Approximate decorrelation and non-isotropic smoothing of time-variable GRACE-type gravity field models   总被引：6，自引：1，他引：6  

Jürgen Kusche 《Journal of Geodesy》2007,81(11):733-749

We discuss a new method for approximately decorrelating and non-isotropically filtering the monthly gravity fields provided by the gravity recovery and climate experiment (GRACE) twin-satellite mission. The procedure is more efficient than conventional Gaussian-type isotropic filters in reducing stripes and spurious patterns, while retaining the signal magnitudes. One of the problems that users of GRACE level 2 monthly gravity field solutions fight is the effect of increasing noise in higher frequencies. Simply truncating the spherical harmonic solution at low degrees causes the loss of a significant portion of signal, which is not an option if one is interested in geophysical phenomena on a scale of few hundred to few thousand km. The common approach is to filter the published solutions, that is to convolve them with an isotropic kernel that allows an interpretation as smoothed averaging. The downside of this approach is an amplitude bias and the fact that it neither accounts for the variable data density that increases towards the poles where the orbits converge nor for the anisotropic error correlation structure that the solutions exhibit. Here a relatively simple regularization procedure will be outlined, which allows one to take the latter two effects into account, on the basis of published level 2 products. This leads to a series of approximate decorrelation transformations applied to the monthly solutions, which enable a successive smoothing to reduce the noise in the higher frequencies. This smoothing effect may be used to generate solutions that behave, on average over all possible directions, very close to Gaussian-type filtered ones. The localizing and smoothing properties of our non-isotropic kernels are compared with Gaussian kernels in terms of the kernel variance and the resulting amplitude bias for a standard signal. Examples involving real GRACE level 2 fields as well as geophysical models are used to demonstrate the techniques. With the new method, we find that the characteristic striping pattern in the GRACE solutions are much more reduced than Gaussian-filtered solutions of comparable signal amplitude and root mean square.  相似文献   

Attenuation effect on seasonal basin-scale water storage changes from GRACE time-variable gravity   总被引：3，自引：0，他引：3  

J. L. Chen  C. R. Wilson  J. S. Famiglietti  Matt Rodell 《Journal of Geodesy》2007,81(4):237-245

In order to effectively recover surface mass or geoid height changes from the gravity recovery and climate experiment (GRACE) time-variable gravity models, spatial smoothing is required to minimize errors from noise. Spatial smoothing, such as Gaussian smoothing, not only reduces the noise but also attenuates the real signals. Here we investigate possible amplitude attenuations and phase changes of seasonal water storage variations in four drainage basins (Amazon, Mississippi, Ganges and Zambezi) using an advanced global land data assimilation system. It appears that Gaussian smoothing significantly affects GRACE-estimated basin-scale seasonal water storage changes, e.g., in the case of 800 km smoothing, annual amplitudes are reduced by about 25–40%, while annual phases are shifted by up to 10°. With these effects restored, GRACE-estimated water storage changes are consistently larger than model estimates, indicating that the land surface model appears to underestimate terrestrial water storage change. Our analysis based on simulation suggests that normalized attenuation effects (from Gaussian smoothing) on seasonal water storage change are relatively insensitive to the magnitude of the true signal. This study provides a numerical approach that can be used to restore seasonal water storage change in the basins from spatially smoothed GRACE data.  相似文献   

Accuracy assessment of the monthly GRACE geoids based upon a simulation     

E. J. O. Schrama  P. N. A. M. Visser 《Journal of Geodesy》2007,81(1):67-80

The purpose of this paper is to demonstrate the effect of geophysical background model errors that affects temporal gravity solutions provided by the Gravity Recovery And Climate Experiment (GRACE). Initial performance estimates by Dickey et al. (1997) suggested a formal geoid RMS error better than 0.1 mm up to spherical harmonic degree 5. Now that the GRACE gravity models and data are available, it is evident that these original expectations were too optimistic. Our hypothesis is that this is partially explained by errors in geophysical background models that need to be applied in the GRACE data reduction, and that this effect was not considered by Dickey et al. (1997). We discuss the results of a closed-loop simulation, where satellite trajectory prediction software is used for the generation of GRACE range-rate data and GRACE orbit solutions with the help of the Global Positioning System (GPS). During the recovery step in our closed-loop simulation, we show that simulated nuisance signals (based on tide and air pressure model differences) map to a 0.7 mm geoid effect for periods longer than 3 months and to less than 0.4 mm for periods shorter than 3 months. The long-period geoid hydrology signal is at a level of 4.5 mm, while the short-period hydrology is at 0.25 mm. The long-period ocean bottom pressure (OBP) signal maps at 0.8 mm and for short periods it is 0.4 mm. We conclude that short-period effects are difficult to observe by GRACE and that long-period effects, like hydrology, are easier to recover than OBP variations.  相似文献   

基于GRACE/GRACE-FO和Swarm卫星研究2002-2020年南极和格陵兰岛冰盖质量时空变化     

陈威  钟敏  冯伟  王长青  李文浩  梁磊 《地球物理学报》2022,65(3):952-964

两极冰盖消融及其质量变化作为全球气候变化的重要指标之一,一直是联合国政府间专门气候委员会IPCC(Intergovernmental Panel on Climate Change)报告的重点关注内容.GRACE(Gravity Recovery and Climate Experiment,2002年4月-2017年...  相似文献   

Analysing the contribution of snow water equivalent to the terrestrial water storage over Canada     

Ala Bahrami  Kalifa Goïta  Ramata Magagi 《水文研究》2020,34(2):175-188

In this study, the spatial and temporal variabilities of terrestrial water storage anomaly (TWSA) and snow water equivalent anomaly (SWEA) information obtained from the Gravity Recovery and Climate Experiment (GRACE) twin satellites data were analysed in conjunction with multisource snow products over several basins in the Canadian landmass. Snow water equivalent (SWE) data were extracted from three different sources: Global Snow Monitoring for Climate Research version 2 (GlobSnow2), Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E), and Canadian Meteorological Centre (CMC). The objective of the study was to understand whether SWE variations have a significant contribution to terrestrial water storage anomalies in the Canadian landmass. The period was considered from December 2002 to March 2011. Significant relationships were observed between TWSA and SWEA for most of the 15 basins considered (53% to 80% of the basins, depending on the SWE products considered). The best results were obtained with the CMC SWE products compared with satellite-based SWE data. Stronger relationships were found in snow-dominated basins (R_s > = 0.7), such as the Liard [root mean square error (RMSE) = 21.4 mm] and Peace Basins (RMSE = 26.76 mm). However, despite high snow accumulation in the north of Quebec, GRACE showed weak or insignificant correlations with SWEA, regardless of the data sources. The same behaviour was observed in the Western Hudson Bay basin. In both regions, it was found that the contribution of non-SWE compartments including wetland, surface water, as well as soil water storages has a significant impact on the variations of total storage. These components were estimated using the Water-Global Assessment and Prognosis Global Hydrology Model (WGHM) simulations and then subtracted from GRACE observations. The GRACE-derived SWEA correlation results showed improved relationships with three SWEA products. The improvement is particularly important in the sub-basins of the Hudson Bay, where very weak and insignificant results were previously found with GRACE TWSA data. GRACE-derived SWEA showed a significant relationship with CMC data in 93% of the basins (13% more than GRACE TWSA). Overall, the results indicated the important role of SWE on terrestrial water storage variations.  相似文献   

不同Mascon模型解比较分析     

郭飞霄  孙中苗  任飞龙  肖云 《大地测量与地球动力学》2019,39(10):1022-1026

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。  相似文献   

基于GRACE卫星重力数据估计格陵兰岛冰盖质量变化   总被引：1，自引：0，他引：1  

冯贵平  王其茂  宋清涛 《海洋学报》2018,40(11):73-84

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。  相似文献   

基于改进的主成分分析法提取GRACE时变重力场信号     

李杰  范东明  游为  李蔚  蒋攀 《大地测量与地球动力学》2018,38(4):414-421

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。  相似文献   

利用GPS卫星轨道确定地球二阶带谐系数的研究     

赵敏星  衷路萍  邹贤才 《测绘地理信息》2021,46(2):47-50

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GPS卫星的精密轨道数据作为伪观测值,使用动力学方法进行C₂₀项确定的可行性研究。结果显示,2017年C₂₀项时间序列的平均值比GRACE更接近卫星激光测距(satellite laser ranging,SLR)的结果,且不存在明显的约160 d的周期信号,表明利用GPS卫星解算C₂₀项具有可行性。同时估计了光压模型P1参数,与GAMIT软件解算结果接近,进一步验证C₂₀项解算结果的可靠性。  相似文献   

长江流域陆地水储量与多源水文数据对比分析   总被引：1，自引：0，他引：1       下载免费PDF全文

王文  王鹏  崔巍 《水科学进展》2015,26(6):759-768

从趋势性、滞后性及相关性三方面,对2002—2013年间GRACE重力卫星反演的长江上游与中游陆地水储量与模型模拟土壤含水量、实测降水和实测径流数据进行了对比分析,并从干旱强度及发展时间两方面评估了标准化陆地水储量指数SWSI、标准化降水指数SPI、标准化径流指数SRI和标准化土壤含水量指数SSMI对区域性干旱的表征能力.结果表明:长江上游地区陆地水储量与降水、径流和土壤水蓄量均无显著变化,而中游地区陆地水储量则与水库蓄量同样具有显著性增加,反映人类活动对中游地区陆地水储量变化有很大影响;各指标指示的各等级干旱月份数量基本相当,但各指标反映的特旱具体月份有较大差别,基于GRACE数据构建的SWSI指标对特大干旱的指示性不好;对比各指标对上游与中游地区干旱事件发展时间,体现出水文干旱、农业干旱对气象干旱存在一定的迟滞关系.  相似文献