A Bayesian approach to the detection of gross errors based on posterior probability     

Q. Gui  Y. Gong  G. Li  B. Li 《Journal of Geodesy》2007,81(10):651-659

Existing methods for gross error detection, based on the mean shift model or the variance inflation model, have hardly considered or taken advantage of the potential prior information on the unknown parameters. This paper puts forward a Bayesian approach for gross error detection when prior information on the unknown parameters is available. Firstly, based on the basic principle of Bayesian statistical inference, the Bayesian method—posterior probability method—for the detection of gross errors is established. Secondly, considering either non-informative priors or normal-gamma priors on the unknown parameters, the computational formula of the posterior probability is given for both the mean shift model and the variance inflation model, respectively, under the condition of unequal weight and independent observations. Finally, as an example, a triangulation network is computed and analyzed, which shows that the method given here is feasible.  相似文献   

闪电定位资料分析     

许洪泽  王振会  冯民学 《河南气象》2007,(1)

对江苏省电力部门和安徽省气象部门的闪电定位资料分析结果表明,两个部门资料中闪电在时间变化和空间分布特征上都比较一致。在分析安徽省气象部门闪电资料时发现,无论是正闪还是负闪,电流峰值都主要集中在0-60kA。  相似文献   

Sensitivity equations for hyperbolic conservation law-based flow models     

Vincent Guinot  Matthieu LeménagerBernard Cappelaere 《Advances in water resources》2007

The present paper focuses on the governing equations for the sensitivity of the variables to the parameters in flow models that can be described by one-dimensional scalar, hyperbolic conservation laws. The sensitivity is shown to obey a hyperbolic, scalar conservation law. The sensitivity is a conserved scalar except in the case of discontinuous flow solutions, where an extra, point source term must be added to the equations in order to enforce conservation. The propagation speed of the sensitivity waves being identical to that of the conserved variable in the original conservation law, the system of conservation laws formed by the original hyperbolic equation and the equation satisfied by the sensitivity is linearly degenerate. A consequence on the solution of the Riemann problem is that rarefaction waves for the variable of the original equation result in vacuum regions for the sensitivity. The numerical solution of the hyperbolic conservation law for the sensitivity by finite volume methods requires the implementation of a specific shock detection procedure. A set of necessary conditions is defined for the discretisation of the source term in the sensitivity equation. An application to the one-dimensional kinematic wave equation shows that the proposed numerical technique allows analytical solutions to be reproduced correctly. The computational examples show that first-order numerical schemes do not yield satisfactory numerical solutions in the neighbourhood of moving shocks and that higher-order schemes, such as the MUSCL scheme, should be used for sharp transients.  相似文献   

Effects of underground cavities on Rayleigh waves—Field and numerical experiments     

A. Nasseri-Moghaddam  G. Cascante  C. Phillips  D.J. Hutchinson 《Soil Dynamics and Earthquake Engineering》2007,27(4):300-313

This paper presents the results of a multi-channel analysis of surface waves (MASW) test conducted over near-surface mine workings, with the objective of delineating the underlying. Numerical studies were carried out to explain and extend the results. The displacement time histories at the surface show amplitude changes in the region over the void, and the Fourier spectra show significant energy concentration on and in the vicinity of the cavity. Different numerical models are constructed and the responses at the surface of the medium and around voids of different sizes and embedment depths are monitored. The numerical results show that part of the incident energy is trapped within the void. The trapped energy bounces back and forth inside the void, until it is attenuated by radiation. The effect of the trapped energy is seen as a concentration of energy over the void region in the frequency domain. The amount of trapped energy is a function of the size and embedment of the void, as well as of the frequency content of the source. The void absorbs part of the energy and radiates it as body waves. Therefore, the recorded responses at the surface carry valuable information about the void. The characteristics of the void can be extracted from the surface responses by analyzing the responses in time, frequency, and spatial domains.  相似文献   

火箭触发闪电通道的亮度特征分析   总被引：2，自引：0，他引：2  

吕伟涛  张义军  周秀骥  孟青  郑栋  马明  王飞  陈绍东  郄秀书 《气象学报》2007,65(6):983-993

利用成像速率为2000幅/s的高速摄像资料,对采用不同触发方式的两次负极性闪电进行了对比分析,结果表明:空中触发方式的上行正先导的起始速度比经典触发方式的低一个量级左右,而前者的触发高度要比后者的高;闪电通道中金属导线汽化部分的余晖时间可达160—170 ms,相对来说,空气离化部分的亮度信息更能真实体现闪电通道中的电流特性。依据闪电通道亮度变化特性的差异,并结合电场变化的观测,可以将回击之后的过程分为3种类型,没有M分量的为连续衰减型,有M分量的可分为独立型和延续型两种,能够与不同类型的延续电流波形相对应。总体上看,有M分量的回击间隔比没有M分量的要长,几何平均值分别为77 ms和37 ms,有M分量的初始连续电流也会比没有M分量的持续更长的时间。回击和M分量发生前闪电通道的相对亮度存在明显的差异,回击前闪电通道的相对亮度很弱,甚至观测不到任何发光现象,而M分量发生前闪电通道仍有较强的发光。  相似文献   

Radar measurements of integral parameters of hailstorms used on hail suppression projects     

Viktor Makitov   《Atmospheric Research》2007,83(2-4):380-388

The exact quantitative estimation of hailstorm precipitation intensity, allowing determining successfully the crop hail damage, is extremely necessary while carrying out of programs of experimental researches of the hail clouds as well as at realization of operative projects on hail suppression. On the other hand, the possibility of obtaining a trustworthy information about changes of hailfall intensity during cloud seeding operations enables to judge more objectively about seeding effect and to make a decision about its beginning and termination. Just because of such a parameter, the kinetic energy of hailfalls presents a great interest for the researchers. As it is known, measuring the kinetic energy of hailfalls is carried out both directly by ground network of hailpads, and by radar methods. The accuracy of the radar methods of the hail kinetic energy measurement strongly depends not only on the choice of an optimum formula for calculation but also on the algorithm used for separating hail and rain parts of radar echo and on the way it was used in the hail–rain mixture zone of precipitation.The method of calculating the kinetic energy of the hailfalls, based on empirical dependence of hail probability P_h on a height of a zone of a radar echo with a reflectivity of 45 dBZ above a level of zero isotherm ΔH₄₅, is offered in the given work. The algorithm of separating hail and rain parts of a radar echo and the way it was applied in a hail–rain mixture zone is described. The examples of hail streaks in contours of radar reflectivity and in isopleths of hail kinetic energy obtained using the given algorithm are shown.In Mendoza province (Argentina), a hail suppression project (1993–1997) for the analysis of the vertical structure of a radar echo with Z_max > 45 dBZ, such new parameter is an integral altitude, was used. This dimensionless parameter is most sensitive to such a condition of radar echo when all four contours of increased reflectivity Z₄₅, Z₅₅, Z₆₅, and Z₇₅ synchronously reach the maximal values. The analysis of time distributions of the main radar parameters of hailstorms on a background of values of integral altitude is resulted. It is shown that local hailfall maximum intensities on the ground are observed after the achievement of maximum integral altitude with a certain delay. It enables to predict zones of the greatest hail damage in a mode of radar observation.  相似文献   

基于边缘特征匹配的遥感影像变化检测预处理方法   总被引：1，自引：0，他引：1  

袁修孝  宋妍 《武汉大学学报(信息科学版)》2007,32(5):381-386

提出了一种基于边缘特征匹配的遥感影像变化检测预处理方法，在进行不同时相遥感影像配准时，一并解求两期影像的辐射校正系数，同时实现两期影像的配准和辐射校正。实验表明，经预处理后，两期影像的色调基本一致，地物没有明显的几何变形。  相似文献   

一种运用纹理和光谱特征消除投影差影响的建筑物变化检测方法     

袁修孝  宋妍 《武汉大学学报(信息科学版)》2007,32(6):489-493

针对不同时期高分辨率遥感影像变化检测中城区建筑物因投影差差异所产生的误检测现象,提出了一种综合应用光谱和纹理特征的建筑物变化检测方法。以变化和未发生变化地物影像的散度作为可分性依据,首先对光谱差分影像在混合高斯密度模型下建模,并采用马尔可夫最小错误概率准则提取初始变化区域,往往含有错判的建筑物。然后将误判建筑物影像类和真实变化影像类构成训练集,通过引入多通道Gabor滤波器,提取训练集的纹理差分特征,并采用分类别PCA变换实施纹理差分特征的选择。最后对选择出的纹理差分特征依据高斯混合密度模型建模,并用马尔可夫最小错误概率提取真变化区域,即可去除光谱信息检测所产生的伪变化。试验表明,本文方法能够较好地解决建筑物变化的错判问题,提高了影像变化检测的精度。  相似文献   

基于正常轮廓更新的自适应异常检测方法     

熊平 《武汉大学学报(信息科学版)》2007,32(9):842-845

根据网络系统发生正常改变的基本特征,提出了确定网络系统正常改变的“三条件”计算方法,其计算结果可作为更新正常轮廓的依据。对正常轮廓的更新问题进行了深入探讨,提出了自适应异常检测的实现机制。并以网络流量分析为例,验证了在异常检测中应用这一方法的可行性。  相似文献   

基于多结构元的形态学边缘检测方法研究     

周春  肖启芝  许凯  吴辞军  秦昆 《地理空间信息》2007,5(4):48-51

针对传统边缘检测算子的缺点,研究了基于数学形态学的边缘检测方法,给出了基于多结构元的抗噪型形态学边缘检测算法的具体流程,进行了实验对比分析,表明该方法具有较好的边缘提取能力和抗噪性。  相似文献