Traction image method for irregular free surface boundaries in finite difference seismic wave simulation

In this study, we propose a new numerical method, named as Traction Image method, to accurately and efficiently implement the traction-free boundary conditions in finite difference simulation in the presence of surface topography. In this algorithm, the computational domain is discretized by boundary-conforming grids, in which the irregular surface is transformed into a 'flat' surface in computational space. Thus, the artefact of staircase approximation to arbitrarily irregular surface can be avoided. Such boundary-conforming gridding is equivalent to a curvilinear coordinate system, in which the first-order partial differential velocity-stress equations are numerically updated by an optimized high-order non-staggered finite difference scheme, that is, DRP/opt MacCormack scheme. To satisfy the free surface boundary conditions, we extend the Stress Image method for planar surface to Traction Image method for arbitrarily irregular surface by antisymmetrically setting the values of normal traction on the grid points above the free surface. This Traction Image method can be efficiently implemented. To validate this new method, we perform numerical tests to several complex models by comparing our results with those computed by other independent accurate methods. Although some of the testing examples have extremely sloped topography, all tested results show an excellent agreement between our results and those from the reference solutions, confirming the validity of our method for modelling seismic waves in the heterogeneous media with arbitrary shape topography. Numerical tests also demonstrate the efficiency of this method. We find about 10 grid points per shortest wavelength is enough to maintain the global accuracy of the simulation. Although the current study is for 2-D P-SV problem, it can be easily extended to 3-D problem.     

Documentary Evidence of an Economic Character as a Source for the Study of Meteorological and Hydrological Extremes and their Impacts on Human Activities

This paper deals with documentary evidence of an economic character as a proxy for direct study of meteorological and hydrological extremes. Taxation records and reports of those who administrated domains and estates are described with respect to information about meteorological and hydrological extremes. Based on data from eight domains or estates from Moravia (in the Czech Republic), frequency series of floods and convective storms (including hailstorms) were developed for the period 1650–1849. One example of disastrous weather, which took place on 10 August 1694 in the Pern?tejn domain, is used to demonstrate the potential for such studies of the intensity of extremes and their impact on human activities. The importance of economic evidence in the instrumental period is shown through tax rebate data contingent upon hailstorm damage in Moravia (1896–1906). The benefits of employing documentary economic evidence for historical climatology and the study of the impact of meteorological and hydrological extremes on human activities are discussed.     

基于微电子系统（MEMS）加速度地震勘探三分量数字检波器简介

基于微电子机械系统（MEMS）制成的微加速度三分量数字地震检波器。集数据采集、处理及传输功能干一体，在结构模型、工作原理、性能指标控制等方面不同于常规检波器，其信号幅值在低于自然频率范围内没有衰减。因其独特的制造技术，MEMS检波器具有超低噪声，大动态范围和极高的向量保真度性能。     

SPOT5影像严格几何纠正方法研究

根据SPOT卫星的成像原理和特点,讨论了对SPOT5卫星影像按共线方程法进行有控制点的几何纠正的方法,经对关中、陕北和陕南三种地形的影像纠正结果进行对比检验,证明了该方法精度达到了较高水平。     

图像数据挖掘软件原型系统的设计与开发

提出了图像数据挖掘软件原型系统的设计与开发的试验框架,阐述了其设计与开发方法,介绍了各个模块的功能、设计与开发情况。     

用旅游图制作导航电子地图中的地图纠正

介绍了一种用三次插值样条对公开出版的旅游图进行纠正,制作汽车导航电子地图的方法,分析了其中存在的问题,提出了解决的办法。     

遥控飞艇数字航空摄影系统

提出快速获得航空影像并及时制作DOM、DLG的一种手段.介绍遥控飞艇数字摄影系统的工作原理,探讨存在的问题.     

全数字摄影测量系统DEM生产的质量控制

目前,数字高程模型(DEM)在理论研究和实践应用方面都有了很大的进展,已在测绘、地质、农业、工程、建筑、军事、导航等多个领域得到了广泛应用,因此高效快捷地生产高精度的DEM是十分必要和迫切的。全数字摄影测量系统DEM生产方案是解决这一问题的有效途径,文章针对该系统的特点,提出了加强质量控制的策略和方法,并阐述了对一些实践问题的解决。     

图像平滑算法比较研究及改进策略

图像平滑作为去除图像中含有噪声的图像增强处理技术，是各种与图像有关软件中必不可少的功能模块。文中在分析噪声模型的基础上，对均值平滑、中值平滑、边缘保持平滑等技术从图像处理空间域中的算法原理、实现方法及效率等方面进行了详细比较。针对图像中含有的不同噪声模型，通过多次试验，得出了值得从事图像处理研究者参考的结论。这将有助于提高图像处理软件开发的效率。     

基于广义Hough变换的不规则形状目标提取方法

提出了一种基于广义Hough变换的不规则形状目标的提取方法。该方法主要包括目标参数描述和目标提取两部分。实验表明，该方法精度好、效率高。