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1.
Four new gravity field models from GOCE, two of them combined with GRACE, are compared here with EGM2008. The objectives are to look into the differences in consecutive ranges of the spherical harmonic expansion globally as well as in selected geographical regions and in the regions of the various data sources used for EGM2008. In general, GOCE is able to contribute to improved global gravity models in the spherical harmonic range between 120 and 200 (and above). The agreement between EGM2008 and the GOCE models is very good in well-surveyed regions such as North America, Europe and Australia, with geoid RMS-differences on the order of 4–6 cm. In other regions, where the surface gravity data available for the development of EGM2008 were poor, such as South America, Africa, South-East Asia or China the RMS-differences are on a level of 30 cm. Here GOCE leads to a significant improvement. These findings are confirmed by the analysis of the areas of the various EGM2008 data sources. In the regions of the so-called “fill-in” data of EGM2008 RMS-geoid height differences are high. In Antarctica GOCE also gives important improvements in terms of spatial resolution and accuracy. In general, the agreement between EGM2008 and the GOCE-models up to degree and order (d/o) 200 is good, with a global (excluding the polar gaps of GOCE orbits, throughout) geoid difference RMS of 11 cm, in the ocean areas 8 cm and 20 cm in the continental areas. GOCE models are better suited for ocean circulation studies because no prior ocean information enters into the data reduction process, as it is the case when deducing gravity anomalies from an altimetric mean sea surface. On the other hand, the good consistency between GOCE-models and EGM2008 in ocean areas very likely indicates that the influence of ocean circulation information on EGM2008 is rather small. The four tested GOCE models behave similarly except at the highest latitudes where GOCE lacks data due to its orbit inclination of 96.5° and some form of regularization which has to be applied. 相似文献
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《Journal of Geodynamics》2010,49(3-5):172-181
This paper is the first presentation of a project called GHYRAF (Gravity and Hydrology in Africa) devoted to the detailed comparison between models and multidisciplinary observations (ground and satellite gravity, geodesy, hydrology, meteorology) of the variations of water storage in Africa from the Sahara arid part to the monsoon equatorial part. We describe the various actions planned in this project. We first detail the actions planned in gravimetry which consist in two main surface gravity experiments: on the one hand the periodic repetition of absolute gravity measurements along a north–south monsoonal gradient of rainfall in West Africa, going from Tamanrasset (20 mm/year) in southern Algeria to Djougou (1200 mm/year) in central Benin; on the other hand the continuous measurements at Djougou (Benin) with a superconducting gravimeter to monitor with a higher sampling rate the gravity changes related to an extreme hydrological cycle. Another section describes the actions planned in GPS which will maintain and develop the present-day existing network in West Africa. The third type of actions deals with hydrology and we review the three sites that will be investigated in this joint hydrogeophysics project namely Wankama (near Niamey) and Bagara (near Diffa) in the Niger Sahelian zone and Nalohou (near Djougou) in the Benin monsoon zone. We also address the question of the ground truth of satellite-derived missions; in this context the GHYRAF project will lead to test the hydrology models by comparison both with in situ and satellite data such as GRACE, as well as to an important increase of our knowledge of the seasonal water cycle in Africa. We finally present preliminary results in GPS based on the analysis of the vertical motion of the Djougou site. The resulting absolute gravity changes related to the 2008 monsoon are finally given. 相似文献
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JIANG Tao LI JianCheng DANG YaMin ZHANG ChuanYin WANG ZhengTao KE BaoGui 《中国科学:地球科学(英文版)》2014,57(7):1637-1644
Regional gravity field modeling with high-precision and high-resolution is one of the most important scientific objectives in geodesy,and can provide fundamental information for geophysics,geodynamics,seismology,and mineral exploration.Rectangular harmonic analysis(RHA)is proposed for regional gravity field modeling in this paper.By solving the Laplace’s equation of gravitational potential in local Cartesian coordinate system,the rectangular harmonic expansions of disturbing potential,gravity anomaly,gravity disturbance,geoid undulation and deflection of the vertical are derived,and so are the formula for signal degree variance and error degree variance of the rectangular harmonic coefficients(RHC).We also present the mathematical model and detailed algorithm for the solution of RHC using RHA from gravity observations.In order to reduce the edge effects caused by periodic continuation in RHA,we propose the strategy of extending the size of computation domain.The RHA-based modeling method is validated by conducting numerical experiments based on simulated ground and airborne gravity data that are generated from geopotential model EGM2008 and contaminated by Gauss white noise with standard deviation of 2 mGal.The accuracy of the 2.5′×2.5′geoid undulations computed from ground and airborne gravity data is 1 and 1.4cm,respectively.The standard error of the gravity disturbances that downward continued from the flight height of 4 km to the geoid is only 3.1 mGal.Numerical results confirm that RHA is able to provide a reliable and accurate regional gravity field model,which may be a new option for the representation of the fine structure of regional gravity field. 相似文献
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捷联式航空重力测量系统与平台式系统相比具有体积小、重量轻、功耗低等许多优点,近些年来取得了显著的研究进展.本文给出了捷联式航空重力测量的两种算法模型:捷联式惯性标量重力测量(SISG)和旋转不变式标量重力测量(RISG)模型,并对其误差模型作了初步讨论.利用我国首套捷联式航空重力仪SGA-WZ01在某海域的部分试验数据,对两种算法模型进行了比较分析,表明其差值之标准差对于200s的滤波长度小于0.5mGal.同时,利用两组重复测线数据估算了不同滤波尺度下的两种算法的内符合精度,表明SISG算法略优于RISG算法.对于200s和300s的滤波长度,SISG的内符合精度分别为1.06mGal和0.80mGal. 相似文献
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The spatial resolution and quality of geopotential models (EGM2008, EIGEN-5C, ITG-GRACE03s, and GOCO-01s) have been assessed as applied to lithospheric structure of the Andean and Central American subduction zones. For the validation, we compared the geopotential models with existing terrestrial gravity data and density models as constrained by seismic and geological data. The quality and resolution of the downward continued geopotential models in the Andes and Central America decrease with increasing topography and depend on the availability of terrestrial gravity data. High resolution of downward continued gravity data has been obtained over the Southern Andes where elevations are lower than 3000 m and sufficient terrestrial gravity data are available. The resolution decreases with an increase in elevation over the north Chilean Andes and Central America. The low resolution in Central America is mainly attributed to limited surface gravity data coverage of the region.To determine the minimum spatial dimension of a causative body that could be resolved using gravity gradient data, a synthetic gravity gradient response of a spherical anomalous mass has been computed at GOCE orbit height (254.9 km). It is shown that the minimum diameter of such a structure with density contrast of 240 kg m−3 should be at least ∼45 km to generate signal detectable at orbit height. The batholithic structure in Northern Chile, which is assumed to be associated with plate coupling and asperity generation, is about 60–120 km wide and could be traceable in GOCE data. Short wavelength anomalous structures are more pronounced in the components of the gravity gradient tensor and invariants than in the gravity field.As the ultimate objective of this study is to understand the state of stress along plate interface, the geometry of the density model, as constrained by combined gravity models and seismic data, has been used to develop dynamic model of the Andean margin. The results show that the stress regime in the fore-arc (high and low) tends to follow the trend of the earthquake distributions. 相似文献
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An experimental development of a computer controlled photoelectric ocular system applied for the LaCoste and Romberg G949 gravimeter made the continuous observation of time variation of gravity possible. The system was operated for half a year in the Sopronbánfalva Geodynamical Observatory to test its capabilities. The primary aim of this development was to provide an alternative and self-manageable solution instead of the standard electronic (Capacitive Position Indicator) reading of this type of gravimeter and use it for the monitoring of Earth tide. It, however, turned out that this system is sensitive enough to observe the effect of variable seismic noise (microseisms) due to the changes of ocean weather in the North Atlantic and North Sea regions at microGal level (1 μGal = 10−8 m/s2). Up to now not much attention was paid to its influence on the quality and accuracy of gravity observations because of the large distance (>1000 km) between the observation place (generally the Carpathian–Pannonian basin) and the locations (centres of storm zones of the northern hydrosphere) of triggering events. Based on an elementary harmonic surface deformation model the noise level of gravity observations was compared to the spectral characteristics of seismic time series recorded at the same time in the observatory. Although the sampling rate of gravity records was 120 s the daily variation of gravity noise level showed significant correlation with the variation of spectral amplitude distribution of the analysed high pass filtered (cut-off frequency = 0.005 Hz) seismograms up to 10 Hz. Also available daily maps of ocean weather parameters were used to support both the correlation analysis and the parameterization of the triggering events of microseisms for further statistical investigations. These maps, which were processed by standard image processing algorithms, provide numerical data about geometrical (distance and azimuth of the storm centres relative to the observation point) and physical (mass of swelling water) quantities. The information can be applied for characterizing the state of ocean weather at a given day which may help the prediction of its influence on gravity measurements in the future. Probably it is the first attempt to analyse quantitatively the effect of ocean weather on gravity observations in this specific area of the Carpathian–Pannonian region. 相似文献
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《Journal of Geodynamics》2010,49(3-5):284-291
The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several μGal yr−1. By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 μGal yr−1 with the thin-skinned tectonic and 0.3 μGal yr−1 with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements. 相似文献
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Mick S. Filmer Christian Hirt Will E. Featherstone 《Studia Geophysica et Geodaetica》2013,57(1):47-66
Gravity-based heights require gravity values at levelled benchmarks (BMs), which sometimes have to be predicted from surrounding observations. We use the Earth Gravitational Model 2008 (EGM2008) and the Australian National Gravity Database (ANGD) as examples of model and terrestrial observed data respectively to predict gravity at Australian National Levelling Network (ANLN) BMs. The aim is to quantify errors that may propagate into the predicted BM gravity values and then into gravimetric height corrections (HCs). Our results indicate that an approximate ±1 arc-min horizontal position error of the BMs causes maximum errors in EGM2008 BM gravity of ~22 mGal (~55 mm in the HC at ~2200 m elevation) and ~18 mGal for ANGD BM gravity because the values are not computed at the true location of the BM. We use RTM (residual terrain modelling) techniques to show that ~50% of EGM2008 BM gravity error in a moderately mountainous region can be accounted for by signal omission. Non-representative sampling of ANGD gravity in this region may cause errors of up to 50 mGals (~120 mm for the Helmert orthometric correction at ~2200 m elevation). For modelled gravity at BMs to be viable, levelling networks need horizontal BM positions accurate to a few metres, while RTM techniques can be used to reduce signal omission error. Unrepresentative gravity sampling in mountains can be remedied by denser and more representative re-surveys, and/or gravity can be forward modelled into regions of sparser gravity. 相似文献
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Pavel Novák 《Surveys in Geophysics》2010,31(1):1-21
During the General Assembly of the European Geosciences Union in April 2008, the new Earth Gravitational Model 2008 (EGM08)
was released with fully-normalized coefficients in the spherical harmonic expansion of the Earth’s gravitational potential
complete to degree and order 2159 (for selected degrees up to 2190). EGM08 was derived through combination of a satellite-based
geopotential model and 5 arcmin mean ground gravity data. Spherical harmonic coefficients of the global height function, that
describes the surface of the solid Earth with the same angular resolution as EGM08, became available at the same time. This
global topographical model can be used for estimation of selected constituents of EGM08, namely the gravitational potentials
of the Earth’s atmosphere, ocean water (fluid masses below the geoid) and topographical masses (solid masses above the geoid),
which can be evaluated numerically through spherical harmonic expansions. The spectral properties of the respective potential
coefficients are studied in terms of power spectra and their relation to the EGM08 potential coefficients is analyzed by using
correlation coefficients. The power spectra of the topographical and sea water potentials exceed the power of the EGM08 potential
over substantial parts of the considered spectrum indicating large effects of global isostasy. The correlation analysis reveals
significant correlations of all three potentials with the EGM08 potential. The potential constituents (namely their functionals
such as directional derivatives) can be used for a step known in geodesy and geophysics as the gravity field reduction or
stripping. Removing from EGM08 known constituents will help to analyze the internal structure of the Earth (geophysics) as
well as to derive the Earth’s gravitational field harmonic outside the geoid (geodesy). 相似文献
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《Journal of Geodynamics》2010,49(3-5):316-324
The superconducting gravimeters (SGs) are the most sensitive and stable gravity sensors currently available. The low drift and high sensitivity of these instruments allow to investigate several geophysical phenomena inducing small- and long-period gravity changes. In order to study such topics, any kind of disturbance of instrumental origin has to be identified and possibly modelled. A critical point in gravity measurement is the alignment of the gravimeter to the local vertical. In fact a tilt of the instrument will lead to an apparent gravity change and can affect the instrumental drift. To avoid these drawbacks, SGs are provided with an “active tilt feedback system” (ATFS) designed to keep the meter aligned to the vertical. We analyse tilt and environmental parameters collected near Strasbourg, France, since 1997 to study the source of the tilt changes and check the capability of the ATFS to compensate them. We also present the outcomes of a calibration test applied to the ATFS output to convert the Tilt Power signals into angles. We find that most of the observed signal has a thermal origin dominated by a strong annual component of about 200 μrad. Nevertheless, our analysis shows that even the tilt due to different geophysical phenomena, other than the thermal ones, can be detected. A clear tidal signal of about 0.05 μrad is detectable thanks to the large data stacking (>11 years). We conclude that (i) the ATFS device compensates the tilt having a thermal origin or coming from any sources and (ii) no significant tilt changes alter the gravity signal, except for the high frequency (>1 mHz) perturbations. 相似文献
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EGM2008地球重力模型数据在中国大陆地区的精度分析 总被引：9，自引：1，他引：8
本文介绍了5′×5 ′的EGM2008地球重力模型及其在全球的精度评价.按照地形变化规律,将中国大陆大致分为7个区域,在10 km网度上,将EGM2008地球重力模型数据与中国地面实测空间重力网格数据进行了对比.由于数据源的问题,中国大陆的模型数据精度普遍低于北美和欧洲.二种数据在地形平坦的东部地区差别较小,向西随着地形复杂程度的增加,二种数据之间的标准差从小于10 mGal增大到50多mGal.畸变点分析表明精度极低的网格点均分布在地形起伏大的地区.总体而言,5′×5′的EGM2008地球重力模型数据在中国大陆将近80％的面积上的精度可达10 mGal之内,可用于小比例尺重力编图和构造研究.在地形起伏较大的中国西部以青藏高原为例进一步比较了EGM2008重力模型和重力测点数据,结果表明在重力点分布稀疏不均匀的地区,平面网格数据难以准确表达重力场信息.由于缺少地面重力数据控制,EGM2008重力模型数据在中国西部精度较低,但模型数据依然在很大程度上提高了空间重力异常信息的丰富程度.将中国区域重力调查成果数据应用于地球模型的构建是一项有意义的工作. 相似文献
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陆地重力观测相较于航空和卫星重力观测,距离场源更近,观测精度相对较高,其静态异常和时变数据已广泛应用于研究多种地球动力学问题.21世纪以来,绝对重力观测技术发展迅速,陆地观测网络日益完善,高精度陆地重力观测数据产品逐渐丰富,基于这些产品的大地测量和地球物理研究不断取得新进展.本文总结了近十几年来高精度陆地重力观测数据在大地测量和地球物理领域的应用进展情况,包括基于重力异常数据构建重力场和大地水准面模型、建立地壳物性结构模型、反演Moho界面形态和估计岩石圈有效弹性厚度,以及利用时变重力数据构建时变重力场模型、探测微弱动力学信号、估计地壳构造变形速率和分析与火山、地震过程的可能关联,最后探讨分析了陆地重力测量的未来发展趋势,可为中国大陆重力观测系统建设与发展规划提供参考. 相似文献
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We present a geoid model for the area of Lake Vostok, Antarctica, from a combination of local airborne gravity, ice-surface and ice-thickness data and a lake bathymetry model. The topography data are used for residual terrain modeling (RTM) in a remove–restore approach together with GOCE satellite data. The quasigeoid is predicted by least-squares collocation (LSC) and subsequently converted to geoid heights. Special aspects of that method in presence of an ice sheet are discussed.It is well known that a body freely floating in water is in a state of hydrostatic equilibrium (HE). This usually applies, e.g., to ice shelves or sea ice. However, it has been shown that this is valid also for the ice sheet covering the subglacial Lake Vostok. Thus, we demonstrate the use of such a refined regional geoid model for glaciological and geophysical applications by means of the HE surface of that lake. The mean quadratic residual geoid signal (0.56 m) w.r.t. the GOCE background model exceeds the residual variations of the estimated apparent lake level (ALL) (0.26 m) within the central part of the lake. An approach considering the actual geopotential at the ALL has been derived and subsequently applied. In this context, downward continuation of the potential field within the ice sheet as well as the latitudinal tilt of off-geoid equipotential surfaces are discussed. In view of the accuracy of the ice-thickness measurements that dominate the total error budget of the estimated ALL these effects are negligible. Thus, the HE surface of subglacial lakes may safely be described by a constant height bias in small-scale regional applications. However, field continuation is significant with respect to the formal uncertainty of the quasigeoid, which is at the level of 5 cm given that accurate airborne gravity data (±2 mGal) are available. 相似文献
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The gravitational effects of water storage variations driven by local precipitation events are modeled for the Walferdange Underground Laboratory for Geodynamics (WULG) in the Grand Duchy of Luxembourg. A modified mass continuity model is implemented, which uses rainfall data from Walferdange as input. In the absence of soil moisture and groundwater level information, the model is empirically parameterized. Model outputs are compared to the gravity time series registered with the Observatory Superconducting Gravimeter CT040 located in the WULG. We find that the model explains 77% of the gravity residuals. In addition, a statistical analysis is carried out to determine the relationship between precipitation, gravity variations and water level changes in the nearby Alzette River. A time delay of 88 ± 34 min between the maximum variation rates of the water level and gravity signal has been calculated. The signals have an admittance of 45 ± 5 cm μGal?1. 相似文献
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GPS data from Crustal Movement Observation Network of China (CMONOC) are used to derive far-field co-seismic displacements induced by the Mw 9.0 Tohoku Earthquake. Significant horizontal displacements about 30 mm, 10 mm, and 20 mm were caused by this large event in northeast China, north China, and on the Korean peninsula respectively. Vectors of relatively large horizontal displacements with dominant east components pointed to the epicenter of this earthquake. The east components show an exponential decay with the longitude, which is characteristic of the decay of the co-seismic horizontal displacements associated with earthquakes of thrust rupture. The exponential fit of the east components shows that the influence of the co-seismic displacements can be detected by GPS at a distance of about 3200 km from the epicenter of the earthquake. By considering the capability of the far field displacements for constraining the inversion of the fault slip model of the earthquake, we use spherically stratified Earth models to simulate the co-seismic displacements induced by this event. Using computations and comparisons, we discuss the effects of parameters of layered Earth models on the results of dislocation modeling. Comparisons of the modeled and observed displacements show that far field GPS observations are effective for constraining the fault slip model. The far field horizontal displacements observed by GPS are used to modify the slips and seismic moments of fault slip models. The result of this work is applicable as a reference for other researchers to study seismic source rupture and crustal deformation. 相似文献
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Time-variable GRACE (Gravity Recovery and Climate Experiment) gravity field solutions are routinely exploited to derive secular and seasonal mass changes on and near the Earth's surface. However, the quantification of mass redistribution from space gravimetry is not a straightforward process. For instance, published linear deglaciation rates of the Greenland ice sheets vary from ≈100 Gt/yr to ≈300 Gt/yr; the discrepancies are subject to applied methodologies, the considered gravity field time-series and the period of investigation. Furthermore, in the recent past discussion has come to the fore whether the temporal behavior of mass variation might be better represented by a second-order polynomial rather than a linear regression model. In summary, the degrees of freedom inherent to GRACE analysis make the detection of mass trends to become a delicate topic. This contribution sensitizes for a more careful review of trends derived from GRACE mass-variation time-series. We point to possible misinterpretation and propose “rules” that improve the consistency of results. 相似文献