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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)  

Public [article]  inJournal of geodesy > vol 95 n° 5 (May 2021) . - n° 56 Titre : Gravitational field modelling near irregularly shaped bodies using spherical harmonics: a case study for the asteroid (101955) Bennu Type de document : Article/Communication Auteurs : Blažej Bucha, Auteur ; Fernando Sanso, Auteur Année de publication : 2021 Article en page(s) : n° 56 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] astéroïde [Termes IGN] champ de gravitation [Termes IGN] champ de pesanteur terrestre [Termes IGN] convergence [Termes IGN] harmonique sphérique [Termes IGN] intégrale de Newton Résumé : (auteur) We apply three spherical-harmonic-based techniques to deliver external gravitational field models of the asteroid (101955) Bennu within its circumscribing sphere. This region is known to be peculiar for external spherical harmonic expansions, because it may lead to a divergent series. The studied approaches are (i) spectral gravity forward modelling via external spherical harmonics, (ii) the least-squares estimation from surface gravitational data using external spherical harmonics and (iii) the combination of internal and external series expansions. While the first method diverges beyond any reasonable doubts, we show that the other two methods may ensure relative accuracy from ∼10−6 to 10−8 in the vicinity of Bennu. This is possible even with the second method, despite the fact that it relies on a single series of external spherical harmonics. Our main motivation was to study conceptual differences between spherical harmonic coefficients from satellite data (analogy to the first method) and from surface gravitational data (the second method). Such coefficients are available through the popular spherical-harmonic-based models of the Earth’s gravitational field and often are combined together. We show that the coefficients from terrestrial data may lead to a divergence effect of partial sums, though excellent accuracy can be achieved when such model is used in full. Under (presently) extreme but realistic conditions, the divergence effect of partial sums may affect many near-surface geoscientific applications, such as the geoid/quasigeoid computation or residual terrain modelling. Computer codes (Fortran, MATLAB) and data produced within the study are made freely available at http://edisk.cvt.stuba.sk/~xbuchab/. Numéro de notice : A2021-347 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-021-01493-w date de publication en ligne : 22/04/2021 En ligne : https://doi.org/10.1007/s00190-021-01493-w Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=97591 [article]

New algorithms for spherical harmonic analysis of area mean values over blocks delineated by equiangular and Gaussian grids / Rong Sun in Journal of geodesy, vol 95 n° 5 (May 2021)  

Public [article]  inJournal of geodesy > vol 95 n° 5 (May 2021) . - n° 47 Titre : New algorithms for spherical harmonic analysis of area mean values over blocks delineated by equiangular and Gaussian grids Type de document : Article/Communication Auteurs : Rong Sun, Auteur Année de publication : 2021 Article en page(s) : n° 47 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] analyse harmonique [Termes IGN] grille [Termes IGN] matrice [Termes IGN] méthode des moindres carrés [Termes IGN] quadrature [Termes IGN] transformation polynomiale Résumé : (auteur) Spherical harmonic analysis is widely used in all aspects of geoscience. Exact quadrature methods are available for the spherical harmonic analysis of band-limited point values at the grid points of equiangular and Gaussian grids. However, no similarly exact quadrature methods are available for the spherical harmonic analysis of area mean values over the blocks delineated by these grids. In this study, new algorithms appropriate for the exact spherical harmonic analysis of the band-limited area mean values over the blocks delineated by equiangular and Gaussian grids are proposed. For band-limited data, precision that is between that of the least-squares estimation method and of the approximate quadrature methods can be achieved by using the new algorithms. Regarding the computational complexity, fewer operations are needed by the new methods as compared to those needed by the least-squares estimation method and the approximate quadrature methods in the preparation stage when the maximum degree of the spherical harmonic analysis is very large. Simulation experiments are performed to compare the ability to recover the spherical harmonic coefficients by using the least-squares estimation method, the approximate quadrature methods and these new algorithms from aliased data with aliasing components of realistic magnitudes. The results suggest that these new algorithms, with time complexity one order less than that of the least-squares estimation method in the solving stage, perform roughly the same as the least-squares estimation method in recovering spherical harmonic coefficients from the aliased data. Numéro de notice : A2021-312 Affiliation des auteurs : non IGN Thématique : MATHEMATIQUE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-021-01495-8 date de publication en ligne : 07/04/2021 En ligne : https://doi.org/10.1007/s00190-021-01495-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=97507 [article]

Characterizing urban land changes of 30 global megacities using nighttime light time series stacks / Qiming Zheng in ISPRS Journal of photogrammetry and remote sensing, vol 173 (March 2021)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 173 (March 2021) . - pp 10 - 23 Titre : Characterizing urban land changes of 30 global megacities using nighttime light time series stacks Type de document : Article/Communication Auteurs : Qiming Zheng, Auteur ; Qihao Weng, Auteur ; Ke Wang, Auteur Année de publication : 2021 Article en page(s) : pp 10 - 23 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] aménagement foncier [Termes IGN] analyse harmonique [Termes IGN] cartographie urbaine [Termes IGN] changement d'utilisation du sol [Termes IGN] croissance urbaine [Termes IGN] détection de changement [Termes IGN] détection du bâti [Termes IGN] éclairage public [Termes IGN] image infrarouge [Termes IGN] image VIIRS [Termes IGN] mégalopole [Termes IGN] série temporelle [Termes IGN] zone urbaine Résumé : (auteur) Worldwide urbanization has brought about diverse types of urban land use and land cover (LULC) changes. The diversity of urban land changes, however, have been greatly under studied, since the major focus of past research has been on urban growth. In this study, we proposed a framework to characterize diverse urban land changes of 30 global megacities using monthly nighttime light time series from VIIRS data. First, we developed a Logistic-Harmonic model to fit VIIRS time series. Second, by leveraging the uniqueness of urban land change and nighttime light data, we incorporated temporal information of VIIRS time series and proposed a new classification scheme to produce monthly maps of built-up areas and to disentangle urban land changes into five categories. Third, we provided an in-depth analysis and comparison of urban land change patterns of the selected megacities. Results demonstrated that the Logistic-Harmonic model yielded a robust performance in fitting VIIRS time series. Temporal features based classification can not only significantly improve the mapping accuracy of built-up areas, especially for regions with heterogeneous built-up and non-built-up landscapes, but also promoted temporal consistency and classification efficiency. Urban land changes occurred in 51% of the built-up pixels of the megacities. Compared with urban growth, other types of urban land change, particularly land use intensification, contributed to an unexpectedly large proportion of the changes (83%). The findings of this study offer an insightful understanding on global urbanization processes in megacities, and evoke further investigation on the environmental and ecological implications of urban land changes. Numéro de notice : A2021-101 Affiliation des auteurs : non IGN Thématique : IMAGERIE/URBANISME Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2021.01.002 date de publication en ligne : 16/01/2021 En ligne : https://doi.org/10.1016/j.isprsjprs.2021.01.002 Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96873 [article]

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ON GLONASS pseudo-range inter-frequency bias solution with ionospheric delay modeling and the undifferenced uncombined PPP / Zheng Zhang in Journal of geodesy, vol 95 n° 3 (March 2021)  

Public [article]  inJournal of geodesy > vol 95 n° 3 (March 2021) . - n°32 Titre : ON GLONASS pseudo-range inter-frequency bias solution with ionospheric delay modeling and the undifferenced uncombined PPP Type de document : Article/Communication Auteurs : Zheng Zhang, Auteur ; Yidong Lou, Auteur ; Zheng Fu, Auteur ; et al., Auteur Année de publication : 2021 Article en page(s) : n°32 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] données GLONASS [Termes IGN] données GNSS [Termes IGN] erreur systématique de code différentiel [Termes IGN] erreur systématique interfréquence d'horloge [Termes IGN] harmonique sphérique [Termes IGN] modèle ionosphérique [Termes IGN] polarisation [Termes IGN] positionnement différentiel [Termes IGN] positionnement ponctuel précis [Termes IGN] retard ionosphèrique [Termes IGN] signal GLONASS Résumé : (auteur) With the development of multi-GNSS, the differential code bias (DCB) has been an increasing interest in the multi-frequency multi-GNSS community. Unlike code division multiple access (CDMA) mode used by GPS, BDS and Galileo etc., the GLONASS signals are modulated with frequency division multiple access (FDMA) mode. Up to now, the FDMA-aware GLONASS bias products are provided by two individual IGS analysis center (AC), i.e., CODE and GFZ. However, only the ionosphere-free (IF) combination IFB of P1 and P2 is available, while it is founded that the GLONASS IFB of GFZ on both frequencies are identical for the same receiver-satellite pair. In this contribution, the GLONASS IFB (inter-frequency bias) solution based on the spherical-harmonic (SH) ionospheric delay modeling as well as the undifferenced and uncombined PPP were carried out and evaluated. Based on the theoretical analysis, observations from 236 CMONOC stations and 172 IGS stations were collected for 2014 March and 2017 March for the numerical verification. The results suggested that the precision of IFB estimates was mainly subjected to the ionospheric status. Concerning the SH ionospheric delay modeling solution, the STD was 0.85 ns and 0.51 ns for 2014 and 2017, respectively. Concerning the undifferenced and uncombined PPP solution, the IFB was further dependent on the signal frequencies, and the STD was 1.43 ns and 1.94 ns for IFB1 and IFB2 in 2014, and the STD was 0.97 ns and 1.17 ns for IFB1 and IFB2 in 2017. When converted to the GF IFB from the individual IFB on each frequency, and compared to that of GF IFB of SH solution, it is revealed that the undifferenced and uncombined PPP solution has its advantages for IFB estimation on each individual frequency, and more efficient in data processing, while the solution based on the SH ionospheric delay modeling has its advantage in the precision of the GF IFB estimates. Thus, it is suggested that the SH model should be preferred for non-time-critical GF IFB concerned-only applications. Otherwise, the undifferenced and uncombined PPP solution is preferred. These IFB on each frequency was further converted to the ionosphere-free IFB and compared with the products of CODE analysis center. Numéro de notice : A2021-221 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-021-01480-1 date de publication en ligne : 22/02/2021 En ligne : https://doi.org/10.1007/s00190-021-01480-1 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=97190 [article]

Assessment of mass-induced sea level variability in the Tropical Indian Ocean based on GRACE and altimeter observations / Shiva Shankar Manche in Journal of geodesy, vol 95 n° 2 (February 2021)  

Public [article]  inJournal of geodesy > vol 95 n° 2 (February 2021) . - n° 19 Titre : Assessment of mass-induced sea level variability in the Tropical Indian Ocean based on GRACE and altimeter observations Type de document : Article/Communication Auteurs : Shiva Shankar Manche, Auteur ; Rabindra K. Nayak, Auteur ; Prakash Chandra Mohanty, Auteur ; et al., Auteur Année de publication : 2021 Article en page(s) : n° 19 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] analyse harmonique [Termes IGN] changement climatique [Termes IGN] données altimétriques [Termes IGN] données GRACE [Termes IGN] Indien (océan) [Termes IGN] masse d'eau [Termes IGN] modèle océanographique [Termes IGN] niveau de la mer [Termes IGN] surcharge océanique [Termes IGN] variabilité [Termes IGN] variation saisonnière Résumé : (auteur) Assessment of mass-induced sea level (MISL) variability in the Tropical Indian Ocean (TIO) was studied using observations from the Gravity Recovery and Climate Experiment (GRACE) during 2003–2017 in conjunction with the steric effects in the sea level anomaly as measured by satellite altimeters. Two steric sea levels were estimated from the ocean model analysis and Argo gridded temperature and salinity fields. These datasets were consistent with each other and to the altimeter measured sea level records. They exhibited a coherent seasonal cycle with unique spatial patterns of amplitude maxima associated with annual and semi-annual harmonics. Steric component remained as a major contributor to the sea level variability at all the time scales. Addition of the GRACE measured MISL to the steric sea level improved the estimation of sea level (as measured by satellite altimeter) over most part of the TIO except over the northern part of the Arabian Sea. It was observed that the MISL had a significant contribution to the sea level variability at intra-seasonal and seasonal time scales and a minor contribution to the sea level inter-annual variability. During all the El Niño years, sea level underwent a large fluctuation coherent to the steric component. A linear barotropic vortex conservation model driven by ocean surface winds explained a major part of the observed MISL high-frequency variability in the Equatorial and southern TIO, and overestimated the observation in the northern TIO. Numéro de notice : A2021-137 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-021-01471-2 date de publication en ligne : 31/01/2021 En ligne : https://doi.org/10.1007/s00190-021-01471-2 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=97010 [article]

Uncertainties and errors in algorithms for elevation gradients / Dong Shi in International journal of geographical information science IJGIS, vol 35 n° 2 (February 2021)  

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A hybrid approach for recovering high-resolution temporal gravity fields from satellite laser ranging / Anno Löcher in Journal of geodesy, vol 95 n° 1 (January 2021)  

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The influence of sea-level changes on geodetic datums along the east coast of China / Yang Liu in Marine geodesy, vol 44 n° 1 (January 2021)  

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Self-consistent determination of the Earth’s GM, geocenter motion and figure axis orientation / Alexandre Couhert in Journal of geodesy, vol 94 n° 12 (December 2020)  

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Compensation of geometric parameter errors for terrestrial laser scanner by integrating intensity correction / Wanli Liu in IEEE Transactions on geoscience and remote sensing, vol 58 n° 10 (October 2020)  

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Spheroidal spline interpolation and its application in geodesy / Mostafa Kiani in Geodesy and cartography, vol 46 n° 3 (October 2020)  

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Geovisualization and harmonic analysis for the exploratory search of localized cyclic recurrences in spatio-temporal event data / Jacques Gautier in Geomatica [en ligne], vol 74 n° 3 (September 2020)  

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Volunteered geographic information research in the first decade: a narrative review of selected journal articles in GIScience / Yingwei Yan in International journal of geographical information science IJGIS, vol 34 n° 9 (September 2020)  

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Detecting abandoned farmland using harmonic analysis and machine learning / Heeyeun Yoon in ISPRS Journal of photogrammetry and remote sensing, vol 166 (August 2020)  

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Improved arctic ocean mass variability inferred from time-variable gravity with constraints and dual leakage correction / Dapeng Mu in Marine geodesy, Vol 43 n° 3 (May 2020)  

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