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Assessing a new velocity field in Greece towards a new semi-kinematic datum / S. Bitharis in Survey review, vol 51 n° 368 (September 2019)  

Public [article]  inSurvey review > vol 51 n° 368 (September 2019) . - pp 450 - 459 Titre : Assessing a new velocity field in Greece towards a new semi-kinematic datum Type de document : Article/Communication Auteurs : S. Bitharis, Auteur ; N. Papadopoulos, Auteur ; C. Pikridas, Auteur ; et al., Auteur Année de publication : 2019 Article en page(s) : pp 450 - 459 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes descripteurs IGN] champ de vitesse [Termes descripteurs IGN] déformation de la croute terrestre [Termes descripteurs IGN] géodynamique [Termes descripteurs IGN] Grèce [Termes descripteurs IGN] réseau géodésique local [Termes descripteurs IGN] système de référence local Résumé : (Auteur) Greece has always been an interesting study area for the geodesists due to its intense geodynamic behaviour. Especially, the exploitation of a modern geodetic velocity field using GNSS becomes a crucial requirement for geodetic purposes. The main aim of the present study is the assessment of a modern geodetic velocity model. This procedure is based on the unification of various reference frames, implemented from individual extended GNSS campaigns in different epochs with the effective involvement of the Hellenic Military Geographic Service. The implementation of geodetic velocities in the inhomogeneous Greek velocity field improves significantly the reliability of transformations, more than 60% with respect to the horizontal component, applying a vice versa time shift to a common epoch. We also emphasise the necessity to adopt a velocity model in order to process regional GNSS networks and therefore to establish a modern semi-kinematic reference frame in Greece. Numéro de notice : A2019-386 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/00396265.2018.1479937 date de publication en ligne : 02/06/2018 En ligne : https://doi.org/10.1080/00396265.2018.1479937 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93476 [article]

Appraisal of the Hellenic Geodetic Reference System 1987 based on backward-transformed ITRF coordinates using a national velocity model / M. Chatzinikos in Survey review, vol 49 n° 356 (November 2017)  

Public [article]  inSurvey review > vol 49 n° 356 (November 2017) . - pp 386 - 398 Titre : Appraisal of the Hellenic Geodetic Reference System 1987 based on backward-transformed ITRF coordinates using a national velocity model Type de document : Article/Communication Auteurs : M. Chatzinikos, Auteur ; C. Kotsakis, Auteur Année de publication : 2017 Article en page(s) : pp 386 - 398 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes descripteurs IGN] champ de vitesse [Termes descripteurs IGN] géodynamique [Termes descripteurs IGN] Grèce [Termes descripteurs IGN] International Terrestrial Reference Frame [Termes descripteurs IGN] transformation de coordonnées Résumé : (Auteur) The paper presents a detailed accuracy evaluation of the Hellenic Geodetic Reference System 1987 (HGRS87), a non-geocentric traditional local datum which was established thirty years ago and it is still used as the official coordinate system for surveying applications in Greece. This is the first time that a large-scale assessment of HGRS87 is performed, which aims to reveal its weakness by quantifying its consistency with a higher quality ITRF/GNSS-based frame over the entire country. A geodetic velocity model is employed in our analysis in an attempt to eliminate the accumulated geodynamical distortions of the (static) HGRS87 coordinates, and thus to provide a more judicious comparison between the underlying frames at a common epoch. Our results show that, even after removing the geodynamical distortions, the average accuracy of HGRS87 at national scale remains worse than 45 cm, yet significant variations exist in its regional accuracy level over different parts of Greece. Numéro de notice : A2017-557 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/00396265.2016.1180797 En ligne : https://doi.org/10.1080/00396265.2016.1180797 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=86618 [article]

GPS coordinate time series measurements in Ontario and Quebec, Canada / Hadis Samadi Alinia in Journal of geodesy, vol 91 n° 6 (June 2017)  

Public [article]  inJournal of geodesy > vol 91 n° 6 (June 2017) . - pp 653 - 683 Titre : GPS coordinate time series measurements in Ontario and Quebec, Canada Type de document : Article/Communication Auteurs : Hadis Samadi Alinia, Auteur ; Christy F. Tiampo, Auteur ; Thomas S. James, Auteur Année de publication : 2017 Article en page(s) : pp 653 - 683 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes descripteurs IGN] Bernese [Termes descripteurs IGN] bruit (théorie du signal) [Termes descripteurs IGN] bruit blanc [Termes descripteurs IGN] champ de vitesse [Termes descripteurs IGN] coordonnées GPS [Termes descripteurs IGN] épaisseur de la glace [Termes descripteurs IGN] Hudson, baie d' [Termes descripteurs IGN] méthode du maximum de vraisemblance (estimation) [Termes descripteurs IGN] Ontario [Termes descripteurs IGN] Québec (Canada) [Termes descripteurs IGN] série temporelle [Termes descripteurs IGN] station permanente Résumé : (Auteur) New precise network solutions for continuous GPS (cGPS) stations distributed in eastern Ontario and western Québec provide constraints on the regional three-dimensional crustal velocity field. Five years of continuous observations at fourteen cGPS sites were analyzed using Bernese GPS processing software. Several different sub-networks were chosen from these stations, and the data were processed and compared to in order to select the optimal configuration to accurately estimate the vertical and horizontal station velocities and minimize the associated errors. The coordinate time series were then compared to the crustal motions from global solutions and the optimized solution is presented here. A noise analysis model with power-law and white noise, which best describes the noise characteristics of all three components, was employed for the GPS time series analysis. The linear trend, associated uncertainties, and the spectral index of the power-law noise were calculated using a maximum likelihood estimation approach. The residual horizontal velocities, after removal of rigid plate motion, have a magnitude consistent with expected glacial isostatic adjustment (GIA). The vertical velocities increase from subsidence of almost 1.9 mm/year south of the Great Lakes to uplift near Hudson Bay, where the highest rate is approximately 10.9 mm/year. The residual horizontal velocities range from approximately 0.5 mm/year, oriented south–southeastward, at the Great Lakes to nearly 1.5 mm/year directed toward the interior of Hudson Bay at stations adjacent to its shoreline. Here, the velocity uncertainties are estimated at less than 0.6 mm/year for the horizontal component and 1.1 mm/year for the vertical component. A comparison between the observed velocities and GIA model predictions, for a limited range of Earth models, shows a better fit to the observations for the Earth model with the smallest upper mantle viscosity and the largest lower mantle viscosity. However, the pattern of horizontal deformation is not well explained in the north, along Hudson Bay, suggesting that revisions to the ice thickness history are needed to improve the fit to observations. Numéro de notice : A2017-287 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern En ligne : http://doi.org/10.1007/s00190-016-0987-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85320 [article]

Active interseismic shallow deformation of the Pingting terraces (Longitudinal Valley – Eastern Taiwan) from UAV high-resolution topographic data combined with InSAR time series / Benoit Deffontaines in Geomatics, Natural Hazards and Risk, vol 8 (2017)  

Public [article]  inGeomatics, Natural Hazards and Risk > vol 8 (2017) . - pp 120 - 136 Titre : Active interseismic shallow deformation of the Pingting terraces (Longitudinal Valley – Eastern Taiwan) from UAV high-resolution topographic data combined with InSAR time series Type de document : Article/Communication Auteurs : Benoit Deffontaines , Auteur ; Kuo-Jen Chang, Auteur ; Johann Champenois, Auteur ; Bénédicte Fruneau , Auteur ; Erwan Pathier, Auteur ; Jyr-Ching Hu, Auteur ; Shih-Ting Lu, Auteur ; Yen-Chiu Liu, Auteur Année de publication : 2017 Projets : 1-Pas de projet / Article en page(s) : pp 120 - 136 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes descripteurs IGN] bande L [Termes descripteurs IGN] champ de vitesse [Termes descripteurs IGN] déformation de la croute terrestre [Termes descripteurs IGN] drone [Termes descripteurs IGN] faille géologique [Termes descripteurs IGN] image aérienne [Termes descripteurs IGN] image ALOS-PALSAR [Termes descripteurs IGN] image radar moirée [Termes descripteurs IGN] modèle numérique de terrain [Termes descripteurs IGN] Taïwan Résumé : (auteur) We focus herein on the location, characterization and the quantification of the most active structural feature of Taiwan: the Longitudinal Valley Fault that corresponds to the suture in between the Philippine and Eurasian Plates. In order to determine and monitor its present inter-seismic deformation, we focus on the Pingting Terraces area, situated in the South Longitudinal Valley (Eastern Taiwan). We first determine the structural geometry issued from both photo-interpretation deduced from new unmanned aerial vehicle (UAV) high-resolution Digital Terrain Model data that we acquired (34.78 km2 with 7.73 cm ground sampling distance), combined with geological field work. In order to characterize and quantify the present deformational patterns over the Pingting terraces, we used an InSAR time series Interferometry algorithm (MT-InSAR) applied to nine L-band SAR images from ALOS satellite acquired over the period 2007–2010. The unprecedented density of measurements (about 120 points per km2 for a total of 6,400 points) gives a continuous overview of the inter-seismic shallow deformation. The structural geometry combined with the mean velocity map (MT-InSAR) reveals two clear active faults situated above the scarps of the Pingting terraces and responsible for up to 7 and 20 mm/yr velocity offset along the radar line of sight. A temporal analysis of the deformation is performed with one measurement at each SAR acquisition date, giving major improvements in the characterization and quantification of the Longitudinal Valley active Fault trace. Numéro de notice : A2017-840 Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/19475705.2016.1181678 date de publication en ligne : 25/07/2016 En ligne : https://doi.org/10.1080/19475705.2016.1181678 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=89350 [article]

Monitoring rock glaciers by combining photogrammetric and GNSS-based methods / Fabian Neyer (2017)  

Public Titre : Monitoring rock glaciers by combining photogrammetric and GNSS-based methods Type de document : Thèse/HDR Auteurs : Fabian Neyer, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2017 Autre Editeur : Zurich : Eidgenossische Technische Hochschule ETH - Ecole Polytechnique Fédérale de Zurich EPFZ Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 99 Importance : 174 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-45-1 Note générale : bibliographie thesis submitted to attain the degree of doctor of sciences of ETH Zurich Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications photogrammétriques [Termes descripteurs IGN] Alpes centrales [Termes descripteurs IGN] champ de vitesse [Termes descripteurs IGN] collocation par moindres carrés [Termes descripteurs IGN] déformation de la croute terrestre [Termes descripteurs IGN] données localisées 3D [Termes descripteurs IGN] glacier [Termes descripteurs IGN] image terrestre [Termes descripteurs IGN] matrice de covariance [Termes descripteurs IGN] pergélisol [Termes descripteurs IGN] reconstruction 3D [Termes descripteurs IGN] rocher [Termes descripteurs IGN] série temporelle [Termes descripteurs IGN] Suisse Index. décimale : 33.60 Applications photogrammétriques - usage combiné de la photogrammétrie et de la lasergrammétrie Résumé : (auteur) Rock glaciers are creeping landforms of perennially frozen ground and belong to the permafrost creeping phenomena. They are mainly composed of rock debris that accumulate in areas of high natural erosion. Ice particles between the rocks cause the moving accumulation in steep terrain to dynamically flow downslope. In the Alpine region, these morphological landforms mainly occur at north-facing mountain slopes in high altitudes above the forest boundary and are known for their sensitivity to climate change. For several decades, rock glaciers have been monitored for scientific aims, while advances in surveying technologies increased the interest in such studies since the 1990s. Modern technologies in remote sensing (e.g., airborne imagery or satellite-based measurement techniques) are often combined with measurements from field campaigns, i.e., measurements taken directly on a rock glacier (e.g., GNSS, laser-scanning, ground temperature measurements, etc). The high-level goal is to enhance the process understanding, especially with respect to the changing climate: various studies indicate an extended risk of slope failures in steep frozen bedrock due to the global temperature increase. Early recognition of increased activities help to inform local authorities in the endangered areas about the potential hazard before such an event. The present work is part of the X-Sense project (Nano-Tera.ch), with an interdisciplinary team of scientists that build and operate new low-cost devices for data acquisition, develop new data processing pipelines and algorithms for evaluation, and also gain new insight of natural processes in these regions. Autonomous measurement systems, developed within other work packages in the X-Sense project, observe different permafrost creep areas with high resolution in space and time. Combined with multi-year observations, the derived surface motions are used to obtain an improved process understanding. This work focuses on the photogrammetric image processing in order to retrieve precise surface displacement estimates. More precisely, image sequences, acquired with two permanently installed commercial digital single-reflex cameras, are used to measure topographic changes in the observed permafrost area. By the combination with high resolution GNSS positioning results, the goal is to obtain precise time series of moving rock boulders at different positions within the field of view. Challenges arising from the combination of different data sets, the development of an automatic processing pipeline, and an improvement of the processing strategy in general, are the main tasks of this thesis. The study site is the bordering area above the Grabengufer rock glacier (Mattervalley VS, Switzerland), known as the Grabengufer rock slide. Local topographic conditions allowed only a partially good installation geometry for the photogrammetric reconstruction. With respect to a 3D reconstruction without the use of GNSS coordinates, an accuracy increase of about one order of magnitude could be achieved in case these high-precision solutions were integrated. More specifically, respective standard deviations for the East, North, and Height components of 6, 5, and 2 cm were achieved. The stated accuracy, maintained throughout the measurement period of nearly four years (summer months), was obtained in an area of approximately 80m×80 m, with a mean distance of 80 m from the two cameras. Position time series of moving rock boulders were filtered using the principles of collocation. Analyzing the correlation characteristics of the stochastic signal, an optimal correlation length was computed and used to extract relevant signals from the noise contaminated time series. Velocity was directly estimated as a derived quantity in the collocation process. Furthermore, the techniques of the adaptive collocation approach is presented. This iterative method uses the principles of a dynamically adjusting anisotropic covariance metric. In an example of 2-dimensional velocity fields it is shown that regional compression and extension areas can be extracted. Results indicate that the observed permafrost area has experienced a mean annual acceleration of about 0.1m/Year between the years 2013 and 2015. During the late summer months of 2015, a prominent temporal acceleration was observed. The mean displacement rate was found to be 0.67m/year, whereas the 3-dimensional displacement is dominated by a translation following the gliding surface. An area in the front of the observed field of view was found to have higher displacement rates, especially during the late summer months, thus it detaches from the otherwise relatively homogeneous flow field. The methods and principles presented in this work show the potential of monitoring permafrost surface displacements using permanently installed optical cameras in combination with positioning results from permanently mounted GNSS stations. These principles can easily be transfered to other monitoring applications and thus contribute to a better understanding of such processes. Note de contenu : 1 Introduction 2 Study Site 3 Image-Based Displacement Estimation 4 Object Point Reconstruction 5 Collocation for Time Series Analysis 6 Results 7 Conclusions 8 Outlook Numéro de notice : 17458 Thématique : IMAGERIE Nature : Thèse étrangère Note de thèse : thèse : Sciences : ETHZ : 2016 En ligne : https://www.sgc.ethz.ch/sgc-volumes/sgk-99.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=89683

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Code-barres	Cote	Support	Localisation	Section	Disponibilité
17458-01	33.60	Livre	Centre de documentation	Photogrammétrie - Lasergrammétrie	Disponible

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