Accuracy assessment of the monthly GRACE geoids based upon a simulation

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.     

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

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...     

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

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.     

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。     

长江流域陆地水储量与多源水文数据对比分析

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.     

几个能量法获取地球重力场模型的关键技术分析

介绍了能量法恢复地球重力场的基本原理,并分别给出了在笛卡尔坐标空间、极坐标空间内的能量守恒公式,探讨了能量常数精度、计算方式与地球重力场反演精度的关系,并通过数值试验进行了计算分析。计算结果表明:对于低轨卫星,在不同坐标空间内转换引起的轨道误差为10-10m量级,对恢复地球重力场模型的阶误差RMS为10-21量级,可以忽略不计;为了获取厘米级的大地水准面,在解算过程中应该将扰动位期望为零时对应的估值作为能量常数初始估计值,将其残差作为未知数一并求解,且能量常数误差应优于0.1 m2s2。     

基线法在卫星重力数据处理中的应用

提出了一种恢复地球重力场并同时改善部分轨道初始参数的方法——基线法。给出了基线法的基本原理,推导了基线参数与直角坐标形式参数的相互转换公式,分析了星间距离和距离变率对基线参数的敏感性。分别用基线法和经典动力学法处理了一组GRACE实际观测数据,结果表明,采用基线法较经典动力学法得到了一个精度更高的地球重力场模型,其大地水准面累积误差(最高60阶)减少了3 cm。     

GRACE卫星观测到的日本9.0级大地震重力前兆信息

利用102个GRACE卫星月重力场模型,提取了2011年3月11日日本9.0级大地震的重力前兆信息,同时利用USGS发布的断层模型结合向上延拓技术计算了理论同震重力变化,并对结果进行了比较和分析.     

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联合卫星测高和卫星重力数据研究热容海平面变化

首先用卫星测高资料计算了1993～2009年6月的全球平均海平面变化。用GRACE(gravity recovery andclimate experiment)时变重力场系数反演了2003～2009年6月全球平均海水质量变化。联合GRACE和卫星测高资料计算了2003～2009年6月的热容海平面变化,该变化呈上升趋势。用日本气象局Ishii等提供的海温数据计算了1993～2006年的海水引起的平均热膨胀海平面变化,1993～2003年间,全球海洋热膨胀引起的热容海平面呈上升趋势,约占同期平均海平面变化的一半。利用ARGO温盐数据计算了2004～2009年6月平均热容海平面变化,也呈上升态势,只是变化速率有所减慢。