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Assessment of observing time-variable gravity from GOCE GPS and accelerometer observations / Pieter N.A.M. Visser in Journal of geodesy, vol 88 n° 11 (November 2014)  

Public [article]  inJournal of geodesy > vol 88 n° 11 (November 2014) . - pp 1029 - 1046 Titre : Assessment of observing time-variable gravity from GOCE GPS and accelerometer observations Type de document : Article/Communication Auteurs : Pieter N.A.M. Visser, Auteur ; W. Van der Wal, Auteur ; E.J.O. Schrama, Auteur ; et al., Auteur Année de publication : 2014 Article en page(s) : pp 1029 - 1046 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] données GOCE [Termes IGN] données GPS [Termes IGN] effet atmosphérique [Termes IGN] gravimétrie spatiale [Termes IGN] orbite [Termes IGN] variable Résumé : (Auteur) An assessment has been made of the possibility to estimate time-variable gravity from GPS-derived orbit perturbations and common-mode accelerometer observations of ESA’s GOCE Earth Explorer. A number of 20-day time series of Earth’s global long-wavelength gravity field have been derived for the period November 2009 to November 2012 using different parameter setups and estimation techniques. These techniques include a conventional approach where for each period, one set of gravity coefficients is estimated, either excluding or including empirical accelerations, and the so-called Wiese approach where higher frequency coefficients are estimated for the very long wavelengths. A principal component analysis of especially the time series of gravity field coefficients obtained by the Wiese approach and the conventional approach with empirical accelerations reveals an annual signal. When fitting this annual signal directly through the time series, the sine component (maximum in spring) displays features that are similar to well-known continental hydrological mass changes for the low latitude areas, such as mass variations in the Amazon basin, Africa and Australia for spatial scales down to 1,500 km. The cosine component (maximum in winter), however, displays large signals that can not be attributed to actual mass variations in the Earth system. The estimated gravity field changes from GOCE orbit perturbations are likely affected by missing GPS observations in case of high ionospheric perturbations during periods of increased solar activity, which is minimal in Summer and maximal towards the end of autumn. Numéro de notice : A2014-563 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0741-9 Date de publication en ligne : 27/06/2014 En ligne : https://doi.org/10.1007/s00190-014-0741-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=74749 [article]

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266-2014111	SL	Revue	Centre de documentation	Revues en salle	Disponible

Spherical harmonic analysis of satellite gradiometry / Reiner Rummel (1993)  

Public Titre : Spherical harmonic analysis of satellite gradiometry Type de document : Rapport Auteurs : Reiner Rummel, Auteur ; Fernando Sanso, Auteur ; Martin Van Gelderen, Auteur ; Radboud Koop, Auteur ; E.J.O. Schrama, Auteur ; Maria Antonia Brovelli, Auteur ; F. Miggliaccio, Auteur ; F. Sacerdote, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 1993 Collection : Netherlands Geodetic Commission Publications on Geodesy Sous-collection : New series num. 39 Importance : 122 p. Format : 20 x 28 cm ISBN/ISSN/EAN : 978-90-6132-247-4 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] analyse harmonique [Termes IGN] gradiométrie [Termes IGN] harmonique sphérique [Termes IGN] méthode des moindres carrés [Termes IGN] poursuite de satellite Index. décimale : 30.60 Géodésie spatiale Résumé : (auteur) In 1988 the European Space Agency started with a series of studies with the goal to prepare the geodetic user community for a dedicated gravity field mission and stimulate cooperation among various groups. Thereby it was left open whether the planned mission should be based on the principle of satellite-to-satellite tracking, on satellite gradiometry or on a combination of these two methods. In the course of these studies it turned out that the group of the dipartimento di ingegneria idraulica, ambientale e del rilevamento of the politecnico di Milano and that of the faculty of geodetic engineering of the Delft University of Technology worked much along the same line. At various occasions very exciting and stimulating exchange of ideas took place between these two groups. In 1991 it was therefore decided to publish the main line of their development in gradiometry analysis, the so-called timewise and spacewise approach, in a joint report. Compared with the benefit it would have been rather cumbersome to try to homogenize the adopted style of presentation and notation of the two groups. Thus little effort was spent on this aspect. We hope that this does not hamper reading. Numéro de notice : 61103 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Rapport de recherche DOI : sans En ligne : https://www.ncgeo.nl/downloads/39Rummel.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=60878

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61103-01	30.60	Livre	Centre de documentation	Géodésie	Disponible
61103-02	30.60	Livre	Centre de documentation	Géodésie	Disponible

The role of orbit errors in processing of satellite altimeter data / E.J.O. Schrama (1989)  

Public Titre : The role of orbit errors in processing of satellite altimeter data Type de document : Rapport Auteurs : E.J.O. Schrama, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 1989 Collection : Netherlands Geodetic Commission Publications on Geodesy Sous-collection : New series num. 33 Importance : 170 p. Format : 20 x 28 cm ISBN/ISSN/EAN : 978-90-6132-239-9 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Technologies spatiales [Termes IGN] altimétrie satellitaire par radar [Termes IGN] données altimétriques [Termes IGN] invariance [Termes IGN] mécanique orbitale [Termes IGN] orbitographie [Termes IGN] pesanteur terrestre [Termes IGN] Seasat [Termes IGN] vitesse radiale Résumé : (auteur) The problem of radial orbit errors in processing of satellite altimeter data is largely due to the inaccuracy of the gravity model which is required for the computation of the trajectory of the spacecraft. A commonly used technique for removing these errors consists of minimizing the crossover differences of profiles measured by the altimeter radar. Several versions of the technique of least squares crossover minimization have been investigated using either SEASAT observations or simulated data. In these adjustments coefficients of error functions are estimated which are either locally defined over short arc segments, globally over long arc segments, or continuously over an entire arc having a length of several days. The solution of the corresponding normal equations consists of a homogeneous and a particular part. For each crossover minimization problem (CMP) the homogeneous solution is always given as an analytical expression describing the invariances of the altimetric sea surface with respect to the crossover differences. These invariances are described by a surface deformation function which is characteristic for the problem in question. The number of coefficients in this function equals to the rank defect of the normal matrix in the CMP. For the particular solution of a local CMP (using "tilt and bias" functions) it was found that 2 non-intersecting and non-overlapping master arc segments have to be fixed. However for global chronological segmented CMP's (using 3 parameter sine-cosine functions) only 1 master arc segment needs to be fixed for a particular solution. For continuous CMP's a particular solution is found by including 9 constraint equations in the form of pseudo observation equations. In this case the error function consists of a Fourier series truncated at a cutoff frequency of 2.3 cycles per revolution including a 2 parameter function modeling a long periodic effect in the orbit. The underlying problem of gravitational radial orbit errors is described by means of the linear perturbations theory, which is based on the Lagrange planetary equations. Additionally the problem is formulated by means of the Hill equations describing perturbed satellite motions in an idealized circular orbit. It is shown that the non-resonant particular radial solution of the Hill equations coincides with the first-order radial solution derived from the linear perturbations theory assuming a near circular orbit. The first-order radial solution has been compared with a simulated signal derived by numerical integration of the equations of motion. The simulated signal consists of the radial differences between two trajectories (resembling the SEASAT 3 day repeat configuration) integrated with different gravity models. It was found that the analytical orbit error model resembles closely the simulated signal after removal of a long periodic effect. The validity of the general solutions of two global CMP's has been investigated by means of a simulation experiment. In this experiment crossover differences are simulated by means of the radial orbit error signal described above. In a second step it is attempted to reconstruct this signal by minimizing the simulated differences. This experiment revealed that the general solution of the segmented CMP appears to be hampered by unrealistic velocity discontinuity effects of successive arc segment error functions. In addition, it fails to describe the C11 and S11 and higher degree and order components of a geographically correlated radial orbit error. This is not surprising since one can prove that the homogeneous solution of the segmented CMP (without velocity discontinuities) corresponds to the C00 and C10 component of the geographically correlated radial orbit error. For this reason the global segmented CMP is reformulated in a continuous approach where it is shown that the homogeneous solution coincides with the geographically correlated radial orbit error. Computations showed that the simulated signal deviates to approximately 15 cm r.m.s. with respect to the general solution of the continuous CMP. Employing the latter technique 5 independent particular solutions of a radial orbit error signal have been computed from SEASAT crossover data. These solutions appear to be highly correlated and suggest the presence of a disturbing effect likely to be caused by gravity modeling errors. Additionally it was found that the individual solutions resemble a concentration of signal near the once per revolution frequency in the radial orbit error spectrum. This solution could in principle be used to improve a part of the gravity model that is used in the trajectory computation of the satellite. In the last part an integrated approach is described where the problem of modeling errors in the orbit, the geoid and the permanent part of the sea surface topography (PST) caused by ocean circulation are considered simultaneously. It is argued that an application of the integrated approach is justified if simultaneously gravity model improvement is performed employing tracking data of other satellites at different inclinations and eccentricities. Other aspects of the integrated approach concern the modeling problems of the PST field, an omission effect of the gravity field and the relation with the global continuous CMP. Numéro de notice : 57963 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Rapport de recherche DOI : sans En ligne : https://www.ncgeo.nl/downloads/33Schrama.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=60322

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Code-barres	Cote	Support	Localisation	Section	Disponibilité
57963-01	21.10	Livre	Centre de documentation	Technologies spatiales	Disponible
57963-02	21.10	Livre	Centre de documentation	Technologies spatiales	Disponible