Possible meteoroid streams associated with (69230) Hermes and 2002 SY50     

T. J. Jopek  G. B. Valsecchi  Cl. Froeschlé 《Earth, Moon, and Planets》2004,95(1-4):5-10

The orbits of (69230) Hermes and 2002 SY₅₀ are similar and the Earth approaches both of them twice: at the end of October the local orbital minimum distances are smaller than 0.007 AU, and at the end of April the distances are smaller than 0.04 AU. This gives us opportunities to observe the meteors associated with these asteroids. Using the geocentric parameters of the orbital close encounters (the theoretical radiants) and our D _N distance function (Valsecchi et al. Mon. Not. R. Astron. Soc. 304 (1999) 743), we searched for meteoroids originated by Hermes and 2002 SY₅₀. A search among 1830 good quality photographic meteors gave negative results: we found no meteor dynamically similar to Hermes or 2002 SY₅₀. In a second search, done in a set of 62150 radio meteors, we applied two methods (M1, M2) and in both cases we found two streams; the streams found with the M1 method had 43 and 30 members, those found with the M2 method had 39 and 14 members. However, these results do not look convincing, due to the small number of common members in the corresponding streams. We therefore conclude that amongst the IAU meteors used in our search there are no compact streams associated with Hermes and 2002 SY₅₀.  相似文献   

Meteor stream identification: a new approach – III. The limitations of statistics     

T. J. Jopek  G. B. Valsecchi  Cl. Froeschlé 《Monthly notices of the Royal Astronomical Society》2003,344(2):665-672

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Réponse aux commentaires d'Azambre et al. et de Rapaille et al.: [C. R. Geoscience 334 (2002) 197]     

Christian Desreumaux  Bernard Clément  Richard Fabre  Bruno Martins-Campina 《Comptes Rendus Geoscience》2004,336(2):173-174

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Intra-interstadial environmental changes in Last Glacial loess revealed by molluscan assemblages from the Upper Palaeolithic site of Amiens-Renancourt 1 (Somme,France)     

Olivier Moine  Pierre Antoine  Sylvie Coutard  Gilles Guérin  Christine Hatté  Clément Paris  Ségolène Saulnier-Copard 《第四纪科学杂志》2021,36(8):1322-1340

The Amiens-Renancourt 1 site recently yielded one of the most important Upper Palaeolithic human occupations of northern France by the number of flint artefacts and especially by the presence of Venus figurines. All the material comes from a single archaeological layer located in a tundra gley bracketed by loess units. A multi-proxy study combining a detailed stratigraphy, luminescence and radiocarbon datings and high-resolution (5 cm per sample) grain size and molluscan analyses was therefore carried out to reconstruct and date the associated environmental changes and to determine the exact context of the human occupation. The chronological frame thus established supports the correlations of the archaeology-bearing tundra gley and of an underlying arctic brown soil with Greenland interstadials GI-4 and GI-3. Composition changes in the molluscan population enabled the identification of transitional and optimum phases and sub-phases within these two pedogenetic horizons. A conceptual correlation model linking molluscan phases with millennial-scale variations of Greenland ice-core and Sieben Hengste speleothem climate records is proposed. The Human occupation appears contemporaneous to the end of the stadial–interstadial transition of GI-3. Synchronous in Amiens-Renancourt 1 and Nussloch, subsequent micro-gleys may also result from a regional/global forcing. Such a level of detail is unprecedented in a loess sequence.  相似文献   

Studying Resource-Dependent Communities Through a Social-Ecological Lens? Examining Complementarity with Existing Research Traditions in Canada     

Sara Teitelbaum  Annie Montpetit  Jean-François Bissonnette  Clément Chion  Guy Chiasson  Frédérik Doyon 《社会与自然资源》2019,32(1):93-112

This article explores the suitability of Ostrom and colleagues' social-ecological systems framework (SESF) for the study of resource-dependent communities in Canada. Through a broad literature about resource-dependent communities in Canada, three main approaches are identified, named staples research, rural development, and sustainability studies. Each of these research traditions is analyzed with regards to a common set of criteria – focus, scale, methods, treatment of institutions, and treatment of environmental dimensions. Research in each category is compared and contrasted with the SESF approach, to identify areas of overlap and divergence. Results indicate that the SESF is unlikely to provide additional benefit in terms of in-depth of social analysis, however, it does provide a unique contribution in terms of its coupled approach to conceiving social and ecological systems and its ability to operationalize these relationships through structured variables.  相似文献   

3D segmentation of single trees exploiting full waveform LIDAR data     

J. Reitberger  Cl. Schnörr  P. Krzystek  U. Stilla 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(6):561-574

This paper highlights a novel segmentation approach for single trees from LIDAR data and compares the results acquired both from first/last pulse and full waveform data. In a first step, a conventional watershed-based segmentation procedure is set up, which robustly interpolates the canopy height model from the LIDAR data and identifies possible stem positions of the tallest trees in the segments calculated from the local maxima of the canopy height model. Secondly, this segmentation approach is combined with a special stem detection method. Stem positions in the segments of the watershed segmentation are detected by hierarchically clustering points below the crown base height and reconstructing the stems with a robust RANSAC-based estimation of the stem points. Finally, a new three-dimensional (3D) segmentation of single trees is implemented using normalized cut segmentation. This tackles the problem of segmenting small trees below the canopy height model. The key idea is to subdivide the tree area in a voxel space and to set up a bipartite graph which is formed by the voxels and similarity measures between the voxels. Normalized cut segmentation divides the graph hierarchically into segments which have a minimum similarity with each other and whose members (= voxels) have a maximum similarity. The solution is found by solving a corresponding generalized eigenvalue problem and an appropriate binarization of the solution vector. Experiments were conducted in the Bavarian Forest National Park with conventional first/last pulse data and full waveform LIDAR data. The first/last pulse data were collected in a flight with the Falcon II system from TopoSys in a leaf-on situation at a point density of 10 points/m². Full waveform data were captured with the Riegl LMS-Q560 scanner at a point density of 25 points/m² (leaf-off and leaf-on) and at a point density of 10 points/m² (leaf-on). The study results prove that the new 3D segmentation approach is capable of detecting small trees in the lower forest layer. So far, this has been practically impossible if tree segmentation techniques based on the canopy height model were applied to LIDAR data. Compared to a standard watershed segmentation procedure, the combination of the stem detection method and normalized cut segmentation leads to the best segmentation results and is superior in the best case by 12%. Moreover, the experiments show clearly that using full waveform data is superior to using first/last pulse data.  相似文献   

Full-waveform topographic lidar: State-of-the-art     

Clément Mallet  Frédéric Bretar 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(1):1-16

Airborne laser scanning (ALS) is an active remote sensing technique providing range data as 3D point clouds. This paper aims at presenting a survey of the literature related to such techniques, with emphasis on the new sensors called full-waveform lidar systems. Indeed, an emitted laser pulse interacts with complex natural and man-made objects leading to a temporal distortion of the returned energy profile. The new technology of full-waveform laser scanning systems permits one to digitize the complete waveform of each backscattered pulse. Full-waveform lidar data give more control to an end user in the interpretation process of the physical measurement and provide additional information about the structure and the physical backscattering characteristics of the illuminated surfaces. In this paper, the theoretical principles of full-waveform airborne laser scanning are first described. Afterwards, a review of the main sensors as well as signal processing techniques are presented. We then discuss the interpretation of full-waveform measures with special interest on vegetated and urban areas.  相似文献   

Contamination des sédiments superficiels des principales rivières du Canton de Genève par les Polychlorobiphényles et DDT     

Dr. Par Cl. Corvi  Dr. J. Vogel 《Aquatic Sciences - Research Across Boundaries》1985,47(1):12-20

The concentrations of PCBs and DDT at the surface of sediments of rivers in the Canton of Geneva were examined. Concentration variations observed along the rivers are discussed. In the case of the Rhône River, recent pollution at the surface of sediments is compared with that of aged underlying layers.  相似文献   

Impact des événements tectono-volcaniques plio-pléistocènes sur la sédimentation en République de Djibouti (Afar Central)     

M. Boucarut  M. Clin  P. Pouchan  Cl. Thibault 《International Journal of Earth Sciences》1985,74(1):123-137

The volcanic and sedimentary successive paleogeographic reconstructions, as well the volcanic emissions as the fluvial, lacustrine and marine deposits, are compared to the tectonic mechanisms, and show that the geologic history is controlled:

1. During Pliocene and lower Pleistocene times, by a collapse tectonics in the Red Sea - Aden Gulf area with a correlative uplift of the Tadjoura - Ali Sabîh hörst (a southern prolongation of the Danakil horst), and by a tectonic shear according to a NE-SW trend, which gives rise to NW-SE trending uplifts and basins (Nazaret phase of the Ethiopian rift).
2. From the middle Pleistocene time, by the progressive opening, according to an EW direction, of the Gulf of Tadjoura, as a western prolongation of the Aden rift. A correlative epiglyptic arching, according to an EW direction, is located westwards. It appears as a superimposed structure with respect to the previous building.

The successive coastal uplifts since the lower Pleistocene are correlated to the successive alluvial deposits, which fit one-another, until the Holocene time included.  相似文献   

The Southern part of the Armorican orogeny: A result of crustal shortening related to reactivation of a pre-Hercynian mafic belt during Carboniferous time     

J.P. Lefort  Cl. Audren  M.D. Max 《Tectonophysics》1982,89(4):359-377

This synthesis of detailed geological and geophysical information relates deep crustal structure to deformation and the emplacement of granites in the South Armorican Massif and the adjacent continental shelf. Near the continental margin a zone of geophysical anomalies is regarded as a nearly complete line of suture between a southern continent and America. A major mafic body in the trace of the supposed suture in interpreted as a relic of probable oceanic crust which has apparently acted as a deflector of regional strain.It is proposed that late in the Hercynian collision history, during late Carboniferous time, compressional strain acted across the mafic body and can be directly related to generation of younger regional structures in the metasediments and to localization of granite emplacement.  相似文献