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1.
The main focus of this paper is to assess the feasibility of utilizing dedicated satellite gravity missions in order to detect large-scale solid mass transfer events (e.g. landslides). Specifically, a sensitivity analysis of Gravity Recovery and Climate Experiment (GRACE) gravity field solutions in conjunction with simulated case studies is employed to predict gravity changes due to past subaerial and submarine mass transfer events, namely the Agulhas slump in southeastern Africa and the Heart Mountain Landslide in northwestern Wyoming. The detectability of these events is evaluated by taking into account the expected noise level in the GRACE gravity field solutions and simulating their impact on the gravity field through forward modelling of the mass transfer. The spectral content of the estimated gravity changes induced by a simulated large-scale landslide event is estimated for the known spatial resolution of the GRACE observations using wavelet multiresolution analysis. The results indicate that both the Agulhas slump and the Heart Mountain Landslide could have been detected by GRACE, resulting in \({\vert }0.4{\vert }\) and \({\vert }0.18{\vert }\) mGal change on GRACE solutions, respectively. The suggested methodology is further extended to the case studies of the submarine landslide in Tohoku, Japan, and the Grand Banks landslide in Newfoundland, Canada. The detectability of these events using GRACE solutions is assessed through their impact on the gravity field. 相似文献
2.
J. Neumeyer F. Barthelmes O. Dierks F. Flechtner M. Harnisch G. Harnisch J. Hinderer Y. Imanishi C. Kroner B. Meurers S. Petrovic Ch. Reigber R. Schmidt P. Schwintzer H. -P. Sun H. Virtanen 《Journal of Geodesy》2006,79(10-11):573-585
Gravity recovery and climate experiment (GRACE)-derived temporal gravity variations can be resolved within the μgal (10?8 m/s 2) range, if we restrict the spatial resolution to a half-wavelength of about 1,500 km and the temporal resolution to 1 month. For independent validations, a comparison with ground gravity measurements is of fundamental interest. For this purpose, data from selected superconducting gravimeter (SG) stations forming the Global Geodynamics Project (GGP) network are used. For comparison, GRACE and SG data sets are reduced for the same known gravity effects due to Earth and ocean tides, pole tide and atmosphere. In contrast to GRACE, the SG also measures gravity changes due to load-induced height variations, whereas the satellite-derived models do not contain this effect. For a solid spherical harmonic decomposition of the gravity field, this load effect can be modelled using degree-dependent load Love numbers, and this effect is added to the satellite-derived models. After reduction of the known gravity effects from both data sets, the remaining part can mainly be assumed to represent mass changes in terrestrial water storage. Therefore, gravity variations derived from global hydrological models are applied to verify the SG and GRACE results. Conversely, the hydrology models can be checked by gravity variations determined from GRACE and SG observations. Such a comparison shows quite a good agreement between gravity variation derived from SG, GRACE and hydrology models, which lie within their estimated error limits for most of the studied SG locations. It is shown that the SG gravity variations (point measurements) are representative for a large area within the accuracy, if local gravity effects are removed. The individual discrepancies between SG, GRACE and hydrology models may give hints for further investigations of each data series. 相似文献
3.
Since its launch in 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has been providing measurements of the
time-varying Earth gravity field. The GRACE mission architecture includes two satellites in near-circular, near-polar orbits
separated in the along-track direction by approximately 220 km (e.g. collinear). A microwave ranging instrument measures changes
in the distance between the spacecraft, while accelerometers on each spacecraft are used to measure changes in distance due
to non-gravitational forces. The fact that the satellites are in near-polar orbits coupled with the fact that the inter-satellite
range measurements are directed in the along-track direction, contributes to longitudinal striping in the estimated gravity
fields. This paper examines four candidate mission architectures for a future gravity recovery satellite mission to assess
their potential in measuring the gravity field more accurately than GRACE. All satellites were assumed to have an improved
measurement system, with an inter-satellite laser ranging instrument and a drag-free system for removal of non-gravitational
accelerations. Four formations were studied: a two-satellite collinear pair similar to GRACE; a four-satellite architecture
with two collinear pairs; a two-satellite cartwheel formation; and a four-satellite cartwheel formation. A cartwheel formation
consists of satellites performing in-plane, relative elliptical motion about their geometric center, so that inter-satellite
measurements are, at times, directed radially (e.g. parallel to the direction towards the center of the Earth) rather than
along-track. Radial measurements, unlike along-track measurements, have equal sensitivity to mass distribution in all directions
along the Earth’s surface and can lead to higher spatial resolution in the derived gravity field. The ability of each architecture
to recover the gravity field was evaluated using numerical simulations performed with JPL’s GIPSY-OASIS software package.
Thirty days of data were used to estimate gravity fields complete to degree and order 60. Evaluations were done for 250 and
400 km nominal orbit altitudes. The sensitivity of the recovered gravity field to under-sampled effects was assessed using
simulated errors in atmospheric/ocean dealiasing (AOD) models. Results showed the gravity field errors associated with the
four-satellite cartwheel formation were approximately one order of magnitude lower than the collinear satellite pair when
only measurement system errors were included. When short-period AOD model errors were introduced, the gravity field errors
for each formation were approximately the same. The cartwheel formations eliminated most of the longitudinal striping seen
in the gravity field errors. A covariance analysis showed the error spectrum of the cartwheel formations to be lower and more
isotropic than that of the collinear formations. 相似文献
4.
Validation of GOCE gravity field models by means of orbit residuals and geoid comparisons 总被引：6，自引：3，他引：3
Three GOCE-based gravity field solutions have been computed by ESA’s high-level processing facility and were released to the
user community. All models are accompanied by variance-covariance information resulting either from the least squares procedure
or a Monte-Carlo approach. In order to obtain independent external quality parameters and to assess the current performance
of these models, a set of independent tests based on satellite orbit determination and geoid comparisons is applied. Both
test methods can be regarded as complementary because they either investigate the performance in the long wavelength spectral
domain (orbit determination) or in the spatial domain (geoid comparisons). The test procedure was applied to the three GOCE
gravity field solutions and to a number of selected pre-launch models for comparison. Orbit determination results suggest,
that a pure GOCE gravity field model does not outperform the multi-year GRACE gravity field solutions. This was expected as
GOCE is designed to improve the determination of the medium to high frequencies of the Earth gravity field (in the range of
degree and order 50 to 200). Nevertheless, in case of an optimal combination of GOCE and GRACE data, orbit determination results
should not deteriorate. So this validation procedure can also be used for testing the optimality of the approach adopted for
producing combined GOCE and GRACE models. Results from geoid comparisons indicate that with the 2 months of GOCE data a significant
improvement in the determination of the spherical harmonic spectrum of the global gravity field between degree 50 and 200
can be reached. Even though the ultimate mission goal has not yet been reached, especially due to the limited time span of
used GOCE data (only 2 months), it was found that existing satellite-only gravity field models, which are based on 7 years
of GRACE data, can already be enhanced in terms of spatial resolution. It is expected that with the accumulation of more GOCE
data the gravity field model resolution and quality can be further enhanced, and the GOCE mission goal of 1–2 cm geoid accuracy
with 100 km spatial resolution can be achieved. 相似文献
5.
6.
针对GRACE Level2卫星时变重力数据后处理方法如何评价的问题,该文以中国数字地震观测网络获得的青藏高原地区地面重力变化图像为参考,基于平均结构相似性等图像相似度指标,研究了与该区域地面重力观测同期、不同后处理方法得到的GRACE卫星重力变化图像的可靠性。结果显示,GRACE卫星重力和地面重力观测结果具有一定的可比性,滑动窗口去相关滤波和高斯400 km滤波的组合方法可以获得最优的处理效果。本文的方法和结论对GRACE及GRACE Follow-On卫星重力数据应用中后处理方法和参数的选取有一定的借鉴意义。 相似文献
7.
为了合理补充重力场恢复与气候试验卫星（Gravity Recovery and Climate Experiment,GRACE）时变重力场的一阶斯托克斯系数（C10、C11、S11）和替换二阶斯托克斯系数（C20）,介绍了相关GRACE-OBP算法及其改进的算法,比较了相应的Chamber Model和4个Sun Model的一阶系数及其计算的地表质量异常,同时比较了基于卫星激光测距观测的Cheng Model与4个Sun Model的C20及其地表质量异常。结果表明,GRACE-OBP算法的一阶系数、卫星激光测距观测的C20及其地表质量异常与改进的GRACE-OBP算法在趋势项上有很大差异,但周年项差异相对较小。利用不同截断阶数和不同机构的GRACE时变重力场模型,对其趋势项和周年项都有一定影响,且对趋势项影响更大。因此,在计算陆地水储量变化时,建议使用改进的GRACE-OBP算法的估计结果,使用较理想的、截断阶数较高的GRACE时变重力模型。 相似文献
8.
Matthieu J. Talpe R. Steven Nerem Ehsan Forootan Michael Schmidt Frank G. Lemoine Ellyn M. Enderlin Felix W. Landerer 《Journal of Geodesy》2017,91(11):1283-1298
We construct long-term time series of Greenland and Antarctic ice sheet mass change from satellite gravity measurements. A statistical reconstruction approach is developed based on a principal component analysis (PCA) to combine high-resolution spatial modes from the Gravity Recovery and Climate Experiment (GRACE) mission with the gravity information from conventional satellite tracking data. Uncertainties of this reconstruction are rigorously assessed; they include temporal limitations for short GRACE measurements, spatial limitations for the low-resolution conventional tracking data measurements, and limitations of the estimated statistical relationships between low- and high-degree potential coefficients reflected in the PCA modes. Trends of mass variations in Greenland and Antarctica are assessed against a number of previous studies. The resulting time series for Greenland show a higher rate of mass loss than other methods before 2000, while the Antarctic ice sheet appears heavily influenced by interannual variations. 相似文献
9.
Attenuation effect on seasonal basin-scale water storage changes from GRACE time-variable gravity 总被引：3，自引：0，他引：3
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
10.
The static gravity field model DGM-1S from GRACE and GOCE data: computation, validation and an analysis of GOCE mission’s added value 总被引：4，自引：2，他引：2
We present a global static model of the Earth’s gravity field entitled DGM-1S based on GRACE and GOCE data. The collection of used data sets includes nearly 7 years of GRACE KBR data and 10 months of GOCE gravity gradient data. The KBR data are transformed with a 3-point differentiation into quantities that are approximately inter-satellite accelerations. Gravity gradients are processed in the instrumental frame. Noise is handled with a frequency-dependent data weighting. DGM-1S is complete to spherical harmonic degree 250 with a Kaula regularization being applied above degree 179. Its performance is compared with a number of other satellite-only GRACE/GOCE models by confronting them with (i) an independent model of the oceanic mean dynamic topography, and (ii) independent KBR and gravity gradient data. The tests reveal a competitive quality for DGM-1S. Importantly, we study added value of GOCE data by comparing the performance of satellite-only GRACE/GOCE models with models produced without GOCE data: either ITG-Grace2010s or EGM2008 depending on which of the two performs better in a given region. The test executed based on independent gravity gradients quantifies this added value as 25–38 % in the continental areas poorly covered with terrestrial gravimetry data (Equatorial Africa, Himalayas, and South America), 7–17 % in those with a good coverage with these data (Australia, North America, and North Eurasia), and 14 % in the oceans. This added value is shown to be almost entirely related to coefficients below degree 200. It is shown that this gain must be entirely attributed to gravity gradients acquired by the mission. The test executed based on an independent model of the mean dynamic topography suggests that problems still seem to exist in satellite-only GRACE/GOCE models over the Pacific ocean, where noticeable deviations between these models and EGM2008 are detected, too. 相似文献
11.
Assessment of observing time-variable gravity from GOCE GPS and accelerometer observations 总被引：2，自引：1，他引：1
P. N. A. M. Visser W. van der Wal E. J. O. Schrama J. van den IJssel J. Bouman 《Journal of Geodesy》2014,88(11):1029-1046
An assessment has been made of the possibility to estimate time-variable gravity from GPS-derived orbit perturbations and common-mode accelerometer observations of ESA’s GOCE Earth Explorer. A number of 20-day time series of Earth’s global long-wavelength gravity field have been derived for the period November 2009 to November 2012 using different parameter setups and estimation techniques. These techniques include a conventional approach where for each period, one set of gravity coefficients is estimated, either excluding or including empirical accelerations, and the so-called Wiese approach where higher frequency coefficients are estimated for the very long wavelengths. A principal component analysis of especially the time series of gravity field coefficients obtained by the Wiese approach and the conventional approach with empirical accelerations reveals an annual signal. When fitting this annual signal directly through the time series, the sine component (maximum in spring) displays features that are similar to well-known continental hydrological mass changes for the low latitude areas, such as mass variations in the Amazon basin, Africa and Australia for spatial scales down to 1,500 km. The cosine component (maximum in winter), however, displays large signals that can not be attributed to actual mass variations in the Earth system. The estimated gravity field changes from GOCE orbit perturbations are likely affected by missing GPS observations in case of high ionospheric perturbations during periods of increased solar activity, which is minimal in Summer and maximal towards the end of autumn. 相似文献
12.
Christoph Förste Roland Schmidt Richard Stubenvoll Frank Flechtner Ulrich Meyer Rolf König Hans Neumayer Richard Biancale Jean-Michel Lemoine Sean Bruinsma Sylvain Loyer Franz Barthelmes Saskia Esselborn 《Journal of Geodesy》2008,82(6):331-346
The recent improvements in the Gravity Recovery And Climate Experiment (GRACE) tracking data processing at GeoForschungsZentrum
Potsdam (GFZ) and Groupe de Recherche de Géodésie Spatiale (GRGS) Toulouse, the availability of newer surface gravity data
sets in the Arctic, Antarctica and North-America, and the availability of a new mean sea surface height model from altimetry
processing at GFZ gave rise to the generation of two new global gravity field models. The first, EIGEN-GL04S1, a satellite-only
model complete to degree and order 150 in terms of spherical harmonics, was derived by combination of the latest GFZ Potsdam
GRACE-only (EIGEN-GRACE04S) and GRGS Toulouse GRACE/LAGEOS (EIGEN-GL04S) mean field solutions. The second, EIGEN-GL04S1 was
combined with surface gravity data from altimetry over the oceans and gravimetry over the continents to derive a new high-resolution
global gravity field model called EIGEN-GL04C. This model is complete to degree and order 360 and thus resolves geoid and
gravity anomalies at half- wavelengths of 55 km at the equator. A degree-dependent combination method has been applied in
order to preserve the high accuracy from the GRACE satellite data in the lower frequency band of the geopotential and to form
a smooth transition to the high-frequency information coming from the surface data. Compared to pre-CHAMP global high-resolution
models, the accuracy was improved at a spatial resolution of 200 km (half-wavelength) by one order of magnitude to 3 cm in
terms of geoid heights. The accuracy of this model (i.e. the commission error) at its full spatial resolution is estimated
to be 15 cm. The model shows a reduced artificial meridional striping and an increased correlation of EIGEN-GL04C-derived
geostrophic meridional currents with World Ocean Atlas 2001 (WOA01) data. These improvements have led to select EIGEN-GL04C
for JASON-1 satellite altimeter data reprocessing.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
Evaluation of the third- and fourth-generation GOCE Earth gravity field models with Australian terrestrial gravity data in spherical harmonics 总被引：1，自引：1，他引：0
In March 2013, the fourth generation of European Space Agency’s (ESA) global gravity field models, DIR4 (Bruinsma et al. in Proceedings of the ESA living planet symposium, 28 June–2 July, Bergen, ESA, Publication SP-686, 2010b) and TIM4 (Migliaccio et al. in Proceedings of the ESA living planet symposium, 28 June–2 July, Bergen, ESA, Publication SP-686, 2010), generated from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) gravity observation satellite was released. We evaluate the models using an independent ground truth data set of gravity anomalies over Australia. Combined with Gravity Recovery and Climate Experiment (GRACE) satellite gravity, a new gravity model is obtained that is used to perform comparisons with GOCE models in spherical harmonics. Over Australia, the new gravity model proves to have significantly higher accuracy in the degrees below 120 as compared to EGM2008 and seems to be at least comparable to the accuracy of this model between degree 150 and degree 260. Comparisons in terms of residual quasi-geoid heights, gravity disturbances, and radial gravity gradients evaluated on the ellipsoid and at approximate GOCE mean satellite altitude ( $h=250$ km) show both fourth generation models to improve significantly w.r.t. their predecessors. Relatively, we find a root-mean-square improvement of 39 % for the DIR4 and 23 % for TIM4 over the respective third release models at a spatial scale of 100 km (degree 200). In terms of absolute errors, TIM4 is found to perform slightly better in the bands from degree 120 up to degree 160 and DIR4 is found to perform slightly better than TIM4 from degree 170 up to degree 250. Our analyses cannot confirm the DIR4 formal error of 1 cm geoid height (0.35 mGal in terms of gravity) at degree 200. The formal errors of TIM4, with 3.2 cm geoid height (0.9 mGal in terms of gravity) at degree 200, seem to be realistic. Due to combination with GRACE and SLR data, the DIR models, at satellite altitude, clearly show lower RMS values compared to TIM models in the long wavelength part of the spectrum (below degree and order 120). Our study shows different spectral sensitivity of different functionals at ground level and at GOCE satellite altitude and establishes the link among these findings and the Meissl scheme (Rummel and van Gelderen in Manusrcipta Geodaetica 20:379–385, 1995). 相似文献
14.
15.
介绍了GRACE重力卫星,并对GRACE重力卫星数据在陆地水储量变化中的应用现状进行分析,总结了GRACE重力卫星数据在陆地水储量变化检测中的数据获取、计算方法和精度分析,以及Grace数据在不同区域尺度陆地水储量变化估算中的应用情况,最后,指出GRACE在水储量应用中的不足和未来的研究方向。 相似文献
16.
在计算GRACE重力场反演中的大气去混频模型时,针对ECMWFop或ERA-Interim大气数据空间水平分辨率不足的问题,提出了一种局部区域高空间水平分辨率大气数据与全球大气数据合理拼接融合的方法。利用欧洲局部区域的大气数据与ERA-Interim大气数据融合计算了一组改进的大气去混频模型,从谱域、空域及星间距离变率残差角度分析了改进大气去混频模型的质量。结果表明改进大气去混频模型相对于常规大气去混频模型的质量提高最大比例为1.87%,与AOD1BRL05相对于RL04的提高比例2.27%相当,验证了高空间水平分辨率大气数据确实有助于提高大气去混频模型质量的结论,为改进GRACE提取局部区域特定质量变化信号提供了一种方法。 相似文献
17.
The nature of the gravity field inverse problem amplifies the noise in the GRACE data, which creeps into the mid and high degree and order harmonic coefficients of the Earth’s monthly gravity fields provided by GRACE. Due to the use of imperfect background models and data noise, these errors are manifested as north-south striping in the monthly global maps of equivalent water heights. In order to reduce these errors, this study investigates the use of the L-curve method with Tikhonov regularization. L-curve is a popular aid for determining a suitable value of the regularization parameter when solving linear discrete ill-posed problems using Tikhonov regularization. However, the computational effort required to determine the L-curve is prohibitively high for a large-scale problem like GRACE. This study implements a parameter-choice method, using Lanczos bidiagonalization which is a computationally inexpensive approximation to L-curve. Lanczos bidiagonalization is implemented with orthogonal transformation in a parallel computing environment and projects a large estimation problem on a problem of the size of about 2 orders of magnitude smaller for computing the regularization parameter. Errors in the GRACE solution time series have certain characteristics that vary depending on the ground track coverage of the solutions. These errors increase with increasing degree and order. In addition, certain resonant and near-resonant harmonic coefficients have higher errors as compared with the other coefficients. Using the knowledge of these characteristics, this study designs a regularization matrix that provides a constraint on the geopotential coefficients as a function of its degree and order. This regularization matrix is then used to compute the appropriate regularization parameter for each monthly solution. A 7-year time-series of the candidate regularized solutions (Mar 2003–Feb 2010) show markedly reduced error stripes compared with the unconstrained GRACE release 4 solutions (RL04) from the Center for Space Research (CSR). Post-fit residual analysis shows that the regularized solutions fit the data to within the noise level of GRACE. A time series of filtered hydrological model is used to confirm that signal attenuation for basins in the Total Runoff Integrating Pathways (TRIP) database over 320 km radii is less than 1 cm equivalent water height RMS, which is within the noise level of GRACE. 相似文献
18.
Recently, a new application of time-dependent gravity observations is emerging: the study of natural hydrological mass changes
and their underlying processes. Complementary to GRACE data and continuous recordings with superconducting gravimeters, repeated
observations with relative instruments on a local network may contribute to gain additional information on spatial changes
in hydrology. The questions that need to be addressed are whether the results of these repeated measurements will be of sufficiently
high resolution and accuracy, as well as how unique the information obtained will be. To examine this, a local gravity network
with maximum point distances of 65 m was established in a hilly area around the Geodynamic Observatory Moxa, Germany. Using
three to five LaCoste & Romberg relative gravimeters repeated measurements were carried out in a seasonal rhythm as well as
at particular events like snowmelt or dryness in 17 campaigns between November 2004 and April 2007. The standard deviations
obtained by least squares adjustment range from ±9 to ±14 nm/s2 for a gravity difference of one campaign, thus for gravity changes between two campaigns from ±13 to ±20 nm/s2. Between the points of the network, spatial gravity changes of up to 171 nm/s2 (139 nm/s2 between two successive campaigns) could be proven significantly. They correlate with changes in the local hydrological situation.
Particularly, a steep slope next to the observatory is identified as a gravimetrically significant hydrological compartment.
The results obtained contribute to an improved reduction of the local hydrological signal in continuous gravity recordings
and provide constraints to hydrological models. 相似文献
19.
利用重力恢复与气候实验(gravity recovery and climate experiment, GRACE)时变地球重力场模型计算得到非洲奥卡万戈三角洲地区2003-01—2014-12的陆地水储量变化信息,分别采用主成分分析(principal component analysis, PCA)和独立成分分析(independent component analysis, ICA)提取质量变化信号,并与全球陆地数据同化系统(global land data assimilation system, GLDAS)的水文模型进行对比。结果显示,在奥卡万戈河流域东北部,水储量表现出很强的周期性变化,两种数据空间特征分布的信号出现在相同位置的成分GRACE-IC1和GLDAS-IC1对应的时间序列的相关系数达到0.85。奥卡万戈三角洲地区水储量从2003-01—2011-10呈现上升趋势,两种数据空间特征分布的信号出现在相同位置的成分GRACE-IC2和GLDAS-IC3对应的时间序列的相关系数达到0.81,说明GRACE反演结果与GLDAS水文模型反演结果在研究区域内具有很强的一致性。引入全球降水气候中心降水数据和Water GAP全球水文模型数据对研究区域陆地水储量变化的原因进行分析。实验结果表明,相对于传统的多项式拟合方法,ICA可以在较大区域内直接对特定位置质量变化信号的时空特征进行提取;对比GRACE数据两种方法分解结果的第3成分可以看出,在空间尺度和时间尺度上,ICA方法对信号的分解能力要优于主成分分析方法。 相似文献
20.
Simulation study of a follow-on gravity mission to GRACE 总被引：9，自引：3，他引：6
The gravity recovery and climate experiment (GRACE) has been providing monthly estimates of the Earth’s time-variable gravity
field since its launch in March 2002. The GRACE gravity estimates are used to study temporal mass variations on global and
regional scales, which are largely caused by a redistribution of water mass in the Earth system. The accuracy of the GRACE
gravity fields are primarily limited by the satellite-to-satellite range-rate measurement noise, accelerometer errors, attitude
errors, orbit errors, and temporal aliasing caused by un-modeled high-frequency variations in the gravity signal. Recent work
by Ball Aerospace & Technologies Corp., Boulder, CO has resulted in the successful development of an interferometric laser
ranging system to specifically address the limitations of the K-band microwave ranging system that provides the satellite-to-satellite
measurements for the GRACE mission. Full numerical simulations are performed for several possible configurations of a GRACE
Follow-On (GFO) mission to determine if a future satellite gravity recovery mission equipped with a laser ranging system will
provide better estimates of time-variable gravity, thus benefiting many areas of Earth systems research. The laser ranging
system improves the range-rate measurement precision to ~0.6 nm/s as compared to ~0.2 μm/s for the GRACE K-band microwave
ranging instrument. Four different mission scenarios are simulated to investigate the effect of the better instrument at two
different altitudes. The first pair of simulated missions is flown at GRACE altitude (~480 km) assuming on-board accelerometers
with the same noise characteristics as those currently used for GRACE. The second pair of missions is flown at an altitude
of ~250 km which requires a drag-free system to prevent satellite re-entry. In addition to allowing a lower satellite altitude,
the drag-free system also reduces the errors associated with the accelerometer. All simulated mission scenarios assume a two
satellite co-orbiting pair similar to GRACE in a near-polar, near-circular orbit. A method for local time variable gravity
recovery through mass concentration blocks (mascons) is used to form simulated gravity estimates for Greenland and the Amazon
region for three GFO configurations and GRACE. Simulation results show that the increased precision of the laser does not
improve gravity estimation when flown with on-board accelerometers at the same altitude and spacecraft separation as GRACE,
even when time-varying background models are not included. This study also shows that only modest improvement is realized
for the best-case scenario (laser, low-altitude, drag-free) as compared to GRACE due to temporal aliasing errors. These errors
are caused by high-frequency variations in the hydrology signal and imperfections in the atmospheric, oceanographic, and tidal
models which are used to remove unwanted signal. This work concludes that applying the updated technologies alone will not
immediately advance the accuracy of the gravity estimates. If the scientific objectives of a GFO mission require more accurate
gravity estimates, then future work should focus on improvements in the geophysical models, and ways in which the mission
design or data processing could reduce the effects of temporal aliasing. 相似文献