Regional hydrologic mapping of flows in stream networks

River low flow (LF) is an important hydrological characteristic used in management of the quantity and quality of water resources. A common way to transpose at-station low flow quantiles to ungaged locations involves development of regional multivariate regression models. In site selection studies of water control facilities, need arises to automate the mapping of LF characteristics onto the stream network in a continuous manner. This would allow estimation of LF at any desired ungaged location. A mapping algorithm is introduced that determines the value of regression model's independent variables (input components) over the drainage area of each stream pixel and calculates the flow (output). The mapping algorithm relies mainly on the digital elevation model (DEM) and its derivatives, such as flow direction and flow accumulation. Furthermore, the contribution of each independent variable of the regional model to the total flow may be plotted to represent the flow profiles along the streams. A case study involving LF mapping in rivers of Gilan province, Iran, where LF quantiles are required for issuing water withdrawal permits as well as maintaining water quality standards, is also described in the paper. Overall, the maps and profiles of flow statistics in the region of interest provide convenient visualization and assessment tools for water resource and environmental engineers. The transposition algorithm may also be applied in regional mapping of other flow characteristics such as flood or average flows.     

基于ArcGIS的洪水淹没分析模拟及可视化

基于数字高程模型(DEM)格网模型,通过改进迭代种子蔓延算法,实现给定水深情况下洪水淹没区的讣算模型,讨论洪水淹没演进过程可视化实现的关键技术,并使用ArcEngine开发包进行二次开发,以二维和二三维两种可视化方式,动态而形象地模拟在指定洪水水位下的洪水淹没演进过程.试验证明,所提出的实现方法切实有效,便于推广应用,为快速、准确及科学地进行洪灾评估洪水风险图的制作提供良好的基础,对洪涝灾害进行评估和预测分析具有重要意义.     

Accuracy assessment of digital elevation models by means of robust statistical methods

Measures for the accuracy assessment of Digital Elevation Models (DEMs) are discussed and characteristics of DEMs derived from laser scanning and automated photogrammetry are presented. Such DEMs are very dense and relatively accurate in open terrain. Built-up and wooded areas, however, need automated filtering and classification in order to generate terrain (bare earth) data when Digital Terrain Models (DTMs) have to be produced. Automated processing of the raw data is not always successful. Systematic errors and many outliers at both methods (laser scanning and digital photogrammetry) may therefore be present in the data sets. We discuss requirements for the reference data with respect to accuracy and propose robust statistical methods as accuracy measures. Their use is illustrated by application at four practical examples. It is concluded that measures such as median, normalized median absolute deviation, and sample quantiles should be used in the accuracy assessment of such DEMs. Furthermore, the question is discussed how large a sample size is needed in order to obtain sufficiently precise estimates of the new accuracy measures and relevant formulae are presented.     

规则格网上双方向性插值DEM精度研究

简要介绍双方向性插值方法的原理,并以线性插值和三次插值过程中的误差传播为基础,利用误差传播定律,推导出双方向性插值方法生成的DEM曲面平均高程误差值,并对线性插值和三次插值公式本身的精度进行分析。     

一种基于点云提取微地形对象的方法

在分析微地形特点以及现有网格DEM在表述微地形中存在的不足的基础上,提出了面向对象的数字高程模型,给出了该模型的形式化描述和以点云为数据源构建面向对象数字高程模型过程中采用的对象边界的识别、特征保持的点云疏化、基于属性近似的网格约化及对象识别等关键步骤的方法。并以实例证明了此过程的可行性。     

GNSS形变监测中系统误差的时空相关性研究

通过大量实测数据分析了系统误差的时空变化规律,论证了具有时空相关性的双差观测值系统误差残差的存在,实现了观测值的滤波及求差,提高了分离微小形变量的精度。     

基于SRTM DEM的InSAR高分辨率山区地表高程重建算法

山体的叠掩和阴影现象造成的信号去相关,一直是InSAR重建山区地表高程的瓶颈之一.为此,提出了一种新的基于粗分辨率SRTM DEM(约90m分辨率)辅助InSAR数据重建山区地表高程的方法.利用SRTM DEM模拟的干涉相位,对ERS-1/2干涉相位做去地形相位处理,得到残余相位.通过对解缠后的残余相位计算方差提取叠掩和阴影区域的噪声,并用平均相位近似恢复噪声区域的相位,然后将其转换为高程,并用SRTM DEM作高程补偿处理,从而实现地表高程重建.最后,定量比较了该方法与传统InSAR技术生成的DEM精度.实验表明,这种方法能有效提高传统InSAR技术生成地表高程的精度,这对提高星载雷达数据的使用效率具有重要意义.     

一种渐进加密三角网LIDAR点云滤波的改进算法

传统滤波算法常常是针对某些特定的具有连续表面的区域来进行,带有一定的局限性。这样不能解决对诸如斜坡、密集植被等复杂地区进行真实准确地形提取的难题。本文提出了一种融合区域增长方法的LIDAR点云数据的滤波方法。该方法在对原始点云数据进行预处理的基础上,生成一个松散的TIN,通过迭代生成加密的TIN,其中通过采用两次区域增长的滤波方法,实现原始地形的提取。最后通过对复杂典型数据的对比实验验证了文中所提出的改进方法的有效性和准确性。     

最短独立闭合环与附合路线的快速搜索方法

提出了一种间接平差误差方程转化为条件平差条件方程的快速且易实现自动化的方法,同时采用矩阵分析理论,通过对条件方程进行特殊的矩阵分块及变换,自动搜索出水准网或GPS网的最短独立闭合环与附合路线,并自动解算出闭合差。上述方法有别于传统的图论理论,不依赖于任何信息文件,算法简单,自动化程度高。     

BOC调制信号多径误差分析

针对导航信号的多径误差分析,在多径误差包络曲线分析方法基础上提出了多径误差包络期望分析方法。与包络曲线分析方法相比,包络期望分析方法能够定量分析导航信号多径误差。基于包络期望分析方法,对同码速率的二进制偏移载波(BOC)调制导航信号与二进制相位控键(BPSK)调制导航信号的多径误差进行了对比分析。结果表明,BOC调制导航信号具有更小的典型多径误差。