重力卫星五年运行对求定地球重力场模型的进展和展望

对近年升空的CHAMP和GRACE和将于2007年升空的GOCE卫星在测定地球重力场方面的技术特点和初步成果进行了回顾、比较和评估。并对它们今后在静态和动态的地球重力场构模方面可能的进展作一展望。现在只用一颗重力卫星的轨道摄动数据，就可以以前所未有的可靠性和精确性来求定地球重力场的长波和部分中波。如CHAMP重力卫星的33个月数据所求定的地球重力场模型,相对于曾利用多颗卫星资料所推算的GR1M5 S1重力场模型,在长波方面的精度和可靠性都有很大改善。而GRACE重力卫星的 110天数据所导出成果的空间分辨率，又优于CHAMP的33个月的数据成果。GRACE卫星还有一个重要任务，就是测定重力场非潮汐的短期性或准实时的变化。还介绍了新发表的一个联合地球重力场模型EIGEN CG03C, 360完全阶次，分辨率约30′。CG03C同CHAMP/GRACE以前的重力场模型比较，在400 km波长的精度方面改善了一个量级，大地水准面的精度改善了3 cm，重力异常的精度改善了0.4 mgal。     

Recent hydrological behavior of the East African great lakes region inferred from GRACE,satellite altimetry and rainfall observations

We have jointly analysed space gravimetry data from the GRACE space mission, satellite altimetry data and precipitation over the East African Great Lakes region, in order to study the spatiotemporal variability of hydrological parameters (total water storage, lake water volume and rainfall). We find that terrestrial water storage (TWS) from GRACE and precipitation display a common mode of variability at interannual time scale, with a minimum in late 2005, followed by a rise in 2006–2007. We argue that this event is due to forcing by the strong 2006 Indian Ocean Dipole (IOD) on East African rainfall. We also show that GRACE TWS is linked to the El Niño-Southern Oscillation cycle. Combination of the altimetry-based lake water volume with TWS from GRACE over the lakes drainage basins allows estimating soil moisture and groundwater volume variations. Comparison with the WGHM hydrological model outputs is performed and discussed.     

Advances, Problems and Prospects of Modern Geodesy Applied in Tibetan Geodynamic Changes

Modern geodetic techniques have developed rapidly in recent years, providing reliable observation data and new effective approaches, and greatly enhancing studies of the Tibetan geodynamics. For instance, the well-known GPS technique has been employed to measure seismic slips for many faults in the Tibetan Plateau. GPS data agree well with the hypothesis of a thickening crust and eastward mass flow. Moreover, absolute gravimetric data have been applied to interpret geophysical phenomena such as crust movement, co-seismic gravity change, GIA, and ground water change. The satellite gravity mission GRACE launched in 2002 provided global gravity models with unprecedentedly high precision and high spatial resolution. It has been used in implementing temporal gravity changes and improving our knowledge of the Earth’s interior, including lithosphere dynamics, mantle viscosity and rheology, plateau uplift, and subduction processing. It is noteworthy that gravity presents unique advantages for the study of Tibetan geodynamics because of its sensitivity to mass migration and dynamic redistribution. To date, great advances have been made in applying modern geodetic data in studying dynamic changes of Tibetan plateau. For instance, the horizontal displacement field from GPS data revealed dynamical characteristics of the present-day Tibetan plateau. The combination of gravity anomalies and topographic data describe the tectonic characteristics of Tibetan plateau. The combination of gravity data and GPS data show present properties of the Tibetan plateau such as crust thickening, Moho’s subsidence, and plateau uplift. GRACE data were used to estimate the distribution of ice/snow melting.     

Terrestrial water dynamics in the lower Ganges—estimates from ENVISAT and GRACE

In this study, the hydrodynamics of lower Ganges basin in India has been monitored using radar altimetry data from environmental satellite (ENVISAT) mission and microgravity data from the Gravity Recovery and Climate Experiment (GRACE) mission. River stage time series have been constructed for different virtual stations on the lower Ganges. Time series for the integrated water volume changes from microgravity measurements have also been constructed to characterize the seasonal and interannual fluctuation patterns in water storage and flux. The ENVISAT dataset indicates an average seasonal river stage fluctuation of 8 m in the lower Ganges River. The GRACE dataset reveals a seasonal fluctuation ranging from 0.18 to 0.40 m in the vertically integrated total water storage in the lower Ganges basin. The two independent datasets show broad similarity in the lower Ganges basin and outline the importance of space-based techniques for monitoring continental water resources.     

Estimation of regional evapotranspiration in the extended Salado Basin (Argentina) from satellite gravity measurements

In this study, regional evapotranspiration is estimated in a wide flatland area that includes Salado River Basin and four tributary basins by using gravity measurements of the space mission Gravity Recovery and Climate Experiment (GRACE). Monthly estimates of large-scale variations in the land-water storage are obtained from the satellite data. Evapotranspiration is computed with the water-balance equation using the GRACE land-water solutions, rainfall data from the Global Precipitation Climatology Center and runoff values obtained as 5% of the precipitation. GRACE-derived evapotranspiration values are consistent with the different climatic scenarios observed, and they satisfactorily agree with estimates provided by a global hydrological model. The overall results show that the method used is a valid tool for characterizing the evapotranspiration in the Argentine Pampas and that it can be used to detect and examine changes in the evapotranspiration pattern associated with the occurrence of extreme climatic events. This study illustrates the ability of GRACE to analyze and predict evapotranspiration and other processes on a regional scale in a flatland area.     

Sensitivity of the Gravity Recovery and Climate Experiment (GRACE) to the complexity of aquifer systems for monitoring of groundwater

The Gravity Recovery and Climate Experiment (GRACE) satellite mission is aimed at assessment of groundwater storage under different terrestrial conditions. The main objective of the presented study is to highlight the significance of aquifer complexity to improve the performance of GRACE in monitoring groundwater. Vidarbha region of Maharashtra, central India, was selected as the study area for analysis, since the region comprises a simple aquifer system in the western region and a complex aquifer system in the eastern region. Groundwater-level-trend analyses of the different aquifer systems and spatial and temporal variation of the terrestrial water storage anomaly were studied to understand the groundwater scenario. GRACE and its field application involve selecting four pixels from the GRACE output with different aquifer systems, where each GRACE pixel encompasses 50–90 monitoring wells. Groundwater storage anomalies (GWSA) are derived for each pixel for the period 2002 to 2015 using the Release 05 (RL05) monthly GRACE gravity models and the Global Land Data Assimilation System (GLDAS) land-surface models (GWSA_GRACE) as well as the actual field data (GWSA_Actual). Correlation analysis between GWSA_GRACE and GWSA_Actual was performed using linear regression. The Pearson and Spearman methods show that the performance of GRACE is good in the region with simple aquifers; however, performance is poorer in the region with multiple aquifer systems. The study highlights the importance of incorporating the sensitivity of GRACE in estimation of groundwater storage in complex aquifer systems in future studies.     

Present rate of uplift in Fennoscandia from GRACE and absolute gravimetry

Fennoscandia is a key region for studying effects of glacial isostatic adjustment. The associated mass variations can be detected by the Gravity Recovery and Climate Experiment (GRACE) satellite mission, which observes the Earth's gravity field since April 2002, as well as by absolute gravimetry field campaigns. Since 2003, annual absolute gravity (AG) measurements have been performed in Fennoscandia by the Institut für Erdmessung (IfE, Institute of Geodesy) of the Leibniz Universität Hannover, Germany, within a multi-national cooperation. This offers a unique opportunity for validation and evaluation of the GRACE results. In this preliminary study, the GRACE results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the FG5-220 gravimeter of the IfE.The results from GRACE monthly solutions provided by different analysis centres show temporal gravity variations in Fennoscandia. The included secular variations are in good agreement with former studies. The uplift centre is located west of the Bothnian Bay, the whole uplift area comprises Northern Europe. Nevertheless, the differences between the GRACE solutions are larger than expected and the different centre-specific processing techniques have a very strong effect on possible interpretations of GRACE results. The comparison of GRACE to the AG measurements reveals that the determined trends fit well with results from GRACE at selected stations, especially for the solution provided by the GFZ. Variations of land hydrology clearly influence results from GRACE and the AG measurements.     

重力卫星五年运行对求定地球重力场模型的进展和展望

对近年升空的CHAMP和GRACE和将于2007年升空的GOCE卫星在测定地球重力场方面的技术特点和初步成果进行了回顾、比较和评估。并对它们今后在静态和动态的地球重力场构模方面可能的进展作一展望。现在只用一颗重力卫星的轨道摄动数据,就可以以前所未有的可靠性和精确性来求定地球重力场的长波和部分中波。如CHAMP重力卫星的33个月数据所求定的地球重力场模型,相对于曾利用多颗卫星资料所推算的GRlM5-S1重力场模型,在长波方面的精度和可靠性都有很大改善。而GRACE重力卫星的110天数据所导出成果的空间分辨率,又优于CHAMP的33个月的数据成果。GRACE卫星还有一个重要任务,就是测定重力场非潮汐的短期性或准实时的变化。还介绍了新发表的一个联合地球重力场模型EIGEN-CG03C,360完全阶次,分辨率约30′。CG03C同CHAMP／GRACE以前的重力场模型比较,在400km波长的精度方面改善了一个量级,大地水准面的精度改善了3cm,重力异常的精度改善了0．4mgal。     

高精度空间加速度计在轨引力标定方案

高精度静电悬浮加速度计是地球重力卫星的关键载荷之一，其灵敏度参数直接关系到非保守力的精确测量，最终将影响地球重力场反演精度。文中，讨论了精度静电悬浮加速度计在轨灵敏度引力标定方案的可行性。理论分析结果表明，通过回转台旋转一个球体吸引质量，可以对分辨率达到10^-10m／s^2的GRACE卫星SuperSTAR静电悬浮加速度计的2个高灵敏轴进行在轨标定。     

Sensitivity of GRACE-derived estimates of groundwater-level changes in southern Ontario,Canada

Amidst changing climates, understanding the world’s water resources is of increasing importance. In Ontario, Canada, low water conditions are currently assessed using only precipitation and watershed-based stream gauges by the Conservation Authorities in Ontario and the Ministry of Natural Resources and Forestry. Regional groundwater-storage changes in Ontario are not currently measured using satellite data by research institutes. In this study, contributions from the Gravity Recovery and Climate Experiment (GRACE) data are compared to a hydrogeological database covering southern Ontario from 2003 to 2013, to determine the suitability of GRACE total water storage estimates for monitoring groundwater storage in this location. Terrestrial water storage data from GRACE were used to determine monthly groundwater storage (GWS) anomaly values. GWS values were also determined by multiplying groundwater-level elevations (from the Provincial Groundwater Monitoring Network wells) by specific yield. Comparisons of GRACE-derived GWS to well-based GWS data determined that GRACE is sufficiently sensitive to obtain a meaningful signal in southern Ontario. Results show that GWS values produced by GRACE are useful for identifying regional changes in groundwater storage in areas with limited available hydrogeological characterization data. Results also indicate that GRACE may have an ability to forecast changes in groundwater storage, which will become useful when monitoring climate shifts in the near future.     

基于GRACE卫星测量得到的中国及其周边地区陆地水量变化

GRACE卫星成功开辟了空间大地测量对地观测的新途径。利用GRACE卫星得到的时变地球重力资料,分析估计了中国及其周边地区陆地水量的变化趋势,较为清晰地揭示了该地区季节性变化特征。进一步采用13点滑动平均的方法扣除了季节性变化,提取了4个特征区域(喜马拉雅南部,新疆与西藏及其周边的亚洲高山区域,中国华北、东北地区和中国南部地区)的陆地水量变化特征信息,这4个区域陆地水量的变化趋势分别为-12.7±0.7、-60.4±2.7、-12.5±0.5和6.6±0.9 km³/a。其中：喜马拉雅南部和亚洲高山区域陆地水量呈现明显的衰减趋势,与Matsuo和Heki模拟冰川质量损失源得到的结果较为一致;但近10年来亚洲高山区域西北部冰川加速融化趋势并不明显。中国华北、东北地区和南部地区水量变化比较复杂,具不稳定的变化趋势。     

Identifying Water Storage Variation in Krishna Basin,India from <Emphasis Type="Italic">in situ</Emphasis> and Satellite based Hydrological Data

Terrestrial water storage (TWS), a sum total of water stored on or beneath the earth’s surface, transits in response to hydroclimatic processes such as precipitation, evapo-transpiration, runoff etc. and serves an indicator of hydrological condition of a region. We analyse spatio-temporal variance of water storage in Krishna Basin, India, derived from in-situ groundwater data and Gravity Recovery and Climate Experiment (GRACE) satellite data in order to determine physical causes of variations, and compare the variance with climatic factors such as Cumulative Rainfall Departure (CRD) and drought index i.e. Standardized Precipitation Index (SPI). GRACE satellite based TWS is found to reflect insitu groundwater changes and also shows a relationship with drought patterns as indicated by a good correlation with SPI. The largest part of TWS represents seasonal flux, and at an interannual scale, TWS depicts spatio-temporal variability in response to drought index viz. SPI. We infer that the groundwater storage derived from GRACE time-variable gravity solutions can be utilised to complement in-situ observations at basin scale and it reflects climatic forcing quite well.     

Research Progress of Groundwater Storage Changes Monitoring in China Based on GRACE Satellite Data

The data acquired by Gravity Recovery and Climate Experiment (GRACE) satellite provides a new way for monitoring groundwater storage changes in China. It is vital to understand its applications in China. This paper systematically reviewed the research progress of groundwater storage monitoring in China based on GRACE data. First, we used the bibliometric analysis and quantitative analysis to clarify trends and characteristics of related studies. Then, we elaborated on the basic principles, methods and uncertainties of groundwater monitoring based on GRACE data. Furthermore, we reviewed the research progress from the aspects of spatial range, accuracies and findings. It was found that the groundwater storage monitoring in China based on GRACE data has gradually received more attention, and the numbers of relevant publications and total citations in both Chinese and English showed an increasing trend. The methods mainly include the principle of water balance and calibration of hydrological models using GRACE satellite data. Most of the relevant studies focused on the North China Plain. The monitoring results are in good agreement with the measured groundwater data, and their correlation coefficients are higher than 0.6. We suggested that the challenges such as low spatial resolution of GRACE data and the uncertainties in monitoring should be considered. In the future, global positioning system, interferometric synthetic aperture radar and groundwater level observation data can be integrated to improve the reliability of groundwater storage monitoring in China.     

Improving the spatial resolution of GRACE-based groundwater storage estimates using a machine learning algorithm and hydrological model

Hydrogeology Journal - The low-resolution characteristic of Gravity Recovery and Climate Experiment (GRACE) satellite data greatly limits their application in many fields at regional or local...     

Application assessment of GRACE and CHIRPS data in the Google Earth Engine to investigate their relation with groundwater resource changes(Northwestern region of Iran)

In recent years, drought has become a global issue, especially in arid and semi-arid areas. It is without doubt that the identification and monitoring of the drought phenomenon can help to reduce the damages that would occur. In addition, rain is one of the factors which directly affect the water levels of underground water reservoirs. This research applied a linear gradient regression method developed on the basis of GRACE, CHIRPS, and data from monitoring wells to investigate the groundwater storage changes.These data have been analyzed on the Google Earth Engine platform. In order to conduct temporal and spatial analyses, the water levels of the aquifer were generated from the monitoring wells and zoned into five classes. Also, the amount of water storage and rain from the year 2003 to 2017 in the West Azerbaijan Province were investigated using the GRACE satellite and the CHIRPS data, respectively. The results obtained from the GRACE satellite data show that the average water level in the underground reservoirs in Iran had started to decrease since 2008 and reached its peak in 2016 with an average decrease of 16 cm in that year. The average annual decline of groundwater level in the studied time period was 5 cm. A chart developed from the CHIRPS annual rainfall data indicates that the biggest decline in rainfall occurred in 2008, and the declining trend has remained steady. Linear analyses were made on GRACE with CHIRPS results and monitoring wells data separately, from which the correlation coefficients are between 86% and 97%, showing generally high correlations. Furthermore, the results obtained from the zoning of the aquifer showed that in the period of 2004 to 2016, due to the decrease in rainfall and the excessive withdrawal of groundwater, the water levels also decreased.     

Groundwater storage variability and annual recharge using well-hydrograph and GRACE satellite data

Most studies using GRACE (Gravity Recovery and Climate Experiment) data for examining water storage anomalies have rich hydrogeological databases. Here, GRACE data are analyzed for southern Mali, Africa, a region with sparse hydrogeological data. GRACE data (2002?C2008) did not overlap with observed groundwater-level data (1982?C2002). Terrestrial water storage from GRACE was corrected for soil moisture using the Global Land Data Assimilation System (GLDAS) model to obtain monthly groundwater storage anomalies and annual net recharge. Historical storage anomalies and net recharge were determined using the water-table fluctuation method for available observation wells. Average annual net recharge averaged 149.1?mm (or 16.4% of annual rainfall) and 149.7?mm (14.8%) from historical water level and GRACE data, respectively. Monthly storage anomaly lows and peaks were observed in May and September, respectively, but have a shift in peak to November using the corrected GRACE data, suggesting that the GLDAS model may poorly predict the timing of soil-water storage in this region. Notwithstanding problems with the GLDAS model, the soil moisture-corrected GRACE data accurately predict the relative timing and magnitude of groundwater-storage changes, suggesting that GRACE data are valuable for identifying long-term regional changes in groundwater storage in areas with sparse hydrogeological data.     

A quantitative approach for hydrological drought characterization in southwestern China using GRACE

A quantitative approach for hydrological drought characterization, based on non-seasonal water storage deficit data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite mission, is assessed. Non-seasonal storage deficit is the negative terrestrial water storage after deducting trend, acceleration and seasonal signals, and it is designated as a drought event when it persists for three or more continuous months. The non-seasonal water storage deficit is used for measuring the hydrological drought in southwestern China. It is found that this storage-deficit method clearly identifies hydrological drought onset, end and duration, and quantifies instantaneous severity, peak drought magnitude, and time to recovery. Moreover, it is found that severe droughts have frequently struck southwestern China in the past several decades, among which, the drought of 2011–2012 was the most severe; the duration was 10 months, the severity was ?208.92 km³/month, and the time to recovery was 17 months. These results compare well with the National Climate Center of China drought databases, which signifies that the GRACE-based non-seasonal water storage deficit has a quantitative effect on hydrological drought characterization and provides an effective tool for researching droughts.     

基于野外资料和Google Earth影像的地质信息识别与提取方法——以塔里木盆地西克尔奥陶系古岩溶露头为例

以塔里木盆地西克尔奥陶系古岩溶露头为研究对象,根据高精度GPS野外定点和Google Earth影像数据的结合,明确了岩溶地质现象在影像图上的响应特征,进而提取定量化的古岩溶信息数据,经过数据处理建立了古岩溶地质模型。本项研究证实了基于野外资料和Google Earth影像的地质信息识别与提取方法的可行性,也表明了该方法能够实现对未开展露头考察的影像图直接提取相应地质信息和采集定量化数据。通过利用这些数据建立岩溶储层地质模型,结合野外资料,综合分析岩溶储层发育的控制因素,进而客观地理解地下岩溶储层特征及分布规律,能够为勘探开发提供有效指导。     

Estimating groundwater storage changes in the Mississippi River basin (USA) using GRACE

Based on satellite observations of Earth’s time variable gravity field from the Gravity Recovery and Climate Experiment (GRACE), it is possible to derive variations in terrestrial water storage, which includes groundwater, soil moisture, and snow. Given auxiliary information on the latter two, one can estimate groundwater storage variations. GRACE may be the only hope for groundwater depletion assessments in data-poor regions of the world. In this study, soil moisture and snow were simulated by the Global Land Data Assimilation System (GLDAS) and used to isolate groundwater storage anomalies from GRACE water storage data for the Mississippi River basin and its four major sub-basins. Results were evaluated using water level records from 58 wells set in the unconfined aquifers of the basin. Uncertainty in the technique was also assessed. The GRACE-GLDAS estimates compared favorably with the well based time series for the Mississippi River basin and the two sub-basins that are larger than 900,000 km². The technique performed poorly for the two sub-basins that have areas of approximately 500,000 km². Continuing enhancement of the GRACE processing methods is likely to improve the skill of the technique in the future, while also increasing the temporal resolution.     

深空对地观测创新工程进展与主要成果

科技创新是地质调查事业发展的第一驱动力。深空对地观测科技创新工程(以下简称工程)是中国地质调查局“地质科技创新计划”的重要组成部分。工程针对我国自主对地观测系统性、整体性不足,卫星业务应用产品类型相对单一,以及数据处理能力较为薄弱等问题,从对地观测数据体系构建、应用系统建设、自然资源与环境变化监测体系创新,以及新型对地观测技术研发等方面开展工作与部署,取得了一系列工作成果。这些成果提高了我国深空对地综合观测能力,提升了基础地质调查、地质环境监测的定量化水平。