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Improving the estimation of fractional-cycle biases for ambiguity resolution in precise point positioning / J. Geng in Journal of geodesy, vol 86 n° 8 (August 2012)  

Public [article]  inJournal of geodesy > vol 86 n° 8 (August 2012) . - pp 579 - 589 Titre : Improving the estimation of fractional-cycle biases for ambiguity resolution in precise point positioning Type de document : Article/Communication Auteurs : J. Geng, Auteur ; C. Shi, Auteur ; M. Ge, Auteur ; et al., Auteur Année de publication : 2012 Article en page(s) : pp 579 - 589 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] données GPS [Termes IGN] erreur systématique [Termes IGN] positionnement ponctuel précis [Termes IGN] résolution d'ambiguïté Résumé : (Auteur) Ambiguity resolution dedicated to a single global positioning system (GPS) station can improve the accuracy of precise point positioning. In this process, the estimation accuracy of the narrow-lane fractional-cycle biases (FCBs), which destroy the integer nature of undifferenced ambiguities, is crucial to the ambiguity-fixed positioning accuracy. In this study, we hence propose the improved narrow-lane FCBs derived from an ambiguity-fixed GPS network solution, rather than the original (i.e. previously proposed) FCBs derived from an ambiguity-float network solution. The improved FCBs outperform the original FCBs by ensuring that the resulting ambiguity-fixed daily positions coincide in nature with the state-of-the-art positions generated by the International GNSS Service (IGS). To verify this improvement, 1 year of GPS measurements from about 350 globally distributed stations were processed. We find that the original FCBs differ more from the improved FCBs when fewer stations are involved in the FCB estimation, especially when the number of stations is less than 20. Moreover, when comparing the ambiguity-fixed daily positions with the IGS weekly positions for 248 stations through a Helmert transformation, for the East component, we find that on 359 days of the year the daily RMS of the transformed residuals based on the improved FCBs is smaller by up to 0.8 mm than those based on the original FCBs, and the mean RMS over the year falls evidently from 2.6 to 2.2 mm. Meanwhile, when using the improved rather than the original FCBs, the RMS of the transformed residuals for the East component of 239 stations (i.e. 96.4% of all 248 stations) is clearly reduced by up to 1.6 mm, especially for stations located within a sparse GPS network. Therefore, we suggest that narrow-lane FCBs should be determined with ambiguity-fixed, rather than ambiguity-float, GPS network solutions. Numéro de notice : A2012-374 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-011-0537-0 Date de publication en ligne : 14/12/2011 En ligne : https://doi.org/10.1007/s00190-011-0537-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31820 [article]

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The spherical Slepian basis as a means to obtain spectral consistency between mean sea level and the geoid / D. Slobbe in Journal of geodesy, vol 86 n° 8 (August 2012)  

Public [article]  inJournal of geodesy > vol 86 n° 8 (August 2012) . - pp 609 - 628 Titre : The spherical Slepian basis as a means to obtain spectral consistency between mean sea level and the geoid Type de document : Article/Communication Auteurs : D. Slobbe, Auteur ; F. Simons, Auteur ; R. Klees, Auteur Année de publication : 2012 Article en page(s) : pp 609 - 628 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] algorithme de Gram-Schmidt [Termes IGN] cohérence (physique) [Termes IGN] filtre passe-bas [Termes IGN] fonction orthogonale [Termes IGN] géoïde gravimétrique [Termes IGN] niveau moyen des mers Résumé : (Auteur) The mean dynamic topography (MDT) can be computed as the difference between the mean sea level (MSL) and a gravimetric geoid. This requires that both data sets are spectrally consistent. In practice, it is quite common that the resolution of the geoid data is less than the resolution of the MSL data, hence, the latter need to be low-pass filtered before the MDT is computed. For this purpose conventional low-pass filters are inadequate, failing in coastal regions where they run into the undefined MSL signal on the continents. In this paper, we consider the use of a bandlimited, spatially concentrated Slepian basis to obtain a low-resolution approximation of the MSL signal. We compute Slepian functions for the oceans and parts of the oceans and compare the performance of calculating the MDT via this approach with other methods, in particular the iterative spherical harmonic approach in combination with Gaussian low-pass filtering, and various modifications. Based on the numerical experiments, we conclude that none of these methods provide a low-resolution MSL approximation at the sub-decimetre level. In particular, we show that Slepian functions are not appropriate basis functions for this problem, and a Slepian representation of the low-resolution MSL signal suffers from broadband leakage. We also show that a meaningful definition of a low-resolution MSL over incomplete spherical domains involves orthogonal basis functions with additional properties that Slepian functions do not possess. A low-resolution MSL signal, spectrally consistent with a given geoid model, is obtained by a suitable truncation of the expansions of the MSL signal in terms of these orthogonal basis functions. We compute one of these sets of orthogonal basis functions using the Gram–Schmidt orthogonalization for spherical harmonics. For the oceans, we could construct an orthogonal basis only for resolutions equivalent to a spherical harmonic degree 36. The computation of a basis with a higher resolution fails due to inherent instabilities. Regularization reduces the instabilities but destroys the orthogonality and, therefore, provides unrealistic low-resolution MSL approximations. More research is needed to solve the instability problem, perhaps by finding a different orthogonal basis that avoids it altogether. Numéro de notice : A2012-375 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0543-x Date de publication en ligne : 20/03/2012 En ligne : https://doi.org/10.1007/s00190-012-0543-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31821 [article]

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Monitoring GOCE gradiometer calibration parameters using accelerometer and star sensor data: methodology and first results / C. Siemes in Journal of geodesy, vol 86 n° 8 (August 2012)  

Public [article]  inJournal of geodesy > vol 86 n° 8 (August 2012) . - pp 629 - 645 Titre : Monitoring GOCE gradiometer calibration parameters using accelerometer and star sensor data: methodology and first results Type de document : Article/Communication Auteurs : C. Siemes, Auteur ; Roger Haagmans, Auteur ; M. Kern, Auteur ; et al., Auteur Année de publication : 2012 Article en page(s) : pp 629 - 645 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GOCE [Termes IGN] étalonnage d'instrument [Termes IGN] GOCE [Termes IGN] gradient de gravitation [Termes IGN] gradiomètre [Termes IGN] série temporelle Résumé : (Auteur) The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite, launched on 17 March 2009, is designed to measure the Earth’s mean gravity field with unprecedented accuracy at spatial resolutions down to 100 km. The accurate calibration of the gravity gradiometer on-board GOCE is of utmost importance for achieving the mission goals. ESA’s baseline method for the calibration uses star sensor and accelerometer data of a dedicated calibration procedure, which is executed every 2 months. In this paper, we describe a method for monitoring the evolution of calibration parameter during that time. The method works with star sensor and accelerometer data and does not require gravity field models, which distinguishes it from other existing methods. We present time series of calibration parameters estimated from GOCE data from 1 November 2009 to 17 May 2010. The time series confirm drifts in the calibration parameters that are present in the results of other methods, including ESA’s baseline method. Although these drifts are very small, they degrade the gravity gradients, leading to the conclusion that the calibration parameters of the ESA’s baseline method need to be linearly interpolated. Further, we find a correction of -36 * 10-6 for one calibration parameter (in-line differential scale factor of the cross-track gradiometer arm), which improves the gravity gradient performance. The results are validated by investigating the trace of the calibrated gravity gradients and comparing calibrated gravity gradients with reference gradients computed along the GOCE orbit using the ITG-Grace-2010s gravity field model. Numéro de notice : A2012-376 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0545-8 Date de publication en ligne : 22/02/2012 En ligne : https://doi.org/10.1007/s00190-012-0545-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31822 [article]

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Optimal regularization for geopotential model GOCO02S by Monte Carlo methods and multi-scale representation of density anomalies / Karl Rudolf Koch in Journal of geodesy, vol 86 n° 8 (August 2012)  

Public [article]  inJournal of geodesy > vol 86 n° 8 (August 2012) . - pp 647 - 660 Titre : Optimal regularization for geopotential model GOCO02S by Monte Carlo methods and multi-scale representation of density anomalies Type de document : Article/Communication Auteurs : Karl Rudolf Koch, Auteur ; J. Brockmann, Auteur ; W.D. Schuh, Auteur Année de publication : 2012 Article en page(s) : pp 647 - 660 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] analyse de variance [Termes IGN] B-Spline [Termes IGN] données GOCE [Termes IGN] méthode de Monte-Carlo [Termes IGN] modèle de géopotentiel [Termes IGN] ondelette Résumé : (Auteur) GOCO02S is a combined satellite-only geopotential model, regularized from degrees 180 to 250 of the expansion into spherical harmonics. To investigate the start of the regularization, the normal equations of GOCO02S have been used to compute additional geopotential models by regularizations beginning at degrees 160, 200, 220 and with no regularization. Three different methods are applied to determine where to start the regularization. The simplest one considers the decrease of the degree variances of the not regularized solution. The second one tests for the same solution the hypothesis that the square root of the degree variance is equal to the value computed by the estimated harmonic coefficients. If the hypothesis has to be rejected for a certain degree, the error degree variance is so large that the estimated harmonic coefficients cannot be trusted anymore so that the regularization has to start at that degree. The third method uses the density anomalies by which the disturbing potential is caused resulting from the geopotential model. The density anomalies are well suited to visualize the effects of the higher degree harmonics. In contrast to the base functions of the harmonic coefficients with global support, the density anomalies are expressed by a B-spline surface with local support. Multi-scale representations were applied and the hypotheses tested that the wavelet coefficients are equal to zero. Accepting the hypotheses means that nonsignificant wavelet coefficients were determined which lead to nonsignificant density anomalies. By comparing these anomalies for different regularizations, the degree where to start the regularization is determined. It turns out that beginning the regularization at degree 180, as was done for GOCO02S, is a correct choice. Numéro de notice : A2012-377 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0546-7 Date de publication en ligne : 24/02/2012 En ligne : https://doi.org/10.1007/s00190-012-0546-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31823 [article]

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Total least squares adjustment in partial errors-in-variables models: algorithm and statistical analysis / P. Xu in Journal of geodesy, vol 86 n° 8 (August 2012)  

Public [article]  inJournal of geodesy > vol 86 n° 8 (August 2012) . - pp 661 - 675 Titre : Total least squares adjustment in partial errors-in-variables models: algorithm and statistical analysis Type de document : Article/Communication Auteurs : P. Xu, Auteur ; J. Liu, Auteur ; C. Shi, Auteur Année de publication : 2012 Article en page(s) : pp 661 - 675 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] analyse de variance [Termes IGN] compensation non linéaire [Termes IGN] compensation par moindres carrés [Termes IGN] modèle d'erreur [Termes IGN] résidu [Termes IGN] traitement de données GNSS Résumé : (Auteur) The weighted total least squares (TLS) method has been developed to deal with observation equations, which are functions of both unknown parameters of interest and other measured data contaminated with random errors. Such an observation model is well known as an errors-in-variables (EIV) model and almost always solved as a nonlinear equality-constrained adjustment problem. We reformulate it as a nonlinear adjustment model without constraints and further extend it to a partial EIV model, in which not all the elements of the design matrix are random. As a result, the total number of unknowns in the normal equations has been significantly reduced. We derive a set of formulae for algorithmic implementation to numerically estimate the unknown model parameters. Since little statistical results about the TLS estimator in the case of finite samples are available, we investigate the statistical consequences of nonlinearity on the nonlinear TLS estimate, including the first order approximation of accuracy, nonlinear confidence region and bias of the nonlinear TLS estimate, and use the bias-corrected residuals to estimate the variance of unit weight. Numéro de notice : A2012-378 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0552-9 Date de publication en ligne : 23/03/2012 En ligne : https://doi.org/10.1007/s00190-012-0552-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31824 [article]

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266-2012081	RAB	Revue	Centre de documentation	En réserve L003	Disponible