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121.
P. Matgen A. El Idrissi J.‐B. Henry N. Tholey L. Hoffmann P. de Fraipont L. Pfister 《水文研究》2006,20(8):1805-1825
Principal components analysis (PCA) is applied to a time series of European Remote Sensing (ERS) synthetic aperture radar (SAR) scenes of the Alzette River floodplain (Grand‐Duchy of Luxembourg). These images cover markedly different hydrological conditions during several winter seasons in order to enable the examination of the decrease of the radar backscattering signal during drying‐up phases following important flood events. At the floodplain scale, with homogeneous land use and constant topography, the first principal components (PCs) are mainly dominated by the variance related to the changing areas. The PCs are thus mainly controlled by subsurface and surface water dynamics. The field observations of a densely equipped piezometric network in the floodplain are used to calculate a mean soil saturation index (SSI) continuously. A classification scheme, based on the PCs and k‐means algorithm, leads to the segmentation of the floodplain into several hydrological behaviour classes with distinctive responses versus changing moisture conditions. To validate this classification method with ground‐based estimations, the relation between the mean backscattering values of microplots within each PCA‐derived hydrological class and the water table measurements, expressed by means of the SSI, is evaluated. Results show that each class of microplots is characterized by the slope of the ‘backscattering–SSI’ function and by the SSI threshold value at which groundwater resurgence appears. The water ponding implies very low signal return due to the specular backscattering effect on the water surface. Based on established relationships between measured initial water table depths, runoff coefficients and rainfall‐induced water table rises, these results are used to discuss the potential of SAR‐derived information in flood management applications. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
122.
I. Couchoud D. Genty D. Hoffmann R. Drysdale D. Blamart 《Quaternary Science Reviews》2009,28(27-28):3263-3274
A stalagmite (BDinf) recovered from an archaeological cave (Bourgeois–Delaunay, La Chaise de Vouthon) in SW France provides a rare, high-resolution, precisely dated continental palaeoclimate record covering the warmest part of the Last Interglacial (128 ± 1–121 ± 1 ka). The growth interval spans the pluvial period recorded in Soreq and Peqiin Cave speleothems (during sapropel event S5), suggesting that the eastern Mediterranean and western Europe experienced relatively wet conditions simultaneously during this part of the Last Interglacial. Stable oxygen and carbon isotope ratios from BDinf show prominent millennial-scale variations, which are interpreted respectively in terms of changes in the amount of rainfall reaching the cave and soil biological activity. The timing of the oxygen isotope changes agrees with similar excursions recorded in speleothems from Corchia Cave (Italy), where close coupling between rainfall amount and regional sea surface temperatures has been demonstrated. Three “warmer–wetter” periods are interspersed with four “cooler–drier” periods. The first “warmer–wetter” period is the most prominent, as is the case at Corchia, and coincides with the SST optimum off western Europe. This is followed by a prominent “cooler–drier” excursion (centred on ~126 ka), which can be linked to a period of increased loess deposition recorded in annually laminated lake sediments from Eifel, Germany. Although there is already ample evidence for Last Interglacial climate instability, we show for the first time that specific climatic events occurred more or less synchronously between southwestern Europe, central Mediterranean (Italy) and northern Europe (Germany). 相似文献
123.
HEAO-B (Einstein) satellite measurements with the Imaging Proportional Counter revealed the W UMa binary system TZ Bootis as an X-ray source. It is estimated that the luminosity ratioL
x/Lvof this system is about 10–3.8 indicating that TZ Bootis is in the transition region between A- and W-type W UMa systems. 相似文献
124.
M. Hoffmann 《Astrophysics and Space Science》1982,83(1-2):203-207
Photoelectric light curves of V1022 Oph inB andV are presented. It has been confirmed that it is a W UMa type eclipsing binary with one of the shortest periods known (P<0.d25). Some general properties of the system have been derived.Based on observations made at the European Southern Observatory (La Silla/Chile) 相似文献
125.
126.
Why do people not learn from flood disasters? Evidence from Vietnam’s northwestern mountains 总被引:4,自引:2,他引:2
Iven Schad Petra Schmitter Camille Saint-Macary Andreas Neef Marc Lamers La Nguyen Thomas Hilger Volker Hoffmann 《Natural Hazards》2012,62(2):221-241
This article explores how the causes and impacts of a flood event as perceived by local people shape immediate responses and future mitigation efforts in mountainous northwest Vietnam. Local flood perception is contrasted with scientific perspectives to determine whether a singular flood event will trigger adjustments in mitigation strategies in an otherwise rarely flood-affected area. We present findings from interdisciplinary research drawing on both socioeconomic and biophysical data. Evidence suggests that individual farmers?? willingness to engage in flood mitigation is curbed by the common perception that flooding is caused by the interplay of a bundle of external factors, with climatic factors and water management failures being the most prominent ones. Most farmers did not link the severity of flooding to existing land use systems, thus underlining the lack of a sense of personal responsibility among farmers for flood mitigation measures. We conclude that local governments cannot depend on there being a sufficient degree of intrinsic motivation among farmers to make them implement soil conservation techniques to mitigate future flooding. Policy makers will need to design measures to raise farmers?? awareness of the complex interplay between land use and hydrology and to enhance collective action in soil conservation by providing appropriate incentives and implementing coherent long-term strategies. 相似文献
127.
Abstract— Yamato 000593, a nakhlite, was analyzed in terms of its magnetic record and magnetomineralogy. The natural remanent magnetization (NRM: 3.55–6.07 times 10?5 Am2/kg) was thermally demagnetized at ~320 °C, and it was unstable against alternating field demagnetization. Based on analyses of thermomagnetic curves, the temperature dependence of hysteresis parameters, and microscopic observations, the magnetic minerals mainly consist of magnetite (0.68 wt% of the sample, including ~5% Fe2TiO4) of less than 100 μm in size, associated with minor amounts of monoclinic pyrrhotite (<0.069 wt% of the sample) and goethite. Thermal demagnetization of NRM at ~330 °C is explained due to an offset of magnetization of antipodal NRM components of magnetite, whereas it is not due to a pyrrhotite Curie point. Large magnetite grains show exsolution texture with ilmenite laths, and are cut by silicate (including goethite) veins that formed along cracks. Numerous single‐domain (SD) and pseudo‐single‐domain (PSD) magnetite grains are scattered in the mesostasis and adjacent olivine grains. Moderate coercive forces of HC = 6.8 mT and HRC = 31.1 mT suggest that Yamato 000593 is fundamentally able to carry a stable NRM; however, NRM was found to be unstable. Accordingly, the meteorite was possibly crystallized at 1.3 Ga under an extremely weak or absent magnetic field, or was demagnetized by impact shock at 12 Ma (ejection age) on Mars. This finding differs from the results of previous paleomagnetic studies of SNC (shergottites, nakhlites, chassignites, and orthopyroxenite) Martian meteorites. The significant dipole magnetic field resulting from the molten metallic core was probably absent during the Amazonian Epoch (after 1.8 Ga) on Mars. 相似文献
128.
K. Ichimoto B. Lites D. Elmore Y. Suematsu S. Tsuneta Y. Katsukawa T. Shimizu R. Shine T. Tarbell A. Title J. Kiyohara K. Shinoda G. Card A. Lecinski K. Streander M. Nakagiri M. Miyashita M. Noguchi C. Hoffmann T. Cruz 《Solar physics》2008,249(2):233-261
The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial
resolution of 0.2 – 0.3 arcsec. A photometric accuracy of 10−3 is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is
required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by
the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end
calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter
of the SOT and its final polarization characteristics. 相似文献
129.
S. Tsuneta K. Ichimoto Y. Katsukawa S. Nagata M. Otsubo T. Shimizu Y. Suematsu M. Nakagiri M. Noguchi T. Tarbell A. Title R. Shine W. Rosenberg C. Hoffmann B. Jurcevich G. Kushner M. Levay B. Lites D. Elmore T. Matsushita N. Kawaguchi H. Saito I. Mikami L. D. Hill J. K. Owens 《Solar physics》2008,249(2):167-196
The Solar Optical Telescope (SOT) aboard the Hinode satellite (formerly called Solar-B) consists of the Optical Telescope Assembly (OTA) and the Focal Plane Package (FPP). The OTA is a 50-cm diffraction-limited
Gregorian telescope, and the FPP includes the narrowband filtergraph (NFI) and the broadband filtergraph (BFI), plus the Stokes
Spectro-Polarimeter (SP). The SOT provides unprecedented high-resolution photometric and vector magnetic images of the photosphere
and chromosphere with a very stable point spread function and is equipped with an image-stabilization system with performance
better than 0.01 arcsec rms. Together with the other two instruments on Hinode (the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS)), the SOT is poised to address many fundamental questions
about solar magnetohydrodynamics. This paper provides an overview; the details of the instrument are presented in a series
of companion papers.
M. Otsubo is a former NAOJ staff scientist. 相似文献
130.
T. Shimizu S. Nagata S. Tsuneta T. Tarbell C. Edwards R. Shine C. Hoffmann E. Thomas S. Sour R. Rehse O. Ito Y. Kashiwagi M. Tabata K. Kodeki M. Nagase K. Matsuzaki K. Kobayashi K. Ichimoto Y. Suematsu 《Solar physics》2008,249(2):221-232
The Hinode Solar Optical Telescope (SOT) is the first space-borne visible-light telescope that enables us to observe magnetic-field
dynamics in the solar lower atmosphere with 0.2 – 0.3 arcsec spatial resolution under extremely stable (seeing-free) conditions.
To achieve precise measurements of the polarization with diffraction-limited images, stable pointing of the telescope (<0.09 arcsec,
3σ) is required for solar images exposed on the focal plane CCD detectors. SOT has an image stabilization system that uses image
displacements calculated from correlation tracking of solar granules to control a piezo-driven tip-tilt mirror. The system
minimizes the motions of images for frequencies lower than 14 Hz while the satellite and telescope structural design damps
microvibration in higher frequency ranges. It has been confirmed from the data taken on orbit that the remaining jitter is
less than 0.03 arcsec (3σ) on the Sun. This excellent performance makes a major contribution to successful precise polarimetric measurements with 0.2 – 0.3 arcsec
resolution.
K. Kobayashi now at NASA/Marshall Space Flight Center, Huntsville, AL 35812, USA. 相似文献