Descripteur
Documents disponibles dans cette catégorie (80)
Ajouter le résultat dans votre panier
Visionner les documents numériques
Affiner la recherche Interroger des sources externes
Etendre la recherche sur niveau(x) vers le bas
Improved constraints on models of glacial isostatic adjustment: A review of the contribution of ground-based geodetic observations / Matt A. King in Surveys in Geophysics, vol 31 n° 5 (September 2010)
[article]
Titre : Improved constraints on models of glacial isostatic adjustment: A review of the contribution of ground-based geodetic observations Type de document : Article/Communication Auteurs : Matt A. King, Auteur ; Zuheir Altamimi , Auteur ; Johannes Böhm , Auteur ; Machiel Bos, Auteur ; Rolf Dach, Auteur ; Pedro Elosegui, Auteur ; François Fund, Auteur ; Manuel Hernández-Pajares, Auteur ; David Lavallée, Auteur ; Paulo Jorge Mendes Cerveira, Auteur ; Nigel Penna, Auteur ; Riccardo Riva, Auteur ; Peter Steigenberger, Auteur ; Tonie M. van Dam, Auteur ; Luca Vittuari, Auteur ; Simon D.P. Williams, Auteur ; Pascal Willis , Auteur Année de publication : 2010 Article en page(s) : pp 465 - 507 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Antarctique
[Termes IGN] bilan de masse
[Termes IGN] calotte glaciaire
[Termes IGN] champ de vitesse
[Termes IGN] données GRACE
[Termes IGN] Groenland
[Termes IGN] mesure géodésique
[Termes IGN] positionnement par DORIS
[Termes IGN] positionnement par GPS
[Termes IGN] positionnement par ITGB
[Termes IGN] positionnement par télémétrie laser sur satellite
[Termes IGN] rebond post-glaciaireRésumé : (auteur) The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is uncertain due to insufficient constraints on our knowledge of past glacial changes and to large simplifications in the underlying Earth models. Consequently, we show differences between models that exceed several mm/year in terms of surface displacement for the two major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement offer the potential for new constraints to be made on GIA models, especially when they are used to improve structural features of the Earth’s interior as to allow for a more realistic reconstruction of the glaciation history. We present the distribution of presently available campaign and continuous geodetic measurements in Greenland and Antarctica and summarise surface velocities published to date, showing substantial disagreement between techniques and GIA models alike. We review the current state-of-the-art in ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise surface velocities. In particular, we focus on known areas of need in GPS observation level models and the terrestrial reference frame in order to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates. Numéro de notice : A2010-663 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10712-010-9100-4 Date de publication en ligne : 16/06/2010 En ligne : https://doi.org/10.1007/s10712-010-9100-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91769
in Surveys in Geophysics > vol 31 n° 5 (September 2010) . - pp 465 - 507[article]Documents numériques
en open access
Improved constraints on models ... - pdf éditeurAdobe Acrobat PDF Identification and modelling of sea level change contributors on GRACE satellite gravity data and their applications to climate monitoring / Bert Wouters (2010)
Titre : Identification and modelling of sea level change contributors on GRACE satellite gravity data and their applications to climate monitoring Type de document : Rapport Auteurs : Bert Wouters, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2010 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 73 Importance : 182 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-316-7 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] changement climatique
[Termes IGN] GRACE
[Termes IGN] Groenland
[Termes IGN] niveau moyen des mers
[Termes IGN] surveillance météorologiqueIndex. décimale : 30.83 Applications océanographiques de géodésie spatiale Résumé : (Auteur) Recently, the Intergovernmental Panel on Climate Change named sea level rise as one of the major challenges of the 21st century. Given the high population density of coastal regions, a small rise of the sea level will have a substantial impact on human society. However, the Earth's climate system is a complex matter arid model predictions of the sea level changes likely to be expected in the coming century currently show a wide spread. Clearly, a thorough understanding of present-day climate variability is imperative narrow this uncertainty band, which on its turn depends on the availability of accurate and detailed observations of our climate.
A valuable contribution to the expanding array of satellites dedicated to observations of the Earth System, are the Gravity Recovery and Climate Experiment (GRACE) satellites, launched in March 2002. This mission is dedicated to observing changes of the Earth's gravity field at (sub-)monthly intervals. At time-scales of a few years, these changes are mostly related to the redistribution of water on the Earth's surface. For example, a thinning of the Greenland ice sheet will manifest itself as a local negative anomaly in the gravity field, whereas the water that is added to the ocean will show up as a predominantly positive anomaly. The main objective of this dissertation is to study how the GRACE observations can be used to improve our knowledge of changes in the Earth's climate systems, and how the data should be processed in order to optimize quality and spatial resolution.
The GRACE data provided by the science teams consist of spherical harmonic coefficients. They show particular correlations between coefficients of identical order and even and odd degree, respectively, due to the mission's architecture and deficiencies in the background models used throughout the processing of the satellite measurements. These noise artifacts show up as striping patterns along the north-south direction in the monthly maps of surface mass changes, hampering the interpretation of the observations. In this dissertation, it is shown that empirical orthogonal function (EOF) analysis is an effective method to reduce the noise in the GRACE data. This statistical tool separates a data set into a number of characteristic (eigen) modes of variance, in combination with an index describing the amplitude of the mode in time, i.e. the principal components. The EOF analysis can be applied to the maps of surface mass changes, in which case the first few modes are related to the annual and long-term trend components. The fourth mode appears to be related to the El Nino/Southern Oscillation. The noise signals arc absorbed by the higher modes, which makes the leading modes largely stripe-free up to a resolution of approximately 400 kilometers.
A further reduction of the noise can be obtained by applying the EOF de-composition directly to the spherical harmonic coefficients, after grouping them following order. The principal components arc compared to a random process and, if the two arc statistically sufficiently alike, not used in the further data processing. A series of tests shows that this approach reduces the noise by 60-80 %, compared the non-filtered case. An important feature of this filter is that it does not alter the shape of the signal and causes less reduction its power, compared to other commonly used filter methods based on the approach of Swenson and Walir (2006).
Using the filtered data, changes in the mass content of the ocean have been studied. The GRACE satellites are capable of capturing seasonal changes in the ocean mass content accurately on a global scale. In combination with sea surface height observations made by satellite altimeter, the steric sea level component (related to changes in the heat and salinity content of the ocean) can be separated as well. A comparison with reference data sets shows that locally a coherent signal can be obtained at a (Gaussian) resolution of approximately 500 km over the oceans. These steric changes dominate the sea level in most of the oceans, but strong ocean bottom pressure fluctuations are observed in several areas, e.g., the Gulf of Carpentaria and the Gulf of Thailand. Estimates of long-term changes in the ocean mass and heat content arc a more challenging problem, and require a longer observation period and a better modeling of mass redistribution in the solid earth and the position of the center of mass of the Earth, two components to which the GRACE observations arc particularly sensitive.
It is found that the global spherical harmonic coefficients contain more information than previously acknowledged. This is demonstrated by using the GRACE data to obtain a picture of the mass balance of the Greenland ice sheet at a regional scale. From the research in this dissertations, it shows that Greenland lost 179 Gigaton each year on average between 2003 and 2008, causing a global mean rise of sea level by 0.5 mm/yr. Comparing the trend in the first few to that in the last few years shows a speed-up of the thinning, which corroborates the picture of an increasingly negative mass balance of the ice sheet since the mid 1990's as indicated by, for example, regional climate models and radar altimetry observations. The majority of the losses occur in the coastal regions in the southeastern sector. The northwestern coastal zones were approximately in balance up to the summer of 2005, but show strong negative trends since. Large year-to-year differences in the mass balance of the ice sheet are observed, with a record loss in the warm summer of 2007. A strong correlation between the GRACE observations in summer and satellite measurements of surface melt area extent is demonstrated. Also, good agreement is found with regional climate modeling data, highlighting the potential of the GRACE observations to validate and improve the numerical models.
A mass redistribution on land will cause a change in the shape of the global geoid. Sea level, when not acted upon by any other forcings, will adjust to this equipotential surface. Therefore, when water is exchanged between ocean and continents (and changes due to ocean dynamics are disregarded), sea level will not rise or fall uniformly, which is known as the so-called self-gravitation effect. Due to their global coverage, the GRACE observations of continental mass distribution are an excellent input to model this phenomenon. Strongest deviations from a uniform distribution are found off the coast of Alaska and in the Bay of Bengal, where differences of more than 100% are found on seasonal time-scales. In these regions, inclusion of the self-gravitation effect into numerical ocean model would result in a better agreement between modeled and observational data.
From the work presented in this dissertation, it shows that the GRACE satellites are an invaluable tool for the monitoring of our climate system. Statistically filtering of the data reveals a wealth of information. In combination with altimetry observations, the GRACE data allows the separation of mass and steric components in sea level on seasonal time scales. Given a longer observational period and an improved understanding of the processes in the solid earth, expected to come available soon thanks to ESA's GOCE missions, long-term trends in these components will be identifiable. Furthermore, the GRACE mission allows us to put a constraint on the contribution of the Greenland ice sheet to present-day sea level rise. The technique to recover these changes can easily be expanded to other regions, such as the Antarctic or the Alaskan glacier fields. The synergy between GRACE data, future missions such as Cryosat-2, which will map height variations of the cryosphere with an unprecedented accuracy, and regional climate models, uncovering the physical processes behind the observed changes, promises a leap forward in our understanding of the mass balance of the ice sheets. Finally, com-paring the modeled deviations from uniform sea level changes with in-situ data such as from tide-gauges, may lead to a direct validation of the aforementioned self-gravitation theory with present-day data.Numéro de notice : 10335 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Rapport de recherche DOI : sans En ligne : https://www.ncgeo.nl/downloads/73Wouters.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62396 Exemplaires(1)
Code-barres Cote Support Localisation Section Disponibilité 10335-01 30.83 Livre Centre de documentation Géodésie Disponible Copenhague : échec ou nouveau départ ? / Alain Chaudron in Revue forestière française, vol 61 n° 6 (novembre - décembre 2009)
[article]
Titre : Copenhague : échec ou nouveau départ ? Type de document : Article/Communication Auteurs : Alain Chaudron, Auteur Année de publication : 2009 Article en page(s) : p. 643-647 Note générale : DOI : 10.4267/2042/32926. Bibliogr Langues : Français (fre) Descripteur : [Termes IGN] changement climatique
[Termes IGN] CopenhagueNuméro de notice : IFN_6062 Affiliation des auteurs : non IGN Thématique : FORET Nature : Article DOI : 10.4267/2042/32926 En ligne : https://doi.org/10.4267/2042/32926 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=73619
in Revue forestière française > vol 61 n° 6 (novembre - décembre 2009) . - p. 643-647[article]Exemplaires(2)
Code-barres Cote Support Localisation Section Disponibilité 133-09061 RAB Revue Centre de documentation En réserve L003 Disponible IFN-001-P001094 PER Revue Nogent-sur-Vernisson Salle périodiques Exclu du prêt Hybridization between Quercus robur and Q. petraea in a mixed oak stand in Denmark / J. Jensen in Annals of Forest Science, Vol 66 n° 7 (October - November 2009)
[article]
Titre : Hybridization between Quercus robur and Q. petraea in a mixed oak stand in Denmark Titre original : Hybridation entre Quercus robur et Q. petraea dans un peuplement mélangé de chênes au Danemark Type de document : Article/Communication Auteurs : J. Jensen, Auteur ; Anders Larsen, Auteur ; Lene R. Nielsen, Auteur ; Joan Cottrell, Auteur Année de publication : 2009 Article en page(s) : n° 706 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] Danemark
[Termes IGN] diversité génétique
[Termes IGN] hybridation naturelle (végétation)
[Termes IGN] peuplement mélangé
[Termes IGN] Quercus pedunculata
[Termes IGN] Quercus sessiliflora
[Vedettes matières IGN] SylvicultureRésumé : (Editeur) Hybridization and mating pattern between Quercus robur and Q. petraea was studied in a 5.8 ha mixed forest stand in Jutland, Denmark which comprises in total 135 Quercus robur and 230 Q. petraea trees. Classification of the oak trees into species was performed using canonical discriminant analysis of a range of leaf morphological traits. Adult trees (365) and offspring (582) were genotyped with eight microsatellite markers. Seedlings were sampled in 2003 and acorns were collected in 2004. Mating patterns of Q. robur and Q. petraea are expected to be different in the northern range of the distribution area and a larger hybridization rate is expected. It is further expected, that pollination from outside sources will be relatively less in small fragmented forest management systems compared to large scale oak forest. The conclusions should be verified through repeated year to year analysis of the mating pattern. Phenological studies revealed that there was no difference in flowering time between species. Data for the adult trees revealed no significant departures from Hardy-Weinberg proportions and there was weak, but significant spatial genetic structure, which supports the idea that the stand is of natural origin. Spatial genetic structure in the first distance class is stronger for Q. petraea. The genetic composition of the offspring was remarkably consistent from year to year. Paternity analysis revealed that, on average, 85% pollination came from fathers within the stand. The direction of the pollen flow varied from year to year. Inter-specific hybridization was high and ranged from 15–17% and from 48–55% for Q. petraea and Q. robur mothers respectively. Paternity analysis revealed that the population was basically outcrossing and only 3.7% of the analysed progeny were the product of selfing. Over the two years of study, approximately 200 trees contributed to the paternity of the next generations.
The study confirms earlier studies with a greater tendency for Q. robur mothers to produce hybrid seeds than Q. petraea mothers. The rate of hybridization is higher in this Danish stand than in comparable studies elsewhere in Europe. Gene flow from outside sources are relatively low.Numéro de notice : A2009-627 Affiliation des auteurs : non IGN Thématique : FORET Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1051/forest/2009058 Date de publication en ligne : 02/10/2009 En ligne : https://www.afs-journal.org/articles/forest/full_html/2009/07/f08308/f08308.html Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=72830
in Annals of Forest Science > Vol 66 n° 7 (October - November 2009) . - n° 706[article]Exemplaires(1)
Code-barres Cote Support Localisation Section Disponibilité IFN-001-P000668 PER Revue Nogent-sur-Vernisson Salle périodiques Exclu du prêt Mean dynamic topography and geostrophic surface currents in the Fram Strait derived from geodetic data / D. Lysaker in Marine geodesy, vol 32 n° 1 (January - March 2009)
[article]
Titre : Mean dynamic topography and geostrophic surface currents in the Fram Strait derived from geodetic data Type de document : Article/Communication Auteurs : D. Lysaker, Auteur Année de publication : 2009 Article en page(s) : pp 42 - 63 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] anomalie de pesanteur
[Termes IGN] circulation géostrophique
[Termes IGN] collocation par moindres carrés
[Termes IGN] Groenland
[Termes IGN] océanographie dynamique
[Termes IGN] surface de la mer
[Termes IGN] SvalbardRésumé : (Auteur) Two mean dynamic topography (MDT) fields are determined in the Fram Strait between Svalbard and Greenland. New airborne gravity anomalies, older data, and two different mean sea surface (MSS) fields are combined using the least squares collocation (LSC) technique. The results are compared to an oceanographic MDT model and two synthetic MDT fields. The same main currents are seen in all fields. Additionally, smaller scale features are revealed in the new MDT fields. Geostrophic surface currents derived from the MDT models are compared to moorings and Lagrangian drifters. The agreement is desultory. The oceanographic data are an inadequate basis of comparison due to data gaps. Nevertheless, it is the only one available. Copyright Taylor & Francis Numéro de notice : A2009-190 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/01490410802662029 En ligne : https://doi.org/10.1080/01490410802662029 Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29820
in Marine geodesy > vol 32 n° 1 (January - March 2009) . - pp 42 - 63[article]Exemplaires(1)
Code-barres Cote Support Localisation Section Disponibilité 230-09011 RAB Revue Centre de documentation En réserve L003 Disponible PermalinkGeoid, sea level and vertical datum of the Arctic improved by ICESAT and GRACE / Henriette Skourup in Geomatica, vol 62 n° 2 (June 2008)PermalinkAnalyse du référentiel interurbain français / C. André (2008)PermalinkPolar Radar for Ice Sheet Measurements (PRISM) / S. Gogineni in Remote sensing of environment, vol 111 n° 2-3 (30 November 2007)PermalinkSatellite evidence of the melting Greenland's ice cap: Ice losses now far surpass ice gains / J. Triglav in Geoinformatics, vol 10 n° 4 (01/06/2007)PermalinkAssessment of long-range kinematic GPS positioning errors by comparison with airborne laser altimetry and satellite altimetry / X. Zhang in Journal of geodesy, vol 81 n° 3 (March 2007)PermalinkSea ice monitoring by L-band SAR: an assessment based on literature and comparisons of JERS-1 and ERS-1 imagery / W. Dierking in IEEE Transactions on geoscience and remote sensing, vol 44 n° 4 (April 2006)PermalinkPermalinkBlowing in the wind / G. Giebel in GEO: Geoconnexion international, vol 4 n° 4 (april 2005)PermalinkRegional simulation of ecosystem CO2 and water vapor exchange for agricultural land using NOAA AVHRR and Terra MODIS satellite data: Application to Zealand, Denmark / Rasmus M. Houborg in Remote sensing of environment, vol 93 n° 1 (30/10/2004)Permalink