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  • 1
    Call number: 6/M 08.0211
    In: International Association of Geodesy symposia
    Description / Table of Contents: Contents: The Molodensky Scalar Boundary Value Problem in Spherical Coordinates.- The Slepian Problem on the Sphere.- White Noise Stochastic BVP's and Cimmino's Theory.- Simulation of the Goce Gravity Field Mission.- Quality Improvement of Global Gravity Field Models by Combining Satellite Gradiometry and Airborne Gravimetry.- The Determination of Geopotential Differences from Satellite-to-Satellite Tracking.- The Topographic Effects of Helmert's Method of Condensation.- Distance Measurement with Electromagnetic Wave Dispersion.- A Global Topographic-Isostatic Model Based on a Loading Theory.- Stochastic Modelling of Non-Stationary Smooth Phenomena.- Deformation Detection According to a Bayesian Approach.- Block Elimination and Weight Matrices.- Construction of An-Isotropic Covariance-Functions Using Sums of Riesz-Representers.- New Covariance Models for Local Applications of Collocation.
    Type of Medium: Monograph available for loan
    Pages: xvii, 362 S. : Ill., graph. Darst., Kt.
    ISBN: 9783540745839 , 3-540-74583-1
    Series Statement: International Association of Geodesy symposia 132
    Classification:
    Geodesy
    Location: Reading room
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geodesy 73 (1999), S. 35-46 
    ISSN: 1432-1394
    Keywords: Key words. Nonlinear dynamical and nonlinear measurement system ; Nonlinear filters ; Bias and accuracy analysis ; Almost unbiased second-order nonlinear filter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. The biases and accuracy of the extended Kalman filter (EKF) and a second-order nonlinear filter (SONF) are discussed from the point of view of a frequentist; these are often derived by applying the relevant conditional quantities to the linear Kalman algorithm under the Bayesian framework. The EKF and the SONF are biased, although the SONF has been derived in the hope of improving first-order filters. Unfortunately the biases of the SONF may be magnified further, because the second-order terms of the relevant Bayesian conditional quantities have never been properly used to derive the SONF from the frequentist point of view. The variance–covariance matrix of the SONF given in the literature is proven to be incorrect up to the second-order approximation, and the correct one is derived. Finally, also from the point of view of a frequentist, an alternative, almost unbiased SONF is proposed, if the randomness of partials is neglected.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 110 (1992), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Determination of surface gravity anomalies from gradiometric observables poses one of the downward continuation problems in physical geodesy. The unstable characteristics of the problem have been well exposed on the base of spectral analysis. The purpose of this paper is to develop a new approach to obtaining the best resolutions of mean gravity anomalies in terms of mean square errors, biases and error variances from the point of view of biased estimation. The three algorithms of ridge regression are presented and a comparison with the LS method is made. The simulation computations have shown that regional 1d̀× 1d̀ mean gravity anomalies can be easily resolved with a mean accuracy of 5 ˜ 7 mgal by employing the ridge estimation techniques. The results may be further improved by using algorithm B. The LS solution, however, results in a mean accuracy of 16.7 mgal, although it is unbiased. Finally, the proposed method is shown to be very different from some present criteria of selection of regularization (or ridge) parameters used in geodetic inversions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 120 (1995), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: To determine displacement and strain fields accurately and reliably, we need to specify several quality arguments to design deforming networks optimally. The purpose of this study is to investigate optimal design problems of deforming networks from the viewpoint of multi-objective optimal theory. Based on accuracy, reliability and the character of a deformation model, a multi-objective optimal technique has been developed for designing a 3-D deforming network. It simultaneously takes into account optimal designs of displacement vectors and principal strain components. A criterion matrix for the principal components of strain is constructed. Numerical results are discussed in terms of objective function values, error ellipsoids of displacement vectors and principal components of strain.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 117 (1994), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Geophysical and geodetic inverse problems are often ill posed. They are smoothed to guarantee stable solutions. Geophysical and geodetic applications of smoothness techniques like Tikhonov's regularization method seem to have been limited to one realization of sampling. However, smoothness (or ridge) parameters are data related but empirically chosen. It is expected that the ridge parameters and thus the resolutions of models will be different from one realization of sampling to another. Therefore, the chief motivation of this paper is to investigate large-sample properties of some smoothness (i.e. biased) estimators in terms of mean-square error. Some potentially applicable biased estimators are included in this simulation. the example is the recovery of local gravity fields from gradiometric observables. On the basis of 500 realizations of sampling, we extensively investigate the mean-square error and bias problems, the best and worst performances, and the statistical properties of ridge parameters. All of the biased estimators indeed improve the least-squares solution, but the sizes of improvement are quite different. If the iterative ridge estimator is employed, the average value of mean-square error roots of surface gravity anomalies is much less than 5 mgal.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 111 (1992), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: For the determination of gravity field parameters using satellite observations, regularization (with, e.g. Kaula's rule) is widely used, because the derived normal equations are ill-conditioned. The procedure is interpreted as a kind of collocation. Alternatively, it can be viewed as biased estimation. Thus several questions arise concerning the bias problem of the estimated geopotential fields, the uncertainty about the proper Kaula's constant column, and the unrealistic accuracy measure of the estimate. These factors may affect its application, depending on the magnitudes of the bias values and the accuracy difference between least-squares (LS) collocation and biased estimation.Two tests are carried out based on the GEM-T1 model. Test A uses the actual GEM-T1 coefficients and because test A is influenced by the biased underestimated values, a second test B assumes that Kaula's rule reflects the magnitudes of the geopotential coefficients. The results show that the coefficients of lower degrees are well determined if Kaula's rule is applied to degree and order 6 and above. In test A, the bias of each coefficient reaches 20 per cent of the estimated value at degree 19, and more than 30 per cent after degree 25. The computation of the mean squared errors of biased estimation indicates that the accuracy measure of LS collocation is very conservative globally. The reason for this is the underestimation of the coefficients. Test B shows that the bias of each coefficient increases to 20 per cent of the estimated value at degree 15 and 30 per cent at degree 19. More than 100 per cent is reached at degree 25. About 4/5 of the total number of the coefficients are too optimistic in accuracy, if the variance-covariance matrix of LS collocation is used.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 110 (1992), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Vertical datum connection is investigated from the viewpoint of quality, i.e. accuracy and reliability, based on the method originally proposed by Rummel & Teunissen (1988). Three simulations are carried out. The levelling accuracy is assumed to be 1 mmkm-1 and the position accuracy of space stations 5 cm. The three error models of the geoid used are that of the Rapp-81 model, that of a tailored gravitational field and that defined by the GEM-T1 variance-covariance matrix. The results show that the quality of the vertical datum connection depends on the relative accuracy of levelling and space stations, but in particular on that of the geoid. It is also related to the number of space stations inside each datum zone and their geographical distribution. Only when an absolute determination of vertical datum is required, does the absolute accuracy of the space stations play an important role.Finally, we discuss an alternative datum connection model using terrestrial gravity anomalies and satellite derived geopotential coefficients.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 127 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Geoscientists have undertaken mapping of the Earth's crustal strain (or stress) fields using a great variety of field data. The output can be represented by a 3-D second-rank symmetric random strain tensor. The random principal strains-land rotations of the random tensor are frequently computed. The accuracy is calculated using a first-order approximation. The distribution aspects of the random principal strains and rotations have received almost no attention in Earth Sciences. A first-order approximation of accuracy may not be sufficient if the signal-to-noise ratio is small, as is often the case for geodetically derived random strain tensors. Therefore, the purpose of this paper is to investigate the distribution and estimation problems of the general 3-D second-rank tensor equation GΛGT=T, where T is a given 3-D second-rank symmetric random tensor, Λ a diagonal (3 × 3) random eigenvalue matrix, and G a (3 × 3) random orientation matrix, which is also orthogonal. Λ and G are to be estimated (or solved) from T. If some eigenvalues coincide, additional conditions are imposed on the eigenvectors so that they can be chosen uniquely. The joint probability density function (pdf) of the random eigenvalues and rotations will be worked out, given a joint pdf of the elements of random tensors T. Because the rotations are of special interest in Earth Sciences, we shall also derive the joint marginal pdf of random rotations. The geometry of eigenspectra will be studied. The biases of random eigenvalues and rotations will be derived, which have been neglected in the past. They can be very crucial in interpreting the pattern of a derived strain field, however, when applied to a real Earth Science problem. The variance-covariance matrices will be computed using a second-order approximation.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geodesy 70 (1996), S. 419-430 
    ISSN: 1432-1394
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract Let there be given a twodimensional symmetric rank two tensor of random type (examples:strain, stress) which is either directly observed or indirectly estimated from observations by an adjustment procedure. Under the assumption of normalityof tensor components we compute the joint probability density functionas well as the marginal probability density functionsof its eigenspectra (eigenvalues) and eigendirections (orientation parameters). Due to the nonlinearity of the relation between eigenspectra-eigendirections and the random tensor components, via the “inverse nonlinear error propagation”biases and aliases of their first and centralized second moments (mean value, variance-covariance) are expressed in terms of Jacobianand Hessianmatrices. The joint probability density function and the first and second moments thus form the fundamental of hypothesis testing and qualify control of eigenspectra (eigenvalues, principal components) and eigendirections (orientation parameters, eigenvectors, principial direction) of a twodimensional, symmetric rank two random tensor.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geodesy 70 (1996), S. 419-430 
    ISSN: 1432-1394
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Let there be given a twodimensional symmetric rank two tensor of random type (examples: strain, stress) which is either directly observed or indirectly estimated from observations by an adjustment procedure. Under the assumption of normality of tensor components we compute the joint probability density function as well as the marginal probability density functions of its eigenspectra (eigenvalues) and eigendirections (orientation parameters). Due to the nonlinearity of the relation between eigenspectra-eigendirections and the random tensor components, via the "inverse nonlinear error propagation" biases and aliases of their first and centralized second moments (mean value, variance-covariance) are expressed in terms of Jacobian and Hessian matrices. The joint probability density function and the first and second moments thus form the fundamental of hypothesis testing and qualify control of eigenspectra (eigenvalues, principal components) and eigendirections (orientation parameters, eigenvectors, principial direction) of a twodimensional, symmetric rank two random tensor.
    Type of Medium: Electronic Resource
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