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Reducing multipath effect of low-cost GNSS receivers for monitoring by considering temporal correlations / Li Zhang in Journal of applied geodesy, vol 14 n° 2 (April 2020)  

Public [article]  inJournal of applied geodesy > vol 14 n° 2 (April 2020) . - pp 167 – 175 Titre : Reducing multipath effect of low-cost GNSS receivers for monitoring by considering temporal correlations Type de document : Article/Communication Auteurs : Li Zhang, Auteur ; Volker Schwieger, Auteur Année de publication : 2020 Article en page(s) : pp 167 – 175 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] atténuation du signal [Termes IGN] corrélation temporelle [Termes IGN] coût [Termes IGN] itération [Termes IGN] ligne de base [Termes IGN] oscillation [Termes IGN] phase [Termes IGN] plan de masse [Termes IGN] qualité des données [Termes IGN] récepteur GNSS [Termes IGN] récepteur monofréquence [Termes IGN] réflecteur [Termes IGN] source d'erreur [Termes IGN] trajet multiple Résumé : (auteur) The investigations on low-cost single frequency GNSS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox GNSS receivers combined with low-cost antennas and self-constructed L1-optimized choke rings can reach an accuracy which almost meets the requirements of geodetic applications (see Zhang and Schwieger [25]). However, the quality (accuracy and reliability) of low-cost GNSS receiver data should still be improved, particularly in environments with obstructions. The multipath effects are a major error source for the short baselines. The ground plate or the choke ring ground plane can reduce the multipath signals from the horizontal reflector (e. g. ground). However, the shieldings cannot reduce the multipath signals from the vertical reflectors (e. g. walls). Because multipath effects are spatially and temporally correlated, an algorithm is developed for reducing the multipath effect by considering the spatial correlations of the adjoined stations (see Zhang and Schwieger [24]). In this paper, an algorithm based on the temporal correlations will be introduced. The developed algorithm is based on the periodic behavior of the estimated coordinates and not on carrier phase raw data, which is easy to use. Because, for the users, coordinates are more accessible than the raw data. The multipath effect can cause periodic oscillations but the periods change over time. Besides this, the multipath effect’s influence on the coordinates is a mixture of different multipath signals from different satellites and different reflectors. These two properties will be used to reduce the multipath effect. The algorithm runs in two steps and iteratively. Test measurements were carried out in a multipath intensive environment; the accuracies of the measurements are improved by about 50 % and the results can be delivered in near-real-time (in ca. 30 minutes), therefore the algorithm is suitable for structural health monitoring applications. Numéro de notice : A2020-217 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2019-0059 date de publication en ligne : 27/03/2020 En ligne : https://doi.org/10.1515/jag-2019-0059 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94910 [article]

A single-receiver geometry-free approach to stochastic modeling of multi-frequency GNSS observables / Baocheng Zhang in Journal of geodesy, vol 94 n°4 (April 2020)  

Public [article]  inJournal of geodesy > vol 94 n°4 (April 2020) Titre : A single-receiver geometry-free approach to stochastic modeling of multi-frequency GNSS observables Type de document : Article/Communication Auteurs : Baocheng Zhang, Auteur ; Pengyu Hou, Auteur ; Teng Liu, Auteur ; Yunbin Yuan, Auteur Année de publication : 2020 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] analyse de variance [Termes IGN] corrélation croisée normalisée [Termes IGN] corrélation temporelle [Termes IGN] fréquence multiple [Termes IGN] méthode des moindres carrés [Termes IGN] méthode robuste [Termes IGN] modèle stochastique [Termes IGN] positionnement ponctuel précis [Termes IGN] récepteur [Termes IGN] traitement de données GNSS [Termes IGN] trajet multiple Résumé : (auteur) The proper choice of stochastic model is of great importance to global navigation satellite system (GNSS) data processing. Whereas extensive investigations into stochastic modeling are mainly based on the relative (or differential) method employing zero and/or short baselines, this work proposes an absolute method that relies upon a stand-alone receiver and works by applying the least-squares variance component estimation to the geometry-free functional model, thus facilitating the characterization of stochastic properties of multi-frequency GNSS observables at the undifferenced level. In developing the absolute method, special care has been taken of the code multipath effects by introducing ambiguity-like parameters to the code observation equations. By means of both the relative and absolute methods, we characterize the precision, cross and time correlation of the code and phase observables of two newly emerging constellations, namely the Chinese BDS and the European Galileo, collected by a variety of receivers of different types at multiple frequencies. Our first finding is that so far as the precision is concerned, the absolute method yields nearly the same numerical values as those derived by the zero-baseline-based relative method. However, the two methods give contradictory results with regard to the cross correlation, which is found (not) to occur between BDS phase observables when use has been made of the relative (absolute) method. Our explanation to this discrepancy is that the cross correlation found in the relative method originates from the parts (antenna, cable, low noise amplifier) shared by two receivers creating a zero baseline. The time correlation is only of significance when the multipath effects are present, as is the case with the short-baseline-based relative method; this correlation turns out to be largely weaker (or ideally absent) in the absolute (or zero-baseline-based relative) method. Moreover, with the absolute method, the stochastic properties determined for two receivers of the same type but subject to different multipath effects are virtually the same. We take this as a convincing evidence that the absolute method is robust against multipath effects. Hence, the absolute method proposed in the present work represents a promising complement to the relative method and appears to be particularly beneficial to GNSS positioning, navigation and timing technologies based on the undifferenced observables, typically the precise point positioning. Numéro de notice : A2020-160 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-020-01366-8 date de publication en ligne : 09/03/2020 En ligne : https://doi.org/10.1007/s00190-020-01366-8 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94817 [article]

An analytic expression for the phase noise of the goldstein–werner filter / Scott Hensley in IEEE Transactions on geoscience and remote sensing, vol 57 n° 9 (September 2019)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 57 n° 9 (September 2019) . - pp 6499 - 6516 Titre : An analytic expression for the phase noise of the goldstein–werner filter Type de document : Article/Communication Auteurs : Scott Hensley, Auteur Année de publication : 2019 Article en page(s) : pp 6499 - 6516 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image radar et applications [Termes IGN] bruit thermique [Termes IGN] corrélation temporelle [Termes IGN] densité spectrale de puissance [Termes IGN] filtrage du bruit [Termes IGN] filtre de Goldstein [Termes IGN] image radar moirée [Termes IGN] interféromètrie par radar à antenne synthétique [Termes IGN] phase [Termes IGN] pouvoir de résolution spectrale [Termes IGN] rapport signal sur bruit [Termes IGN] transformation de Fourier Résumé : (auteur) Interferogram filtering for noise reduction is a key to many radar interferometric applications. Repeat pass radar interferometry often uses data with less than ideal correlation levels resulting from either long spatial or temporal baselines or changes between observations leading to high levels of temporal correlation. To maximize the utility of such pairs filtering the interferogram to get maximal noise reduction is often needed. One technique that has proved quite useful in the geophysical community is power spectral or Goldstein–Werner filtering of the interferogram whereby a power-weighted version of the Fourier transform is used to enhance fringe visibility. Although this paper defining the filter briefly touched upon the spatial resolution and noise reduction induced by the filter, it did not provide a useful formula for predicting the phase noise after filtering. This paper derives a formula for the phase noise obtained from power spectral filtering albeit under the restriction of several simplifying assumptions to make the problem analytically tractable. In particular, it is assumed that the interferometric phase is locally well approximated by a linear phase ramp with nonlinear phase perturbations small in a spectral energy sense compared to the linear term. Numéro de notice : A2019-343 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2019.2906549 date de publication en ligne : 25/04/2019 En ligne : http://doi.org/10.1109/TGRS.2019.2906549 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93378 [article]

Ground displacement measurements / Louis-Marie Gauer (2019)

Public Titre : Ground displacement measurements Type de document : Mémoire Auteurs : Louis-Marie Gauer, Auteur Editeur : Champs-sur-Marne : Ecole nationale des sciences géographiques ENSG Année de publication : 2019 Importance : 42 p. Format : 21 x 30 cm Note générale : Bibliographie Rapport de projet pluridisciplinaire, cycle ING2 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image radar et applications [Termes IGN] chaîne de traitement [Termes IGN] corrélation temporelle [Termes IGN] déformation de la croute terrestre [Termes IGN] données spatiotemporelles [Termes IGN] hydrocarbure [Termes IGN] image radar [Termes IGN] surveillance géologique Index. décimale : PROJET Mémoires : Rapports de projet - stage des ingénieurs de 2e année Résumé : (Auteur) Ce projet a pour but de déterminer s’il est possible de mesurer des déplacements du sol à partir de données satellite. Deux méthodes différentes ont été étudiées: une méthode issue de l’analyse du déplacement de pixels par corrélation de deux images et une seconde méthode analysant l’évolution de la phase d’images RADAR au cours du temps en des points précis. Le but de ces mesures est d’aider à la recherche d’hydrocarbures de manière plus rapide et sans déplacement sur zone. De même, elles devraient aussi aider à la surveillance de l’exploitation de ces hydrocarbures dans les cas où ces exploitations mèneraient à des déplacements du sol dangereux pour les populations aux alentours. Ces deux méthodes ont par la suite mené à la mise en place d’une chaîne de traitement et d’une documentation associée, depuis la réception des données à l’obtention des résultats. Note de contenu : INTRODUCTION 1. Pixel correlation in visible pictures 1.1 Theory 1.2 Softwares 1.3 Results 2. InSAR 2.1 Theory 2.2 Provider, Softwares and Workflow 2.3 Tests and results CONCLUSION APPENDIX 2.4 MicMac 2.5 InSAR Numéro de notice : 26104 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Mémoire de projet pluridisciplinaire Organisme de stage : Terra-Scan Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93849

Satellite remote sensing of the variability of the continental hydrology cycle in the lower Mekong basin over the last two decades / Binh Pham-Duc (2018)  

Public Titre : Satellite remote sensing of the variability of the continental hydrology cycle in the lower Mekong basin over the last two decades Type de document : Thèse/HDR Auteurs : Binh Pham-Duc, Auteur ; Catherine Prigent, Directeur de thèse ; Filipe Aires, Directeur de thèse Editeur : Paris : Sorbonne Université Année de publication : 2018 Importance : 234 p. Format : 21 x 30 cm Note générale : bibliographie Thèse de doctorat de Sciences de l'Environnement, Sorbonne Université Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] carte hydrographique [Termes IGN] changement climatique [Termes IGN] classification par réseau neuronal [Termes IGN] climat tropical [Termes IGN] corrélation temporelle [Termes IGN] eau de surface [Termes IGN] image Aqua-MODIS [Termes IGN] image Landsat-8 [Termes IGN] image Sentinel-SAR [Termes IGN] Mekong (fleuve) [Termes IGN] modèle hydrographique [Termes IGN] précipitation [Termes IGN] série temporelle [Termes IGN] surveillance hydrologique [Termes IGN] télédétection spatiale [Termes IGN] variation saisonnière Index. décimale : THESE Thèses et HDR Résumé : (auteur) Surface water is essential for all forms of life since it is involved in almost all processes of life on Earth. Quantifying and monitoring surface water and its variations are important because of the strong connections between surface water, other hydrological components (groundwater and soil moisture, for example), and the changing climate system. Satellite remote sensing of land surface hydrology has shown great potential in studying hydrology from space at regional and global scales. In this thesis, different techniques using several types of satellite estimates have been made to study the variation of surface water, as well as other hydrological components in the lower Mekong basin (located in Vietnam and Cambodia) over the last two decades. This thesis focuses on four aspects. First, the use of visible/infrared MODIS/Terra satellite observations to monitor surface water in the lower Mekong basin is investigated. Four different classification methods are applied, and their results of surface water maps show similar seasonality and dynamics. The most suitable classification method, that is specially designed for tropical regions, is chosen to produce regular surface water maps of the region at 500 m spatial resolution, from January 2001 to present time. Compared to reference data, the MODIS-derived surface water time series show the same amplitude, and very high temporal correlation for the 2001-2007 period (> 95%). Second, the use of SAR Sentinel-1 satellite observations for the same objective is studied. Optical satellite data are replaced by SAR satellite data to benefit the ability of their microwave wavelengths to pass through clouds. Free-cloud Landsat-8 satellite imagery are set as targets to train and optimize a Neural Network (NN). Predicted surface water maps (30 m spatial resolution) are built for the studied region from January 2015 to present time, by applying a threshold (0.85) to the output of the NN. Compared to reference free-cloud Landsat-8 surface water maps, results derived from the NN show high spatial correlation (_90%), as well as true positive detection of water pixels (_90%). Predicted SAR surface water maps are also compared to floodability maps derived from topography data, and results show high consistency between the two independent maps with 98% of SAR-derived water pixels located in areas with a high probability of inundation (>60%). Third, the surface water volume variation is calculated as the product of the surface water extent and the surface water height. The two components are validated with other hydrological products, and results show good consistencies. The surface water height are linearly interpolated over inundated areas to build monthly maps at 500 m spatial resolution, then are used to calculate changes in the surface water volume. Results show high correlations when compared to variation of the total land surface water volume derived from GRACE data (95%), and variation of the in situ discharge estimates (96%). Fourth, two monthly global multi-satellite surface water products (GIEMS & SWAMPS) are compared together over the 1993-2007 period at regional and global scales. Ancillary data are used to support the analyses when available. Similar temporal dynamics of global surface water are observed when compared GIEMS and SWAMPS, but _50% of the SWAMPS inundated surfaces are located along the coast line. Over the Amazon and Orinoco basins, GIEMS and SWAMPS have very high water surface time series correlations (95% and 99%, respectively), but SWAMPS maximum water extent is just a half of what observed from GIEMS and SAR estimates. SWAMPS fails to capture surface water dynamics over the Niger basin since its surface water seasonality is out of phase with both GIEMS- and MODIS-derived water extent estimates, as well as with in situ river discharge data. Note de contenu : 1- Introduction 2- Surface water monitoring within the Mekong Delta and Cambodia using visible and Infrared MODIS satellite observations 3- Surface water monitoring within the Mekong Delta and Cambodia using SAR Sentinel-1 satellite observations 4- Toward the analyses of the change in surface water volume within the lower Mekong Delta 5- Comparison between Global Terrestrial Surface Water datasets 6- Conclusions and perspectives Numéro de notice : 25731 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse française Note de thèse : Thèse de Doctorat : Sciences de l'Environnement : Observatoire de Paris : 2018 Organisme de stage : Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique LERMA (Observatoire de Paris) nature-HAL : Thèse DOI : sans En ligne : https://tel.archives-ouvertes.fr/tel-02109003 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94914

Filtrage de Kalman à bruits corrélés pour le positionnement précis / Ulrich Mambou Kuipou (2016) 

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Three-Corner Hat for the assessment of the uncertainty of non-linear residuals of space-geodetic time series in the context of terrestrial reference frame analysis / Claudio Abbondanza in Journal of geodesy, vol 89 n° 4 (April 2015)  

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