排序方式： 共有114条查询结果，搜索用时 15 毫秒
91.
Least-squares collocation may be used for the estimation of spherical harmonic coefficients and their error and error correlations
from GOCE data. Due to the extremely large number of data, this requires the use of the so-called method of Fast Spherical
Collocation (FSC) which requires that data is gridded equidistantly on each parallel and have the same uncorrelated noise
on the parallel. A consequence of this is that error-covariances will be zero except between coefficients of the same signed
order (i.e., the same order and the same coefficient type C–C or S–S). If the data distribution and the characteristics of the data noise are symmetric with respect to the equator, then, within
a given order and coefficient type, the error-covariances amongst coefficients whose degrees are of different parity also
vanish. The deviation from this “ideal” pattern has been studied using data-sets of second order radial derivatives of the
anomalous potential. A total number of points below 17,000 were used having an equi-angular or an equal area distribution
or being associated with points on a realistic GOCE orbit but close to the nodes of a grid. Also the data were considered
having a correlated or an uncorrelated noise and three different signal covariance functions. Grids including data or not
including data in the polar areas were used. Using the functionals associated with the data, error estimates of coefficients
and error-correlations between coefficients were calculated up to a maximal degree and order equal to 90. As expected, for
the data-distributions with no data in the polar areas the error-estimates were found to be larger than when the polar areas
contained data. In all cases it was found that only the error-correlations between coefficients of the same order were significantly
different from zero (up to 88%). Error-correlations were significantly larger when data had been regarded as having non-zero
error-correlations. Also the error-correlations were largest when the covariance function with the largest signal covariance
distance was used. The main finding of this study was that the correlated noise has more pronounced impact on gridded data
than on data distributed on a realistic GOCE orbit. This is useful information for methods using gridded data, such as FSC. 相似文献
92.
Optimal multi-step collocation: application to the space-wise approach for GOCE data analysis 总被引：5，自引：3，他引：2
Collocation is widely used in physical geodesy. Its application requires to solve systems with a dimension equal to the number
of observations, causing numerical problems when many observations are available. To overcome this drawback, tailored step-wise
techniques are usually applied. An example of these step-wise techniques is the space-wise approach to the GOCE mission data
processing. The original idea of this approach was to implement a two-step procedure, which consists of first predicting gridded
values at satellite altitude by collocation and then deriving the geo-potential spherical harmonic coefficients by numerical
integration. The idea was generalized to a multi-step iterative procedure by introducing a time-wise Wiener filter to reduce
the highly correlated observation noise. Recent studies have shown how to optimize the original two-step procedure, while
the theoretical optimization of the full multi-step procedure is investigated in this work. An iterative operator is derived
so that the final estimated spherical harmonic coefficients are optimal with respect to the Wiener–Kolmogorov principle, as
if they were estimated by a direct collocation. The logical scheme used to derive this optimal operator can be applied not
only in the case of the space-wise approach but, in general, for any case of step-wise collocation. Several numerical tests
based on simulated realistic GOCE data are performed. The results show that adding a pre-processing time-wise filter to the
two-step procedure of data gridding and spherical harmonic analysis is useful, in the sense that the accuracy of the estimated
geo-potential coefficients is improved. This happens because, in its practical implementation, the gridding is made by collocation
over local patches of data, while the observation noise has a time-correlation so long that it cannot be treated inside the
patch size. Therefore, the multi-step operator, which is in theory equivalent to the two-step operator and to the direct collocation,
is in practice superior thanks to the time-wise filter that reduces the noise correlation before the gridding. The criteria
for the choice of this filter are investigated numerically. 相似文献
93.
Wenyan Sui Junru Guo Jun Song Zhiliang Liu Meng Wang Xibin Li Yanzhao Fu Yongquan Li Yu Cai Linhui Wang Lingli Li Xiaofang Guo Wenting Zuo 《海洋学报(英文版)》2021,40(3):142-152
The new gravity field models of gravity field and steady-state ocean circulation explorer(GOCE), TIM_R6 and DIR_R6, were released by the European Space Agency(ESA) in June 2019. The sixth generation of gravity models have the highest possible signal and lowest error levels compared with other GOCE-only gravity models, and the accuracy is significantly improved. This is an opportunity to build high precision geostrophic currents. The mean dynamic topography and geostrophic currents have been calculated by the 5 th(TIM_R5 and DIR_R5), 6 th(TIM_R6 and DIR_R6) release of GOCE gravity field models and ITSG-Grace2018 of GRACE gravity field model in this study. By comparison with the drifter results, the optimal filtering lengths of them have been obtained(for DIR_R5, DIR_R6, TIM_R5 and TIM_R6 models are 1° and for ITSG-Grace2018 model is 1.1°). The filtered results show that the geostrophic currents obtained by the GOCE gravity field models can better reflect detailed characteristics of ocean currents. The total geostrophic speed based on the TIM_R6 model is similar to the result of the DIR_R6 model with standard deviation(STD) of 0.320 m/s and 0.321 m/s, respectively. The STD of the total velocities are 0.333 m/s and 0.325 m/s for DIR_R5 and TIM_R5. When compared with ITSG-Grace2018 results, the STD(0.344 m/s) of total geostrophic speeds is larger than GOCE results, and the accuracy of geostrophic currents obtained by ITSG-Grace2018 is lower. And the absolute errors are mainly distributed in the areas with faster speeds, such as the Antarctic circumpolar circulation, equatorial region, Kuroshio and Gulf Stream areas. After the remove-restore technique was applied to TIM_R6 MDT, the STD of total geostrophic speeds dropped to 0.162 m/s. 相似文献
94.
GOCE采用的高低卫-卫跟踪和卫星重力梯度测量技术在恢复重力场方面各有所长并互为补充,如何有效利用这两类观测数据最优确定地球重力场是GOCE重力场反演的关键问题。本文研究了联合高低卫-卫跟踪和卫星重力梯度数据恢复地球重力场的最小二乘谱组合法,基于球谐分析方法推导并建立了卫星轨道面扰动位T和径向重力梯度Tzz、以及扰动位T和重力梯度分量组合{Tzz-Txx-Tyy}的谱组合计算模型与误差估计公式。数值模拟结果表明,谱组合计算模型可以有效顾及各类数据的精度和频谱特性进行最优联合求解。采用61天GOCE实测数据反演的两个180阶次地球重力场模型WHU_GOCE_SC01S（扰动位和径向重力梯度数据求解）和WHU_GOCE_SC02S（扰动位和重力梯度分量组合数据求解）,结果显示后者精度优于前者,并且它们的整体精度优于GOCE时域解,而与GOCE空域解的精度接近,验证了谱组合法的可行性与有效性。 相似文献
95.
96.
卫星重力研究:21世纪大地测量研究的新热点 总被引：18，自引：8，他引：18
卫星重力发射将大大改善人们对地球重力场的了解 ,最近一些年已经和将要发射的 CHAMP、GRACE及GOCE卫星将把现有静态中长波长部分重力场的精度提高 1- 2个量级 ,并提供长波部分重力场随时间变化的信息。本文对这一大地测量的新进展作了简单叙述 相似文献
97.
A spatiospectral localization method is discussed for processing the global geopotential coefficients from satellite mission
data to investigate time-variable gravity. The time-variable mass variation signal usually appears associated with a particular
geographical area yielding inherently regional structure, while the dependence of the satellite gravity errors on a geographical
region is not so evident. The proposed localization amplifies the signal-to-noise ratio of the (non-stationary) time-variable
signals in the geopotential coefficient estimates by localizing the global coefficients to the area where the signal is expected
to be largest. The results based on localization of the global satellite gravity coefficients such as Gravity Recovery And
Climate Experiment (GRACE) and Gravity and Ocean Circulation Explorer (GOCE) indicate that the coseismic deformation caused
by great earthquakes such as the 2004 Sumatra–Andaman earthquake can be detected by the low-low tracking and the gradiometer
data within the bandwidths of spherical degrees 15–30 and 25–100, respectively. However, the detection of terrestrial water
storage variation by GOCE gradiometer is equivocal even after localization. 相似文献
98.
The GOCE satellite observes gravity gradients with unprecedented accuracy and resolution. The GOCE observations are reliable within a well-defined measurement bandwidth. In this study, different finite and infinite impulse response filters have been designed to obtain the demanded pass. Exhaustive time and frequency domain investigations prove that the proposed infinite impulse response filter can be a real competitor of the existing solution of the filtering problem. 相似文献
99.
R. Rummel 《Earth, Moon, and Planets》2004,94(1-2):3-11
Precise global geoid and gravity anomaly information serves essentially three different kinds of applications in Earth sciences:
gravity and geoid anomalies reflect density anomalies in oceanic and continental lithosphere and the mantle; dynamic ocean
topography as derived from the combination of satellite altimetry and a global geoid model can be directly transformed into
a global map of ocean surface circulation; any redistribution or exchange of mass in Earth system results in temporal gravity
and geoid changes. After completion of the dedicated gravity satellite missions GRACE and GOCE a high standard of global gravity
determination, both of the static and of the time varying field will be attained. Thus, it is the right time to investigate
the future needs for improvements in the various fields of Earth sciences and to define the right strategy for future gravity
field satellite missions. 相似文献
100.
???????????????????????Ч???????????????????????????????????? ???GOCE??????????????????????????????????????????????????????????????????????????????С????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????С????????????????????????????????????????? 相似文献