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Combinatorial optimization applied to VLBI scheduling / A. Corbin in Journal of geodesy, vol 94 n°2 (February 2020)
Titre : Combinatorial optimization applied to VLBI scheduling Type de document : Article/Communication Auteurs : A. Corbin, Auteur ; B. Niedermann, Auteur ; Axel Nothnagel, Auteur ; et al., Auteur Année de publication : 2020 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes descripteurs IGN] analyse combinatoire (maths)
[Termes descripteurs IGN] données VGOS
[Termes descripteurs IGN] interférométrie à très grande base
[Termes descripteurs IGN] positionnement par ITGB
[Termes descripteurs IGN] programmation linéaire
[Termes descripteurs IGN] retard troposphérique zénithal
[Termes descripteurs IGN] station VLBI
[Termes descripteurs IGN] téléscope
[Termes descripteurs IGN] temps universel coordonnéRésumé : (auteur) Due to the advent of powerful solvers, today linear programming has seen many applications in production and routing. In this publication, we present mixed-integer linear programming as applied to scheduling geodetic very-long-baseline interferometry (VLBI) observations. The approach uses combinatorial optimization and formulates the scheduling task as a mixed-integer linear program. Within this new method, the schedule is considered as an entity containing all possible observations of an observing session at the same time, leading to a global optimum. In our example, the optimum is found by maximizing the sky coverage score. The sky coverage score is computed by a hierarchical partitioning of the local sky above each telescope into a number of cells. Each cell including at least one observation adds a certain gain to the score. The method is computationally expensive and this publication may be ahead of its time for large networks and large numbers of VLBI observations. However, considering that developments of solvers for combinatorial optimization are progressing rapidly and that computers increase in performance, the usefulness of this approach may come up again in some distant future. Nevertheless, readers may be prompted to look into these optimization methods already today seeing that they are available also in the geodetic literature. The validity of the concept and the applicability of the logic are demonstrated by evaluating test schedules for five 1-h, single-baseline Intensive VLBI sessions. Compared to schedules that were produced with the scheduling software sked, the number of observations per session is increased on average by three observations and the simulated precision of UT1-UTC is improved in four out of five cases (6 μs average improvement in quadrature). Moreover, a simplified and thus much faster version of the mixed-integer linear program has been developed for modern VLBI Global Observing System telescopes. Numéro de notice : A2020-153 Affiliation des auteurs : non IGN Thématique : MATHEMATIQUE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-020-01348-w date de publication en ligne : 29/01/2020 En ligne : https://doi.org/10.1007/s00190-020-01348-w Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94786
in Journal of geodesy > vol 94 n°2 (February 2020)[article]
Titre de série : Relativistic geodesy, ch. 2 Titre : Chronometric geodesy: Methods and applications Type de document : Chapitre/Contribution Auteurs : Pacôme Delva, Auteur ; Heiner Denker, Auteur ; Guillaume Lion Editeur : Springer International Publishing Année de publication : 2019 Collection : Fundamental Theories of Physics num. 196 Projets : ITOC / , AdOC / , FIRST-TF / Importance : pp 25 - 85 Note générale : bibliographie
This research was supported by the European Metrology Research Programme (EMRP) within the Joint Research Project “International Timescales with Optical Clocks” (SIB55 ITOC), as well as the Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Centre 1128 “Relativistic Geodesy and Gravimetry with Quantum Sensors (geo-Q)”, project C04. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. We gratefully acknowledge financial support from Labex FIRST-TF and ERC AdOC (Grant No. 617553).Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes descripteurs IGN] champ de pesanteur terrestre
[Termes descripteurs IGN] chronométrie
[Termes descripteurs IGN] décalage d'horloge
[Termes descripteurs IGN] échelle de temps
[Termes descripteurs IGN] horloge atomiqueRésumé : (auteur) The theory of general relativity was born more than one hundred years ago, and since the beginning has striking prediction success. The gravitational redshift effect discovered by Einstein must be taken into account when comparing the frequencies of distant clocks. However, instead of using our knowledge of the Earth’s gravitational field to predict frequency shifts between distant clocks, one can revert the problem and ask if the measurement of frequency shifts between distant clocks can improve our knowledge of the gravitational field. This is known as chronometric geodesy. Since the beginning of the atomic time era in 1955, the accuracy and stability of atomic clocks were constantly ameliorated, with around one order of magnitude gained every ten years. Now that the atomic clock accuracy reaches the low 10−18 in fractional frequency, and can be compared to this level over continental distances with optical fibres, the accuracy of chronometric geodesy reaches the cm level and begins to be competitive with classical geodetic techniques such as geometric levelling and GNSS/geoid levelling. Moreover, the building of global timescales requires now to take into account these effects to the best possible accuracy. In this chapter we explain how atomic clock comparisons and the building of timescales can benefit from the latest developments in physical geodesy for the modelization and realization of the geoid, as well as how classical geodesy could benefit from this new type of observable, which are clock comparisons that are directly linked to gravity potential differences. Numéro de notice : H2019-006 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Chapître / contribution nature-HAL : ChOuvrScient DOI : 10.1007/978-3-030-11500-5_2 date de publication en ligne : 10/02/2019 En ligne : https://doi.org/10.1007/978-3-030-11500-5_2 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95546
Titre : High performance clocks and gravity field determination Type de document : Article/Communication Auteurs : Jurgen Müller, Auteur ; D. Dirkx, Auteur ; S. M. Kopeikin, Auteur ; Guillaume Lion Année de publication : 2018 Projets : 3-projet - voir note / , AdOC / Note générale : bibliographie
Jürgen Müller gratefully acknowledges support by the DFG Sonderforschungsbereich (SFB 1128: geo-Q) Relativistic Geodesy and Gravimetry with Quantum Sensors.Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes descripteurs IGN] champ de pesanteur terrestre
[Termes descripteurs IGN] chronométrie
[Termes descripteurs IGN] échelle de temps
[Termes descripteurs IGN] gravimétrie spatiale
[Termes descripteurs IGN] horloge atomique
[Termes descripteurs IGN] International Terrestrial Reference Frame
[Termes descripteurs IGN] potentiel de pesanteur terrestre
[Termes descripteurs IGN] relativité généraleRésumé : (auteur) Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in manufacturing high-precision atomic clocks have rapidly improved their accuracy and stability over the last decade that approached the level of 10−18. This notable achievement along with the direct sensitivity of clocks to the strength of the gravitational field make them practically important for various geodetic applications that are addressed in the present paper. Based on a fully relativistic description of the background gravitational physics, we discuss the impact of those highly-precise clocks on the realization of reference frames and time scales used in geodesy. We discuss the current definitions of basic geodetic concepts and come to the conclusion that the advances in clocks and other metrological technologies will soon require the re-definition of time scales or, at least, clarification to ensure their continuity and consistent use in practice. The relative frequency shift between two clocks is directly related to the difference in the values of the gravity potential at the points of clock’s localization. According to general relativity the relative accuracy of clocks in 10−18 is equivalent to measuring the gravitational red shift effect between two clocks with the height difference amounting to 1 cm. This makes the clocks an indispensable tool in high-precision geodesy in addition to laser ranging and space geodetic techniques. We show how clock measurements can provide geopotential numbers for the realization of gravity-field-related height systems and can resolve discrepancies in classically-determined height systems as well as between national height systems. Another application of clocks is the direct use of observed potential differences for the improved recovery of regional gravity field solutions. Finally, clock measurements for space-borne gravimetry are analyzed along with closely-related deficiencies of this method like an extra-ordinary knowledge of the spacecraft velocity, etc. For all these applications besides the near-future prospects, we also discuss the challenges that are related to using those novel clock data in geodesy. Numéro de notice : A2018-197 Affiliation des auteurs : LaSTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s11214-017-0431-z date de publication en ligne : 30/11/2017 En ligne : https://doi.org/10.1007/s11214-017-0431-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=89864
in Space Science Reviews > vol 214 n° 1 (February 2018)[article]
Titre : Time for mapping Type de document : Monographie Auteurs : Sybille Lammes, Auteur ; Chris Perkins, Auteur ; Alex Gekker, Auteur ; et al., Auteur Editeur : Manchester [Royaume-Uni] : Manchester University Press Année de publication : 2018 Collection : European Research Council Importance : 289 p. ISBN/ISSN/EAN : 978-1-5261-2252-0 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Cartographie numérique
[Termes descripteurs IGN] analyse spatiale
[Termes descripteurs IGN] données spatiotemporelles
[Termes descripteurs IGN] échelle de temps
[Termes descripteurs IGN] OpenStreetMap
[Termes descripteurs IGN] représentation cartographique
[Termes descripteurs IGN] représentation du temps
[Termes descripteurs IGN] temps réel
[Termes descripteurs IGN] visualisation cartographiqueRésumé : (éditeur) "The digital era has brought about huge transformations in the map itself, which to date have been largely conceptualised in spatial terms. Novel objects, forms, processes and approaches have emerged and pose new, pressing questions about the temporality of digital maps and contemporary mapping practices: in spite of its implicit spatiality, digital mapping is strongly grounded in time. This collection brings time back into the map, taking up Doreen Massey's critical concern for 'ongoing stories' in the world; it asks how mapping enrols time into these narratives. Maps often seek to ‘freeze’ and ‘fix’ the world, looking to represent, document or capture dynamic phenomena. This collection examines how these processes are impacted by digital cartographic technologies that, arguably, have disrupted our understanding of time as much as they have provided coherence. The book consists of twelve chapters from experts in the field. Each addresses a different type of digital mapping practice and analyses it in relation to temporality. Cases discussed range from locative art projects, OpenStreetMap mapping parties, sensory mapping, Google Street View, to visual mapping, smart city dashboards and crisis mapping. Authors from different disciplinary positions consider how a temporal lens might focus attention on different aspects of digital mapping. This kaleidoscopic approach demonstrates a rich plethora of ways for understanding the temporal modes of digital mapping and the interdisciplinary background of the authors allows multiple positions to be developed and contrasted." Note de contenu : Introduction: mapping times
1- Ephemerality/mobility
2- Stitching memories
3- (In)formalisingNuméro de notice : 25579 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Monographie En ligne : http://library.oapen.org/handle/20.500.12657/30006 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95210
Titre : PerSE : visual analytics for calendar related spatiotemporal periodicity detection and analysis Type de document : Article/Communication Auteurs : Brian Swedberg, Auteur ; Donna J. Peuquet, Auteur Année de publication : 2017 Article en page(s) : pp 577 - 597 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Termes descripteurs IGN] analyse visuelle
[Termes descripteurs IGN] application web
[Termes descripteurs IGN] calendrier
[Termes descripteurs IGN] démonstration de faisabilité
[Termes descripteurs IGN] dimension temporelle
[Termes descripteurs IGN] exploration de données géographiques
[Termes descripteurs IGN] filtrage d'information
[Termes descripteurs IGN] fréquence
[Termes descripteurs IGN] interactivité
[Termes descripteurs IGN] sciences humaines et sociales
[Termes descripteurs IGN] utilisateur
[Vedettes matières IGN] GéovisualisationRésumé : (Auteur) Periodicity is embedded in all societies. As most of us organize our lives based on temporal structures, it is hard to imagine what life would be like without it. We experience periodicity through naturally occurring rhythms that exist in nature, such as sunrise/sunset, seasonal changes in the weather, and the tides. We also experience it through abstract means via cultural, political, religious ties, such as the weekend, Independence Day, and Ramadan. Forms of periodicity, like the examples above, are foundational to making sense of human activity because they provide contextual rationale and frame normaility. However, disparate calendars (e.g. Islamic vs. Gregorian), localized idiosyncrasies, and other variables greatly complicate the analytical ability to uncover and understand human activity at a given time within a specified region. We have developed PerSE (Periodicity in Spatiotemporal Events): a web application designed to aid users in the detection and analysis of calendar related periodicity in spatiotemporal event data sets via exploratory user interaction. PerSE is composed of several crossfiltering views: the Map, Attribute View, Time-Wheel, Timeline, and Table. Users interactively set and release filters on one or more of the views to detect and analyze calendar related periodicity. This paper illustrates the utility of PerSE through an in-depth description of the tool and proof of concept usage example. Numéro de notice : A2017-382 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1007/s10707-016-0280-z En ligne : https://doi.org/10.1007/s10707-016-0280-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85813
in Geoinformatica [en ligne] > vol 21 n° 3 (July - September 2017) . - pp 577 - 597[article]PermalinkPermalinkPermalinkPermalinkJournées 2013, Systèmes de référence spatio-temporels, Paris, 16 - 18 September 2014 / Nicole Capitaine (2014)
PermalinkPermalinkPermalinkPermalinkPermalinkAnnuaire du Bureau des longitudes, Guide de données astronomiques 2012 pour l'observation du ciel / Bureau des longitudes (2011)
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