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Performance of miniaturized atomic clocks in static laboratory and dynamic flight environments / Ankit Jain in GPS solutions, vol 25 n° 1 (January 2021)
Titre : Performance of miniaturized atomic clocks in static laboratory and dynamic flight environments Type de document : Article/Communication Auteurs : Ankit Jain, Auteur ; Thomas Krawinkel, Auteur ; Steffen Schön, Auteur ; Andreas Bauch, Auteur Année de publication : 2021 Article en page(s) : 16 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes descripteurs IGN] décalage d'horloge
[Termes descripteurs IGN] fréquence
[Termes descripteurs IGN] horloge atomique
[Termes descripteurs IGN] horloge du récepteur
[Termes descripteurs IGN] oscillateur
[Termes descripteurs IGN] récepteur GNSS
[Termes descripteurs IGN] stabilité
[Termes descripteurs IGN] variance d'AllanRésumé : (auteur) Miniaturized atomic clocks with high frequency stability as local oscillators in global navigation satellite system (GNSS) receivers promise to improve real-time kinematic applications. For a number of years, such oscillators are being investigated regarding their overall technical applicability, i.e., transportability, and performance in dynamic environments. The short-term frequency stability of these clocks is usually specified by the manufacturer, being valid for stationary applications. Since the performance of most oscillators is likely degraded in dynamic conditions, various oscillators are tested to find the limits of receiver clock modeling in dynamic cases and consequently derive adequate stochastic models to be used in navigation. We present the performance of three different oscillators (Microsemi MAC SA.35m, Spectratime LCR-900 and Stanford Research Systems SC10) for static and dynamic applications. For the static case, all three oscillators are characterized in terms of their frequency stability at Physikalisch-Technische Bundesanstalt, Germany's national metrology institute. The resulting Allan deviations agree well with the manufacturer's data. Furthermore, a flight experiment was conducted in order to evaluate the performance of the oscillators under dynamic conditions. Here, each oscillator is replacing the internal oscillator of a geodetic-grade GNSS receiver and the stability of the receiver clock biases is determined. The time and frequency offsets of the oscillators are characterized with regard to the flight dynamics recorded by a navigation-grade inertial measurement unit. The results of the experiment show that the frequency stability of each oscillator is degraded by about at least one order of magnitude compared to the static case. Also, the two quartz oscillators show a significant g-sensitivity resulting in frequency shifts of − 1.2 × 10−9 and + 1.5 × 10−9, respectively, while the rubidium clocks are less sensitive, thus enabling receiver clock modeling and strengthening of the navigation performance even in high dynamics. Numéro de notice : A2021-003 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-020-01036-4 date de publication en ligne : 13/10/2020 En ligne : https://doi.org/10.1007/s10291-020-01036-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96081
in GPS solutions > vol 25 n° 1 (January 2021) . - 16 p.[article]
Titre : Positioning stability improvement with inter-system biases on multi-GNSS PPP Type de document : Article/Communication Auteurs : Byung-Kyu Choi, Auteur ; Hasu Yoon, Auteur Année de publication : 2018 Article en page(s) : pp. 239 - 248 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement
[Termes descripteurs IGN] affaiblissement géométrique de la précision
[Termes descripteurs IGN] erreur systématique inter-systèmes
[Termes descripteurs IGN] positionnement par GNSS
[Termes descripteurs IGN] positionnement ponctuel précis
[Termes descripteurs IGN] précision du positionnement
[Termes descripteurs IGN] stabilitéRésumé : (auteur) The availability of multiple signals from different Global Navigation Satellite System (GNSS) constellations provides opportunities for improving positioning accuracy and initial convergence time. With dual-frequency observations from the four constellations (GPS, GLONASS, Galileo, and BeiDou), it is possible to investigate combined GNSS precise point positioning (PPP) accuracy and stability. The differences between GNSS systems result in inter-system biases (ISBs). We consider several ISB values such as GPS-GLONASS, GPS-Galileo, and GPS-BeiDou. These biases are compliant with key parameters defined in the multi-GNSS PPP processing. In this study, we present a unified PPP method that sets ISB values as fixed or constant. A comprehensive analysis that includes satellite visibility, position dilution of precision, position accuracy is performed to evaluate a unified PPP method with constrained cut-off elevation angles. Compared to the conventional PPP solutions, our approach shows more stable positioning at a constrained cut-off elevation angle of 50 degrees. Numéro de notice : A2018-432 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2018-0005 date de publication en ligne : 05/04/2018 En ligne : https://doi.org/10.1515/jag-2018-0005 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90999
in Journal of applied geodesy > vol 12 n° 3 (July 2018) . - pp. 239 - 248[article]
Titre : Biodiversity effects on ecosystem functioning in a 15-year grassland experiment: patterns, mechanisms, and open questions Type de document : Article/Communication Auteurs : Wolfgang W. Weisser, Auteur ; Christiane Roscher, Auteur ; Sebastian Meyer, Auteur ; et al., Auteur Année de publication : 2017 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Ecologie
[Termes descripteurs IGN] azote
[Termes descripteurs IGN] biomasse
[Termes descripteurs IGN] carbone
[Termes descripteurs IGN] écosystème
[Termes descripteurs IGN] gaz à effet de serre
[Termes descripteurs IGN] nutriment
[Termes descripteurs IGN] placette d'échantillonnage
[Termes descripteurs IGN] potassium
[Termes descripteurs IGN] puits de carbone
[Termes descripteurs IGN] richesse floristique
[Termes descripteurs IGN] sol
[Termes descripteurs IGN] stabilitéRésumé : (auteur) In the past two decades, a large number of studies have investigated the relationship between biodiversity and ecosystem functioning, most of which focussed on a limited set of ecosystem variables. The Jena Experiment was set up in 2002 to investigate the effects of plant diversity on element cycling and trophic interactions, using a multi-disciplinary approach. Here, we review the results of 15 years of research in the Jena Experiment, focussing on the effects of manipulating plant species richness and plant functional richness. With more than 85,000 measures taken from the plant diversity plots, the Jena Experiment has allowed answering fundamental questions important for functional biodiversity research.
First, the question was how general the effect of plant species richness is, regarding the many different processes that take place in an ecosystem. About 45% of different types of ecosystem processes measured in the ‘main experiment’, where plant species richness ranged from 1 to 60 species, were significantly affected by plant species richness, providing strong support for the view that biodiversity is a significant driver of ecosystem functioning. Many measures were not saturating at the 60-species level, but increased linearly with the logarithm of species richness. There was, however, great variability in the strength of response among different processes. One striking pattern was that many processes, in particular belowground processes, took several years to respond to the manipulation of plant species richness, showing that biodiversity experiments have to be long-term, to distinguish trends from transitory patterns. In addition, the results from the Jena Experiment provide further evidence that diversity begets stability, for example stability against invasion of plant species, but unexpectedly some results also suggested the opposite, e.g. when plant communities experience severe perturbations or elevated resource availability. This highlights the need to revisit diversity-stability theory.
Second, we explored whether individual plant species or individual plant functional groups, or biodiversity itself is more important for ecosystem functioning, in particular biomass production. We found strong effects of individual species and plant functional groups on biomass production, yet these effects often occurred mostly in addition to, but not instead of, effects of plant species richness.
Third, the Jena Experiment assessed the effect of diversity on multitrophic interactions. The diversity of most organisms responded positively to increases in plant species richness, and the effect was stronger for above- than for belowground organisms, and stronger for herbivores than for carnivores or detritivores. Thus, diversity begets diversity. In addition, the effect on organismic diversity was stronger than the effect on species abundances.
Fourth, the Jena Experiment aimed to assess the effect of diversity on N, P and C cycling and the water balance of the plots, separating between element input into the ecosystem, element turnover, element stocks, and output from the ecosystem. While inputs were generally less affected by plant species richness, measures of element stocks, turnover and output were often positively affected by plant diversity, e.g. carbon storage strongly increased with increasing plant species richness. Variables of the N cycle responded less strongly to plant species richness than variables of the C cycle.
Fifth, plant traits are often used to unravel mechanisms underlying the biodiversity-ecosystem functioning relationship. In the Jena Experiment, most investigated plant traits, both above- and belowground, were plastic and trait expression depended on plant diversity in a complex way, suggesting limitation to using database traits for linking plant traits to particular functions.
Sixth, plant diversity effects on ecosystem processes are often caused by plant diversity effects on species interactions. Analyses in the Jena Experiment including structural equation modelling suggest complex interactions that changed with diversity, e.g. soil carbon storage and greenhouse gas emission were affected by changes in the composition and activity of the belowground microbial community. Manipulation experiments where particular organisms, e.g. belowground invertebrates, were excluded from plots in split-plot experiments, supported the important role of the biotic component for element and water fluxes.
Seventh, the Jena Experiment aimed to put the results into the context of agricultural practices in managed grasslands. The effect of increasing plant species richness from 1 to 16 species on plant biomass was, in absolute terms, as strong as the effect of a more intensive grassland management, using fertiliser and increasing mowing frequency. Potential bioenergy production from high-diversity plots was similar to that of conventionally used energy crops. These results suggest that diverse ‘High Nature Value Grasslands’ are multifunctional and can deliver a range of ecosystem services including production-related services.
A final task was to assess the importance of potential artefacts in biodiversity–ecosystem functioning relationships, caused by the weeding of the plant community to maintain plant species composition. While the effort (in hours) needed to weed a plot was often negatively related to plant species richness, species richness still affected the majority of ecosystem variables. Weeding also did not negatively affect monoculture performance; rather, monocultures deteriorated over time for a number of biological reasons, as shown in plant-soil feedback experiments.
To summarize, the Jena Experiment has allowed for a comprehensive analysis of the functional role of biodiversity in an ecosystem. A main challenge for future biodiversity research is to increase our mechanistic understanding of why the magnitude of biodiversity effects differs among processes and contexts. It is likely that there will be no simple answer. For example, among the multitude of mechanisms suggested to underlie the positive plant species richness effect on biomass, some have received limited support in the Jena Experiment, such as vertical root niche partitioning. However, others could not be rejected in targeted analyses. Thus, from the current results in the Jena Experiment it seems likely that the positive biodiversity effect results from several mechanisms acting simultaneously in more diverse communities, such as reduced pathogen attack, the presence of more plant growth promoting organisms, less seed limitation, and increased trait differences leading to complementarity in resource uptake. Distinguishing between different mechanisms requires careful testing of competing hypotheses. Biodiversity research has matured such that predictive approaches testing particular mechanisms are now possible.Numéro de notice : A2017-352 Affiliation des auteurs : non IGN Thématique : BIODIVERSITE/FORET Nature : Article DOI : 10.1016/j.baae.2017.06.002 date de publication en ligne : 26/06/2017 En ligne : https://doi.org/10.1016/j.baae.2017.06.002 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85690
in Basic and Applied Ecology > vol [26/06/2017][article]
Titre : Deformation monitoring of the submillimetric UPV calibration baseline Type de document : Article/Communication Auteurs : Luis García-Asenjo, Auteur ; Sergio Baselga, Auteur ; Pascual Garrigues, Auteur Année de publication : 2017 Article en page(s) : pp 107 - 114 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes descripteurs IGN] base géodésique
[Termes descripteurs IGN] déformation géométrique
[Termes descripteurs IGN] distancemètre
[Termes descripteurs IGN] étalonnage d'instrument
[Termes descripteurs IGN] mécomètre
[Termes descripteurs IGN] stabilité
[Termes descripteurs IGN] Valence (Espagne)Résumé : (Auteur) A 330 m calibration baseline was established at the Universitat Politècnica de València (UPV) in 2007. Absolute scale was subsequently transferred in 2012 from the Nummela Standard Baseline in Finland and distances between pillars were determined with uncertainties ranging from 0.1 mm to 0.3 mm. In order to assess the long-term stability of the baseline, three field campaigns were carried out from 2013 to 2015 in a co-operative effort with the Universidad Complutense de Madrid (UCM), which provided the only Mekometer ME5000 distance meter available in Spain. Since the application of the ISO17123-4 full procedure did not suffice to come to a definite conclusion about possible displacements of the pillars, we opted for the traditional geodetic network approach. This approach had to be adapted to the case at hand in order to deal with problems such as the geometric weakness inherent to calibration baselines and scale uncertainty derived from both the use of different instruments and the high correlation between the meteorological correction and scale determination. Additionally, the so-called the maximum number of stable points method was also tested. In this contribution, it is described the process followed to assess the stability of the UPV submillimetric calibration baseline during the period of time from 2012 to 2015. Numéro de notice : A2017-284 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article En ligne : https://doi.org/10.1515/jag-2016-0018 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85317
in Journal of applied geodesy > vol 11 n° 2 (June 2017) . - pp 107 - 114[article]
Titre : Assessment of the DORIS network monumentation Type de document : Article/Communication Auteurs : Jérôme Saunier Année de publication : 2016 Article en page(s) : pp 2725 - 2741 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes descripteurs IGN] DORIS
[Termes descripteurs IGN] Global Geodetic Observing System
[Termes descripteurs IGN] stabilitéRésumé : (auteur) Stability of the monumentation is essential for precise positioning applications to minimize velocity uncertainties and noises in the position data. In charge of the DORIS global tracking network deployment since the beginning, IGN, in consultation with CNES, designed three standard monuments compliant with the DORIS system requirements and general geodetic specifications, and suitable for various site configurations: building roofs, concrete pedestals or pillars. This paper describes the monument types in use in the DORIS network according to the current required specifications and provides a comparative assessment of the stability of the monuments over the network based on three methods: a theoretical study of the mechanical behavior of the metallic structures, a misclosure analysis taken during ground surveys and a qualitative approach taking into account different factors. This overview of the network monumentation gives new key numbers following the previous network assessment performed by Fagard (2006). Significant improvements have been made following the continuous efforts to renovate the network monumentation. These results are relevant for the Global Geodetic Observing System (GGOS) goals of measurement stability for the geodetic techniques. Today, two-thirds of the DORIS network monuments are compliant with the standards aiming at stability of 0.1 mm/y. This stability result has been measured for 16 of the 58 stations more than 10 y after its installation while monuments with more than 1 mm antenna tilts are over 10 y old when specifications were less stringent. The grading and scoring grid drawn up for each monument led to the mapping of the stability of the current DORIS network. Finally, we present a number of further actions to monitor the monument stability and provide new elements for the network monumentation assessment, exploring two different approaches: analysis of the time series and direct measurements using devices placed on each monument. Numéro de notice : A2016--186 Affiliation des auteurs : IGN (2012-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.asr.2016.02.026 date de publication en ligne : 09/03/2016 En ligne : https://doi.org/10.1016/j.asr.2016.02.026 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91822
in Advances in space research > vol 58 n° 12 (15 December 2016) . - pp 2725 - 2741[article]PermalinkPermalinkPermalinkPermalinkPermalinkPermalinkPermalinkLocal ties, VLBI-GPS eccentricities and combination of geodetic reference frames / Claudio Abbondanza (2008)
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