Analytic element modelling for strip aquifers

The Analytic Element Method (AEM) provides a convenient tool for groundwater flow analysis in unbounded continuous domains. The AEM is based on the superposition of analytic functions, known as elements, useful at both regional and local scales. In this study, analytic elements for strip aquifers are presented. Such aquifers occur in riverine or coastal deposits and in outcrop zones of confined aquifers. Local flow field is modelled indirectly, using a reference plane related to the aquifer domain through the Schwarz‐Christoffel transform. The regional flow is obtained as a solution of the one‐dimensional flow equation. The proposed methodology was tested by modelling two hypothetical situations, which were compared to exact solutions. It is shown that regional boundaries can be reproduced exactly while local fields are adequately reproduced with analytic elements. The developed elements are applied to simulate a real flow field in northeastern Brazil showing good agreement with measured water levels. Copyright © 2011 John Wiley & Sons, Ltd.     

The Fourier Integral Method: An efficient spectral method for simulation of random fields

The Fourier Integral Method (FIM) of spectral simulation, adapted to generate realizations of a random function in one, two, or three dimensions, is shown to be an efficient technique of non-conditional geostatistical simulation. The main contribution is the use of the fast Fourier transform for both numerical calculus of the density spectral function and as generator of random finite multidimensional sequences with imposed covariance. Results obtained with the FIM are compared with those obtained by other classic methods: Shinozuka and Jan Method in 1D and Turning Bands Method in 2D and 3D, the points for and against different methodologies are discussed. Moreover, with the FIM the simulation of nested structures, one of which can be a nugget effect and the simulation of both zonal and geometric anisotropy is straightforward. All steps taken to implement the FIM methodology are discussed.     

HOUGH变换在海浪遥感图像处理中的应用

本文提出了一种以FIOUGH变换为基础的海浪波长波向分析法,并对SEASAT合成孔径雷达获取的海洋遥感图像进行了方向和波长分析。该方法模拟人类纹理视觉机理,首先应用CFCM动态聚类方法对波峰、波谷和过渡带进行分类,然后采用随机行走模型对分类图像进行滤波,以获得整图的全局走向信息,再以此先验信息为先导对分类后的纹理图像进行定向跟踪拟合,得到代表海浪波峰的直线族图,最后在再对此图进行HOUGH变换和分析的基础上得到精确的波长与波向。     

n—D Radon变换与波动方程偏移

本文把Ｒａｄｏｎ变换公式推广到任意ｎ维的情况。同时结合ｎ维Ｒａｄｏｎ变换和摄动理论提出了一种既能用于地面资料又能用于ＶＳＰ资料的偏移方法。     

Exploratory spectral analysis of hydrological times series

Current methods of estimation of the univariate spectral density are reviewed and some improvements are made. It is suggested that spectral analysis may perhaps be best thought of as another exploratory data analysis (EDA) tool which complements, rather than competes with, the popular ARMA model building approach. A new diagnostic check for ARMA model adequacy based on the nonparametric spectral density is introduced. Additionally, two new algorithms for fast computation of the autoregressive spectral density function are presented. For improving interpretation of results, a new style of plotting the spectral density function is suggested. Exploratory spectral analyses of a number of hydrological time series are performed and some interesting periodicities are suggested for further investigation. The application of spectral analysis to determine the possible existence of long memory in natural time series is discussed with respect to long riverflow, treering and mud varve series. Moreover, a comparison of the estimated spectral densities suggests the ARMA models fitted previously to these datasets adequately describe the low frequency component. Finally, the software and data used in this paper are available by anonymous ftp from fisher.stats.uwo.ca.     

三维F－K域DMO方法及应用效果

在常速情况下，从三维时距方程出发，通过倾角代换，将三维倾角时差分裂为两个正交方向上的二维倾角时差，然后在这两个正交方向上分别做一次二维倾角时差校正，便可达到三维倾角时差校正的目的．应用实例表明这种三维ＤＭＯ分裂方法是切实有效的．     

A Fourier transform method for the interpretation of self-potential anomalies due to two-dimensional inclined sheets of finite depth extent

The self-potential anomaly due to a two-dimensional inclined sheets of finite depth extent has been analysed in the frequency domain using the Fourier transform. Expression for the Fourier amplitude and phase spectra are derived. The Fourier amplitude and phase spectra are analysed so as to evaluate the parameters of the sheet. Application of this method on two anomalies (synthetic and field data) has given good results.     

频谱成像技术在稠油热采地震监测中的应用

频谱成像技术可有效的描述地质反射层厚度的非连续性和岩性的非均质性,其在理论上主要是依据薄层反射的调谐原理,过去通常采用以离散傅里叶变换为基础的算法,但是,该方法存在着明显的局限性,因为估算的地震振幅谱的重要特征是所选时窗长度的函数.如果所选时窗过短,振幅谱会与变换窗函数褶积,失去频率的局部化特征,而且过短的时窗会使子波的旁瓣呈现为单一反射的假象.增加时窗长度,会改善频率的分辨率.但如果所选时窗过长,时窗内的多个反射会使振幅谱以槽痕为特征,很难分清单个反射的振幅谱特征.由于在实际运用中,以傅里叶变换相关的算法的时窗问题,难以选择好时窗长度,而且无法定量分析时窗长度产生的偏差,因而会使振幅谱的估算产生偏差.以小波变换为基础的时频分析技术成了非平稳性信号的重要分析工具,在很多实际应用中已取代了傅里叶变换的分析方法.以小波变换为基础的瞬时谱分析技术能得到精确的时频分析结果,同时避免了时窗问题.它反映出了储层在纵向上时间及厚度上变化情况和横向上的地质不连续性的信息,因此能使解释人员快速而有效地描述储层特征的空间变化.