Precise GRACE baseline determination using GPS

Precision relative navigation is an essential aspect of spacecraft formation flying missions, both from an operational and a scientific point of view. When using GPS as a relative distance sensor, dual-frequency receivers are required for high accuracy at large inter-satellite separations. This allows for a correction of the relative ionospheric path delay and enables double difference integer ambiguity resolution. Although kinematic relative positioning techniques demonstrate promising results for hardware-in-the-loop simulations, they were found to lack an adequate robustness in real-world applications. To overcome this limitation, an extended Kalman Filter modeling the relative spacecraft dynamics has been developed. The filter processes single difference GPS pseudorange and carrier phase observations to estimate the relative position and velocity along with empirical accelerations and carrier phase ambiguities. In parallel, double difference carrier phase ambiguities are resolved on both frequencies using the least square ambiguity decorrelation adjustment (LAMBDA) method in order to fully exploit the inherent measurement accuracy. The combination of reduced dynamic filtering with the LAMBDA method results in smooth relative position estimates as well as fast and reliable ambiguity resolution. The proposed method has been validated with data from the gravity recovery and climate experiment (GRACE) mission. For an 11-day data arc, the resulting solution matches the GRACE K-Band Ranging System measurements with an accuracy of 1 mm, whereby 83% of the double difference ambiguities are resolved.     

卫星重力测量数据处理软件系统的设计

介绍了自主开发的卫星重力测量数据处理软件GRASTAR,给出了该软件的整体设计框架和功能。该软件主要采用动力学法实现,应用CHAMP卫星和GRACE卫星的观测数据反演地球重力场模型。利用模拟方法验证了该软件的正确性,并利用GRASTAR处理了126 d的CHAMP卫星数据,解算出直到40阶次重力场模型的初步结果。     

Short-arc analysis of intersatellite tracking data in a gravity mapping mission

 A technique for the analysis of low–low intersatellite range-rate data in a gravity mapping mission is explored. The technique is based on standard tracking data analysis for orbit determination but uses a spherical coordinate representation of the 12 epoch state parameters describing the baseline between the two satellites. This representation of the state parameters is exploited to allow the intersatellite range-rate analysis to benefit from information provided by other tracking data types without large simultaneous multiple-data-type solutions. The technique appears especially valuable for estimating gravity from short arcs (e.g. less than 15 minutes) of data. Gravity recovery simulations which use short arcs are compared with those using arcs a day in length. For a high-inclination orbit, the short-arc analysis recovers low-order gravity coefficients remarkably well, although higher-order terms, especially sectorial terms, are less accurate. Simulations suggest that either long or short arcs of the Gravity Recovery and Climate Experiment (GRACE) data are likely to improve parts of the geopotential spectrum by orders of magnitude. Received: 26 June 2001 / Accepted: 21 January 2002     

Comparison of present SST gravity field models

IntroductionSince 2000 , with the launch of CHAMP satellite,several series of high-accuracy and high-resolutionstatic Earth’s gravityfield models have been createdbased on aboundent SST data. With these models ,the research in solid geophysics ,oceangraphy,andgeodesy can be promoted greatly[1].In this paper ,the SSTgravity models’accura-cyin various frequently domainis studied.First-ly,the difference among these models is compu-ted and compared,and then their accuracyis an-alyzed. Fina…     

不同Mascon模型解比较分析

简要介绍不同机构发布的Mascon模型解数据,并在全球和区域尺度上对Mascon模型解、球谐系数法以及GLDAS水文模型陆地水储量变化计算结果进行对比分析。结果表明,不同Mascon模型解具有较好的一致性;与球谐系数法反演结果相比,Mascon模型解能提高反演结果信噪比值,空间分辨率更高,保留更多有效信号,与GLDAS水文模型结果相关性更好;不同Mascon模型解中,JPL Mascon模型解信噪比值最大,与GLDAS水文模型时间序列相关性最好。     

中国西部区域GRACE卫星重力变化

针对研究中国西部长期重力变化的问题,该文利用GRACE月重力场模型,基于Slepian变换构建中国西部区域局部重力场,并采用GIA和GLDAS等模型扣除相应误差,通过时间序列分析方法得到该区域2003—2013年卫星重力变化。结果表明,东天山呈现负重力变化,可能由区域冰川消融引起的;西天山的正重力变化,应与冰川小幅增加和构造运动引起的壳幔物质积累有关;青藏高原内陆正重力变化可能由区域地壳抬升、粘弹性地壳的构造应变以及壳幔物质的质量迁移与积累引起;青藏高原边界区域的负重力变化,应与冰川加速消融以及地下水抽取有关。Slepian方法较好地克服了滤波平滑处理带来的重力变化信号压制及细节平滑,可为中国西部的地壳运动、地震活动和气候变化等研究提供数据支撑。     

基于经验正交函数分解的GRACE时变地球重力场滤波处理

针对传统GRACE去相关滤波方法很难同时完美实现真实信号的保留与条带误差的削弱等问题,提出将经验正交函数滤波与去相关滤波相结合的改进策略。分别对真实GRACE数据和模拟数据进行滤波处理,结果表明,改进的滤波方法继承了经验正交函数滤波方法与去相关滤波方法的优点,能够在尽可能地削弱南北条带误差影响的同时,最大程度地保留真实地球物理信号。     

基于改进的主成分分析法提取GRACE时变重力场信号

针对主成分分析法提取时变重力场模型信号中存在信号泄漏和去条带噪声不明显的问题,提出对球谐位系数主成分分析的改进方法。首先对球谐位系数进行主成分分析,提取主要的模态,再对不同模态根据其自身噪声特点选择合适的滤波方法和参数,最后在此基础上进行信号提取。以CSR发布的2005-01~2013-12(108个月)GRACE时变地球重力场模型进行实验,提取2006-06和2006-12等效水高数据和改进前的主成分分析进行比较,表明此方法在有效地剔除条带误差的同时又使得信号泄漏减小。     

基于GRACE卫星重力数据估计格陵兰岛冰盖质量变化

重力场恢复与气候试验（GRACE）卫星为高分辨率地监测全球冰川质量变化提供了一种新的手段。本文利用2003年1月至2014年12月Level-2 RL05的GRACE产品,进行去相关误差滤波、高斯滤波和海洋-陆地信号泄漏改正后,得到了格陵兰岛冰盖质量变化的时间序列,分析了格陵兰岛冰盖质量变化的长期趋势项,并与ICESat的结果进行了比较验证。研究表明,在2003年1月至2014年12月之间,格陵兰岛冰盖质量减小速率约为（-260±43）Gt/a,对全球海平面的贡献约为（0.72±0.12）mm/a,对同时期海平面上升的贡献占25.8%,并且格陵兰岛冰盖消融有着很强的区域差异性,冰盖消融的区域主要集中在边缘区域,中部内陆地区的冰盖质量则有增加的趋势。并进一步和ICESat的结果进行了比较分析,ICESat的结果显示格陵兰岛冰盖质量减小速率约为（-174±43）~（-184.8±28.2）Gt/a,而GRACE的结果则为（-209.4±26.3）Gt/a,有着较好的一致性,并且区域分布特征也符合较好。     

利用GRACE及气象数据评估GLDAS水文模型在青藏高原的适用性

以青藏高原地区为研究背景,以评估水文模型在该区的影响因素、改善条件及其整体适应性为研究目标,利用GRACE重力卫星对比水文模型模拟的陆地水变化,以及地面气象实测数据对比降雨与温度两项重要指标,采用相关与误差分析法评价水文模型输入参数,将其作为模型预测数据与实际观测数据进行对比分析。结果表明,GLDAS/Noah各项指标与GRACE更为相近,降雨与气温数据除夏冬两季存在幅值差异外,整体上周年幅值与相位都存在较高NSE系数,表明GLDAS模型的降雨及气温输入参数与地面观测数据有较高的一致性。