共查询到18条相似文献，搜索用时 406 毫秒
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本文基于GRACE最新重力场模型RL05序列研究了高斯滤波、Wiener滤波、各向异性滤波三种方法在长江流域水储量变化监测中的适用性,计算了应用三种方法得到的水储量变化速率。通过与长江流域水文模型的比较,高斯滤波平滑半径为430km时所得的结果与Wiener滤波基本一致,但各向异性滤波反演的结果与水文模型更为接近,并且优于前面两种方法。研究结果表明GRACE RL05时变重力场球谐系数误差存在各向异性的分布特征,因此各向异性滤波更适用于GRACE区域水储量变化的研究。 相似文献
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多通道奇异谱组合滤波反演水储量变化 总被引：1，自引：0，他引：1
针对GRACE时变重力场球谐系数的高阶次项中含有的较高噪声会造成反潢结果产生误差的问题,该文采用多通道奇异谱分析和高斯滤波相结合的方案来滤除GRACE数据中的噪声,并与普遍使用的去相关滤波和高斯滤波相结合的方案进行了对比验证。首先利用这两种方法分别计算了2007年4、10月份的全球水储量变化,结果显示,这两种方法反演的结果基本相同,而多通道奇异谱分析与高斯滤波相组合的方法提高了信噪比,减弱了信号泄露误差,验证了该组合方案的可行性。然后又分别计算了亚马逊流域2004—2010年的水储量时间变化序列,并与GLDAS水文模型进行了对比验证,结果显示,这两种方法得到的水储量时间序列变化趋势基本相同,各自之间具有强相关性,进一步说明了该文方案在GRACE数据滤波中的可行性。 相似文献
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各向异性组合滤波法反演陆地水储量变化 总被引：2，自引：1，他引：1
地球时变重力场模型反演陆地水储量变化已为全球气候变化研究作出巨大贡献,考虑到时变重力场模型球谐系数中存在相关性,其高阶次项具有较大的误差,需采用最优的滤波方法进行空间平滑。本文提出一种新的各向异性组合滤波方法,其基本思想是将改进的高斯滤波法与均方根(root mean square,RMS)滤波法组合,即对球谐系数的低阶次采用改进的高斯滤波法,而高阶次采用RMS滤波法。首先分析了最新的GRACE RL05系列时变重力场模型系数误差特性,基于全球水储量变化反演结果,分析比较了高斯滤波、改进的高斯滤波、RMS滤波和DDK滤波与本文提出的组合滤波法的有效性及精度,并利用模型结果进行了验证,计算结果表明,组合滤波法的中误差最小。研究结果表明,本文提出的组合法相比于先前的滤波方法,可有效地过滤高阶次的噪声,消除南北条带误差,同时减少信号泄漏,提高信噪比,保留更多有效的地球物理信号,进而提高反演精度。 相似文献
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受测量误差等因素影响，直接使用GRACE时变重力场模型的地表质量变化反演结果呈现严重条带噪声，必须采用滤波消除。本文对不同滤波方法进行了试验分析，以信噪比最大为准则，确定了不同滤波方法的最优滤波参数，并在此基础上提出了一种各向异性组合滤波方法。该方法根据时变重力场模型球谐系数误差特性，结合各向异性高斯滤波和均方根滤波特点，对精度较高的低次项系数采用较大权重以保留更多有效信号，而对精度较差的高次项系数采用较小权重以压制噪声。不同于传统的两步法组合滤波，该方法仅需进行一步滤波处理。试验结果表明，本文提出的各向异性组合滤波方法计算步骤简单，能够有效消除条带噪声；与单一滤波和传统两步法组合滤波方法相比，提高了反演结果信噪比，保留了更多真实信号。 相似文献
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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
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根据GRACE时变重力场模型和高斯平滑原理,编写了全球任意一点的重力异常计算程序,计算2011日本地震区域前后共7个月的重力异常值。结果显示,在大地震前后,地震区域重力异常呈现正负异常交替和迁移现象,并随着地震的临近,这种现象会越来越明显。最后绘制全球1°格网的等效水高速率变化图,借此分析地震影响产生的全球质量变化。 相似文献
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《武汉大学学报(信息科学版)》2016,(11)
利用UTCSR发布的2003-01~2013-07GRACE RL05月平均重力场模型,分析比较了高斯滤波、各向异性滤波、扇形滤波和维纳滤波,并结合去相关滤波在反演南极地区冰盖质量变化方面的差异。通过计算得到以下结论:1基于121组重力场模型阶方差分布得到维纳滤波与半径为300km的高斯滤波效果最为接近,说明300km滤波半径完全可以满足质量变化信号的提取;2在一定范围内,提高滤波半径能提高反演结果信噪比,建议南极区域的滤波半径为500km;采用相同滤波半径,不同空间滤波算法计算的质量变化率基本一致,在南极区域可以选取任一滤波方法;3与其他算法相比,去相关滤波算法能在一定程度消除球谐系数中存在的系统误差,改善反演结果。 相似文献
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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
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刘晓莉 《测绘与空间地理信息》2014,(8):89-91
使用GRACE反演地球表层的质量异常,其结果取决于构造的平滑函数即滤波方法。本文阐述了两种在经典高斯滤波基础上构造的Fan滤波和Non-isotropic Gaussian(Non)滤波,两者均对GRACE的阶和次起作用。在同一阶下,两者的权重随着次数的升高而衰减,但衰减的趋势不同,比如在20阶时,Fan滤波呈抛物线变化,而Non滤波则为线性衰减;在40和60阶,两者均呈抛物线变化。使用CSR发布的GRACE Level-2 RL05数据反演地表质量异常,两者的结果相近。 相似文献
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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
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Observations of spatio-temporal variations in the geopotential using the GRACE satellites have been used to estimate recent mass fluxes from polar ice sheets and glaciers. However, these estimates have not considered the potential bias associated with the migration of water that accompanies the ice melt. This migration is driven by the diminished gravitational attraction of the melting ice reservoir, and this migration, as well as the crustal loading it induces, will contribute to the observed geopotential anomaly. The extent to which this contribution contaminates the ice mass flux estimates depends on how far the smoothing filters applied to the GRACE data extend beyond the ice margins into the ocean. Using the Antarctic Peninsula as a case study, we estimate the magnitude of this bias for a range of melt areas and Gaussian smoothing filter radii. We conclude that GRACE estimates of ice mass loss over the Antarctic Peninsula are systematically overestimating the loss by up to 10 $\%$ for filter radii of less than 500 km. 相似文献
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提出了一种三层组合滤波的去噪方法,在小波BayesShrink阈值与自适应中值滤波的基础上增加第三层Wiener滤波,利用Wiener滤波对信噪比高的信号去噪效果好的特点可有效去除残留的混合噪声,为了在去噪过程中保留影像的边缘,在滤波过程中加入了边缘提取算法,对影像的细节进行保留使去噪后的影像更加清晰。试验表明,本文提出的三层滤波方法在去除遥感影像常见的高斯与脉冲混合噪声时,效果要明显优于传统的两层组合滤波算法。 相似文献
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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
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Estimation of mass change trends in the Earth’s system on the basis of GRACE satellite data, with application to Greenland 总被引：1，自引：1，他引：0
C. Siemes P. Ditmar R. E. M. Riva D. C. Slobbe X. L. Liu H. Hashemi Farahani 《Journal of Geodesy》2013,87(1):69-87
The Gravity Recovery and Climate Experiment (GRACE) satellite mission measures the Earth’s gravity field since March 2002. We propose a new filtering procedure for post-processing GRACE-based monthly gravity field solutions provided in the form of spherical harmonic coefficients. The procedure is tuned for the optimal estimation of linear trends and other signal components that show a systematic behavior over long time intervals. The key element of the developed methodology is the statistically optimal Wiener-type filter which makes use of the full covariance matrices of noise and signal. The developed methodology is applied to determine the mass balance of the Greenland ice sheet, both per drainage system and integrated, as well as the mass balance of the ice caps on the islands surrounding Greenland. The estimations are performed for three 2-year time intervals (2003–2004, 2005–2006, and 2007–2008), as well as for the 6-year time interval (2003–2008). The study confirms a significant difference in the behavior of the drainage systems over time. The average 6-year rate of mass loss in Greenland is estimated as 165 ± 15 Gt/year. The rate of mass loss of the ice caps on Ellesmere Island (together with Devon Island), Baffin Island, Iceland, and Svalbard is found to be 22 ± 4, 21 ± 6, 17 ± 9, and 6 ± 2 Gt/year, respectively. All these estimates are corrected for the effect of glacial isostatic adjustment. 相似文献