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Fast calculation of gravitational effects using tesseroids with a polynomial density of arbitrary degree in depth / Fang Ouyang in Journal of geodesy, vol 96 n° 12 (December 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 12 (December 2022) . - n° 97 Titre : Fast calculation of gravitational effects using tesseroids with a polynomial density of arbitrary degree in depth Type de document : Article/Communication Auteurs : Fang Ouyang, Auteur ; Long-wei Chen, Auteur ; Zhi-gang Shao, Auteur Année de publication : 2022 Article en page(s) : n° 97 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de gravitation [Termes IGN] coordonnées sphériques [Termes IGN] discrétisation [Termes IGN] intégrale de Newton [Termes IGN] inversion [Termes IGN] quadrature [Termes IGN] tesseroid [Termes IGN] transformation rapide de Fourier Résumé : (auteur) Fast and accurate calculation of gravitational effects on a regional or global scale with complex density environment is a critical issue in gravitational forward modelling. Most existing significant developments with tessroid-based modelling are limited to homogeneous density models or polynomial ones of a limited order. Moreover, the total gravitational effects of tesseroids are often calculated by pure summation in these methods, which makes the calculation extremely time-consuming. A new efficient and accurate method based on tesseroids with a polynomial density up to an arbitrary order in depth is developed for 3D large-scale gravitational forward modelling. The method divides the source region into a number of tesseroids, and the density in each tesseroid is assumed to be a polynomial function of arbitrary degree. To guarantee the computational accuracy and efficiency, two key points are involved: (1) the volume Newton’s integral is decomposed into a one-dimensional integral with a polynomial density in the radial direction, for which a simple analytical recursive formula is derived for efficient calculation, and a surface integral over the horizontal directions evaluated by the Gauss–Legendre quadrature (GLQ) combined with a 2D adaptive discretization strategy; (2) a fast and flexible discrete convolution algorithm based on 1D fast Fourier transform (FFT) and a general Toepritz form of weight coefficient matrices is adopted in the longitudinal dimension to speed up the computation of the cumulative contributions from all tesseroids. Numerical examples show that the gravitational fields predicted by the new method have a good agreement with the corresponding analytical solutions for spherical shell models with both polynomial and non-polynomial density variations in depth. Compared with the 3D GLQ methods, the new algorithm is computationally more accurate and efficient. The calculation time is significantly reduced by 3 orders of magnitude as compared with the traditional 3D GLQ methods. Application of the new algorithm in the global crustal CRUST1.0 model further verifies its reliability and practicability in real cases. The proposed method will provide a powerful numerical tool for large-scale gravity modelling and also an efficient forward engine for inversion and continuation problems. Numéro de notice : A2022-896 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s00190-022-01688-9 Date de publication en ligne : 05/12/2022 En ligne : https://doi.org/10.1007/s00190-022-01688-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102248 [article]

A new data-adaptive network design methodology based on the k-means clustering and modified ISODATA algorithm for regional gravity field modeling via spherical radial basis functions / Rasit Ulug in Journal of geodesy, vol 96 n° 12 (December 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 12 (December 2022) . - n° 91 Titre : A new data-adaptive network design methodology based on the k-means clustering and modified ISODATA algorithm for regional gravity field modeling via spherical radial basis functions Type de document : Article/Communication Auteurs : Rasit Ulug, Auteur ; Mahmut Onur Karslıoglu, Auteur Année de publication : 2022 Article en page(s) : n° 91 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] analyse de groupement [Termes IGN] Auvergne [Termes IGN] centroïde [Termes IGN] champ de pesanteur local [Termes IGN] champ de pesanteur terrestre [Termes IGN] classification barycentrique [Termes IGN] classification ISODATA [Termes IGN] Colorado (Etats-Unis) [Termes IGN] fonction de base radiale [Termes IGN] largeur de bande [Termes IGN] modèle de géopotentiel local [Termes IGN] modèle numérique de terrain Résumé : (auteur) In this study, a new data-adaptive network design methodology called k-SRBF is presented for the spherical radial basis functions (SRBFs) in regional gravity field modeling. In this methodology, the cluster centers (centroids) obtained by the k-means clustering algorithm are post-processed to construct a network of SRBFs by replacing the centroids with the SRBFs. The post-processing procedure is inspired by the heuristic method, Iterative Self-Organizing Data Analysis Technique (ISODATA), which splits clusters within the user-defined criteria to avoid over- and under-parameterization. These criteria are the minimum spherical distance between the centroids and the minimum number of samples for each cluster. The bandwidth (depth) of each SRBF is determined using the generalized cross-validation (GCV) technique in which only the observations within the radius of impact area (RIA) are used. The numerical tests are carried out with real and simulated data sets to investigate the effect of the user-defined criteria on the network design. Different bandwidth limits are also examined, and the appropriate lower and upper bandwidth limits are chosen based on the empirical signal covariance function and user-defined criteria. Also, additional tests are performed to verify the performance of the proposed methodology in combining different types of observations, such as terrestrial and airborne data available in Colorado. The results reveal that k-SRBF is an effective methodology to establish a data-adaptive network for SRBFs. Moreover, the proposed methodology improves the condition number of normal equation matrix so that the least-squares procedure can be applied without regularization considering the user-defined criteria and bandwidth limits. Numéro de notice : A2022-877 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s00190-022-01681-2 Date de publication en ligne : 22/11/2022 En ligne : https://doi.org/10.1007/s00190-022-01681-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102190 [article]

On study of the Earth topography correction for the GRACE surface mass estimation / Fan Yang in Journal of geodesy, vol 96 n° 12 (December 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 12 (December 2022) . - n° 95 Titre : On study of the Earth topography correction for the GRACE surface mass estimation Type de document : Article/Communication Auteurs : Fan Yang, Auteur ; Zhicai Luo, Auteur ; Hao Zhou, Auteur ; et al., Auteur Année de publication : 2022 Article en page(s) : n° 95 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GRACE [Termes IGN] formule de Stokes [Termes IGN] géoïde gravimétrique [Termes IGN] itération [Termes IGN] masse de la Terre [Termes IGN] topographie Résumé : (auteur) Traditional conversion from gravity Stokes coefficients into the surface mass, e.g., in the GRACE(-FO) applications, presumes the Earth as a perfect sphere that is apparently against the reality. Recent studies manage to correct the conversion by considering the Earth’s oblateness, in another word, the Earth is treated as an ellipsoid. However, the Earth’s geometry is far more complicated due to the topography, so that neither a sphere nor an ellipsoid is exact. Evidences from recent studies and this one demonstrate that any geometrical approximation of the Earth shape like a presumed sphere will inevitably lead to a bias in the surface mass estimation from GRACE gravity fields, resulting in a possible misinterpretation of geophysical signals that may occur in polar regions or mountain areas. In this context, we propose an iterative scaling factor method to numerically realize a more accurate surface mass estimate, considering a more realistic geometry of the Earth including its oblateness, topography and geoid undulation. Verified with a series of simulations, the proposed method is found to be efficient (less than four iterations), reliable (after a broad range of tests) and universally accurate (reducing at least 80% of the bias). Relative to our method, the mean linear trend in 2002–2015 estimated from GRACE under an ideal spherical Earth is found to be underestimated by about 3.1% and 5.5% over Greenland and West Antarctica, respectively. Among the trend underestimation, the topography-related contribution takes up − 0.5% (0.79 Gt/yr, the negative sign denotes an overestimation) and − 0.4% (0.34 Gt/yr), respectively. Although the value is small, it is a systematic bias worth considering, for example, it is greater than the influence (0.3 Gt/yr on the trend estimation over West Antarctica) by switching atmospherical de-aliasing products from RL05 to RL06. Besides, the topography-induced bias rapidly increases to 2.7% (0.26 mm/yr) at mountain Himalayas, which is even larger than the ellipsoid-induced bias (0.19 mm/yr). Based on the results obtained so far, the topography-induced bias is found to be roughly one order of magnitude smaller than GRACE’s present measurement error; nevertheless, it will be relevant once the GRACE is improved toward its baseline accuracy. In particular, the topography correction should be considered for NGGM that expects to map the Earth gravity field in an unprecedented accuracy and spatial resolution. Numéro de notice : A2022-878 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s00190-022-01683-0 Date de publication en ligne : 02/12/2022 En ligne : https://doi.org/10.1007/s00190-022-01683-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102189 [article]

The employment of quasi-hexagonal grids in spherical harmonic analysis and synthesis for the earth's gravity field / Xingxing Li in Journal of geodesy, vol 96 n° 11 (November 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 11 (November 2022) . - n° 89 Titre : The employment of quasi-hexagonal grids in spherical harmonic analysis and synthesis for the earth's gravity field Type de document : Article/Communication Auteurs : Xingxing Li, Auteur ; Jiancheng Li, Auteur ; Xiaochong Tong, Auteur ; et al., Auteur Année de publication : 2022 Article en page(s) : n° 89 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] harmonique sphérique [Termes IGN] icosahèdre [Termes IGN] système de grille globale discrète [Termes IGN] théorème de Legendre Résumé : (auteur) Numéro de notice : A2022-837 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-022-01653-6 Date de publication en ligne : 09/11/2022 En ligne : https://doi.org/10.1007/s00190-022-01653-6 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102034 [article]

Spherical harmonic synthesis of area-mean potential values on irregular surfaces / Blažej Bucha in Journal of geodesy, vol 96 n° 10 (October 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 10 (October 2022) . - n° 68 Titre : Spherical harmonic synthesis of area-mean potential values on irregular surfaces Type de document : Article/Communication Auteurs : Blažej Bucha, Auteur Année de publication : 2022 Article en page(s) : n° 68 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de gravitation [Termes IGN] convergence [Termes IGN] harmonique sphérique [Termes IGN] surface hétérogène [Termes IGN] transformation de Legendre [Termes IGN] transformation rapide de Fourier Résumé : (auteur) We present a method to integrate external solid spherical harmonic expansions at geographical grids residing on undulated surfaces. It can be used to evaluate area-mean potential values on planetary surfaces that vary within grid cells. This is in contrast with available methods, which assume cells with a constant spherical radius only. When formulating the technique, we took advantage of 2D spherical Fourier methods to improve the computational speed. The price to be paid are high memory requirements, even with moderate maximum harmonic degrees such as 100 (both of the potential and of the irregular surface). In numerical experiments, we validate the method against independent area-mean potential values to prove its correctness. A study of the series behavior below the sphere of convergence shows that the series may diverge on planetary topographies, similarly as it is with its point-value counterpart. The method can be utilized in numerical studies of the change of boundary method, one of the pivotal concepts of recent high-degree models such as EGM2008. A numerical implementation is made available through CHarm, a C library to work with spherical harmonics up to high degrees. CHarm is accessible via https://github.com/blazej-bucha/charm. Numéro de notice : A2022-736 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-022-01658-1 Date de publication en ligne : 27/09/2022 En ligne : https://doi.org/10.1007/s00190-022-01658-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=101708 [article]

Dense mantle flows periodically spaced below ocean basins / Isabelle Panet in Earth and planetary science letters, vol 594 (15 September 2022)  

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Deep mass redistribution prior to the 2010 Mw 8.8 Maule (Chile) Earthquake revealed by GRACE satellite gravity / Marie Bouih in Earth and planetary science letters, vol 584 (15 April 2022)  

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Applications and challenges of GRACE and GRACE follow-on satellite gravimetry / Jianli Chen in Surveys in Geophysics, vol 43 n° 1 (February 2022)  

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Efficient variance component estimation for large-scale least-squares problems in satellite geodesy / Yufeng Nie in Journal of geodesy, vol 96 n° 2 (February 2022)  

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GROOPS: A software toolkit for gravity field recovery and GNSS processing / Torsten Mayer-Gürr in Computers & geosciences, vol 155 (October 2021)  

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On determination of the geoid from measured gradients of the Earth's gravity field potential / Pavel Novák in Earth-Science Reviews, vol 221 (October 2021)  

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Tropospheric and range biases in Satellite Laser Ranging / Mateusz Drożdżewski in Journal of geodesy, vol 95 n° 9 (September 2021)  

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Gravitational field modelling near irregularly shaped bodies using spherical harmonics: a case study for the asteroid (101955) Bennu / Blažej Bucha in Journal of geodesy, vol 95 n° 5 (May 2021)  

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Strategy for the realisation of the International Height Reference System (IHRS) / Laura Sánchez in Journal of geodesy, vol 95 n° 4 (April 2021)  

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What have we learnt from Icesat on Greenland ice sheet change and what to expect from Icesat 2 / Blaženka Bukač in Geodetski vestnik, vol 65 n° 1 (March - May 2021)  

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