共查询到20条相似文献，搜索用时 46 毫秒
1.
《Journal of Geodesy》1975,49(3):241-257
The parallelism of geodetic and satellite systems to the average terrestrial system is examined, under the assumption that
a geodetic system is a fixed framework invariant with respect to geodetic network adjustment. In this case a geodetic system
is rotated with respect to the average terrestrial system only about the ellipsoid normal of the initial point. The method
is demonstrated using coordinates and covariance matrices for BC-4 and SECOR satellite tracking stations computed by Mueller
and his co-workers. It is shown that the NAD geodetic system is scaled significantly larger than the satellite systems; the
SECOR satellite systems have significant Z-rotations with respect to the average terrestrial system; and the ETH geodetic
system may have a significant rotation with respect to the average terrestrial system. 相似文献
2.
Petr Vaníček 《Journal of Geodesy》1979,53(3):221-225
It is shown that for linear parametric adjustment models all the least-squares equations can be obtained from a commutative
diagram, where the observation and parameter spaces are regarded as covariant. Their contravariant counterparts are defined
through the metric property of the covariance matrix of the observations. 相似文献
3.
基于方差分量估计的拟合推估及其在GIS误差纠正的应用 总被引：2，自引：0，他引：2
拟合推估解算必须首先求得信号向量的方差协方差矩阵,该协方差矩阵一般通过选定的协方差函数,并通过已测点数据进行拟合得到。显然观测噪声的先验方差协方差阵与拟合得到的随机信号的方差协方差矩阵必须相互协调,即观测噪声向量和信号向量的权矩阵所对应的方差因子应该一致,否则将对固定效应和随机效应参数的估计带来系统性的影响。应用方差分量估计来协调拟合推估模型中观测噪声和信号向量的随机模型,并分别从极大似然估计、MINQUE估计、赫尔默特方差分量估计三方面构建了拟合推估模型的方差分量解,最后利用新提出的理论与方法,对一幅实际的扫描地形图进行误差纠正,结果表明基于方差分量估计的拟合推估法能够提高扫描地形图的精度。 相似文献
4.
In collocation applications, the prior covariance matrices or weight matrices between the signals and the observations should
be consistent to their uncertainties; otherwise, the solution of collocation will be distorted. To balance the covariance
matrices of the signals and the observations, a new adaptive collocation estimator is thus derived in which the corresponding
adaptive factor is constructed by the ratio of the variance components of the signals and the observations. A maximum likelihood
estimator of the variance components is thus derived based on the collocation functional model and stochastic model. A simplified
Helmert type estimator of the variance components for the collocation is also introduced and compared to the derived maximum
likelihood type estimator. Reasonable and consistent covariance matrices of the signals and the observations are arrived through
the adjustment of the adaptive factor. The new adaptive collocation with related adaptive factor constructed by the derived
variance components is applied in a transformation between the geodetic height derived by GPS and orthometric height. It is
shown that the adaptive collocation is not only simple in calculation but also effective in balancing the contribution of
observations and the signals in the collocation model. 相似文献
5.
Stochastic significance of peaks in the least-squares spectrum 总被引：3，自引：1，他引：2
S. D. Pagiatakis 《Journal of Geodesy》1999,73(2):67-78
The least-squares spectral analysis method is reviewed, with emphasis on its remarkable property to accept time series with
an associated, fully populated covariance matrix. Two distinct cases for the input covariance matrix are examined: (a) it
is known absolutely (a-priori variance factor known); and (b) it is known up to a scale factor (a-priori variance factor unknown),
thus the estimated covariance matrix is used. For each case, the probability density function that underlines the least-squares
spectrum is derived and criteria for the statistical significance of the least-squares spectral peaks are formulated. It is
shown that for short series (up to about 150 values) with an estimated covariance matrix (case b), the spectral peaks must
be stronger to be statistically significant than in the case of a known covariance matrix (case a): the shorter the series
and the lower the significance level, the higher the difference becomes. For long series (more than about 150 values), case
(b) converges to case (a) and the least-squares spectrum follows the beta distribution. The results of this investigation are formulated in two new theorems.
Received: 27 May 1997/Accepted: 30 September 1998 相似文献
6.
顾及框架点坐标误差的三维基准转换严密模型 总被引：1，自引：1，他引：0
框架点坐标是由观测数据通过平差得到的,不可避免地受到观测误差的影响。针对原框架和目标框架坐标均存在误差、非公共点与公共点间存在相关性,以及转换系数矩阵中仅部分元素存在误差的实际情况,提出了同时考虑框架内误差以及转换点间相关性的基准转换严密模型,该模型将公共点和非公共点联合处理,同时计算坐标转换参数和所有点的坐标转换值,推导出了新的严格坐标转换公式,该公式为传统坐标转换公式基础上增加一改正量的形式;进一步,推导了原框架和目标框架坐标的方差不一致情况下的坐标转换模型的自适应解法;最后,利用"陆态网络工程"2000个区域站的实测坐标进行坐标转换验证,结果表明,这种严密模型较传统坐标转换模型具有更高的坐标转换精度。 相似文献
7.
佘彬彬 《武汉大学学报(信息科学版)》1989,(1)
本文同时顾及地面网尺度系统误差和卫星网尺度系统误差对各自网点坐标的影响,对联合平差中常用的两种7参数转换模型:Bursa模型和Molodensky模型进行了分析比较,在此基础上,提出了一种新的7参数转换模型;建立了甚长基线(VLBI)、卫星网和地面网联合平差的数学模型,并用模拟数据进行了数值分析,得到了一些有益结论。 相似文献
8.
The proper identification and removal of outliers in the combination of rates of vertical displacements derived from GPS,
tide gauges/satellite altimetry, and GRACE observations is presented. Outlier detection is a necessary pre-screening procedure
in order to ensure reliable estimates of stochastic properties of the observations in the combined least-squares adjustment
(via rescaling of covariance matrices) and to ensure that the final vertical motion model is not corrupted and/or distorted
by erroneous data. Results from this study indicate that typical data snooping methods are inadequate in dealing with these
heterogeneous data sets and their stochastic properties. Using simulated vertical displacement rates, it is demonstrated that
a large variety of outliers (random scattered and adjacent, as well as jointly influential) can be dealt with if an iterative
re-weighting least-squares adjustment is combined with a robust median estimator. Moreover, robust estimators are efficient
in areas weakly constrained by the data, where even high quality observations may appear to be erroneous if their estimates
are largely influenced by outliers. Four combined models for the vertical motion in the region of the Great Lakes are presented.
The computed vertical displacements vary between − 2 mm/year (subsidence) along the southern shores and 3 mm/year (uplift)
along the northern shores. The derived models provide reliable empirical constraints and error bounds for postglacial rebound
models in the region. 相似文献
9.
G. Fotopoulos 《Journal of Geodesy》2005,79(1-3):111-123
The well-known statistical tool of variance component estimation (VCE) is implemented in the combined least-squares (LS) adjustment of heterogeneous height data (ellipsoidal, orthometric and geoid), for the purpose of calibrating geoid error models. This general treatment of the stochastic model offers the flexibility of estimating more than one variance and/or covariance component to improve the covariance information. Specifically, the iterative minimum norm quadratic unbiased estimation (I-MINQUE) and the iterative almost unbiased estimation (I-AUE) schemes are implemented in case studies with observed height data from Switzerland and parts of Canada. The effect of correlation among measurements of the same height type and the role of the systematic effects and datum inconsistencies in the combined adjustment of ellipsoidal, geoid and orthometric heights on the estimated variance components are investigated in detail. Results give valuable insight into the usefulness of the VCE approach for calibrating geoid error models and the challenges encountered when implementing such a scheme in practice. In all cases, the estimated variance component corresponding to the geoid height data was less than or equal to 1, indicating an overall downscaling of the initial covariance (CV) matrix was necessary. It was also shown that overly optimistic CV matrices are obtained when diagonal-only cofactor matrices are implemented in the stochastic model for the observations. Finally, the divergence of the VCE solution and/or the computation of negative variance components provide insight into the selected parametric model effectiveness. 相似文献
10.
卫星重力径向梯度数据的最小二乘配置调和分析 总被引：3，自引：2，他引：1
本文深入研究了利用卫星重力梯度径向分量确定地球引力场位系数的最小二乘配置(LSC)调和分析方法。首先论述了最小二乘配置法的原理,推导了扰动引力梯度观测量与球谐系数之间的协方差和自协方差矩阵,在扰动引力梯度观测数据为等经差规则网格数据的情况下,引力位与扰动引力梯度之间的协方差矩阵具有分块Toeplitz循环阵的结构,有效的利用FFT变换技术将其降阶;研究利用截断奇异值分解法（TSVD）解决协方差阵的病态性问题;最后得到了引力梯度径向分量的最小二乘配置调和分析的完整计算公式。模拟试算结果表明,基于TSVD的最小二乘配置调和分析方法,能够以较高的精度还原全球重力场,验证了本文算法的有效性和实用性。 相似文献
11.
Summary Using a data set of 260 000 gravity anomalies it is shown that common characteristics for a local covariance function exist
in an area as large as Canada excluding the Rocky Mountains. After eliminating global features by referencing the data to
the GEM-10 satellite solution, the shape of the covariance function is remarkably consistent from one sample area to the next.
The determination of the essential parameters and the fitting of the covariance function are discussed in detail.
To test the reliability of the derived function, deflections of the vertical are estimated at about 230 stations where astrogeodetic
data are available. Results show that the standard error obtained from the discrepancies is about1″ for each component and that the error covariance matrix of least-squares collocation reflects this accuracy remarkably well. 相似文献
12.
针对遥感反演土壤湿度空间相关的误差协方差难以估计的问题,提出了一种遥感反演数据误差空间协方差估算方法——3类数据集成分析误差协方差（triple collocation covariance,TC_Cov）,将土壤湿度场的每个单元（像元）看作一个空间随机变量,用两个随机变量表示的土壤湿度值的时间序列作为样本进行空间协方差估计,由任何两个随机变量的协方差形成多个随机变量（随机场）的协方差矩阵。利用先进散射计（ad-vanced scatterometer,ASCAT）和热带降雨测量卫星（tropical rainfall measuring mission,TRMM）的遥感土壤湿度数据以及ERA-Interim土壤湿度再分析数据作为TC_Cov方法的输入数据,分别估算了ERA-Interim、AS-CAT和TRMM在澳大利亚Murrumbidgee流域的土壤湿度误差协方差矩阵,验证了估算方法的合理性和可行性。 相似文献
13.
The use of sampling-based Monte Carlo methods for the computation and propagation of large covariance matrices in geodetic applications is investigated. In particular, the so-called Gibbs sampler, and its use in deriving covariance matrices by Monte Carlo integration, and in linear and nonlinear error propagation studies, is discussed. Modifications of this technique are given which improve in efficiency in situations where estimated parameters are highly correlated and normal matrices appear as ill-conditioned. This is a situation frequently encountered in satellite gravity field modelling. A synthetic experiment, where covariance matrices for spherical harmonic coefficients are estimated and propagated to geoid height covariance matrices, is described. In this case, the generated samples correspond to random realizations of errors of a gravity field model.
AcknowledgementsThe authors are indebted to Pieter Visser and Pavel Ditmar for providing simulation output that was used in the GOCE error generation experiments. Furthermore, the NASA/NIMA/OSU team is acknowledged for providing public ftp access to the EGM96 error covariance matrix. The two anonymous reviewers are thanked for their valuable comments. 相似文献
14.
Statistical modeling for the mitigation of GPS multipath delays from day-to-day range measurements 总被引：1，自引：0，他引：1
Based on a least-squares model for double-difference GPS pseudoranges and carrier-phases, measurement residuals expressed
in time series during an observation session are positively correlated between one sidereal day and the preceding days. As
a result of the satellite’s period, the phenomenon, which takes place at a user receiving site, is attributed to multipath
interference. Examples from a weekly measurement dataset of control baselines are shown, where the known end-point coordinates
also serve as a benchmark for assessing positioning accuracy. The system of error equations for mixed-model adjustment is
divided into two subsystems. One set of the error equations is related to the real range measurements, while the other involves
the pseudo-observation with an empirical sample variance. According to the existing correlation between day-to-day residual
estimates, a multipath-mitigating algorithm is proven to improve the accuracy of the GPS height determination by at least
40%. It is also found that the algorithm depends on a variance-component estimator that adaptively scales an error covariance
matrix for both the real range and empirical delay measurements. 相似文献
15.
GPS Solutions - The true covariance matrix of the GPS phase observations is unknown and has to be assumed or estimated. The variance of the least-squares residuals was empirically shown to have an... 相似文献
16.
An iterative solution of weighted total least-squares adjustment 总被引：9，自引：0，他引：9
Total least-squares (TLS) adjustment is used to estimate the parameters in the errors-in-variables (EIV) model. However, its
exact solution is rather complicated, and the accuracies of estimated parameters are too difficult to analytically compute.
Since the EIV model is essentially a non-linear model, it can be solved according to the theory of non-linear least-squares
adjustment. In this contribution, we will propose an iterative method of weighted TLS (WTLS) adjustment to solve EIV model
based on Newton–Gauss approach of non-linear weighted least-squares (WLS) adjustment. Then the WLS solution to linearly approximated
EIV model is derived and its discrepancy is investigated by comparing with WTLS solution. In addition, a numerical method
is developed to compute the unbiased variance component estimate and the covariance matrix of the WTLS estimates. Finally,
the real and simulation experiments are implemented to demonstrate the performance and efficiency of the presented iterative
method and its linearly approximated version as well as the numerical method. The results show that the proposed iterative
method can obtain such good solution as WTLS solution of Schaffrin and Wieser (J Geod 82:415–421, 2008) and the presented numerical method can be reasonably applied to evaluate the accuracy of WTLS solution. 相似文献
17.
高分五号(GF-5)搭载的高光谱传感器兼顾宽覆盖和高分辨率的特性,但在实际应用中宽覆盖范围内各种地物类别的标注十分困难。当标记样本很少甚至没有标记样本时,遥感图像分类异常困难。此时,可以采用域适应方法,借助已标记的历史数据(源域)实现对未标记数据(目标域)的分类。本文提出了一种基于稀疏矩阵变换的关联对齐域适应分类算法。首先,利用稀疏矩阵变换估计源域和目标域的协方差矩阵;然后,运用协方差关联对齐方法估计源域到目标域的变换矩阵;接着,运用估计得到的变换矩阵将源域数据进行变换,使得其与目标域对齐;最后,在变换后的源域数据上建立分类器,实现对目标域数据的分类。本文的算法在两个真实的GF-5高光谱数据集上进行了验证。实验结果表明,本文算法要优于常用的子空间对齐算法和关联对齐算法。特别地,在黄河口GF-5数据上,本文算法比原始关联对齐方法的最近邻分类准确率提升了3.5%,支持向量机分类准确率提升了2.3%。 相似文献
18.
Haim B. Papo 《Journal of Geodesy》1973,47(1):89-95
Least squares adjustment processes occasionally utilize constants with a known degree of uncertainty. If the covariance matrix
of the adjusted parameters is estimated without considering those uncertainties the resulting estimate is invariably too optimistic.
A method is proposed by which without altering the values of the adjusted parameters their a posteriori (after the adjustment)
covariance matrix can be improved by the inclusion of the effect of uncertainties in the constants. 相似文献
19.
Lq估计的渐近方差-协方差矩阵及其特点 总被引：3，自引：2，他引：1
针对由独立同分布误差膨胀而成的独立不等精度误差,根据未知参数的M估计的Bahadur型线性表达式,本文导出了由观测量、残差向量、参数估计量和观测量平差向量组成的基本向量的Bahadur型表达式.进一步地,根据方差传播定律导出了M估计的基本向量的渐近方差-协方差矩阵,该矩阵由3个多余参数决定,第三多余参数由本文定义.对Lq范估计,分别计算了误差分别为正态分布和q范分布时的3个多余参数,以及相应的基本向量的方差协方差矩阵.对最小二乘估计,残差向量与参数估计量和观测量的平差向量统计独立,相应的协方差矩阵为零,这一性质与误差分布无关.对正态分布的Lq估计,残差向量与参数估计量和观测量平差向量的协方差不为零;而对q范分布的Lq估计,即是相应的极大似然估计,残差向量与参数估计量和观测量平差向量的协方差为零.文中所得公式和结论可用于统计分析. 相似文献
20.
E. Mysen 《Journal of Geodesy》2017,91(1):41-52
The Kalman filter is derived directly from the least-squares estimator, and generalized to accommodate stochastic processes with time variable memory. To complete the link between least-squares estimation and Kalman filtering of first-order Markov processes, a recursive algorithm is presented for the computation of the off-diagonal elements of the a posteriori least-squares error covariance. As a result of the algebraic equivalence of the two estimators, both approaches can fully benefit from the advantages implied by their individual perspectives. In particular, it is shown how Kalman filter solutions can be integrated into the normal equation formalism that is used for intra- and inter-technique combination of space geodetic data. 相似文献