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1.
Evaluation and validation of mascon recovery using GRACE KBRR data with independent mass flux estimates in the Mississippi Basin 总被引:1,自引:1,他引:0
S. Klosko D. Rowlands S. Luthcke F. Lemoine D. Chinn M. Rodell 《Journal of Geodesy》2009,83(9):817-827
The direct recovery of surface mass anomalies using GRACE KBRR data processed in regional solutions provides mass variation
estimates with 10-day temporal resolution. The approach undertaken herein uses a tailored orbit estimation strategy based
solely on the KBRR data and directly estimates mass anomalies from the GRACE data. We introduce a set of temporal and spatial
correlation constraints to enable high resolution mass flux estimates. The Mississippi Basin, with its well understood surface
hydrological modelling available from the Global Land Data Assimilation System (GLDAS), which uses advanced land surface modeling
and data assimilation techniques, and a wealth of groundwater data, provides an opportunity to quantitatively compare GRACE
estimates of the mass flux in the entire hydrological column with those available from independent and reliable sources. Evaluating
GRACE’s performance is dependent on the accuracy ascribed to the hydrological information, which in and of itself is a complex
challenge (Rodell in Hydrogeol J, doi:, 2007). Nevertheless, the Mississippi Basin is one of the few regions having a large hydrological signal that can support
a meaningful GRACE comparison on the spatial scale resolved by GRACE. The isolation of the hydrological signal is dependent
on the adequacy of the forward mass flux modeling for tides and atmospheric pressure variations. While these models have non-uniform
global performance they are excellent in the Mississippi Basin. Through comparisons with the independent hydrology, we evaluate
the effect on the solution of changing correlation times and distances in the constraints, altering the parameter recovery
for areas external to the Mississippi Basin, and changing the relative strength of the constraints with respect to the KBRR
data. The accuracy and stability of the mascon solutions are thereby assessed, especially with regard to the constraints used
to stabilize the solution. We show that the mass anomalies, as represented by surface layer of water within regional cells
have accuracy estimates of ±2–3 cm on par with the best hydrological estimates and consistent with our accuracy estimates
for GRACE mass anomaly estimates. These solutions are shown to be very stable, especially for the recovery of semi-annual
and longer period trends, where for example, the phase agreement for the dominant annual signal agrees at the 10-day level
of resolution provided by GRACE. This validation confirms that mascons provide critical environmental data records for a wide
range of applications including monitoring ground water mass changes. 相似文献
2.
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
3.
Improved GRACE science results after adjustment of geometric biases in the Level-1B K-band ranging data 总被引:3,自引:1,他引:2
Martin Horwath Jean-Michel Lemoine Richard Biancale Stéphane Bourgogne 《Journal of Geodesy》2011,85(1):23-38
The GRACE (Gravity Recovery and Climate Experiment) satellite mission relies on the inter-satellite K-band microwave ranging
(KBR) observations. We investigate systematic errors that are present in the Level-1B KBR data, namely in the geometric correction.
This correction converts the original ranging observation (between the two KBR antennas phase centers) into an observation
between the two satellites’ centers of mass. It is computed from data on the precise alignment between both satellites, that
is, between the lines joining the center of mass and the antenna phase center of either satellite. The Level-1B data used
to determine this alignment exhibit constant biases as large as 1–2 mrad in terms of pitch and yaw alignment angles. These
biases induce non-constant errors in the Level-1B geometric correction. While the precise origin of the biases remains to
be identified, we are able to estimate and reduce them in a re-calibration approach. This significantly improves time-variable
gravity field solutions based on the CNES/GRGS processing strategy. Empirical assessments indicate that the systematic KBR
data errors have previously induced gravity field errors on the level of 6–11 times the so-called GRACE baseline error level.
The zonal coefficients (from degree 14) are particularly affected. The re-calibration reduces their rms errors by about 50%.
As examples for geophysical inferences, the improvement enhances agreement between mass variations observed by GRACE and in-situ
ocean bottom pressure observations. The improvement also importantly affects estimates of inter-annual mass variations of
the Antarctic ice sheet. 相似文献
4.
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
5.
重力卫星GRACE(gravity recovery and climate experiment)监测斯堪的纳维亚半岛陆地水储量变化会受到冰川均衡调整(GIA)信号的严重影响。首先根据该地区绝对重力和GPS并址观测数据计算了GIA重力和垂直位移的实测线性比值,利用该比值和GPS网观测的垂直位移速度场得到了GIA重力。然后,对GRACE观测的重力变化速率进行GIA重力改正,进而可分离陆地水储量变化趋势,避免了使用GIA模型所带来的巨大不确定性,并根据观测数据完整估计了所得结果的不确定性。最后与水文模型作对比分析。结果表明,实测的GIA重力-垂直位移线性比值为0.148±0.020μGal/mm(1Gal=10-2 m/s2),该结果检验了Wahr的理论近似值且与北美实测的结果非常接近。2003年1月至2011年3月期间,斯堪的纳维亚半岛陆地水储量存在明显的增加趋势,信号的主体位于半岛南端的维纳恩湖附近,总的水量增加速率为4.6±2.1km3/a,数据观测期间的累积增加水量为38±17km3。研究结果与WGHM水文模型的结果有较好的一致性,相关系数达到0.69,而与GLDAS水文模型的相关性略小。 相似文献
6.
Approximate decorrelation and non-isotropic smoothing of time-variable GRACE-type gravity field models 总被引:6,自引:1,他引:6
Jürgen Kusche 《Journal of Geodesy》2007,81(11):733-749
We discuss a new method for approximately decorrelating and non-isotropically filtering the monthly gravity fields provided
by the gravity recovery and climate experiment (GRACE) twin-satellite mission. The procedure is more efficient than conventional
Gaussian-type isotropic filters in reducing stripes and spurious patterns, while retaining the signal magnitudes. One of the
problems that users of GRACE level 2 monthly gravity field solutions fight is the effect of increasing noise in higher frequencies.
Simply truncating the spherical harmonic solution at low degrees causes the loss of a significant portion of signal, which
is not an option if one is interested in geophysical phenomena on a scale of few hundred to few thousand km. The common approach
is to filter the published solutions, that is to convolve them with an isotropic kernel that allows an interpretation as smoothed
averaging. The downside of this approach is an amplitude bias and the fact that it neither accounts for the variable data
density that increases towards the poles where the orbits converge nor for the anisotropic error correlation structure that
the solutions exhibit. Here a relatively simple regularization procedure will be outlined, which allows one to take the latter
two effects into account, on the basis of published level 2 products. This leads to a series of approximate decorrelation
transformations applied to the monthly solutions, which enable a successive smoothing to reduce the noise in the higher frequencies.
This smoothing effect may be used to generate solutions that behave, on average over all possible directions, very close to
Gaussian-type filtered ones. The localizing and smoothing properties of our non-isotropic kernels are compared with Gaussian
kernels in terms of the kernel variance and the resulting amplitude bias for a standard signal. Examples involving real GRACE
level 2 fields as well as geophysical models are used to demonstrate the techniques. With the new method, we find that the
characteristic striping pattern in the GRACE solutions are much more reduced than Gaussian-filtered solutions of comparable
signal amplitude and root mean square. 相似文献
7.
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
8.
Statistically optimal estimation of Greenland Ice Sheet mass variations from GRACE monthly solutions using an improved mascon approach 总被引:1,自引:0,他引:1
We present an improved mascon approach to transform monthly spherical harmonic solutions based on GRACE satellite data into mass anomaly estimates in Greenland. The GRACE-based spherical harmonic coefficients are used to synthesize gravity anomalies at satellite altitude, which are then inverted into mass anomalies per mascon. The limited spectral content of the gravity anomalies is properly accounted for by applying a low-pass filter as part of the inversion procedure to make the functional model spectrally consistent with the data. The full error covariance matrices of the monthly GRACE solutions are properly propagated using the law of covariance propagation. Using numerical experiments, we demonstrate the importance of a proper data weighting and of the spectral consistency between functional model and data. The developed methodology is applied to process real GRACE level-2 data (CSR RL05). The obtained mass anomaly estimates are integrated over five drainage systems, as well as over entire Greenland. We find that the statistically optimal data weighting reduces random noise by 35–69%, depending on the drainage system. The obtained mass anomaly time-series are de-trended to eliminate the contribution of ice discharge and are compared with de-trended surface mass balance (SMB) time-series computed with the Regional Atmospheric Climate Model (RACMO 2.3). We show that when using a statistically optimal data weighting in GRACE data processing, the discrepancies between GRACE-based estimates of SMB and modelled SMB are reduced by 24–47%. 相似文献
9.
卫星重力探测技术为监测全球陆地水储量变化提供了新的技术手段。采用Level-2 Release-05版本GRACE时变重力场模型数据计算了2010年全球陆地水储量的月变化;着重研究了扇形滤波对反演结果的影响;并结合GLDAS水文模型数据对反演结果进行了验证分析。实验结果表明:GRACE反演结果 GLDAS水文模型结果在时空分布上符合较好;扇形滤波能够削弱GRACE时变重力场模型的高阶项误差影响,有效去除反演结果中的条带状噪声。 相似文献
10.
G. Bourda 《Journal of Geodesy》2008,82(4-5):295-305
The temporal variations of the Earth’s gravity field, nowadays routinely determined from satellite laser ranging (SLR) and
GRACE (Gravity Recovery And Climate Experiment), are related to changes in the Earth’s rotation rate through the Earth’s inertia
tensor. We study this connection from actual data by comparing the traditional length-of-day (LOD) measurements provided by
the International Earth Rotation and Reference Systems Service (IERS) to the variations of the degree-2 and order-0 Stokes
coefficient of the gravity field determined from fitting the orbits of the LAGEOS-1 and −2 satellites since 1985. The two
series show a good correlation (0.62) and similar annual and semi-annual signals, indicating that the gravity-field-derived
LOD is valuable. Our analysis also provides evidence for additional signals common to both series, especially at a period
near 120 days, which could be due to hydrological effects. 相似文献
11.
This study evaluates the performance of two widely used GRACE solutions (CNES/GRGS RL02 and CSR RL04) in deriving annual and
inter-annual water mass variations in the Black Sea for the period 2003–2007. It is demonstrated that the GRACE derived water
mass variations in the Black Sea are heavily influenced by the leakage of hydrological signals from the surrounding land.
After applying the corresponding correction, we found a good agreement with water mass variations derived from steric-corrected
satellite altimetry observations. Both GRACE and altimetry show significant annual water mass variations of roughly 7 cm amplitude
peaking in May and a semi-annual signal of roughly 3 cm peaking in June and in December. The amplitude of the annual water
mass signal varies significantly from year to year and is significantly larger during 2004–2006 than in 2003 and 2007. This
is also in agreement with the steric corrected altimetry. 相似文献
12.
John W. Crowley Jerry X. Mitrovica Richard C. Bailey Mark E. Tamisiea James L. Davis 《Journal of Geodesy》2008,82(1):9-13
We combine satellite gravity data from the gravity recovery and climate experiment (GRACE) and precipitation measurements
from the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center’s (CPC) Merged Analysis of Precipitation
(CMAP) and the Tropical Rainfall Measuring Mission (TRMM), over the period from mid-2002 to mid-2006, to investigate the relative
importance of sink (runoff and evaporation) and source (precipitation) terms in the hydrological balance of the Amazon Basin.
When linear and quadratic terms are removed, the time-series of land water storage variations estimated from GRACE exhibits
a dominant annual signal of 250 mm peak-to-peak, which is equivalent to a water volume change of ~1,800 km3. A comparison of this trend with accumulated (i.e., integrated) precipitation shows excellent agreement and no evidence of
basin saturation. The agreement indicates that the net runoff and evaporation contributes significantly less than precipitation
to the annual hydrological mass balance. Indeed, raw residuals between the de-trended water storage and precipitation anomalies
range from ±40 mm. This range is consistent with stream-flow measurements from the region, although the latter are characterized
by a stronger annual signal than our residuals, suggesting that runoff and evaporation may act to partially cancel each other. 相似文献
13.
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
14.
The purpose of this paper is to demonstrate the effect of geophysical background model errors that affects temporal gravity
solutions provided by the Gravity Recovery And Climate Experiment (GRACE). Initial performance estimates by Dickey et al.
(1997) suggested a formal geoid RMS error better than 0.1 mm up to spherical harmonic degree 5. Now that the GRACE gravity
models and data are available, it is evident that these original expectations were too optimistic. Our hypothesis is that
this is partially explained by errors in geophysical background models that need to be applied in the GRACE data reduction,
and that this effect was not considered by Dickey et al. (1997). We discuss the results of a closed-loop simulation, where
satellite trajectory prediction software is used for the generation of GRACE range-rate data and GRACE orbit solutions with
the help of the Global Positioning System (GPS). During the recovery step in our closed-loop simulation, we show that simulated
nuisance signals (based on tide and air pressure model differences) map to a 0.7 mm geoid effect for periods longer than 3 months
and to less than 0.4 mm for periods shorter than 3 months. The long-period geoid hydrology signal is at a level of 4.5 mm,
while the short-period hydrology is at 0.25 mm. The long-period ocean bottom pressure (OBP) signal maps at 0.8 mm and for
short periods it is 0.4 mm. We conclude that short-period effects are difficult to observe by GRACE and that long-period effects,
like hydrology, are easier to recover than OBP variations. 相似文献
15.
Zhigui Kang Byron Tapley Srinivas Bettadpur John Ries Peter Nagel Rick Pastor 《Journal of Geodesy》2006,80(6):322-331
The GRACE (gravity recovery and climate experiment) satellites, launched in March 2002, are each equipped with a BlackJack GPS onboard receiver for precise orbit determination and gravity field recovery. Since launch, there have been significant improvements in the background force models used for satellite orbit determination, most notably the model for the geopotential. This has resulted in significant improvements to orbit accuracy for very low altitude satellites. The purpose of this paper is to investigate how well the orbits of the GRACE satellites (about 470 km in altitude) can currently be determined using only GPS data and based on the current models and methods. The orbit accuracy is assessed using a number of tests, which include analysis of orbit fits, orbit overlaps, orbit connecting points, satellite Laser ranging residuals and K-band ranging (KBR) residuals. We show that 1-cm radial orbit accuracy for the GRACE satellites has probably been achieved. These precise GRACE orbits can be used for such purposes as improving gravity recovery from the GRACE KBR data and for atmospheric profiling, and they demonstrate the quality of the background force models being used. 相似文献
16.
17.
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
18.
A sliding window technique is used to create daily-sampled Gravity Recovery and Climate Experiment (GRACE) solutions with the same background processing as the official CSR RL04 monthly series. By estimating over shorter time spans, more frequent solutions are made using uncorrelated data, allowing for higher frequency resolution in addition to daily sampling. Using these data sets, high-frequency GRACE errors are computed using two different techniques: assuming the GRACE high-frequency signal in a quiet area of the ocean is the true error, and computing the variance of differences between multiple high-frequency GRACE series from different centers. While the signal-to-noise ratios prove to be sufficiently high for confidence at annual and lower frequencies, at frequencies above 3 cycles/year the signal-to-noise ratios in the large hydrological basins looked at here are near 1.0. Comparisons with the GLDAS hydrological model and high frequency GRACE series developed at other centers confirm CSR GRACE RL04’s poor ability to accurately and reliably measure hydrological signal above 3–9 cycles/year, due to the low power of the large-scale hydrological signal typical at those frequencies compared to the GRACE errors. 相似文献
19.
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
20.
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