基于北斗导航系统的我国地基增强格网模型研究

基于全国均匀分布的210个北斗地基增强基准站观测数据,提出基于非差非组合精密单点方法获取空间相关的延迟误差及残差,研究利用反距离加权法、克里金插值法以及球谐函数法建立了中国区域的三种地基增强格网模型。使用单频伪距单点定位方法对中国区域的北斗地基增强格网模型定位精度进行了评估,验证结果表明本文建立的格网模型的定位精度达到米级,可满足大众用户的需求。     

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Spatial distribution and content of soil organic matter in an agricultural field in eastern Canada,as estimated from geostatistical tools

Soil erosion induces soil redistribution within the landscape and thus contributes to the spatial variability of soil quality. This study complements a previous experimentation initiated by the authors focusing on soil redistribution as a result of soil erosion, as indicated by caesium‐137 (¹³⁷Cs) measurements, in a small agricultural field in Canada. The spatial variability of soil organic matter (SOM) was characterized using geostatistics, which consider the randomized and structured nature of spatial variables and the spatial distribution of the samples. The spatial correlation of SOM (in percentages) patterns in the topsoil was established taking into account the spatial structure present in the data. A significant autocorrelation and reliable variograms were found with a R² ≥ 0·9, thus demonstrating a strong spatial dependence. Ordinary Kriging (OK) interpolation provided the best cross validation (r² = 0·35). OK and inverse distance weighting power two (IDW2) interpolation approaches produced similar estimates of the total SOM content of the topsoil (0–20 cm) of the experimental field, i.e. 211 and 213 tonnes, respectively. However, the two approaches produced differences in the spatial distribution patterns and the relative magnitude of some SOM content classes. The spatialization of SOM and soil redistribution variability – as evidenced by ¹³⁷Cs measurements – is a first step towards the assessment of the impact of soil erosion on SOM losses to recommend conservation measures. Copyright © 2009 John Wiley & Sons, Ltd.     

塑性混凝土弹性模量室内试验研究

通过4种变形标距的弹性模量试验,研究了塑性混凝土弹性模量的合适测试方法。塑性混凝土棱柱体试件设置300mm、200mm、150mm和100mm共4种测试标距,其中300mm标距下的力和位移数据采用计算机自动采集,其余标距采用人工读数。结果表明,利用自动采集数据模式测得塑性混凝土弹性模量值最稳定,且其值远远小于人工读数模式下的值;一般而言,测试标距小,弹性模量值大,全长标距下弹性模量值最小;利用自动采集数据模式下得到单轴压缩应力应变曲线具有典型初始压缩弯曲段、较长的下降段,而人工读数下几乎不能测出初始压缩弯曲段,而主要表现为较长直线上升段。分析了塑性混凝土利用普通混凝土弹性模量计算公式的不足,提出利用其单轴峰值强度的0.3倍、0.7倍对应的点计算其弹性模量。同时提出室内测试塑性混凝土弹性模量试验时不需预压。     

Investigation on the stochastic simulation of strong ground motions for Bucharest area

This short article evaluates the stochastic method of ground motion simulation for Bucharest area using both the single-corner frequency model and recently introduced double-corner frequency models. A dedicated Q model is derived using ground motions obtained during the largest Vrancea earthquakes from the past 30 years. The simulated ground motions are tested against the observed data from the Vrancea earthquakes of August 1986 and May 1990. Moreover, the observed data are also compared against simulations obtained using the Q model derived by Oth et al. (2008). Finally, the results of the simulations show that the derived Q model is better suited for larger magnitude events, while the Q model of Oth et al. (2008) provides better results for smaller earthquakes.     

Sediment connectivity: a framework for understanding sediment transfer at multiple scales

A major challenge for geomorphologists is to scale up small‐magnitude processes to produce landscape form, yet existing approaches have been found to be severely limited. New ways to scale erosion and transfer of sediment are thus needed. This paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales. We propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment, and movement of sediment between different zones within a catchment: over hillslopes, between hillslopes and channels, and within channels. Using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end‐members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity. Sediment‐travel distance – when combined with an entrainment parameter reflecting the frequency–magnitude response of the system – maps onto these end‐members, providing a coherent conceptual model for the upscaling of erosion predictions. This conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape‐evolution models. Thus, further research on the controls and dynamics of travel distances under different modes of transport is fundamental. Copyright © 2014 John Wiley & Sons, Ltd.     

加权总体最小二乘点云平面拟合定权方法探讨

针对加权总体最小二乘点云数据平面拟合方法中缺少统一定权准则的问题,提出以先验入射角及距离定权两种方法。利用稳健估计构造了基于强度值定权的稳健加权最小二乘、基于先验入射角定权的加权最小二乘与基于距离定权的加权最小二乘3种新的平面拟合算法,并应用于拟合扫描不同反射材质获取的平面点云数据。算例表明,〖JP2〗以距离定权构造的距离加权总体最小二乘法的各项精度指标均优于其他算法,拟合效果最好。     

河北地区气温内插模型及检验方

以1965—1999年河北省逐月平均气温为研究对象,采用一元线性回归法和IDW(Inverse Distance Weighted)相结合的方法,将温度插值到河北省整个区域,绘制河北省温度空间分布图,实现河北省年内各月平均气温空间填图;同时,分析了河北省冬季和夏季各月的月平均温度的误差精度。结果表明：插值的结果与观测值的相关系数(R)在12个月均大于0.82,显示插值方法具有较好的模拟精度,可用于气温的空间插值和特征分析。     

中国东北地区重力场研究——利用改进的三方向小子域滤波划分主构造线及大地构造单元

利用重力异常进行大地构造单元的划分是区域重力资料处理与解释的重要任务.为了精细地划分中国东北地区大地构造单元及其分界线位置,对三方向小子域滤波进行了改进,探讨了改进的三方向小子域滤波的合理性.利用小子域及改进的三方向小子域滤波对研究区布格重力异常进行处理,并与欧拉反褶积反演结果进行对比分析.结果表明,改进的三方向小子域滤波在识别平面断裂的应用中具有更好的效果.综合分析东北地区布格重力异常特征、小子域和改进的三方向小子域滤波结果,划分出延续性较好、规模较大的断裂18条.对研究区重力异常进行了分区,描述了一、二级异常的分区特点,给出了东北地区大地构造单元的基本格架.黑河-齐齐哈尔-白城等重要构造线平面位置的确定突破了传统的重力异常分区模式,指出东北地区NE向构造具有走滑特征,且走滑距离具有由西向东逐渐增大的特点.     

塔里木河下游植物调查最小取样面积分析

采用巢式样方法,对塔里木河下游两个断面6条样带38块64 m×64 m样地进行调查,选用线性和非线性种-面积模型,对调查区不同比例因子植物调查最小取样面积、最小取样面积与不同地下水条件的关系进行了分析。根据种-面积曲线的最优模型,当比例因子取值包括群落50%、60%、70%、80%和90%的植物种类时,最小调查样地面积分别为418 m2、707 m2、1 138 m2、1 702 m2和2 656 m2;随着离河距离增加,物种数减少,植物的生长势降低。当比例因子取值包括群落50%植物种类、地下水埋深由离河50 m的1.57 m到离河1 500 m的7.53 m变化时,离河不同距离各级最小取样面积变化较大,地下水条件是植物种类调查最小取样面积变化的关键因素。