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991.
T. J. Lee 《Astrophysics and Space Science》1989,160(1-2):249-253
There are a number of parallels between the UKIRT and the JNLT both of which are major astronomical facilities of nations which do not have premier observing sites in their own country. Some elements of experience with UKIRT relevant to the JNLT are described. These include matters related to personnel and to instruments.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
992.
Groundwater flows and travel times were analyzed under a landfill site characterized by a thick unsaturated zone, in an arid environment, using two-dimensional models. Transport in the unsaturated zone is important in arid environments with thick vadose zones and usually determines the travel time of groundwater from the landfill site to the regulatory compliance surface. The combined use of a parallel flow (Dupuit-Forchheimer) areal model and vertical cross-sectional model is explored at a site typical in the utility industry. Flow paths and travel times to the compliance zone are obtained for use in landfill site design or environmental impact assessments. Sensitivity analysis shows that boundary conditions are important factors influencing the entire analysis and thus need to be confirmed with field measurements. 相似文献
993.
A fracture mechanics model is developed for the initiation and propagation of a crack through a porous ice layer of finite thickness under gravitational overburden. It is found that surface cracks generated in response to a tidally induced stress field may penetrate through the entire outer brittle layer if a subsurface ocean is present on Europa. Such penetration is found to be very unlikely in the absence of an ocean. A cycloidal crack would then form as a sequence of near instantaneous discrete failures, each extending roughly the brittle layer thickness in range, linked with a much lower apparent propagation speed set by the moving tidal stress field. The implications of this porous ice fracture model for ice-penetrating radar scattering loss and seismic activity are quantified. 相似文献
994.
H. Bruntt D. Stello J. C. Suárez T. Arentoft T. R. Bedding M. Y. Bouzid Z. Csubry T. H. Dall Z. E. Dind S. Frandsen R. L. Gilliland A. P. Jacob H. R. Jensen Y. B. Kang S.-L. Kim L. L. Kiss H. Kjeldsen J.-R. Koo J.-A. Lee C.-U. Lee J. Nuspl C. Sterken R. Szabó 《Monthly notices of the Royal Astronomical Society》2007,378(4):1371-1384
995.
Improving debris flow monitoring in Taiwan by using high-resolution rainfall products from QPESUMS 总被引:2,自引:2,他引:2
Chien-Yuan Chen Lee-Yao Lin Fan-Chieh Yu Ching-Sheng Lee Chun-Chieh Tseng An-Hsiang Wang Kei-Wai Cheung 《Natural Hazards》2007,40(2):447-461
Debris flow is commonly initiated by torrential rain and its triggering is correlated to the hydrological, geological, and
geomorphic conditions on site. In spite of the important effects of geology and topography, rainfall characteristic is the
main external triggering factor to debris flow and is a predominant parameter for real-time monitoring. Due to the scarcity
of sufficient spatial ground-based rainfall data in hill areas, quantitative precipitation estimation using remote-sensing
techniques such as radar and satellite is needed for debris flow pre-warning. The QPESUMS (Quantitative Precipitation Estimation
and Segregation Using Multiple Sensors) system was acquired to retrieve spatial rainfall data during the rainfall period from
June 30 to July 6 in 2004 when Typhoon Mindulle and southwesterly flow struck Taiwan. The retrieved data were used for setting
up the debris flow monitoring algorithm. With the aid of multiple platforms of meteorological observations, a rainfall threshold
isohyet in a pilot area was mapped for debris flow monitoring. The rainfall monitoring algorithm based on QPESUMS provides
more detailed information than the limited number of ground-based rainfall stations for interpreting the spatial distributions
of rainfall events, and therefore is more suitable for debris-flow monitoring. 相似文献
996.
The likelihood ratio, logistic regression, and artificial neural networks models are applied and verified for analysis of
landslide susceptibility in Youngin, Korea, using the geographic information system. From a spatial database containing such
data as landslide location, topography, soil, forest, geology, and land use, the 14 landslide-related factors were calculated
or extracted. Using these factors, landslide susceptibility indexes were calculated by likelihood ratio, logistic regression,
and artificial neural network models. Before the calculation, the study area was divided into two sides (west and east) of
equal area, for verification of the models. Thus, the west side was used to assess the landslide susceptibility, and the east
side was used to verify the derived susceptibility. The results of the landslide susceptibility analysis were verified using
success and prediction rates. The verification results showed satisfactory agreement between the susceptibility map and the
existing data on landslide locations. 相似文献
997.
998.
Dependence of Waterline Mapping on Radar Frequency Used for SAR Images in Intertidal Areas 总被引:1,自引:0,他引:1
Kim D.-J. Moon W. M. Park S.-E. Kim J.-E. Lee H.-S. 《Geoscience and Remote Sensing Letters, IEEE》2007,4(2):269-273
Waterline detection in the intertidal areas was investigated through synthetic aperture radar (SAR) images and field measurements. Two valuable facts were found in this letter: 1) A discrepancy of waterlines between L- and P-band airborne SAR images was discovered and investigated through precise global positioning system measurements and the theory of the SAR imaging mechanism. In the intertidal areas having low slopes, the Bragg waves resonant with the radar signal can reside in different depths depending on the radar frequency, with the result that the boundary between water and land can be mapped differently in the respective SAR images. 2) Intertidal areas covered with a water film present low radar backscatter in SAR images, which can cause mislocation of waterlines 相似文献
999.
平面P波在饱和半空间中洞室周围的散射(I):解析解 总被引:1,自引:0,他引:1
利用波函数展开法给出了入射平面P波在饱和半空间中圆形洞室周围散射问题的一个解析解。半空间假定为无粘性流体饱和介质,满足Biot理论。采用一种基于实验数据的孔隙率和模量之间的线性关系来确定Biot模型中的介质参数。解答考虑了透水边界和非透水边界两种情况。对边界条件进行了数值检验,结果表明,随着级数截断项数的增大,边界残量衰减很快。解答为进一步研究入射波频率和角度、边界渗透条件、孔隙率、泊松比等参数对散射的影响奠定了基础。 相似文献
1000.
3D magnetotelluric modelling including surface topography 总被引:9,自引:0,他引:9
Myung Jin Nam Hee Joon Kim Yoonho Song Tae Jong Lee Jeong-Sul Son Jung Hee Suh 《Geophysical Prospecting》2007,55(2):277-287
An edge finite‐element method has been applied to compute magnetotelluric (MT) responses to three‐dimensional (3D) earth topography. The finite‐element algorithm uses a single edge shape function at each edge of hexahedral elements, guaranteeing the continuity of the tangential electric field while conserving the continuity of magnetic flux at boundaries. We solve the resulting system of equations using the biconjugate gradient method with a Jacobian preconditioner. The solution gives electric fields parallel to the slope of a surface relief that is often encountered in MT surveys. The algorithm is successfully verified by comparison with other numerical solutions for a 3D‐2 model for comparison of modelling methods for EM induction and a ridge model. We use a 3D trapezoidal‐hill model to investigate 3D topographic effects, which are caused mainly by galvanic effects, not only in the Zxy mode but also in the Zyx mode. If a 3D topography were approximated by a two‐dimensional topography therefore errors occurring in the transverse electric mode would be more serious than those in the transverse magnetic mode. 相似文献