共查询到20条相似文献，搜索用时 15 毫秒
1.
In view of the pivotal role that continental water storage plays in the Earth’s water, energy and biogeochemical cycles, the
temporal and spatial variations of water storage for large areas are presently not known with satisfactory accuracy. Estimates
of the seasonal storage change vary between less than 50 mm water equivalent in areas with uniform climatic conditions to
450 mm water equivalent in tropical river basins with a strong seasonality of the climate. Due to the lack of adequate ground-based
measurements of water storage changes, the evapotranspiration rate, which depends on the actual climatic and environmental
conditions, is only an approximation for large areas until now, or it is based on the assumption that storage changes level
out for long time periods. Furthermore, the partitioning of the water storage changes among different storage components is
insufficiently known for large scales. The direct measurement of water storage changes for large areas by satellite-based
gravity field measurements is thus of uttermost importance in the field of hydrology in order to close the water balance at
different scales in space and time, and to validate and improve the predictive capacity of large-scale hydrological models.
Due to the high spatial variability of hydrological processes temporal and spatial resolutions beyond that of GRACE are essential
for a spatial differentiation in evapotranspiration and water storage partitioning. 相似文献
2.
Efficient Determination of Global Gravity Field from Satellite-to-satellite Tracking Mission 总被引：2，自引：0，他引：2
Shin-Chan Han 《Celestial Mechanics and Dynamical Astronomy》2004,88(1):69-102
The gravity field dedicated satellite missions like CHAMP, GRACE, and GOCE are supposed to map the Earth's global gravity field with unprecedented accuracy and resolution. New models of the Earth's static and time-variable gravity fields will be available every month as one of the science products from GRACE. A method for the efficient gravity field recovery is presented using in situ satellite-to-satellite observations at altitude and results on static as well as temporal gravity field recovery are shown. Considering the energy relationship between the kinetic energy of the satellite and the gravitational potential, the disturbing potential observations can be computed from the orbital state vector, using high-low GPS tracking data, low–low satellite-to-satellite GRACE measurements, and data from 3-axis accelerometers. The solution method is based on the conjugate gradient iterative approach to efficiently recover the gravity field coefficients and approximate error covariance up to degree and order 120 every month. Based on the monthly GRACE noise-only simulation, the geoid was obtained with an accuracy of a few cm and with a resolution (half wavelength) of 160 km. However, the geoid accuracy can become worse by a factor of 6–7 because of spatial aliasing. The approximate error covariance was found to be a very good accuracy measure of the estimated coefficients, geoid, and gravity anomaly. The temporal gravity field, representing the monthly mean continental water mass redistribution, was recovered in the presence of measurement noise and high frequency temporal variation. The resulting recovered temporal gravity fields have about 0.3 mm errors in terms of geoid height with a resolution of 670 km. 相似文献
3.
G. Ramillien S. Bouhours A. Lombard A. Cazenave F. Flechtner R. Schmidt 《Global and Planetary Change》2008,60(3-4):381-392
Seasonal and inter-annual change in land water storage (expressed in terms of water volume change) over 27 large river basins worldwide are estimated from monthly GRACE geoids solutions computed at GFZ from February 2003 to February 2006. The largest annual water volume change is found in the Amazon basin, followed by the Parana, Ob, Orinoco, Tocantins, Niger, Congo, Ganges, Mekong, and Brahmaputra. In terms of trend over the 3-year period, positive and negative values are observed but in a number of cases computed trends are at the noise level. However significant negative trends are found in the Amazon, Ganges, Mississippi, Nile, Parana, and Zambezi basins, indicating water mass loss over that period. Positive trends (water mass gain) are marginally significant. We have computed the land water contribution to sea level change. On average over the 3-year time span, we find that the net effect is positive (net loss of water in terrestrial reservoirs), on the order of 0.19 +/− 0.06 mm/yr. If sustained over a longer time span than considered here, such a value may become comparable to the ice sheets contribution to sea level rise. 相似文献
4.
大气、陆地水储量和海水质量分布变化与地球低阶引力场球谐系数的关系 总被引：4，自引：1，他引：3
大气、固体地球及海洋组成了一个复杂、变化的地球动力学系统，这一系统中的任一质量分布变化都将产生地球引力场变化。采用全球7000多个地面气象台站的月平均降水及温度资料、NCEP提供气压月均值、TOPEX／Poseidon卫星测高资料和WOA98海水温度及盐度模型计算了大气、陆地水储量和海水质量分布变化引起地球低阶引力场系数变化。比较综合大气、陆地水储量和海水质量分布变化对带谐项J2，J3，J4影响的计算结果和人卫激光卫星的测定结果，可以看出，大气、陆地水储量和海水质量分布变化是引起地球低阶引力场系数周年变化的重要激发源。 相似文献
5.
GRACE重力计划在揭示地球系统质量重新分布中的应用 总被引：3，自引：0，他引：3
2002年3月成功发射的美德合作卫星重力计划GRACE(Gravity Recovery And ClimateExperiment),即将提供空间分辨率约为200 km而时间分辨率为1个月的时变地球重力场模型序列。GRACE计划的星座由两颗相距约220 km,高度保持为300-500 km、倾角保持约90°的近极轨卫星组成。由于采用星载GPS和非保守力加速度计等高精度定轨技术,以及高精度的星一星跟踪数据反演地球重力场,在几百公里和更大空间尺度上, GRACE重力场的精度大大超过此前的卫星重力计划。根据GRACE时变重力场反演的地球系统质量重新分布,将对固体地球物理、海洋物理、气候学以及大地测量等应用有重要的意义。虽然其设计寿命只有5 yr,但研究表明GRACE的结果可用于研究北极冰长期时间尺度的变化,并进而研究极冰融化对全球气候变化,特别是对海平面长期变化的影响。在季节性时间尺度上,利用GRACE重力场反演的质量重新分布足以揭示平均小于1 cm的地表水变化,或小于1 mbar。的海底压强变化。除了巨大的社会效益和经济效益外,这些变化对了解地球系统的物质循环(主要是水循环)和能量循环有非常重要的意义。介绍GRACE重力场揭示的地球系统质量重新分布,为理解其地球物理应用提供必需的准备;同时针对我国大陆和沿海地区的地球物理应用提出初步的设想。 相似文献
6.
Ernst J. O. Schrama 《Earth, Moon, and Planets》2004,94(1-2):143-163
Purpose of this article is to demonstrate the effect of background geophysical corrections on a follow-on gravity mission.
We investigate the quality of two effects, tides and atmospheric pressure variations, which both act as a surface load on
the lithosphere. In both cases direct gravitational attraction of the mass variations and the secondary potential caused by
the deformation of the lithosphere are sensed by a gravity mission. In order to assess the current situation we have simulated
GRACE range-rate errors which are caused by differences in present day tide and atmospheric pressure correction models. Both
geophysical correction models are capable of generating range-rate errors up to 10 μm/s and affect the quality of the recovered temporal and static gravity fields. Unlike missions such as TOPEX/Poseidon where
tides can be estimated with the altimeter, current gravity missions are only to some degree capable of resolving these (geo)physical
limitations. One of the reasons is the use of high inclination low earth orbits without a repeating ground track strategy.
The consequence is that we will face a contamination of the gravity solution, both in the static and the time variable part.
In the conclusions of this paper we provide suggestions for improving this situation, in particular in view of follow-on gravity
missions after GRACE and GOCE, which claim an improved capability of estimating temporal variations in the Earth’s gravity
field. 相似文献
7.
The inversion of the variation in the land water storage in Southwest China is carried out by taking advantage of the data obtained by the earth gravity satellite GRACE (Gravity Recovery and Climate Experiment) for 64 months from January 2005 to April 2010. The result shows that by selecting an appropriate Gauss radius (R = 600 km) and taking the average gravitational field of the adopted data as the back-ground gravitational field, the land water storage in Southwest China inverted on the basis of the GRACE data reflects the drought in Southwest China at the beginning of 2010 very well. 相似文献
8.
卫星跟踪卫星模式中轨道参数需求分析 总被引：8，自引：0，他引：8
首次基于半解析法利用GRACE(Gravity Recovery and Climate Experiment)双星K波段星间速度误差、GPS接收机轨道误差和加速度计非保守力误差影响累计大地水准面精度的联合模型开展了卫星跟踪卫星模式中轨道参数的需求分析.建议我国将来首颗重力卫星的平均轨道高度设计为400 km和平均星间距离设计为220 km较优.此研究不仅为我国将来卫星重力测量计划中轨道参数的优化选取以及全球重力场精度的有效和快速估计提供了理论基础和计算保证,同时对将来国际GRACE Follow-On地球重力测量计划和GRAIL(Gravity Recovery and Interior Laboratory)月球重力探测计划的发展方向具有一定的指导意义. 相似文献
9.
R. Rummel 《Earth, Moon, and Planets》2004,94(1-2):3-11
Precise global geoid and gravity anomaly information serves essentially three different kinds of applications in Earth sciences:
gravity and geoid anomalies reflect density anomalies in oceanic and continental lithosphere and the mantle; dynamic ocean
topography as derived from the combination of satellite altimetry and a global geoid model can be directly transformed into
a global map of ocean surface circulation; any redistribution or exchange of mass in Earth system results in temporal gravity
and geoid changes. After completion of the dedicated gravity satellite missions GRACE and GOCE a high standard of global gravity
determination, both of the static and of the time varying field will be attained. Thus, it is the right time to investigate
the future needs for improvements in the various fields of Earth sciences and to define the right strategy for future gravity
field satellite missions. 相似文献
10.
11.
Jean Emmanuel Sicart Pierre Ribstein Bernard Francou Bernard Pouyaud Thomas Condom 《Global and Planetary Change》2007,59(1-4):27
A glaciological program has been undertaken since 1991 on Zongo glacier in Bolivia (6000–4850 m asl, 2.4 km2, 16°S). This program involves mass balance measurements, hydrological studies and energy balance investigations. On outer-tropical glaciers, melting and snow accumulation are both maximum in the wet season (austral summer), whereas the dry season (winter) is a period of low ablation. Errors on each term of the glaciological (stakes, snow-pits and integration method of the measurements) and hydrological (precipitation, discharge and runoff coefficient of free ice areas) methods are investigated to estimate the overall accuracy of the mass balance measurements. The hydrological budget is less than the glaciological one (mean difference: 60 cm w.e. per year), but both methods reproduce similar inter-annual variations. Errors in assessment of evaporation or water storage inside the glacier cannot explain the discrepancy. Errors using the glaciological method are large (around ± 40 cm w.e. per year), but no bias can explain the departure from the hydrological balance. Errors on discharge measurements are small and the uncertainty on the runoff coefficient has a minor effect on the mass balance. We concluded that hydrological budgets are too low due to the catch deficiency of rain gauges and absence of precipitation measurements at high altitudes, emphasizing the difficulty to assess snowfall distribution in high mountainous basins. 相似文献
12.
A summary is offered of the potential benefits of future measurements of temporal variations in gravity for the understanding
of ocean dynamics. Two types of process, and corresponding amplitudes are discussed: ocean basin scale pressure changes, with
a corresponding amplitude of order 1 cm of water, or 1 mm of geoid height, and changes in along-slope pressure gradient, at
cross-slope length scales corresponding to topographic slopes, with a corresponding amplitude of order 1 mm of water, or a
maximum of about 0.01 mm of geoid. The former is feasible with current technology and would provide unprecedented information
about abyssal ocean dynamics associated with heat transport and climate. The latter would be a considerable challenge to any
foreseeable technology, but would provide an exceptionally clear, quantitative window on the dynamics of abyssal ocean currents,
and strong constraints on ocean models. Both options would be limited by the aliassing effect of rapid mass movements in the
earth system, and it is recommended that any future mission take this error source explicitly into account at the design stage.
For basin-scale oceanography this might involve a higher orbit than GRACE or GOCE, and the advantages of exact-repeat orbits
and multiple missions should be considered. 相似文献
13.
To use basin stratigraphy for studying past climate change, it is important to understand the influence of evolving boundary conditions (river discharge and sediment flux, initial bathymetry, sea level, subsidence) and the complex interplay of the redistribution processes (plumes, turbidity currents, debris flows). To provide understanding of this complexity, we have employed source to sink numerical models to evaluate which process dominates the observed variability in a sedimentary record of two coastal Pacific basins, Knight Inlet in British Columbia and the Eel Margin of northern California.During the last glacial period, the Eel River supplied comparatively more sediment with a less variable flux to the ocean, while today the river is dominated by episodic events. Model results show this change in the variability of sediment flux to be as important to the deposit character as is the change in the volume of sediment supply. Due to the complex interaction of flooding events and ocean storm events, the more episodic flood deposits of recent times are less well preserved than the flood deposits associated with an ice-age climate.In Knight Inlet, the evolving boundary conditions (rapidly prograding coastline, secondary transport by gravity flows from sediment failures) are a strong influence on the sedimentary record. The delta and gravity flow deposits punctuate the sedimentary record formed by hemipelagic sedimentation from river plumes. Missing time intervals due to sediment failures can take away the advantage of the otherwise amplified lithologic record of discharge events, given the enclosed nature of the fjord basin. 相似文献
14.
J. Flury 《Earth, Moon, and Planets》2004,94(1-2):83-91
An overview of advances in ice research which can be expected from future satellite gravity missions is given. We compare
present and expected future accuracies of the ice mass balance of Antarctica which might be constrained to 0.1–0.3 mm/year
of sea level equivalent by satellite gravity data. A key issue for the understanding of ice mass balance is the separation
of secular and interannual variations. For this aim, one would strongly benefit from longer uninterrupted time series of gravity
field variations (10 years or more). An accuracy of 0.01 mm/year for geoid time variability with a spatial resolution of 100
km would improve the separability of ice mass balance from mass change due to glacial isostatic adjustment and enable the
determination of regional variations in ice mass balance within the ice sheets. Thereby the determination of ice compaction
is critical for the exploitation of such high accuracy data. A further benefit of improved gravity field models from future
satellite missions would be the improvement of the height reference in the polar areas, which is important for the study of
coastal ice processes. Sea ice thickness determination and modelling of ice bottom topography could be improved as well. 相似文献
15.
极端质量比旋进系统是空间引力波探测器最重要的波源之一。对引力波的探测需要高精度波形模版。当前主流的极端质量比旋进系统引力波计算模型中,人们一般将小质量天体当作试验粒子进行计算,而忽略了其结构及自身引力对背景引力场的影响。利用Mathisson-Papapetrou-Dixon方程研究延展体在弯曲时空中的运动,以及小天体自旋和质量多极矩对引力波信号识别产生的影响。结果表明,质量比在10?6-10?4范围的旋进系统,其自旋达到很大时,自旋对延展体的轨道运动有不可忽略的影响;在质量比10?4-10?2区间内,需要考虑中心黑洞潮汐作用导致的白矮星形变;在质量比大于10?4,且白矮星自旋很大时,其自旋产生的形变会对小天体轨道运动产生不可忽略的影响。大质量黑洞潮汐作用导致的恒星级黑洞或中子星产生的形变可以忽略,中子星和黑洞的自旋会对轨道运动产生不可忽略的影响,而自旋产生的四极矩对轨道运动不产生影响。 相似文献
16.
After GRACE and GOCE there will still be need and room for improvement of the knowledge (1) of the static gravity field at
spatial scales between 40 km and 100 km, and (2) of the time varying gravity field at scales smaller than 500 km. This is
shown based on the analysis of spectral signal power of various gravity field components and on the comparison with current
knowledge and expected performance of GRACE and GOCE. Both, accuracy and resolution can be improved by future dedicated gravity
satellite missions. For applications in geodesy, the spectral omission error due to the limited spatial resolution of a gravity
satellite mission is a limiting factor. The recommended strategy is to extend as far as possible the spatial resolution of
future missions, and to improve at the same time the modelling of the very small scale components using terrestrial gravity
information and topographic models.We discuss the geodetic needs in improved gravity models in the areas of precise height
systems, GNSS levelling, inertial navigation and precise orbit determination. Today global height systems with a 1 cm accuracy
are required for sea level and ocean circulation studies. This can be achieved by a future satellite mission with higher spatial
resolution in combination with improved local and regional gravity field modelling. A similar strategy could improve the very
economic method of determination of physical heights by GNSS levelling from the decimeter to the centimeter level. In inertial
vehicle navigation, in particular in sub-marine, aircraft and missile guidance, any improvement of global gravity field models
would help to improve reliability and the radius of operation. 相似文献
17.
M. E. McCulloch 《Astrophysics and Space Science》2014,349(2):957-959
It is shown here that Newton’s gravity law can be derived from the uncertainty principle. The idea is that as the distance between two bodies in mutual orbit decreases, their uncertainty of position decreases, so their momentum and hence the force on them must increase to satisfy the uncertainty principle. When this result is summed over all the possible interactions between the Planck masses in the two bodies, Newton’s gravity law is obtained. This model predicts that masses less than the Planck mass will be unaffected by gravity and so it may be tested by looking for an abrupt decrease in the density of space dust, for masses above the Planck mass. 相似文献
18.
A. Cazenave K. Dominh S. Guinehut E. Berthier W. Llovel G. Ramillien M. Ablain G. Larnicol 《Global and Planetary Change》2009,65(1-2):83-88
From the IPCC 4th Assessment Report published in 2007, ocean thermal expansion contributed by ～ 50% to the 3.1 mm/yr observed global mean sea level rise during the 1993–2003 decade, the remaining rate of rise being essentially explained by shrinking of land ice. Recently published results suggest that since about 2003, ocean thermal expansion change, based on the newly deployed Argo system, is showing a plateau while sea level is still rising, although at a reduced rate (～ 2.5 mm/yr). Using space gravimetry observations from GRACE, we show that recent years sea level rise can be mostly explained by an increase of the mass of the oceans. Estimating GRACE-based ice sheet mass balance and using published estimates for glaciers melting, we further show that ocean mass increase since 2003 results by about half from an enhanced contribution of the polar ice sheets – compared to the previous decade – and half from mountain glaciers melting. Taking also into account the small GRACE-based contribution from continental waters (< 0.2 mm/yr), we find a total ocean mass contribution of ～ 2 mm/yr over 2003–2008. Such a value represents ～ 80% of the altimetry-based rate of sea level rise over that period. We next estimate the steric sea level (i.e., ocean thermal expansion plus salinity effects) contribution from: (1) the difference between altimetry-based sea level and ocean mass change and (2) Argo data. Inferred steric sea level rate from (1) (～ 0.3 mm/yr over 2003–2008) agrees well with the Argo-based value also estimated here (0.37 mm/yr over 2004–2008). Furthermore, the sea level budget approach presented in this study allows us to constrain independent estimates of the Glacial Isostatic Adjustment (GIA) correction applied to GRACE-based ocean and ice sheet mass changes, as well as of glaciers melting. Values for the GIA correction and glacier contribution needed to close the sea level budget and explain GRACE-based mass estimates over the recent years agree well with totally independent determinations. 相似文献
19.
Several contemporary modified models of gravity predict the existence of a non-Newtonian Yukawa-type correction to the classical
gravitational potential. We study the motion of a secondary celestial body under the influence of the corrected gravitational
force of a primary. We derive two equations to approximate the periastron time rate of change and its total variation over
one revolution (i.e., the difference between the anomalistic period and the Keplerian period) under the influence of the non-Newtonian
radial acceleration. Kinematically, this influence produces apsidal motion. We performed numerical estimations for Mercury,
for the companion star of the pulsar PSR 1913+16, and for the extrasolar Planet b of the star HD 80606. We also considered
the case of the artificial Earth satellite GRACE-A, but the results present a low degree of reliability from a practical standpoint. 相似文献
20.
Hong Zhang 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):189-195
Radio Doppler data generated by the Deep Space Network (DSN) from the recent encounters of the Galileo spacecraft with the Galilean satellites have been used to determine the mass (GM) and unnormalized quadruple gravity coefficients in the external gravitational fields of the Galilean satellites. Therefore, a series of internal structure models, which satisfy the given constraints for the mean density and the mean moment of inertia, can be presented by solving Emden equations. And some dynamical parameters can also be calculated based on the density distributions given by internal structure models. 相似文献