Development of a tundra-specific snow water equivalent retrieval algorithm for satellite passive microwave data

Airborne and satellite brightness temperature (T_B) measurements were combined with intensive field observations of sub-Arctic tundra snow cover to develop the framework for a new tundra-specific passive microwave snow water equivalent (SWE) retrieval algorithm. The dense snowpack and high sub-grid lake fraction across the tundra mean that conventional brightness temperature difference approaches (such as the commonly used 37 GHz-19 GHz) are not appropriate across the sub-Arctic. Airborne radiometer measurements (with footprint dimensions of approximately 70 × 120 m) acquired across sub-Arctic Canada during three field campaigns during the 2008 winter season were utilized to illustrate a slope reversal in the 37 GHz T_B versus SWE relationship. Scattering by the tundra snowpack drives a negative relationship until a threshold SWE value is reached near 130 mm at which point emission from the snowpack creates a positive but noisier relationship between 37 GHz T_B and SWE.The change from snowpack scattering to emission was also evident in the temporal evolution of 37 GHz T_B observed from satellite measurements. AMSR-E brightness temperatures (2002/03-2006/07) consistently exhibited decreases through the winter before reaching a minimum in February or March, followed by an increase for weeks or months before melt. The cumulative absolute change (Σ|Δ37V|) in vertically polarized 37 GHz T_B was computed at both monthly and pentad intervals from a January 1 start date and compared to ground measured SWE from intensive and regional snow survey campaigns, and climate station observations. A greater (lower) cumulative change in |Δ37V| was significantly related to greater (lower) ground measured SWE (r² = 0.77 with monthly averages; r² = 0.67 with pentad averages). Σ|Δ37V| was only weakly correlated with lake fraction: monthly r² values calculated for January through April 2003-2007 were largely less than 0.2. These results indicate that this is a computationally straightforward and viable algorithmic framework for producing tundra-specific SWE datasets from the complete satellite passive microwave record (1979 to present).     

一种互联网海量情报规则优化方法

现在很多部门都需要通过规则处理海量情报数据,规则的数量一旦达到海量级规模,对规则的处理技术的要求将会变得越来越高,海量规则的优化将是一个十分重要的问题.文中展示了一种海量规则的优化方法.若两个规则网最后的计算结果是一样的,则可以认为这两个规则网是等价的.基于该等价规则模块的变换可以将代价小的规则模块替换掉代价大的规则模块,从而以后可以选择一种代价最小的规则模块.本文提出规则网模块等价替换的5种优化方法,并对其做了相应的证明.通过优化,可以使得海量规则网处于计算代价尽量最小状态,以此减少处理机的计算工作量.分析表明,通过等价规则替换,可以大大提高规则处理效率.     

基于光照强度的PIN光电二极管响应时间分析

在PIN光电二极管应用中发现,光照强度对响应速度具有很大影响.论文研究了光强对响应速度的影响,提出了内部PIN结等效电场模型,并搭建了实验电路对PIN光电二极管在不同光照强度下的响应速度进行检测,验证提出的结模型,很好的解释了光电二极管从无光照到有光照这一过程中,光强越强,响应时间越短;而当光电二极管从有光照到无光照这一过程中,光强越强,响应时间越长这一现象.提出的模型和实验验证为光电二极管在响应速度要求较高的系统中的应用提供了理论分析依据,也为进一步提高PIN光电二极管的速度提出了有益的探索.     

Correcting for the influence of frozen lakes in satellite microwave radiometer observations through application of a microwave emission model

The spatial resolution of passive microwave observations from space is of the order of tens of kilometers with currently available instruments, such as the Special Sensor Microwave/Imager (SSM/I) and Advanced Microwave Scanning Radiometer (AMSR-E). The large field of view of these instruments dictates that the observed brightness temperature can originate from heterogeneous land cover, with different vegetation and surface properties.In this study, we assess the influence of freshwater lakes on the observed brightness temperature of AMSR-E in winter conditions. The study focuses on the geographic region of Finland, where lakes account for 10% of the total terrestrial area. We present a method to mitigate for the influence of lakes through forward modeling of snow covered lakes, as a part of a microwave emission simulation scheme of space-borne observations. We apply a forward model to predict brightness temperatures of snow covered sceneries over several winter seasons, using available data on snow cover, vegetation and lake ice cover to set the forward model input parameters. Comparison of model estimates with space-borne observations shows that the modeling accuracy improves in the majority of examined cases when lakes are accounted for, with respect to the case where lakes are not included in the simulation. Moreover, we present a method for applying the correction to the retrieval of Snow Water Equivalent (SWE) in lake-rich areas, using a numerical inversion method of the forward model. In a comparison to available independent validation data on SWE, also the retrieval accuracy is seen to improve when applying the influence of snow covered lakes in the emission model.     

三峡库区生态屏障范围界定

为有效保护三峡库区生态环境,应在库区175m淹没线以上建立生态屏障区。本文针对生态屏障的内涵及其具有的功能,提出了具体的生态屏障界定标准并建立了数学模型,提出了生态屏障建设相对适宜度。以忠县洋渡镇作为实例,利用Grid-Xinanjiang产流模型,计算研究区域内各网格单元的产流开始时间;利用网格水滴汇流模型,统计研究区各网格单元到达库区175m淹没线的汇流时间;利用收集到的地形、地貌和土地利用等资料统计研究区各单元的地形起伏、土壤质地、生态屏障投资费用等情况,在此基础上得到了洋渡镇生态屏障建设相对适宜度分布情况。通过计算缓冲区情景与高程情景下不同阈值的生态屏障平均相对适宜度变化曲线,确定了相应情景的生态屏障范围阈值;并通过对比2种阈值的生态屏障范围与适宜度的分布图,认为高程情景优于缓冲区情景。     

水管冷却热传导计算模型能量分析

对水管冷却有限元法和水管冷却等效热传导法的相关性进行了研究,采用同一套有限元网格,仿真分析了混凝土浇筑仓的非稳定温度场和徐变应力场,对比分析了两种水管冷却计算模型计算的混凝土浇筑仓平均温度和弹性应变能及黏性应变能.水管冷却等效热传导法计算的混凝土平均温度与水管冷却有限元法计算的平均温度接近,前者是后者的等效平均,但两者的同一节点温度不一样,且差异有时还比较大.由于前者是后者温度的等效平均,所以前者和后者的弹性应变能和黏性应变能接近,但两者的同一节点的应力不一样,因此其差异有时也比较大.     

考虑填充墙作用的框架结构Pushover分析

通过对"汶川地震"中框架填充墙的破坏情况进行调查分析,给出了框架填充墙的主要破坏形式,并总结发生破坏的原因;针对砌体填充墙框架结构在地震作用下的受力特点,提出结构简化计算模型(框架-斜撑模型),利用等效轴向刚度推导出斜撑宽度;结合实际工程,采用框架-斜撑模型对已建的框架填充墙结构进行Pushover分析,对结构的抗震能力做出评估。结果表明:①填充墙消耗了大量的地震能量,对周边部分构件起到了保护作用;②填充墙的参与,改变了结构的受力状态,结构薄弱部位也发生了变化。     

INFLUENCE OF STRUCTURE ON HYDRAULIC CHARACTERISTICS OF T SHAPE FISHWAY

While dams cut off the migratory route of fish, and affect their growth and breeding, fishways are built to restore the connectivity of rivers and facilitate the life cycle of these migratory fish. This paper proposes a new kind of fishway called the "T shape fishway", and studies it by using both numerical simulations and physical experimental methods with the aim to design a fishway in China for migratory fish with swimming and jumping capability much poorer, such as schizothorax davidi and schizothorax prenanti, as compared with migratory fish in other places of the world, like trout and salmon. It is indicated that the range of velocity in each regular pool of the T shape fishway is from 0.42 m/s to 1.22 m/s when the flow discharge Q is 350 L/s, and there are no large vortex zones found there. This study shows that the T shape fishway can meet the requirements of these migratory fish quite well in terms of velocity and flow patterns in China.     

连续刚构箱梁剪力滞效应分析

以靖远黄河大桥这一五跨连续刚构箱梁桥为工程背景,运用当量截面法计算靖远桥的剪力滞系数。分析其简化计算,将结果与ANSYS分析结果进行比较。     

聚合物熔体挤出流动中的弹性行为

研究了聚合物熔体挤出过程中出口压力降ΔＰｅｘｉｔ与剪切应力τｗ和挤出胀大比Ｂ三者之间的关系。提出了描述这一关系的方程：ΔＰｅｘｉｔ＝τｗ（Ｂ＾４－１）＾０５／３。初步验证，用该方程计算的ΔＰｅｘｉｔ值与文献提供的毛细管挤出实测值有较好的一致性。