多时相TM影像决策树模型的水稻识别提取

决策树模型的多时相TM影像的小尺度水稻信息提取在我国还鲜有研究。为此,本文利用水稻生长在潮湿土壤这一特性,选取TM影像中对植物含水量和土壤湿度反应敏感的短波红外波段(1.55~1.75μm),以及反映植物覆盖率、植物长势的红光波段(0.62~0.69μm)和近红外波段(0.76~0.96μm),计算水稻移栽期、灌浆期和成熟期3个时期的归一化植被指数(NDVI)和土壤含水量指数(LSWI),提出一种时间差异的决策树水稻提取模型,以唐山市滦南县南部区域为例开展了研究。经过野外实地验证表明:该模型能有效区分出水域、玉米和菜地等较易与水稻混淆的地物,水稻提取的生产者精度和用户精度分别为95.18%和98.84%,分别比单一时相高出6.78%和7.54%。     

面向属性值分类的决策树研究

为了提高当前决策树构建的准确度,降低计算复杂度,以粒分辨关系为理论基础将属性按其值划分为若干子集(粒)作为基本判决单位,提出叶、枝划分集的逻辑式判定算法,将条件属性粒的长度作为可分配的树叶量,而其对应的决策粒作为可接受的树枝量,用叶、枝比例的强度判定该属性粒的分辨力,进而从全局分辨关系直接判定出划分属性,由顶向下进行决策树的构建。实例分析的结果表明,算法简洁且精准。     

Climate,vegetation, and soil controls on hydraulic redistribution in shallow tree roots

Hydraulic redistribution defined as the translocation of soil moisture by plant root systems in response to water potential gradients is a phenomenon widely documented in different climate, vegetation, and soil conditions. Past research has largely focused on hydraulic redistribution in deep tree roots with access to groundwater and/or winter rainfall, while the case of relatively shallow (i.e., ≈1–2 m deep) tree roots has remained poorly investigated. In fact, it is not clear how hydraulic redistribution in shallow root zones is affected by climate, vegetation, and soil properties. In this study, we developed a model to investigate the climate, vegetation, and soil controls on the net direction and magnitude of hydraulic redistribution in shallow tree root systems at the growing season to yearly timescale. We used the model to evaluate the effect of hydraulic redistribution on the water stress of trees and grasses. We found that hydraulic lift increases with decreasing rainfall frequency, depth of the rooting zone, root density in the deep soil and tree leaf area index; at the same time for a given rainfall frequency, hydraulic lift increases with increasing average rainstorm depth and soil hydraulic conductivity. We propose that water drainage into deeper soil layers can lead to the emergence of vertical water potential gradients sufficient to explain the occurrence of hydraulic lift in shallow tree roots without invoking the presence of a shallow water table or winter precipitation. We also found that hydraulic descent reduces the water stress of trees and hydraulic lift reduces the water stress of grass with important implications on tree–grass interactions.     

Tree root mounds and their role in transporting soil on forested landscapes

The growth and decay of tree roots can stir and transport soil. This is one process that contributes to the mass‐movement of soil on hillslope. To explore the efficiency of this process, we document the mounding of soil beside Ponderosa and Lodgepole pine trees in the forests that dominate the mid‐elevations of Colorado's Boulder Creek watershed. Mounds are best expressed around Ponderosa pines, reaching vertical displacements above the far‐field slopes of order 10–20 cm, fading into the slope by roughly 100 cm distance from the trunks with common diameters of 30 cm. Positive mounding occurs on all sides of trees on slopes, indicating that the mounding is not attributable to deflection of a creeping flow of soil around the tree, but rather to the insertion of root volume on all sides in the subsurface. Mounding is commonly asymmetric even on cross‐slope profiles. Significant variation in the mound sizes results in no clear relationship between tree diameter and root volume displaced. These observations motivated the development of a discrete element model of tree root growth using the LIGGGHTS model, in which grains we specified to be ‘root cells’ were allowed to enlarge within the simulated granular matrix. Mounding could be reproduced, with the majority of the vertical displacement of the surface being attributable to reduction of the bulk density due to dilation of the granular matrix during root enlargement. Finally, we develop a previous analysis of the role of roots in transporting soil during growth and decay cycles. We find that even in shallow soils, the root‐cycle can drive significant soil transport down forested montane slopes. Copyright © 2013 John Wiley & Sons, Ltd.     

对象关系数据库中的时空索引机制研究

时空数据库是近年来地理信息科学与数据库技术领域研究和应用的热点,其中时空数据模型和时空数据索引技术是时空数据库的关键。为了提高时空数据库查询处理的效率,在基于时间片的连续快照模型基础上,改进了PP-TPR树索引。该索引技术不仅可以处理普通的空间查询（点查询和范围查询）,在时间维度上还可以支持单纯时间维度的查询、历史状态查询、预期状态查询以及时空一体化的复杂查询。在实例研究中,采用对象关系数据库PostgreSQL作为时空数据类型和时空数据索引的实现平台,初步验证了上述时空索引技术的有效性和实用性。     

横向各向同性介质中地震波走时模拟

横向各向同性介质是地球内部广泛分布的一种各向异性介质.针对这种介质,我们对各向同性介质的最小走时树走时模拟方法进行了推广,推广后的方法可适用于非均匀、对称轴任意倾斜的横向各向同性介质模型.为保证计算效率,最小走时树的构建采用了一种子波传播区域随地震波传播动态变化的改进算法.对于弱各向异性介质,我们使用了一种新的地震波群速度近似表示方法,该方法基于用射线角近似表示相角的思想,对3种地震波（qP, qSV和qSH）均有较好的精度.应用本文地震波走时模拟方法对均匀介质、横向非均匀介质模型进行了计算,并将后者结果与弹性波方程有限元方法的模拟结果进行了对比,结果表明两者符合得很好.本文方法可用于横向各向同性介质的深度偏移及地震层析成像的深入研究.     

重力式幕墙加预应力锚杆及钻孔小桩组合基坑支护体系

采用重力式幕墙加预应力锚杆及钻孔小桩组合基坑支护体系 ,方法简单 ,既节省投资 ,又可保证工期 ,且止水效果相当好。     

Seismic Hazard of Honduras

In this paper we have described the proceduresused, input data applied and results achieved in ourefforts to develop seismic hazard maps of Honduras.The probabilistic methodology of Cornell is employed.Numerical calculations were carried out by making useof the computer code SEISRISK III. To examine theimpact of uncertainties in seismic and structuralcharacteristics, the logic tree formalism has beenused. We compiled a de-clustered earthquake cataloguefor the region comprising 1919 earthquakes occurringduring the period from 1963 to 1997. Unified momentmagnitudes were introduced. Definition of aseismotectonic model of the whole region under review,based on geologic, tectonic and seismic information,led to the definition of seven seismogenetic zones forwhich seismic characteristics were determined. Fourdifferent attenuation models were considered. Resultsare expressed in a series of maps of expected PGA for60% and 90% probabilities of nonexceedence in a50-year interval which corresponds to return periodsof 100 and 475 years, respectively. The highest PGAvalues of about 0.4g (90% probability ofnon-exceedence) are expected along the borders withGuatemala and El Salvador.     

Reconstruction of the Past Climate From Tree Rings Over Western Himalaya, India

RECONSTRUCTION OF THE PAST CLIMATE FROM TREE RINGS OVER WESTERN HIMALAYA, INDIA     

地震多重分形计算的最小生成树法

目前地震分形计算的方法很多,但各方法或多或少都存在一些问题．本文引入一种地震分形计算的新方法——最小生成树法（minimal spanning tree）,对其算法作了重要的修改,并通过对乌什、乌苏、唐山和海城4个区域震例的研究,得出大震前后地震时空分布多重分形谱由集中变疏张,反映了分形结构复杂性的增加、地震时空分布不均匀性的增加．由点集的数值模拟表明:强震前后多重分形谱变化的物理本质是地震分布由均一到不均一,由简单到复杂的变化过程．