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Triangulated spherical splines for geopotential reconstruction / M.J. Lai in Journal of geodesy, vol 83 n° 8 (August 2009)  

Public [article]  inJournal of geodesy > vol 83 n° 8 (August 2009) . - pp 695 - 708 Titre : Triangulated spherical splines for geopotential reconstruction Type de document : Article/Communication Auteurs : M.J. Lai, Auteur ; C.K. Shum, Auteur ; V. Baramidze, Auteur ; P. Wenston, Auteur Année de publication : 2009 Article en page(s) : pp 695 - 708 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur local [Termes IGN] champ de pesanteur terrestre [Termes IGN] Earth Gravity Model 1996 [Termes IGN] équation de Laplace [Termes IGN] fonction spline [Termes IGN] fonction spline d'interpolation [Termes IGN] modèle de géopotentiel [Termes IGN] potentiel de pesanteur terrestre Résumé : (Auteur) We present an alternate mathematical technique than contemporary spherical harmonics to approximate the geopotential based on triangulated spherical spline functions, which are smooth piecewise spherical harmonic polynomials over spherical triangulations. The new method is capable of multi-spatial resolution modeling and could thus enhance spatial resolutions for regional gravity field inversion using data from space gravimetry missions such as CHAMP, GRACE or GOCE. First, we propose to use the minimal energy spherical spline interpolation to find a good approximation of the geopotential at the orbital altitude of the satellite. Then we explain how to solve Laplace’s equation on the Earth’s exterior to compute a spherical spline to approximate the geopotential at the Earth’s surface. We propose a domain decomposition technique, which can compute an approximation of the minimal energy spherical spline interpolation on the orbital altitude and a multiple star technique to compute the spherical spline approximation by the collocation method. We prove that the spherical spline constructed by means of the domain decomposition technique converges to the minimal energy spline interpolation. We also prove that the modeled spline geopotential is continuous from the satellite altitude down to the Earth’s surface. We have implemented the two computational algorithms and applied them in a numerical experiment using simulated CHAMP geopotential observations computed at satellite altitude (450 km) assuming EGM96 (n max = 90) is the truth model. We then validate our approach by comparing the computed geopotential values using the resulting spherical spline model down to the Earth’s surface, with the truth EGM96 values over several study regions. Our numerical evidence demonstrates that the algorithms produce a viable alternative of regional gravity field solution potentially exploiting the full accuracy of data from space gravimetry missions. The major advantage of our method is that it allows us to compute the geopotential over the regions of interest as well as enhancing the spatial resolution commensurable with the characteristics of satellite coverage, which could not be done using a global spherical harmonic representation. Copyright Springer Numéro de notice : A2009-323 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-008-0283-0 En ligne : https://doi.org/10.1007/s00190-008-0283-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29953 [article]

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An absolute calibration site for radar altimeters in the continental domain: Lake Issykkul in Central Asia / J.F. Cretaux in Journal of geodesy, vol 83 n° 8 (August 2009)  

Public [article]  inJournal of geodesy > vol 83 n° 8 (August 2009) . - pp 723 - 735 Titre : An absolute calibration site for radar altimeters in the continental domain: Lake Issykkul in Central Asia Type de document : Article/Communication Auteurs : J.F. Cretaux, Auteur ; Stéphane Calmant, Auteur ; V. Romanovski, Auteur ; et al., Auteur Année de publication : 2009 Article en page(s) : pp 723 - 735 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] altimètre radar [Termes IGN] Asie centrale [Termes IGN] erreur instrumentale [Termes IGN] erreur systématique [Termes IGN] étalonnage d'instrument Résumé : (Auteur) Altimetry missions such as Topex/Poseidon, Jason-1, GFO and ENVISAT have been widely used in the continental domain over lakes, rivers and wetland although they were mostly dedicated to oceanic studies. Knowledge of the instrumental biases is a key issue. Numerous sites have been dedicated to calibration purposes, either in the oceanic domain (Harvest offshore platform in California, Corsica, Bass Strait in Australia) or over lakes (Lake Erie in United States). A new site (Lake Issykkul in Kirghizstan) is proposed for calibration in the continental domain. This lake is covered by past (T/P) and current radar altimetry satellites (Jason-1, T/P, GFO, and ENVISAT). Several in situ water levels and local meteorological variables are available at the site. Located in a mountainous area, it offers an opportunity for calibration far away from all other existing sites and very different environment contexts. Two GPS campaigns have been conducted on the lake in 2004 and in 2005. They consisted of cruises with stations installed onboard a boat following the satellite ground tracks, and onshore settings. This enabled estimating a bias for each altimeter and each tracking algorithm available. Biases obtained for Envisat, GFO, T/P and Jason-1 using the default ocean tracker (respectively, 48.1 + 6.6, 7.5 + 4.0, 0 + 4.3 and 7.0 + 5.5 cm) agree with biases published at the other calibration sites. For Jason-1, there is a significant disagreement with results obtained in the ocean field (7 cm instead of 13 cm) but is coherent with bias obtained on the Lake Erie site. Erroneous estimates of the sea state bias correction from non-oceanic-like waveforms is discussed as a possible explanation. Errors in the ionospheric, wet and dry tropospheric corrections for the continental domain are also highlighted and quantified. Copyright Springer Numéro de notice : A2009-324 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 0.1007/s00190-008-0285-y En ligne : https://doi.org/10.1007/s00190-008-0285-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29954 [article]

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Geoid and high resolution sea surface topography modelling in the mediterranean from gravimetry, altimetry and GOCE data: evaluation by simulation / R. Barzaghi in Journal of geodesy, vol 83 n° 8 (August 2009)  

Public [article]  inJournal of geodesy > vol 83 n° 8 (August 2009) . - pp 751 - 772 Titre : Geoid and high resolution sea surface topography modelling in the mediterranean from gravimetry, altimetry and GOCE data: evaluation by simulation Type de document : Article/Communication Auteurs : R. Barzaghi, Auteur ; N. Tselfes, Auteur ; I.N. Tziavos, Auteur ; G. Vergos, Auteur Année de publication : 2009 Article en page(s) : pp 751 - 772 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] données altimétriques [Termes IGN] données GOCE [Termes IGN] géoïde local [Termes IGN] hauteurs de mer [Termes IGN] levé gravimétrique [Termes IGN] Méditerranée, mer [Termes IGN] surface de la mer Résumé : (Auteur) The determination of local geoid models has traditionally been carried out on land and at sea using gravity anomaly and satellite altimetry data, while it will be aided by the data expected from satellite missions such as those from the Gravity field and steady-state ocean circulation explorer (GOCE). To assess the performance of heterogeneous data combination to local geoid determination, simulated data for the central Mediterranean Sea are analyzed. These data include marine and land gravity anomalies, altimetric sea surface heights, and GOCE observations processed with the space-wise approach. A spectral analysis of the aforementioned data shows their complementary character. GOCE data cover long wavelengths and account for the lack of such information from gravity anomalies. This is exploited for the estimation of local covariance function models, where it is seen that models computed with GOCE data and gravity anomaly empirical covariance functions perform better than models computed without GOCE data. The geoid is estimated by different data combinations and the results show that GOCE data improve the solutions for areas covered poorly with other data types, while also accounting for any long wavelength errors of the adopted reference model that exist even when the ground gravity data are dense. At sea, the altimetric data provide the dominant geoid information. However, the geoid accuracy is sensitive to orbit calibration errors and unmodeled sea surface topography (SST) effects. If such effects are present, the combination of GOCE and gravity anomaly data can improve the geoid accuracy. The present work also presents results from simulations for the recovery of the stationary SST, which show that the combination of geoid heights obtained from a spherical harmonic geopotential model derived from GOCE with satellite altimetry data can provide SST models with some centimeters of error. However, combining data from GOCE with gravity anomalies in a collocation approach can result in the estimation of a higher resolution geoid, more suitable for high resolution mean dynamic SST modeling. Such simulations can be performed toward the development and evaluation of SST recovery methods. Copyright Springer Numéro de notice : A2009-325 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-008-0292-z En ligne : https://doi.org/10.1007/s00190-008-0292-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29955 [article]

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Accuracy assessment of the GPS-based slant total electron content / C. Brunini in Journal of geodesy, vol 83 n° 8 (August 2009)  

Public [article]  inJournal of geodesy > vol 83 n° 8 (August 2009) . - pp 773 - 785 Titre : Accuracy assessment of the GPS-based slant total electron content Type de document : Article/Communication Auteurs : C. Brunini, Auteur ; F. Azpilicueta, Auteur Année de publication : 2009 Article en page(s) : pp 773 - 785 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] calibrage [Termes IGN] erreur systématique [Termes IGN] étalonnage d'instrument [Termes IGN] ionosphère [Termes IGN] positionnement par GPS [Termes IGN] teneur totale en électrons Résumé : (Auteur) The main scope of this research is to assess the ultimate accuracy that can be achieved for the slant total electron content (sTEC) estimated from dual-frequency global positioning system (GPS) observations which depends, primarily, on the calibration of the inter-frequency biases (IFB). Two different calibration approaches are analyzed: the so-called satellite-by-satellite one, which involves levelling the carrier-phase to the code-delay GPS observations and then the IFB estimation; and the so-called arc-by-arc one, which avoids the use of code-delay observations but requires the estimation of arc-dependent biases. Two strategies are used for the analysis: the first one compares calibrated sTEC from two co-located GPS receivers that serve to assess the levelling errors; and the second one, assesses the model error using synthetic data free of calibration error, produced with a specially developed technique. The results show that the arc-by-arc calibration technique performs better than the satellite-by-satellite one for mid-latitudes, while the opposite happens for low-latitudes. Copyright Springer Numéro de notice : A2009-326 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-008-0296-8 En ligne : https://doi.org/10.1007/s00190-008-0296-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29956 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-09071	SL	Revue	Centre de documentation	Revues en salle	Disponible