精度控制机构引入到闭环中.然后,粗测量敏感器和粗控执行机构由数学模型替代.最后,通过地面实时系统将控制系统、星务计算机、载荷计算机和整星电源系统组成了实时仿真验证系统.实验结果表明:在地面半物理条件下,可以达到导星进入开小窗条件,y、z轴稳定度达到2(″)/10 s及5(″)/100 s.导星敏感器可以提高姿态测量精度和姿态控制的稳定度.满足控制稳定度在亚角秒级别卫星的要求.     

北斗卫星整网集中式自主定轨算法研究

由于分布式定轨算法只能得到局部次优解,为进一步提升北斗卫星自主导航算法精度,对北斗卫星整网 集中式定轨算法在轨实现方法进行研究。设计了基于推广卡尔曼滤波算法的整网集中式定轨算法及其在轨实 现流程,并利用北斗卫星上的龙芯1E300 处理器对算法精度及工程可行性进行了评估。仿真结果表明,整网集 中式算法精度优于分布式导航算法。且通过在龙芯1E300 处理器上仿真验证可知,集中式导航算法已具备星 上使用条件。     

基于TLE数据的空间目标EDR分类及观测需求计算

根据能量耗散率（EDR）的定义及空间目标的大气阻力摄动加速度公式,推导出一种由卫星两行根数（TLE）数据计算空间目标EDR的方法. 该方法无需计算空间目标弹道系数和大气模型,EDR计算误差可在1%以下,并且运算量极小. 此外,通过空间目标相对轨道的协方差矩阵描述空间目标的定轨精度,并结合扩展卡尔曼滤波方程,提出一种计算平面轨道下不同EDR空间目标的定轨精度-观测需求曲线的方法. 仿真验证了EDR计算方法的有效性,并给出了雷达对不同EDR分类的目标观测时对应的定轨精度-观测需求曲线. 结果表明当观测稀疏时,目标轨道预报误差正比于EDR,而观测较多时,会有观测饱和现象.      

Variation of satellite transponder delay

For precise orbit determination of geosynchronous earth orbit(GEO)satellites using transfer ranging observations,it is generally assumed that the variation of the satellite transponder delay is very small and that it can be solved as a constant parameter together with satellite orbit parameters.However,this assumption is too general and it reduces the accuracy of orbit determination for GEO satellites.To study and analyse the impact of the satellite transponder delay on GEO satellites orbit determination,two schemes were proposed.First,the satellite transponder delay was eliminated by forming single-difference observations between two ground stations;second,the satellite transponder delay was described as a constant parameter.The preliminary results demonstrate a difference of about1–2 m between the two schemes when used for precise orbit determination of GEO satellites.By fixing the GEO satellite orbit and other relevant parameters estimated by single-difference model,we inversed the instantaneous transponder delay from non-difference observation.It was found that the satellite transponder delay has a distinct diurnal variation,with an amplitude of 3–4 m.The findings of this paper are helpful in establishing an accurate model of satellite transponder delay and in improving the accuracy of GEO satellites orbit determinations and predictions.     

GEO导航卫星多种观测资料联合精密定轨

针对跟踪站少、观测几何条件差以及轨道机动后GEO导航卫星精密定轨问题,提出了用激光观测数据解算无线电测距离观测数据设备时延、用CODE模型参数和多频载波相位数据进行电离层延迟精确修正的精密定轨和轨道快速恢复的处理体制.通过在轨实测数据实验证明,利用激光标定的距离观测数据组合设备时延精度优于1ns;基于3站观测数据GEO卫星精密定轨结果,RMS为0.25m;24h数据定轨结果重叠12小轨道径向互差0.55m,位置互差约1.62m;预报12h轨道重叠弧段互差为径向3.63m,位置互差8.51m;定轨结果与激光比对残差约0.10m,预报2h轨道比对残差约0.18m,预报24h轨道比对残差约2.04m.GEO卫星轨道机动后2～3h,动力学定轨结果能够恢复到与激光比对残差小于1m、与精密定轨结果比对位置互差约30m的水平.试验及分析结果表明,所提出的GEO精度定轨技术方案可靠、稳定.     

Improved threshold retracker for satellite altimeter waveform retracking over coastal sea

Data quality is a key factor for the application of satellite altimetry to geodesy and oceanography. Accuracy of altimetry is limited in the coastal area because the altimeter waveforms are seriously contaminated by topography and environmental pollution. So waveform retracking is needed to compute the range correction of geophysical data records (GDRs) for better accuracy. In this paper, a new waveform retracker named the improved threshold retracker (ITR) is put forward. The retracker first builds sub-waveforms based on leading edges detected in a waveform, then determines the middle point of each leading edge to compute the retracking range correction, finally calculates the referenced sea surface heights according to the geoid undulation from a local geopotential model and tide heights from an ocean tide model, and compares it with all retracking ranges to determine the best one. As a test, altimeter waveforms of Geosat/GM are retracked around the Taiwan coastal area. The result shows that accuracy of ITR method is two times better than that of the β-5-parameter function-fitting method and threshold method, and three times better than that of GDRs. ITR can efficiently improve the altimetry accuracy of the coastal sea area.     

Satellite orbit determination by transfer with differenced ranges

The original idea of orbit determination called "determination of satellite orbit by transfer" was proposed by the National Time Service Center,Chinese Academy of Sciences.It shows that the system is very stable and the orbit determination accuracy is improved greatly.A new observation mode called "differenced ranges between master station and slave stations by transfer" is introduced.It is the development of "determination of satellite orbit by transfer".In principle,the differenced ranges between master station and slave stations have a high angular resolution,and strongly constrains in the transverse direction of satellite orbit,perpendicular to the line-of-sight.The principle of "differenced ranges between master station and slave stations by transfer" is discussed in detail.And differenced ranges in combination with ranging data were used to determine satellite’s orbit and orbit prediction under different arc observations.It shows that orbit determination accuracy for orbit prediction can be improved with differenced ranges in combination with ranging data.     

太阳能电池阵的功率预测

为实现卫星太阳能电池阵的功率预测,在工程上常用太阳能电池的单指数等效电路模型的基础上,考虑了串联电阻,提高了I-V特性方程模型精度。利用某地球同步卫星在轨6年的太阳能电池阵的输出功率数据,求出了太阳能电池阵在卫星寿命过程中每年的衰减因子,代入功率预测模型,预测结果表明,预测精度可以满足工程上的要求。该功率预测模型适用于其他同类型地球同步轨道卫星的太阳能电池阵的功率预测。     

一种基于模型转换的GLONASS历书预报算法

通过对GLONASS历书预报算法的研究,提出了一种基于模型转换的GLONASS历书预报算法. 该算法采用最小二乘估计方法将一天内的GLONASS卫星精密轨道数据拟合成一组轨道根数,采用建立的历书转换模型将该组轨道根数转换成GLONASS历书参数. 采用STK(satellite tool kit)软件产生的精密轨道数据对该算法进行了验证. 同时将该算法应用于GLONASS导航信号模拟器并用JAVAD 112T商用接收机进行长时间的实测. 结果表明,该算法简便、有效且准确度高,完全满足导航用户对历书预报精度的需求.      

用于地空通信的单轨小卫星组网轨道特性研究

提出了采用小卫星组网的方法来解决战斗机超视距通信问题。为实现某一局部区域的超视距通信保障，提出并设计了单轨道小卫星组网方案，多颗小卫星单轨道组网实现简单，只要数量足够多，就能够实现对局部区域的连续通信覆盖，满足对局部区域作战的超视距通信需要；研究了单颗小卫星的在不同高度时覆盖范围半径、覆盖区域与地心的夹角等特性；研究了小卫星组网时，在轨道高度为780 km，不同数量的小卫星组网通信宽度、相临小卫星覆盖范围的重叠宽度和夹角等特性。     

Satellite orbit determination combining C-band ranging and differenced ranges by transfer

The constraint in the transverse direction of satellite orbit with differenced ranges between master station and slave stations by transfer as an angular observation data is explained in theory. Differenced ranges in combination with C-band ranging by transfer were used in satellite orbit determination. The position error of overlapped orbit differences for combining is less than that for ranging only. The residual of predicted orbit forward 5.5 days for combining is 3.1762 m, while the residual for ranging only with the same duration is 3.5380 m. Both the orbital overlapping and orbit prediction experimentations can testify the constraint in the transverse direction of satellite orbit with differenced ranges, and the results show that the accuracy of orbit determination and orbit prediction is improved by combining differenced ranges and C-band ranging.