Simulated estimation of hydrological loads from GRACE

Four different basin functions are developed to estimate water storage variations within individual river basins from time variations in the Stokes coefficients now available from the GRACE mission. The four basin functions are evaluated using simulated data. Basin functions differ in how they minimize effects of three major error sources: measurement error; leakage of signal from one region to another; and errors in the atmospheric pressure field removed during GRACE data processing. Three of the basin functions are constant in time, while the fourth changes monthly using information about the signal (hydrologic and oceanic load variations). To test basin functions performance, Stokes coefficient variations from land and ocean models are synthesized, and error levels 50 and 100 times greater than pre-launch GRACE error estimate are used to corrupt them. Errors at 50 times pre-launch estimates approximately simulate current GRACE data. GRACE recovery of water storage variations is attempted for five different river basins (Amazon, Mississippi, Lena, Huang He and Oranje), representing a variety of sizes, locations, and signal variance. In the large basins (Amazon, Mississippi and Lena), water storage variations are recovered successfully at both error levels. As the error level increases from 50 to 100 times, basin functions change their shape, yielding less atmospheric pressure error and more leakage error. Amplitude spectra of measurement and atmospheric pressure errors have different shapes, but the best results are obtained when both are used in basin function design. When high-quality information about the signal is available, for example from climate and ocean models, changing the basin function each month can reduce leakage error and improve estimates of time variable water storage within basins.     

基于SLR的GRACE卫星定轨中重力场模型对轨道精度的影响

以GRACE卫星为例,分析比较利用SLR观测资料进行卫星定轨时,采用不同重力场模型对GRACE卫星定轨精度的影响;以及重力场截断阶引起的积分轨道差异;同时,将定轨结果与采用GPS确定的定轨结果进行比较,分析与GPS定轨结果的差异.实验证明.重力场模型选择GGM02C的定轨结果优于选择JGM-3的定轨结果,基于SLR的定...     

Sumatra-Adaman大地震同震和震后形变的GRACE卫星检测

利用CSR公布的RL-04版GRACE卫星月重力场模型计算了9.1级Sumatra-Adaman大地震的同震和震后形变效应。数值结果表明,GRACE能够监测到的同震和震后形变量为-20～10cm的等效水高,为大地震同震和震后形变监测提供了一种独特、有效的方法。     

GRACE时变重力数据的后处理方法研究进展

重力场是反映地球介质密度变化和在各种环境(固体地球潮汐、内部热流、固体和液体之间质量的交换、表面负荷和地震构造运动等)下动力学特征的最基本和最直接的物理量。GRACE(Gravity Recovery and Climate Experiment)卫星作为探测全球重力场的工具已经为科研工作者提供了超过10 a的全球时变重力场数据。由于GRACE数据存在固有误差,GRACE数据产品需要进行后处理对局部重力场进行研究。回顾整理了GRACE数据后处理中的处理方法,包括高斯滤波法及非各向同性滤波法,位系数去相关法,主成分分析法,小波分解法,Slepian方法,以及顾及先验信息的改进算法等,并对GRACE后处理算法的后续改进和发展进行了展望。     

根据人卫激光测距、GRACE和地球物理模型求解地球低阶重力场季节变化

本文利用2002年4月至2010年10月的Lageos1和Lageos2两颗激光卫星观测数据、GRACE以及地球物理模型三种独立的方法计算地球低阶重力场系数J 的变化,根据大气压强数据计算 J 时分别按反变气压计（IB）和非反变气压计(NIB)两种假设进行计算。通过分析 J 的季节特性表明,大气在NIB假设下得到的周年振幅比在IB假设下得到的振幅大3倍左右,相位相差47°;大气和陆地水的质量变化对 J 周年变化的贡献占主导地位,海洋的影响最小;大气、海洋和陆地水得到 J 半年振幅和相位值与SLR得到的振幅和相位值吻合较差,尤其是在IB假设下大气得到的结果与SLR结果相差最大; SLR、GRACE和地球物理模型三种独立方法得到的 J 周年项之间吻合相对较好,GRACE得到的周年振幅比SLR得到的周年振幅大50%左右, SLR观测得到的 J 周年振幅介于在NIB和IB两种假设下地球物理模型得到的结果之间;GRACE与SLR得到的 J 半年项的振幅相同,在IB假设下AOW得到的 J 半年振幅和相位与SLR结果差异最大。     

用GRACE星间速度恢复地球重力场

本文首先给出了用星间速度恢复地球重力场的数学模型,然后用GRACE卫星30天的星间速度观测值计算了一个100阶的地球重力场模型DQM2006S2。为了对这一模型的精度进行评述,将它与EGM 96,EIGEN-CHAMP03S和GGM01S3个地球重力场模型作了比较,并用这一模型计算了高程异常与GPS/水准实际观测值进行了比较,结果表明:DQM2006S2模型精度优于EGM 96和EIGEN-CHAMP03S模型精度,但是不及GGM01S模型精度。精度不及GGM01S的原因是GGM01S模型使用了111天的星间速度数据,其数据量约为DQM2006S2模型使用数据量的4倍。     

利用GRACE数据检测日本Mw9.0地震同震和震后重力变化

基于德国地学中心（GFZ）发布的GRACE RL05月重力场模型数据,考虑全球陆地同化系统陆地水储量的影响,采用300 km的扇形滤波,利用叠积法提取了日本Mw9.0地震的同震和震后重力时变信号,并利用最小二乘拟合的方法计算了两个同震重力变化极值点在地震前后85个月的重力年变率。结果表明：土壤水分和雪水引起的重力变化为-0.34~0.09 μgal;利用GRACE数据检测到的同震重力变化为-5.3~4.2 μgal,与基于PSGRN/PSCMP模型计算的结果在空间分布和量级上具有较好的一致性;震后5 a震中附近区域的重力整体上呈现增加趋势,断层上盘所在的日本海域与下盘所在的太平洋区域重力增加的最大值分别为2.6、4.5 μgal,下盘重力增加较大,可能与断层下盘所在地层的黏滞性相对较低有关。     

GRACE卫星非差精密定轨精度分析

随着星载GPS接收机性能和精密轨道、钟差产品精度的提高,星载GPS观测技术已成为确定CHAMP、GRACE和GOCE等低轨卫星精密轨道的重要手段。文章以GRACE卫星为例,分别利用非差弱动力法和非差运动学方法精密确定其轨道,并将结果和美国喷气动力实验室(JPL)事后精密轨道对比。结果表明:GRACE卫星非差弱动力法和非差运动学定轨精度均可达到厘米级;在使用相同的星历、钟差等产品时,弱动力法定轨精度略微优于运动学方法。此外,本文采用超快预报精密星历实时确定GRACE卫星轨道时精度也优于10cm。     

A simulation study of the errors of omission and commission for GRACE RL01 gravity fields

This paper examines the influence that certain omission and commission errors can have on the gravity field models estimated from the initial release of data (RL01) from the Gravity Recovery And Recovery Experiment (GRACE) satellite mission. The effects of omission errors were analyzed by limiting the degree and order to which the GPS and K-band range-rate (KBR) measurement partials were extended in the solution process. The commission error studies focused on the impact of an imperfect mean reference gravity field model on the solution. Combinations of both of these error sources were also explored. The nature of these errors makes them difficult to distinguish from the true gravity signal, so the exploration of these error sources was performed using simulations; however, comparisons to real-data solutions are provided. The results show how each of the specific error sources investigated influences the gravity field solution. The simulations also show how all of the errors examined can be sufficiently mitigated through the appropriate choice of processing parameters.     

利用高分辨率水文模型提高GRACE卫星的空间分辨率

为克服GRACE卫星数据空间分辨率粗糙的局限性,本文以高空间分辨率的PCR-GLOBWB数据为基础,构建了加权、乘权及误差分配降尺度方法,将GRACE卫星在河北省的水储量变化数据的空间分辨率由0.50°提高至0.05°。结果表明：加权降尺度方法不仅保留了GRACE数据的原始空间分布特征,还刻画了局部细节特征;误差分配降尺度方法结果较为理想,但在格网交界处的信号存在跳跃现象;乘权降尺度方法表现最差,与GRACE存在明显差异。经实测数据验证可知,加权降尺度方法与实测值拟合程度最好,相关系数最高可达0.81。本文为获取河北省高空间分辨率地下水储量数据提供了有效保障。     

Wavelet Modeling of Regional and Temporal Variations of the Earth’s Gravitational Potential Observed by GRACE

This work is dedicated to the wavelet modeling of regional and temporal variations of the Earth’s gravitational potential observed by the GRACE (gravity recovery and climate experiment) satellite mission. In the first part, all required mathematical tools and methods involving spherical wavelets are provided. Then, we apply our method to monthly GRACE gravity fields. A strong seasonal signal can be identified which is restricted to areas where large-scale redistributions of continental water mass are expected. This assumption is analyzed and verified by comparing the time-series of regionally obtained wavelet coefficients of the gravitational signal originating from hydrology models and the gravitational potential observed by GRACE. The results are in good agreement with previous studies and illustrate that wavelets are an appropriate tool to investigate regional effects in the Earth’s gravitational field. Electronic Supplementary Material Supplementary material is available for this article at     

GRACE卫星时变重力场的小波多尺度分解——以2008年汶川Ms8.0大地震为例

根据UTCSR发布的GRACE卫星资料,计算了汶川及其周边地区的卫星时变重力场,并利用小波多尺度分析方法对卫星重力场进行分解,得到了反映不同深度的重力场细节和逼近。通过研究各个细节和逼近成分的重力场变化,结合区域构造运动的特点,对GRACE观测的时变重力场及汶川地震的动力机制进行了初步解释和讨论。结果表明,4阶细节和4阶逼近较好地揭示了汶川地区构造形变和深部物质流动引起的重力变化,而且这种震前重力变化特征满足地震孕育发生的条件。     

联合GRACE/GOCE重力场模型和GPS/水准数据确定我国85高程基准重力位

GRACE、GOCE卫星重力计划的实施,对确定高精度重力场模型具有重要贡献。联合GRACE、GOCE卫星数据建立的重力场模型和我国均匀分布的649个GPS/水准数据可以确定我国高程基准重力位,但我国高程基准对应的参考面为似大地水准面,是非等位面,将似大地水准面转化为大地水准面后确定的大地水准面重力位为62 636 854.395 3m~2s~(-2),为提高高阶项对确定大地水准面的贡献,利用高分辨率重力场模型EGM2008扩展GRACE/GOCE模型至2190阶,同时将重力场模型和GPS/水准数据统一到同一参考框架和潮汐系统,最后利用扩展后的模型确定的我国大地水准面重力位为62 636 852.751 8m~2s~(-2)。其中组合模型TIM_R4+EGM2008确定的我国85高程基准重力位值62 636 852.704 5m~2s~(-2)精度最高。重力场模型截断误差对确定我国大地水准面的影响约16cm,潮汐系统影响约4~6cm。     

利用GPS卫星轨道确定地球二阶带谐系数的研究

重力恢复和气候实验(gravity recovery and climate experiment,GRACE)任务受限于卫星的低轨极地轨道性质和编队模式,确定的重力场模型C20项存在不足.与之相比,全球定位系统(global positioning system,GPS)卫星为倾斜轨道,卫星数量多,将G PS卫星的精...     

利用星载GPS历元差分计算的平均加速度反演地球重力场

提出了一个新的重力场反演方法,该方法利用由星载GPS相位数据直接求得的卫星平均加速度来反演地球重力场,而无需计算卫星的几何轨道。该方法的优点在于无需求解模糊度参数,并且相邻历元间的系统误差可以有效消除。利用CHAMP和GRACE卫星数据反演重力场模型的算例显示,利用该方法相比利用几何轨道反演重力场获得的重力场模型质量可提高20%左右。     

Variations in the accuracy of gravity recovery due to ground track variability: GRACE,CHAMP, and GOCE

Following an earlier recognition of degraded monthly geopotential recovery from GRACE (Gravity Recovery And Climate Experiment) due to prolonged passage through a short repeat (low order resonant) orbit, we extend these insights also to CHAMP (CHAllenging Minisatellite Payload) and GOCE (Gravity field and steady state Ocean Circulation Explorer). We show wide track-density variations over time for these orbits in both latitude and longitude, and estimate that geopotential recovery will be as widely affected as well within all these regimes, with lesser track density leading to poorer recoveries. We then use recent models of atmospheric density to estimate the future orbit of GRACE and warn of degraded performance as other low order resonances are encountered in GRACE’s free fall. Finally implications for the GOCE orbit are discussed.     

Accuracy assessment of the GPS-based slant total electron content

The main scope of this research is to assess the ultimate accuracy that can be achieved for the slant total electron content (sTEC) estimated from dual-frequency global positioning system (GPS) observations which depends, primarily, on the calibration of the inter-frequency biases (IFB). Two different calibration approaches are analyzed: the so-called satellite-by-satellite one, which involves levelling the carrier-phase to the code-delay GPS observations and then the IFB estimation; and the so-called arc-by-arc one, which avoids the use of code-delay observations but requires the estimation of arc-dependent biases. Two strategies are used for the analysis: the first one compares calibrated sTEC from two co-located GPS receivers that serve to assess the levelling errors; and the second one, assesses the model error using synthetic data free of calibration error, produced with a specially developed technique. The results show that the arc-by-arc calibration technique performs better than the satellite-by-satellite one for mid-latitudes, while the opposite happens for low-latitudes.     

Accuracy assessment of the GPS-TEC calibration constants by means of a simulation technique

During the last 2 decades, Global Positioning System (GPS) measurements have become a very important data-source for ionospheric studies. However, it is not a direct and easy task to obtain accurate ionospheric information from these measurements because it is necessary to perform a careful estimation of the calibration constants affecting the GPS observations, the so-called differential code biases (DCBs). In this paper, the most common approximations used in several GPS calibration methods, e.g. the La Plata Ionospheric Model (LPIM), are applied to a set of specially computed synthetic slant Total Electron Content datasets to assess the accuracy of the DCB estimation in a global scale scenario. These synthetic datasets were generated using a modified version of the NeQuick model, and have two important features: they show a realistic temporal and spatial behavior and all a-priori DCBs are set to zero by construction. Then, after the application of the calibration method the deviations from zero of the estimated DCBs are direct indicators of the accuracy of the method. To evaluate the effect of the solar activity radiation level the analysis was performed for years 2001 (high solar activity) and 2006 (low solar activity). To take into account seasonal changes of the ionosphere behavior, the analysis was repeated for three consecutive days close to each equinox and solstice of every year. Then, a data package comprising 24 days from approximately 200 IGS permanent stations was processed. In order to avoid unwanted geomagnetic storms effects, the selected days correspond to periods of quiet geomagnetic conditions. The most important results of this work are: i) the estimated DCBs can be affected by errors around ±8 TECu for high solar activity and ±3 TECu for low solar activity; and ii) DCB errors present a systematic behavior depending on the modip coordinate, that is more evident for the positive modip region.     

基于能量守恒的星间距离变率与地球重力场频谱关系的建立与分析

The spectral relationship between range-rate measurements and the gravity potential for low-low satellite-to-satellite tracking mission was established based on the energy conservation theory. Then the performances of satellite separation, the orbital altitude, and the accuracy of range-rate measurements in recovering the earth’s gravity field were simulated and analyzed by this method. Finally, the cumulative geoid errors of the reference mode were obtained by using the configuration parameters of the GRAC...     

GPS运行轨道仿真系统的设计与开发

为了进行航天器系统仿真技术研究,本文提出了应用虚拟现实技术开发GPS运行轨道仿真系统框架体系:利用Matlab仿真,得到并验证了通过对SP3星历数据处理构建正确三维仿真运行轨道的方法;完成了实时交互的三维可视化仿真系统主要功能的实现;最终取得了良好的仿真效果,有利于GPS用户系统的设计与监控.