排序方式： 共有19条查询结果，搜索用时 218 毫秒
1.
一种基于InSAR相干系数的SAR阴影提取方法 总被引：1，自引：0，他引：1
给出了一种新的阴影提取方法,根据阴影区域在InSAR相干系数图上的特性,利用Sigma滤波和最优阈值分割算法实现阴影的自动提取。实验结果表明,本方法是一种高效的阴影提取方法。 相似文献
2.
N. Nirupama 《Natural Hazards》2009,48(1):11-16
For the assessment of tsunami risk and vulnerability, one has to make use of past tsunami observations. The most comprehensive
tsunami databases for the world have been prepared by the National Geophysical Data Center of USA which are listed on their
website for all the four oceans as well as the following marginal seas: Caribbean Sea, Mediterranean Sea, Black Sea, Red Sea
and Gulf of Mexico. The dataset goes back as far as the first century AD and lists the events on a confidence rating scale
of 0–4; 0 being an erroneous entry and 4 being a definite tsunami. Based on these various datasets for different geographical
areas, a comprehensive global dataset was prepared in this study, which included only tsunami events with confidence rating
of 3 and 4, meaning either probable or definite. In this composite and abridged global tsunami database there is no distinction
either according to geography or tsunami strength as implied by its impact on the coast. A simple and straightforward statistical
analysis suggests an almost complete randomness and no patterns that can be used for future tsunami predictions with a few
minor exceptions. 相似文献
3.
Radar speckle reduction and derived texture measures for land cover/use classification: a case study
This study examined the appropriateness of radar speckle reduction for deriving texture measures for land cover/use classifications. Radarsat-2 C-band quad-polarised data were obtained for Washington, DC, USA. Polarisation signatures were extracted for multiple image components, classified with a maximum-likelihood decision rule and thematic accuracies determined. Initial classifications using original and despeckled scenes showed despeckled radar to have better overall thematic accuracies. However, when variance texture measures were extracted for several window sizes from the original and despeckled imagery and classified, the accuracy for the radar data was decreased when despeckled prior to texture extraction. The highest classification accuracy obtained for the extracted variance texture measure from the original radar was 72%, which was reduced to 69% when this measure was extracted from a 5 × 5 despeckled image. These results suggest that it may be better to use despeckled radar as original data and extract texture measures from the original imagery. 相似文献
4.
Sensitivity studies with a new generalized coordinate ocean model are performed in order to compare the behavior of bottom boundary layers (BBLs) when terrain-following (sigma or combined sigma and z-level) or z-level vertical grids are used, but most other numerical aspects remain unchanged. The model uses a second-order turbulence closure scheme that provides surface and BBL mixing and results in a quite realistic climatology and deep water masses after 100 year simulations with a coarse resolution (1° × 1°) basin-scale terrain-following grid. However, with the same turbulence scheme but using a z-level grid, the model was unable to produce dense water masses in the deep ocean. The latter is a known problem for coarse resolution z-level models, unless they include highly empirical BBL schemes.A set of dense water overflow experiments with high-resolution grids (10 and 2.5 km) are used to investigate the influence of model parameters such as horizontal diffusivity, vertical mixing, horizontal resolution, and vertical resolution on the simulation of bottom layers for the different coordinate systems. Increasing horizontal diffusivity causes a thinner BBL and a bottom plume that extends further downslope in a sigma grid, but causes a thicker BBL and limited downslope plume extension in a z-level grid. A major difference in the behavior of the BBL in the two grids is due to the larger vertical mixing generated by the turbulence scheme over the step-like topography in the z-level grid, compared to a smaller vertical mixing and a more stably stratified BBL in the sigma grid. Therefore, the dense plume is able to maintain its water mass better and penetrates farther downslope in the sigma grid than in the z-level grid. Increasing horizontal and vertical resolution in the z-level grid converges the results toward those obtained by a much coarser resolution sigma coordinate grid, but some differences remain due to the basic differences in the mixing process in the BBL. 相似文献
5.
Low-order pressure gradient schemes in sigma coordinate models: The seamount test revisited 总被引：1，自引：0，他引：1
This paper revisits the classic seamount test used in numerous previous studies to evidence the sigma errors of the pressure gradient force (PGF) and their long-term effects on circulation. Two kinds of analysis are developed. We first consider the initial PGF errors. Then, the global level of erroneous kinetic energy is computed along a 180-day simulation. The long-term circulation appears to be better correlated to the initial vorticity errors than to the initial error diagnostics.The original feature of this study is to reconsider the currently admitted idea that Density-Jacobian type PGFs perform better than the primitive sigma formulation discretized in a straightforward way (hereafter Straightforward-Primitive PGF). Errors on the discrete hydrostatic pressure are actually closely related to the way the density field is initialized. If a mass conserving method is preferred to a straightforward initialization, the rectangular integral of the Straightforward-Primitive PGF is likely to be more accurate than the trapezoidal rule usually involved in Density-Jacobian PGFs. Errors on the vorticity field of the Straightforward-Primitive PGF depend on the discretization of the hydrostatic correction term. A modified version of the Straightforward-Primitive PGF is shown to be in better agreement with the concept of bottom torque consistency. The seamount tests show that this so-called Modified-Primitive PGF performs globally better than the current low-order Density-Jacobian PGFs. 相似文献
6.
The vertical one-dimensional sea-ice thermodynamic problem using the principle of conservation of enthalpy is revisited here using (1) the Bitz and Lipscomb (1999) finite-difference approach (FD), (2) a reformulation of the sigma-level transformation of Huwald et al. (2005b) (FV) and (3) a Finite Element approach also in sigma coordinates (FE). These three formulations are compared in terms of physics, numerics, and performance, in order to identify the best choice for large-scale climate models. The BL99 formulation sequentially treats the diffusion of heat and the changes in the vertical position of the ice-snow layers. In contrast, the FV sigma-level transformation elegantly treats both simultaneously. The original FV formulation suffers however from slow convergence. The convergence can nonetheless be improved significantly with a few simple modifications to the original code. The three formulations are compared following the experimental protocol of the Sea Ice Model Intercomparison Project for ice thermodynamics (SIMIP2). It is found that all formulations converge to the same solution. The FD approach, however, suffers from the added cost of the remapping step at large number of ice layers (we include in the appendix an optimized version of the FD code–written by one of the reviewer–that resolves this issue). Finally the FE formulation results in a sub-surface temperature over-estimation at low resolution, a problem which disappears at high resolution. Hence, only FD and FV are found suitable for climate models. 相似文献
7.
目的：运用精益六西格玛方法研究64排CT检查流程,减少患者无效等待时间,提高单台64排CT检查患者的流通量。方法：运用和实施精益六西格玛管理体系5步法,按登记时间、检查前时间、检查时间、打印时间、收片时间、报告时间、取片时间,随机抽取160名患者分析其各阶段时间,找出致患者侯检时间延长的关键因素;对传统检查流程中导致等... 相似文献
8.
太平洋深海沉积物中富集稀土元素(REY,包括钇),被认为是富有潜力的新型稀土资源。(含)沸石粘土、深海粘土和多金属软泥是主要的富含REY的沉积物类型,其中(含)沸石粘土和深海粘土在中、西北太平洋海盆大面积分布,而多金属软泥则多分布于靠近东太平洋洋脊热液活动的深海盆地中。目前关于中、西北太平洋海盆的深海粘土和(含)沸石粘土已有较多的研究,但关于多金属软泥中REY的研究较少。不同区域、不同类型深海沉积物中的稀土元素赋存状态有何差异?影响稀土富集的机制又是什么目前尚不清楚,也就进一步影响了对深海沉积物稀土资源的勘查和开发工作。本文分析对比了太平洋不同区域不同类型深海沉积物的地球化学特征及矿物学特征。结果表明,总体上,中、西北太平洋海盆深海沉积物中,尤其是(含)沸石粘土中的REY含量明显高于东太平洋海盆多金属软泥REY含量,其REY的富集主要与磷酸盐有关。超常富集REY(∑REY>2000×10^(-6))的沉积物中的CaO/P_(2)O_(5)比值趋向于一致(~1.4),几乎接近于磷灰石CaO/P2O5比值(~1.3),因此REY主要赋存载体为磷灰石,该区沉积物中REY的富集可能受到磷酸盐化的影响;东太平洋海盆多金属软泥明显受到热液影响,铁和锰的含量明显增加,但其∑REY含量集中于500×10^(-6)~800×10^(-6),不随铁和锰的增加而变化,REY的富集仍与磷酸盐关系密切,而与铁锰物质和铝硅酸盐关系不大。中、西北太平洋海盆富稀土的深海沉积物形成时处于较强的氧化环境,同时又有充足的含磷物质补给,才造成REY在该区沉积物中的超常富集;而东太平洋海盆多金属软泥虽然处于氧化环境,但缺少足够的磷补给,所以其∑REY含量通常低于中、西北太平洋海盆沸石粘土中∑REY含量。 相似文献
9.
Ditching often takes place for a ground-effect wing (WIG) ship. During the ditching, the extreme load developed by water impacts may cause damages to structures, posing a great threat to the safety of crew and passengers. In the paper, a weakly compressible smoothed particle hydrodynamics (SPH) model combined with enhanced numerical techniques has been adopted to tackle the ditching problems. In order to handle the motion of a rigid body in the three-dimensional ditching problems, the six degrees-of-freedom (6-DOF) equations of motion are incorporated into the SPH scheme. The accuracy of the SPH model is validated through two benchmarks, respectively, the two-dimensional wedge water entry and the three-dimensional stone-skipping. The former is aimed to validate the prediction of pressures during the free surface impact while the latter is a good case for testing the coupling motions of the rigid body. Furthermore, the ditching of the real scale WIG ship under different conditions is simulated with the established SPH model, through which some useful conclusions are drawn. 相似文献
10.
24位高分辨率本安型瑞利波探测仪的研究 总被引：1，自引：1，他引：0
利用Σ-Δ24位ADC、嵌入式PC/104工控机和CPLD技术,开发了一种具有实时数字化采集系统的24位高分辨率本安型瑞利波探测仪,本文介绍了MRD-Ⅲ型瑞利波探测仪的用途、特点、系统组成、软硬件设计方法和应用效果等。 相似文献