NDVI 时间序列数据集重建方法述评

基于NOAA/AVHRR、SPOT/VEGETATION 以及MODIS 等卫星影像得到的归一化植被指数(NDVI,Normalized Difference Vegetation Index) 时序资料已经在植被动态变化监测、宏观植被覆盖分类和植物生物物理参数反演方面得到了广泛的应用, 但由于受云层、天气等因素的影响,NDVI 数据集存在大量的噪声, 因此对NDVI 时间序列数据集进行重建, 提高NDVI 数据集质量的研究逐步受到关注。对近年来普遍使用的几种NDVI 时间序列数据集重建方法(最大值合成、最佳指数斜率提取、中值迭代滤波、时间窗内的线性内插、傅里叶变换、S2G 滤波) 进行了详细介绍并评述了这些方法的优缺点。     

国道214 线西藏境滑塌灾害遥感调查研究

国道214 线西藏境位于西藏东南部, 连接青海省和云南省, 是西藏东南部地区重要的交通干线, 该公路对于改善西藏投资环境, 发展藏东经济, 实施西部大开发战略, 巩固国防, 加强民族团结都具有极其重要的意义。该路段地形地貌复杂, 构造发育, 地质灾害频发, 严重影响公路的畅通。利用ETM 遥感影像, 结合已有研究资料和野外调查等手段, 对国道214 线西藏境的崩塌和滑坡进行研究, 并对这些地质灾害的发育状况和危害特征进行了评价。     

.NET环境下基于MapObjects-组件的WebGIS应用研究

为了在Web环境中重用现有的基于MapObjects组件的代码资源，以IIS托管MapObjects应用的形式，提出了一种新的WebGIS解决方案：在.NET环境下基于MapObjects2.2 采用C＃语言进行开发，由IIS托管的服务器端嵌入MapObjects组件以提供GIS功能服务，交互页面部分采用ASP.NET实现，页面元素与代码分离，结构清晰，安全性高；客户端无需下载、安装插件，借助通用浏览器即可访问WebGIS服务，提高了其可用性。并以此方案作为系统框架，基于该机制实现了网络版兰州城市交通电子地图，验证了该方案的可行性。
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NONLINEAR ANALYSIS FOR FROST-HEAVING FORCE OF LAND BRIDGES ON QING-TIBET RAILWAY IN COLD REGIONS

ABSTRACT

A mathematical mechanical model and the governing differential equations of the coupled problem of temperature, moisture migrating, and stress fields with phase change, are first derived from the theory of heat transfer, the theory of moisture migration, and frozen soil mechanics. Then the finite element formulas of this problem are obtained by using Galerkin's method. Using the finite element formulas, a nonlinear analysis for the frost-heaving process of the land bridge in the next 20 years is made. The calculated results show that only soil at the bottom of the pile generates plastic deformation, and the deformation is quite small; therefore, the studied land bridge is safe.     

Numerical study on the effect of frost heave prevention with different canal lining structures in seasonally frozen ground regions

Frost heave damage problems in canal linings are a common phenomenon in seasonally frozen ground regions. These problems are regarded as interactions between heat transport and moisture flow processes. To research the influence of frost heave prevention in two types of canal structures in the Ningxia irrigation district of China, a two-dimensional coupled heat transport and moisture flow model was used to analyze temperature characteristics in the traditional canal lining structure and a new type of canal lining structure for frost heave prevention. The simulated results from this numerical model are in agreement with in situ temperature measurements for both canal lining structures. The in situ measurement results show that the new canal lining structure exhibits low seepage, low thermal conductivity, quick drainage speed and less uneven deformation. Therefore, this new canal lining structure is a good choice for frost heave prevention in seasonally frozen ground regions.     

昆仑山垭口多年冻土区钻孔气体组分分析

昆仑山垭口多年冻土区2个钻孔的气体组分和同位素数据显示,钻孔气体中烃类气体以CH4为主,含微量的C2H6、C3H8和C4H10。钻孔-1泥浆气体的C1/（C2＋C3）值介于163～1 642之间;钻孔-2岩心和泥浆气体主要为CH4气体组分,未检出C2H6等气体组分,同时δ13CCH4〈-60‰,属于微生物成因气。2个钻孔的CO2含量低于15%,而且δ13 CCO2值介于-26.8‰～-20‰之间,小于-10‰,说明其为有机成因气。     

高温冻结粉土的累积应变和临界动应力

 在－0.95 ℃恒温状态下对青藏人工冻结粉土试样进行不同动应力幅值下的振动单轴压缩试验,获得2种频率下不同动应力幅值时冻土试样累积应变和振动次数之间的关系曲线,发现冻土的累积应变随着振动次数的增加呈增长的趋势,且表现出稳定型、破坏型和临界型3种形态;在振动次数相同时,动应力幅值越大,累积应变越大;加载初始阶段应变速率随时间的增大而减小,且应变速率对数与时间对数间均有较好的线性关系,但随着振动时间的增加,破坏型曲线的应变速率达到一个最小值后开始增大,稳定型曲线的应变速率则在一定幅度的范围内波动;振动频率越高、动应力幅值越大,应变速率越大;振动频率越高,临界动应力越小。     

In-situ test study on the cooling effect of two-phase closed thermosyphon in marshy permafrost regions along the Chaidaer-Muli Railway, Qinghai Province, China

More than half of the recently built 142-km long Chaidaer-Muli Railway (CMR) in northern Qinghai Province, China travels across warm (≥−1 °C), ice-rich permafrost in wetlands on the southern flank of the Qilian Mountains. In comparison with the Qinghai-Tibet Railway from Golmud to Lhasa, the CMR traverses mostly across wetlands underlain by more ice-rich permafrost. Warm and ice-rich permafrost is sensitive to human activities and environmental changes, which can result in changes in the active layer thickness and permafrost temperatures, inducing instability and failure of infrastructures in permafrost regions. Thermosyphons were adopted in a quarter of the whole CMR route. For studying the cooling effect of the thermosyphon technique, two monitoring sites with different mean annual ground temperatures were installed since 2007. According to analysis of the ground temperature monitoring results from 2007 to 2010, the thermosyphon technique cooled the underlying permafrost and raised the permafrost table. The CMR has been put in operation since February 2010. The deformation monitoring data from 2008 to 2010 showed that the maximum accumulated settlement was 0.08 m and the minimum was 0.01 m. The settlements mainly happened in the initial months after the embankment construction was finished. In-situ monitoring results indicate that the thermosyphon technique has effect on cooling down the underlying permafrost and keeping the thermal stability of embankment in the unstable, marshy and ice-rich cold regions.     

Numerical study on cooling characteristics of two-phase closed thermosyphon embankment in permafrost regions

The two-phase closed thermosyphon (TPCT) is an effective heat transfer device decreasing the ground temperature around it in cold season, but not absorbing heat energy in warm season. In this paper, in order to research the efficiency of the TPCT applied to the embankment in permafrost regions, a three-dimension model for the TPCT embankment was presented based on the work characteristics of the TPCT and on the related heat transfer theories. The numerical results showed that 1) the model can reasonably solve the coupled heat transfer problem of air-TPCT-soil for TPCT embankment; 2) the TPCT embankment is effective to protect the underlying permafrost and to ensure the stability of roadway in permafrost regions; furthermore, it could play rapidly a cooling effect and approach a thermal balance state after 5 years of construction; and 3) the TPCT, if combined with other engineering methods such as insulation, crushed rock, etc., can be an more effective engineering measure to ensure the stability of roadway engineering in warm permafrost regions.     

Numerical analysis of wind speed variation under awning boards covering embankment side slopes

To protect the permafrost under the embankment from thawing and to ensure the safety and smoothness of the road, the use of shading boards (awnings) was one of the main measures applied along the side slopes of the Qinghai-Tibet Highway, the Qinghai-Tibet Railway and the Qingkang-Highway embankments. Aside from the shading effect acting against solar irradiation such constructions may also help to channel the natural wind flow and thus contribute to the cooling of the embankment and the underlying ground by enhancing the natural wind flow close to the surface. In this study we present results from numerical finite element simulations of the air flow under two different awning designs, with the aim to find an optimal geometry and awning height to be applied in future engineering work. We compare the air flow profiles across and along the awning headroom and investigate the influence of embankment slope inclination on the flow under the awning.