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1.
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
2.
卫星重力测量是当前探测全球一致、高精度和高分辨率地球重力场的高效技术手段,主要包括高低卫星跟踪卫星测量（satellite-to-satellite tracking in high-low mode, SST-hl）、低低卫星跟踪卫星测量（satellite-to-satellite tracking in low-low mode, SST-ll）和卫星重力梯度测量（satellite gravity gradiometry,SGG）。系统总结了利用卫星重力测量技术（包括SST-hl、SST-ll和SGG及多模式组合）反演地球重力场的主要方法,评述了利用挑战性小卫星有效载荷（challenging mini-satellite payload, CHAMP）、重力恢复与气候实验（gravity recovery and climate experiment, GRACE）/ GRACE继任者（GRACE follow-on, GRACE -FO）和地球重力场和海洋环流探索器（gravity field and steady-state ocean circulation explorer, GOCE）卫星重力数据构建静态和时变重力场模型的最新进展,并对当前具有代表性的地球重力场模型精度进行了分析和评估,以期对未来的地球重力场研究及其地学应用提供参考。 相似文献
3.
4.
M. Kern T. Preimesberger M. Allesch R. Pail J. Bouman R. Koop 《Journal of Geodesy》2005,78(9):509-519
The satellite missions CHAMP, GRACE, and GOCE mark the beginning of a new era in gravity field determination and modeling. They provide unique models of the global stationary gravity field and its variation in time. Due to inevitable measurement errors, sophisticated pre-processing steps have to be applied before further use of the satellite measurements. In the framework of the GOCE mission, this includes outlier detection, absolute calibration and validation of the SGG (satellite gravity gradiometry) measurements, and removal of temporal effects. In general, outliers are defined as observations that appear to be inconsistent with the remainder of the data set. One goal is to evaluate the effect of additive, innovative and bulk outliers on the estimates of the spherical harmonic coefficients. It can be shown that even a small number of undetected outliers (<0.2 of all data points) can have an adverse effect on the coefficient estimates. Consequently, concepts for the identification and removal of outliers have to be developed. Novel outlier detection algorithms are derived and statistical methods are presented that may be used for this purpose. The methods aim at high outlier identification rates as well as small failure rates. A combined algorithm, based on wavelets and a statistical method, shows best performance with an identification rate of about 99%. To further reduce the influence of undetected outliers, an outlier detection algorithm is implemented inside the gravity field solver (the Quick-Look Gravity Field Analysis tool was used). This results in spherical harmonic coefficient estimates that are of similar quality to those obtained without outliers in the input data. 相似文献
5.
卫星跟踪卫星技术的进展及应用前景 总被引：9，自引：4，他引：5
卫星跟踪卫星技术被认为是 2 1世纪初最有价值和应用前景的高效重力探测技术 ,旨在测定中长波重力场的精细结构及时间相依变化。本文首先简要阐述卫星跟踪卫星技术的发展背景及概况 ,其次介绍目前已经实施和将要实施的卫星跟踪卫星计划 CHAMP和 GRACE的进展情况 ,最后讨论该技术在精化地球重力场和研究相关地学问题中的应用前景。 相似文献
6.
7.
For science applications of the gravity recovery and climate experiment (GRACE) monthly solutions, the GRACE estimates of \(C_{20}\) (or \(J_{2}\)) are typically replaced by the value determined from satellite laser ranging (SLR) due to an unexpectedly strong, clearly non-geophysical, variation at a period of \(\sim \)160 days. This signal has sometimes been referred to as a tide-like variation since the period is close to the perturbation period on the GRACE orbits due to the spherical harmonic coefficient pair \(C_{22}/S_{22}\) of S2 ocean tide. Errors in the S2 tide model used in GRACE data processing could produce a significant perturbation to the GRACE orbits, but it cannot contribute to the \(\sim \)160-day signal appearing in \(C_{20}\). Since the dominant contribution to the GRACE estimate of \(C_{20}\) is from the global positioning system tracking data, a time series of 138 monthly solutions up to degree and order 10 (\(10\times 10\)) were derived along with estimates of ocean tide parameters up to degree 6 for eight major tides. The results show that the \(\sim \)160-day signal remains in the \(C_{20}\) time series. Consequently, the anomalous signal in GRACE \(C_{20}\) cannot be attributed to aliasing from the errors in the S2 tide. A preliminary analysis of the cross-track forces acting on GRACE and the cross-track component of the accelerometer data suggests that a temperature-dependent systematic error in the accelerometer data could be a cause. Because a wide variety of science applications relies on the replacement values for \(C_{20}\), it is essential that the SLR estimates are as reliable as possible. An ongoing concern has been the influence of higher degree even zonal terms on the SLR estimates of \(C_{20}\), since only \(C_{20}\) and \(C_{40}\) are currently estimated. To investigate whether a better separation between \(C_{20}\) and the higher-degree terms could be achieved, several combinations of additional SLR satellites were investigated. In addition, a series of monthly gravity field solutions (\(60\times 60\)) were estimated from a combination of GRACE and SLR data. The results indicate that the combination of GRACE and SLR data might benefit the resonant orders in the GRACE-derived gravity fields, but it appears to degrade the recovery of the \(C_{20}\) variations. In fact, the results suggest that the poorer recovery of \(C_{40}\) by GRACE, where the annual variation is significantly underestimated, may be affecting the estimates of \(C_{20}\). Consequently, it appears appropriate to continue using the SLR-based estimates of \(C_{20}\), and possibly also \(C_{40}\), to augment the existing GRACE mission. 相似文献
8.
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
9.
Christian Siemes 《Journal of Geodesy》2018,92(1):33-45
The GOCE gravity gradiometer measured highly accurate gravity gradients along the orbit during GOCE’s mission lifetime from March 17, 2009, to November 11, 2013. These measurements contain unique information on the gravity field at a spatial resolution of 80 km half wavelength, which is not provided to the same accuracy level by any other satellite mission now and in the foreseeable future. Unfortunately, the gravity gradient in cross-track direction is heavily perturbed in the regions around the geomagnetic poles. We show in this paper that the perturbing effect can be modeled accurately as a quadratic function of the non-gravitational acceleration of the satellite in cross-track direction. Most importantly, we can remove the perturbation from the cross-track gravity gradient to a great extent, which significantly improves the accuracy of the latter and offers opportunities for better scientific exploitation of the GOCE gravity gradient data set. 相似文献
10.
GPS data collected by satellite gravity missions can be used for extracting the long-wavelength part of the Earth’s gravity field. We propose a new data processing method which makes use of the ‘average acceleration’ approach to gravity field modelling. In this method, satellite accelerations are directly derived from GPS carrier phase measurements with an epoch-differenced scheme. As a result, no ambiguity solutions are needed and the systematic errors that do not change much from epoch to epoch are largely eliminated. The GPS data collected by the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite mission are used to demonstrate the added value of the proposed method. An analysis of the residual accelerations shows that accelerations derived in this way are more precise, with noise being reduced by about 20 and 5% at the cross-track component and the other two components, respectively, as compared to those based on kinematic orbits. The accelerations obtained in this way allow the recovery of the gravity field to a slightly higher maximum degree compared to the solution based on kinematic orbits. Furthermore, the gravity field solution has an overall better performance. Errors in spherical harmonic coefficients are smaller, especially at low degrees. The cumulative geoid height error is reduced by about 15 and 5% up to degree 50 and 150, respectively. An analysis in the spatial domain shows that large errors along the geomagnetic equator, which are caused by a high electron density coupled with large short-term variations, are substantially reduced. Finally, the new method allows for a better observation of mass transport signals. In particular, sufficiently realistic signatures of regional mass anomalies in North America and south-west Africa are obtained. 相似文献
11.
We present an alternate mathematical technique than contemporary spherical harmonics to approximate the geopotential based
on triangulated spherical spline functions, which are smooth piecewise spherical harmonic polynomials over spherical triangulations.
The new method is capable of multi-spatial resolution modeling and could thus enhance spatial resolutions for regional gravity
field inversion using data from space gravimetry missions such as CHAMP, GRACE or GOCE. First, we propose to use the minimal
energy spherical spline interpolation to find a good approximation of the geopotential at the orbital altitude of the satellite.
Then we explain how to solve Laplace’s equation on the Earth’s exterior to compute a spherical spline to approximate the geopotential
at the Earth’s surface. We propose a domain decomposition technique, which can compute an approximation of the minimal energy
spherical spline interpolation on the orbital altitude and a multiple star technique to compute the spherical spline approximation
by the collocation method. We prove that the spherical spline constructed by means of the domain decomposition technique converges
to the minimal energy spline interpolation. We also prove that the modeled spline geopotential is continuous from the satellite
altitude down to the Earth’s surface. We have implemented the two computational algorithms and applied them in a numerical
experiment using simulated CHAMP geopotential observations computed at satellite altitude (450 km) assuming EGM96 (n
max = 90) is the truth model. We then validate our approach by comparing the computed geopotential values using the resulting
spherical spline model down to the Earth’s surface, with the truth EGM96 values over several study regions. Our numerical
evidence demonstrates that the algorithms produce a viable alternative of regional gravity field solution potentially exploiting
the full accuracy of data from space gravimetry missions. The major advantage of our method is that it allows us to compute
the geopotential over the regions of interest as well as enhancing the spatial resolution commensurable with the characteristics
of satellite coverage, which could not be done using a global spherical harmonic representation.
The results in this paper are based on the research supported by the National Science Foundation under the grant no. 0327577. 相似文献
12.
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
13.
Wavelet Modeling of Regional and Temporal Variations of the Earth’s Gravitational Potential Observed by GRACE 总被引：1，自引：0，他引：1
This work is dedicated to the wavelet modeling of regional and temporal variations of the Earth’s gravitational potential
observed by the GRACE (gravity recovery and climate experiment) satellite mission. In the first part, all required mathematical
tools and methods involving spherical wavelets are provided. Then, we apply our method to monthly GRACE gravity fields. A
strong seasonal signal can be identified which is restricted to areas where large-scale redistributions of continental water
mass are expected. This assumption is analyzed and verified by comparing the time-series of regionally obtained wavelet coefficients
of the gravitational signal originating from hydrology models and the gravitational potential observed by GRACE. The results
are in good agreement with previous studies and illustrate that wavelets are an appropriate tool to investigate regional effects
in the Earth’s gravitational field.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
14.
B. S. Sheard G. Heinzel K. Danzmann D. A. Shaddock W. M. Klipstein W. M. Folkner 《Journal of Geodesy》2012,86(12):1083-1095
The Gravity Recovery and Climate Experiment (GRACE) has demonstrated that low–low satellite-to-satellite tracking enables monitoring the time variations of the Earth’s gravity field on a global scale, in particular those caused by mass-transport within the hydrosphere. Due to the importance of long-term continued monitoring of the variations of the Earth’s gravitational field and the limited lifetime of GRACE, a follow-on mission is currently planned to be launched in 2017. In order to minimise risk and the time to launch, the follow-on mission will be basically a rebuild of GRACE with microwave ranging as the primary instrument for measuring changes of the intersatellite distance. Laser interferometry has been proposed as a method to achieve improved ranging precision for future GRACE-like missions and is therefore foreseen to be included as demonstrator experiment in the follow-on mission now under development. This paper presents the top-level architecture of an interferometric laser ranging system designed to demonstrate the technology which can also operate in parallel with the microwave ranging system of the GRACE follow-on mission. 相似文献
15.
Kinematic positions of Low Earth Orbiters based on GPS tracking are frequently used as pseudo-observations for single satellite gravity field determination. Unfortunately, the accuracy of the satellite trajectory is partly limited because the receiver synchronization error has to be estimated along with the kinematic coordinates at every observation epoch. We review the requirements for GPS receiver clock modeling in Precise Point Positioning (PPP) and analyze its impact on kinematic orbit determination for the two satellites of the Gravity Recovery and Climate Experiment (GRACE) mission using both simulated and real data. We demonstrate that a piecewise linear parameterization can be used to model the ultra-stable oscillators that drive the GPS receivers on board of the GRACE satellites. Using such a continuous clock model allows position estimation even if the number of usable GPS satellites drops to three and improves the robustness of the solution with respect to outliers. Furthermore, simulations indicate a potential accuracy improvement of the satellite trajectory of at least 40 % in the radial direction and up to 7 % in the along-track and cross-track directions when a 60-s piecewise linear clock model is estimated instead of epoch-wise independent receiver clock offsets. For PPP with real GRACE data, the accuracy evaluation is hampered by the lack of a reference orbit of significantly higher accuracy. However, comparisons with a smooth reduced-dynamic orbit indicate a significant reduction of the high-frequency noise in the radial component of the kinematic orbit. 相似文献
16.
The temporal changes of the Earth’s gravity field can be observed on a global scale with low–low satellite-to-satellite tracking (SST) missions. One of the largest restrictions of the quality of low–low SST gravity fields is temporal aliasing. This study investigates the design of optimal satellite orbits for temporal gravity retrieval regarding temporal aliasing. We present a method with which optimal altitudes for the orbit of a gravity satellite mission with the goal of temporal gravity retrieval can be identified. The two basic orbit frequencies, the rates of the argument of the latitude and the ascending node, determine the mapping of the signal measured along the orbit onto the spherical harmonic (SH) spectrum. The main spectral characteristics of temporal aliasing are maxima at specific SH orders. The magnitude of the effects depends on the basic frequencies. This is analyzed with numerical low–low SST closed-loop simulations including both tidal and non-tidal background models and GRACE-like observation noise. Analyses of actual monthly GRACE solutions show that these characteristics do not depend on the low–low SST processing method. Optimal orbits are found in specific altitude bands. The best altitude bands regarding temporal aliasing for polar low Earth orbiters (LEOs) are around 301, 365, 421 and 487 km. In these bands, major aliasing effects do not occur for SH degrees and orders below 70. This study gives unique and in-depth insights into the mechanism of temporal aliasing. As it provides an important orbit design approach, it is independent of any (post-) processing method to reduce temporal aliasing. 相似文献
17.
Integrated adjustment of CHAMP, GRACE, and GPS data 总被引：16，自引：3，他引：13
Various types of observations, such as space-borne Global positioning system (GPS) code and phase data, accelerometer data, K-band range and range-rate data, and ground-based satellite laser ranging data of the CHAllenging Minisatellite Payload (CHAMP) and GRAvity Climate Experiment (GRACE) satellite missions, are used together with ground-based GPS code and phase data in a rigorous adjustment to eventually solve for the ephemerides of the CHAMP, GRACE, and GPS satellites, geocenter variations, and low-degree gravity field parameters. It turns out that this integrated adjustment considerably improves the accuracy of the ephemerides for the high and low satellites, geocenter variations, and gravity field parameters, compared to the case when the adjustment is carried out stepwise or in individual satellite solutions.Acknowledgments. This study has been supported by the German Ministry of Education and Research through the Geotechnologies Programme grants 03F0333A/CHAMP and 03F0326A/GRACE. 相似文献
18.
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
19.
Pavel Ditmar Jo?o Teixeira da Encarna??o Hassan Hashemi Farahani 《Journal of Geodesy》2012,86(6):441-465
Spectral analysis of data noise is performed in the context of gravity field recovery from inter-satellite ranging measurements acquired by the satellite gravimetry mission GRACE. The motivation of the study is two-fold: (i) to promote a further improvement of GRACE data processing techniques and (ii) to assist designing GRACE follow-on missions. The analyzed noise realizations are produced as the difference between the actual GRACE inter-satellite range measurements and the predictions based on state-of-the-art force models. The exploited functional model is based on the so-called “range combinations,” which can be understood as a finite-difference analog of inter-satellite accelerations projected onto the line-of-sight connecting the satellites. It is shown that low-frequency noise is caused by limited accuracy of the computed GRACE orbits. In the first instance, it leads to an inaccurate estimation of the radial component of the inter-satellite velocities. A large impact of this component stems from the fact that it is directly related to centrifugal accelerations, which have to be taken into account when the measured range-accelerations are linked with inter-satellite accelerations. Another effect of orbit inaccuracies is a miscalculation of forces acting on the satellites (particularly, the one described by the zero-degree term of the Earth’s gravitational field). The major contributors to the noise budget at high frequencies (above 9?mHz) are (i) ranging sensor errors and (ii) limited knowledge of the Earth’s static gravity field at high degrees. Importantly, we show that updating the model of the static field on the basis of the available data must be performed with a caution as the result may not be physical due to a non-unique recovery of high-degree coefficients. The source of noise in the range of intermediate frequencies (1–9?mHz), which is particularly critical for an accurate gravity field recovery, is not fully understood yet. We show, however, that it cannot be explained by inaccuracies in background models of time-varying gravity field. It is stressed that most of the obtained results can be treated as sufficiently general (i.e., applicable in the context of a statistically optimal estimation based on any functional model). 相似文献
20.
B. Tapley J. Ries S. Bettadpur D. Chambers M. Cheng F. Condi B. Gunter Z. Kang P. Nagel R. Pastor T. Pekker S. Poole F. Wang 《Journal of Geodesy》2005,79(8):467-478
A new generation of Earth gravity field models called GGM02 are derived using approximately 14 months of data spanning from
April 2002 to December 2003 from the Gravity Recovery And Climate Experiment (GRACE). Relative to the preceding generation,
GGM01, there have been improvements to the data products, the gravity estimation methods and the background models. Based
on the calibrated covariances, GGM02 (both the GRACE-only model GGM02S and the combination model GGM02C) represents an improvement
greater than a factor of two over the previous GGM01 models. Error estimates indicate a cumulative error less than 1 cm geoid
height to spherical harmonic degree 70, which can be said to have met the GRACE minimum mission goals.
Electronic Supplementary Material Supplementary material is available in the online version of this article at 相似文献