Improving MODIS Spatial Resolution for Snow Mapping Using Wavelet Fusion and ARSIS Concept   总被引：1，自引：0，他引：1  

Sirguey  P. Mathieu  R. Arnaud  Y. Khan  M.M. Chanussot  J. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(1):78-82

We propose to fuse the high spatial content of two 250-m spectral bands of the moderate resolution imaging spectroradiometer (MODIS) into its five 500-m bands using wavelet-based multiresolution analysis. Our objective was to test the effectiveness of this technique to increase the accuracy of snow mapping in mountainous environments. To assess the performance of this approach, we took advantage of the simultaneity between the advanced spaceborne thermal emission and reflection radiometer (ASTER) and MODIS sensors. With a 15-m spatial resolution, the ASTER sensor provided reference snow maps, which were then compared to MODIS-derived snow maps. The benefit of the method was assessed through the investigation of various metrics, which showed an improvement from 3% to 20%. Therefore, the enhanced snow map is of great benefit for environmental and hydrological applications in steep terrain.  相似文献   

Frequency and intensity of high-altitude floods over the last 3.5 ka in northwestern French Alps (Lake Anterne)     

Charline Giguet-Covex  Fabien Arnaud  Dirk Enters  Jérôme Poulenard  Laurent Millet  Pierre Francus  Fernand David  Pierre-Jérôme Rey  Bruno Wilhelm  Jean-Jacques Delannoy 《Quaternary Research》2012,77(1):12-22

In central Western Europe, several studies have shown that colder Holocene periods, such as the Little Ice Age, also correspond to wet periods. However, in mountain areas which are highly sensitive to erosion processes and where precipitation events can be localized, past evolution of hydrological activity might be more complicated. To assess these past hydrological changes, a paleolimnological approach was applied on a 13.4-m-long sediment core taken in alpine Lake Anterne (2063 m asl) and representing the last 3.5 ka. Lake sedimentation is mainly composed of flood deposits triggered by precipitation events. Sedimentological and geochemical analyses show that floods were more frequent during cold periods while high-intensity flood events occurred preferentially during warmer periods. In mild temperature conditions, both flood patterns are present. This underlines the complex relationship between flood hazards and climatic change in mountain areas. During the warmer and/or dryer times of the end of Iron Age and the Roman Period, both the frequency and intensity of floods increased. This is interpreted as an effect of human-induced clearing for grazing activities and reveals that anthropogenic interferences must be taken into account when reconstructing climatic signals from natural archives.  相似文献   

Microbial diversity in contaminated soils along the T22 trench of the Chernobyl experimental platform     

Virginie Chapon  Laurie Piette  Marie-Hélène Vesvres  Frédéric Coppin  Claire Le Marrec  Richard Christen  Nicolas Theodorakopoulos  Laureline Février  Sviatoslav Levchuk  Arnaud Martin-Garin  Catherine Berthomieu  Claire Sergeant 《Applied Geochemistry》2012

The diversity of bacterial communities exposed to radioactive contamination in Chernobyl soils was examined by a combination of molecular and culture-based approaches. A set of six radioactive soil samples, exhibiting high levels of ¹³⁷Cs contamination, were collected from the T22 trench. Three samples were also collected in nearby soils with low contamination. Complex bacterial community structures were observed in both highly and weakly contaminated samples, using a molecular approach targeting the 16S rRNA gene. However, the presence of specific populations within samples from highly contaminated soils could not be revealed by statistical analysis of the DGGE profiles. More than 200 culturable isolates, representative of dominant morphotypes, were grouped into 83 Operational Taxonomic Units (OTUs) and affiliated to Firmicutes, Actinobacteria, Alpha-, Beta-, Gamma-Proteobacteria and Bacteroïdetes. No specific pattern linked to contamination was observed for these culturable bacteria. The results show that both highly and weakly contaminated soils host a wide diversity of bacteria, suggesting that long term exposure to radionuclides does not lead to the extinction of bacterial diversity.  相似文献   

日晕测量与日晕光度计外缘杂散光抑制试验     

刘念平  刘煜  申远灯  张雪飞  曹文达  Arnaud Jean 《天文学报》2011,52(2)

为配合大型太阳设备西部选址工作,研制了一架现代日晕光度计(Sky Brightness Monitor,SBM).前期实验对日晕光度计性能进行了测试,同时积累了云南部分址点的日晕数据.资料分析结果显示,轿子雪山正午前后的日晕水平最低可至日面中心强度百万分之几的量级(蓝波段).这表明该日晕光度计内部杂散光水平已达到了国际同类产品的标准.日晕光度计的内部杂散光源主要来自两部分:镜筒前端中性滤光片(ND4)固定套圈的边缘衍射(视场靠内区域)和镜筒内置光阑的边缘衍射(视场靠外区域).针对后者进行的变换光阑孔径大小试验结果证实,适当缩小光阑孔径可有效减小数据中视场靠外区域的衍射光干扰.  相似文献   

Mid-Holocene and Last Glacial Maximum climate simulations with the IPSL model—part I: comparing IPSL_CM5A to IPSL_CM4   总被引：1，自引：0，他引：1  

Masa Kageyama  Pascale Braconnot  Laurent Bopp  Arnaud Caubel  Marie-Alice Foujols  Eric Guilyardi  Myriam Khodri  James Lloyd  Fabien Lombard  Véronique Mariotti  Olivier Marti  Tilla Roy  Marie-Noëlle Woillez 《Climate Dynamics》2013,40(9-10):2447-2468

The climates of the mid-Holocene (MH), 6,000 years ago, and of the Last Glacial Maximum (LGM), 21,000 years ago, have extensively been simulated, in particular in the framework of the Palaeoclimate Modelling Intercomparion Project. These periods are well documented by paleo-records, which can be used for evaluating model results for climates different from the present one. Here, we present new simulations of the MH and the LGM climates obtained with the IPSL_CM5A model and compare them to our previous results obtained with the IPSL_CM4 model. Compared to IPSL_CM4, IPSL_CM5A includes two new features: the interactive representation of the plant phenology and marine biogeochemistry. But one of the most important differences between these models is the latitudinal resolution and vertical domain of their atmospheric component, which have been improved in IPSL_CM5A and results in a better representation of the mid-latitude jet-streams. The Asian monsoon’s representation is also substantially improved. The global average mean annual temperature simulated for the pre-industrial (PI) period is colder in IPSL_CM5A than in IPSL_CM4 but their climate sensitivity to a CO₂ doubling is similar. Here we show that these differences in the simulated PI climate have an impact on the simulated MH and LGM climatic anomalies. The larger cooling response to LGM boundary conditions in IPSL_CM5A appears to be mainly due to differences between the PMIP3 and PMIP2 boundary conditions, as shown by a short wave radiative forcing/feedback analysis based on a simplified perturbation method. It is found that the sensitivity computed from the LGM climate is lower than that computed from 2 × CO₂ simulations, confirming previous studies based on different models. For the MH, the Asian monsoon, stronger in the IPSL_CM5A PI simulation, is also more sensitive to the insolation changes. The African monsoon is also further amplified in IPSL_CM5A due to the impact of the interactive phenology. Finally the changes in variability for both models and for MH and LGM are presented taking the example of the El-Niño Southern Oscillation (ENSO), which is very different in the PI simulations. ENSO variability is damped in both model versions at the MH, whereas inconsistent responses are found between the two versions for the LGM. Part 2 of this paper examines whether these differences between IPSL_CM4 and IPSL_CM5A can be distinguished when comparing those results to palaeo-climatic reconstructions and investigates new approaches for model-data comparisons made possible by the inclusion of new components in IPSL_CM5A.  相似文献   

ASCA and ROSAT observations of nearby cluster cooling flows     

S. W. Allen  A. C. Fabian  R. M. Johnstone  K. A. Arnaud  P. E. J. Nulsen 《Monthly notices of the Royal Astronomical Society》2001,322(3):589-613

We present a detailed analysis of the X-ray properties of the cooling flows in a sample of nearby, X-ray-bright clusters of galaxies using high-quality ASCA spectra and ROSAT X-ray images. We demonstrate the need for multiphase models to consistently explain the spectral and imaging X-ray data for the clusters. The mass deposition rates of the cooling flows, independently determined from the ASCA spectra and ROSAT images, exhibit reasonable agreement. We confirm the presence of intrinsic X-ray absorption in the clusters using a variety of spectral models. We also report detections of 100-μm infrared emission, spatially coincident with the cooling flows, in several of the systems studied. The observed infrared fluxes and flux limits are in good agreement with the predicted values owing to reprocessed X-ray emission from the cooling flows. We present precise measurements of the abundances of iron, magnesium, silicon and sulphur in the central regions of the Virgo and Centaurus clusters. Our results firmly favour models in which a high mass fraction (70–80 per cent) of the iron in the X-ray gas in these regions originates from Type Ia supernovae. Finally, we present a series of methods which may be used to estimate the ages of cooling flows from X-ray data. The results for the present sample of clusters indicate ages of between 2.5 and 7 Gyr. If the ages of cooling flows are primarily set by subcluster merger events, then our results suggest that in the largest clusters, mergers with subclusters with masses of ∼30 per cent of the final cluster mass are likely to disrupt cooling flows.  相似文献   

Using a rainfall stochastic generator to detect trends in extreme rainfall   总被引：4，自引：3，他引：1  

Philippe Cantet  Jean-No?l Bacro  Patrick Arnaud 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(3):429-441

An original approach is proposed to estimate the impacts of climate change on extreme events using an hourly rainfall stochastic generator. The considered generator relies on three parameters. These parameters are estimated by average, not by extreme, values of daily climatic characteristics. Since climate changes should result in parameters instability in time, the paper focuses on testing the presence of linear trends in the generator parameters. Maximum likelihood tests are used under a Poisson–Pareto-Peak-Over-Threshold model. A general regionalization procedure is also proposed which offers the possibility to work on both local and regional scales. From the daily information of 139 rain gauge stations between 1960 and 2003, changes in heavy precipitations in France and their impacts on quantile predictions are investigated. It appears that significant changes occur mainly between December and May for the rainfall occurrence which increased during the four last decades, except in the Mediterranean area. Using the trend estimates, one can deduced that these changes, up to now, do not affect quantile estimations.  相似文献   

Petrology and Ar-Ar dating of granulites from the Galicia Bank (Spain): African craton relics in Western Europe     

Véronique Gardien  Nicolas Arnaud  Laurent Desmurs 《Geodinamica Acta》2013,26(2-3):103-117

Abstract

Intermediate orthogranulites were collected on the western flank of the Galicia bank during the Galinaute II cruise in 1995. The petrography of these rocks reveals two types of granulites. The first type is hydrous granulites with K-feldspar + plagioclase + quartz + orthopyroxene + hornblende + garnet + biotite + opaque + zircon + apatite assemblage. Both hornblende and orthopyroxene define a weak foliation plane. A late deformation event is expressed by some fractures cross-cutting the foliation. The second is anhydrous granulites with K-feldspar + plagioclase + quartz + orthopyroxene + clinopyroxene + opaque + zircon + apatite assemblage. The rocks display a granoblastic texture and are affected by brittle deformation as testified by the development of numerous microfractures. The P-T conditions (7 ± 1 Kbar, 750 ± 50 °C) calculated from two representative samples demonstrate that the rocks equilibrated under granulite facies conditions. Ar-Ar dating gives Precambrian ages ranging between ca. 2500–2000 Ma for the amphibole from the hydrous granulite and 1600–1500 Ma for the core of the K-feldspar from the anhydrous and hydrous granulites. A younger age of 900 Ma is obtained from the recrystallized rims of the K-feldspar from the two samples. These data indicate that the granulitic rocks in the Galicia Bank had already been exhumed and cooled below ca. 140–400 °C (blocking T° for K-feldspar) in Precambrian times (900 Ma). Given the very well preserved granulitic minerals assemblage of the rocks, the granulites behaved as competent and metastable boudins during their exhumation. The granulitic samples were previously interpreted as fragments of the lower continental crust sampled by the main detachment fault during Cretaceous rifting, but they were part of an upper continental crust from the Precambrian. Geochronological data and petrological assemblages suggest that the granulite blocks in the Galicia Bank probably were derived from the North Armorican Domain (northern part of France) where a Precambrian terrain outcrops. The opening of the Bay of Biscay could be responsible for the scattering of the Precambrian terrain and may explain the presence of the granulitic blocks on both sides of the Bay of Biscay. During the subduction of Europe below the Iberian peninsula the granulite blocks were transported southward and incorporated into a Cretaceous conglomerate forming the accrecionary prism on the Northern Iberia Margin. The granulite facies blocks found on the Galicia Bank represent another example of Gondwanian relics supporting the idea that the West European plate belonged to the West African craton during the Proterozoic. © 2000 Éditions scientifiques et médicales Elsevier SAS  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987113000327   总被引：1，自引：0，他引：1  

Arnaud Pecher  Nicholas Arndt  Alexander Jean  Arthur Bauville  Clement Ganino  Charlotte Athurion 《地学前缘(英文版)》2013,4(5):571-581

The Panzhihua intrusion in southwest China is part of the Emeishan large igneous province and host of a large Fe-Ti-V ore deposit.In previous interpretations it was considered to be a layered,differentiated sill with the ore deposits at its base.New structural and petrological data suggest instead that the intrusion has an open S-shape,with two near-concordant segments joined by a discordant dyke-like segment. During emplacement of the main intrusion,multiple generations of mafic dykes invaded carbonate wall rocks,producing a large contact aureole.In the central segment,magmatic layering is oriented oblique to the walls of the intrusion.This layering cannot have formed by crystal settling or in-situ growth on the floor of the intrusion;instead we propose that it resulted from inward solidification of multiple,individually operating,convection cells.Ore formation was triggered by interaction of magma with carbonate wall rocks.  相似文献   

La méthode SHYREG débit—application sur 1605 bassins versants en France métropolitaine     

Yoann Aubert  Patrick Arnaud  Pierre Ribstein  Jean-Alain Fine 《水文科学杂志》2013,58(5):993-1005

Résumé

La méthode SHYREG est une approche développée pour la connaissance régionale de l’aléa pluvial (SHYREG pluie) et hydrologique (SHYREG débit) en tout point du territoire français. Elle est basée sur le couplage d’un générateur stochastique de pluie horaire et d’un modèle hydrologique. Cet article présente les résultats de la mise en ?uvre de la méthode sur 1605 bassins versants répartis sur la France métropolitaine. Sur les fréquences courantes (c.à.d. périodes de retour inférieures à 10 ans), la méthode restitue correctement les quantiles de débit de crue ajustés à une loi statistique sur les observations (loi GEV, selon le critère de Nash-Sutcliffe). Plusieurs critères sont utilisés pour valider l’extrapolation des débits à des fréquences extrêmes: (a) en la confrontant à de longues chroniques de débits observés, (b) en analysant dans le modèle hydrologique la saturation du réservoir de production synonyme de comportement asymptotique avec les pluies, et (c) en étudiant la stabilité de la méthode à travers les critères statistiques.