The form of the reflection operator and extended image gathers for a dipping plane reflector in two space dimensions

The reflection operator for a simple flat‐lying interface can be thought of as the set of all its plane‐wave reflection coefficients or as the set of virtual surveys with sources and receivers along the interface. When there is dip, however, it is necessary to include the varying effects of propagation between the virtual‐survey level and the interface. Hence, step one in this paper is to derive the reflection operator for a dipping plane interface as observed at a datum level some distance away. The key assumption is that the aperture at the datum level is sufficient to characterize the reflector properties around a particular point. This translates into an assumption that the dip is moderate, though no explicit small‐angle approximation is required. The second step is to find the apparent reflection operator that would relate data that have been extrapolated from the datum towards and possibly beyond the reflector using an assumed migration velocity. This apparent reflection operator is closely related to extended common‐image gathers. The apparent reflection operator may be analysed asymptotically in terms of rays and other signals, shedding light on the structure of extended image gathers. In keeping with the virtual‐survey idea, the results are considered in a subsurface space‐time or slowness‐time domain at various extrapolation levels around the interface. An important distinction is drawn between using subsurface midpoint‐offset coordinates and the wavefield coordinates of the incident and reflected waves. The latter reveal more clearly the effects of dip, because they lead to a more asymmetric apparent reflection operator. Properties such as an up‐dip shift of a traveltime minimum and its associated curvature theoretically provide information about the reflector location and dip and the migration‐velocity error. The space‐time form of the reflection operator can be highly intricate around the offset‐time origin and it was described for a simple flat interface in a background paper. To avoid a layer of mathematics, the reflection‐operator formulas presented here are in the intermediate space‐frequency domain. They are analysed by considering their stationary‐phase and branch‐point high‐frequency contributions. There is no Born‐like assumption of weak reflector contrast and so wide‐angle, total reflection and head‐wave effects are included. Snell’s law is an explicit part of the theory. It is hoped that the work will therefore be a step towards the goal of unifying amplitude‐versus‐offset, imaging and waveform inversion.     

重力异常图中的边界增强和提取技术

对比了重磁勘探领域中4种典型的边界增强方法：Tilt导数、Tilt导数的水平梯度、Theta角和归一化的标准偏差,它们都能放大与边界有关的高频异常。增强后异常幅值极大值与地质体边界对应的情况可用近似边界法自动提取,而异常幅值拐点与边界对应的情况可以引入Canny边界检测算子来提取。理论模型试验表明：用Canny算子提取Tilt导数图边界与用近似边界检测法提取其它边界增强图的边界相比,前者提取的边界位置与真实位置更吻合,虚假边界更少。应用该方法对梅山铁矿的局部重力异常进行了处理,勾画出铁矿的大致范围。     

在频率—波数域消除海上地震资料中的虚反射的一种方法

消除虚反射是海上地震勘探资料处理中的一个重要问题,本文提出一种在频率－波数域消除虚反射的方法,并给出了消除虚反射滤波因子的形式,然后利用此方法对合成地震记录进行了消除效果验证。     

Wallis 滤波在影像匹配中的应用

介绍了Wallis滤波器的基本原理和特性,将其应用于影像点特征提取和影像匹配,并列出了部分结果。     

单纯形投影算子理论及在资料分析中的应用 Ⅰ.在方程模型资料预测中的应用

本文根据混沌系统奇怪吸引子在相空间中的伸缩和折叠的几何特征,建立了单纯形投影算子（simplexprojectionoperator）预测方法．该方法主要侧重考虑了被预测点的局部非线性特征及Lyapunov特征指数,避免了传统预测函数和方程的模拟问题,减少了模拟参量．对Lorenz方程和Logistic映射资料进行预测分析的结果表明,此方法简单易行,缩短了计算时间,在预测时问尺度及精度上具有较强的预测能力．     

A method for estimating specimen tangent stiffness for hybrid simulation

Researchers have long recognized the importance and potential benefits of utilizing the tangent stiffness matrix of a test specimen in hybrid simulations employing implicit and mixed‐integration schemes. However, the computation of the tangent stiffness matrix during testing has proved to be challenging, particularly for test specimens with more than one degree of freedom (dof). This paper presents a new methodology that is more straightforward and simpler than existing techniques for computing the tangent stiffness matrix of a multi‐dof test specimen. The proposed method is combined with the operator‐splitting method (OSM), and the capabilities, advantages and limitations of the new formulation are demonstrated through several examples. The accuracy, stability, and error propagation characteristics of the modified OSM are also studied theoretically as well as numerically. The research results show that the proposed algorithm provides results that are better than those produced via the regular OSM alone, especially for damped structures undergoing highly inelastic behavior during testing. Copyright © 2008 John Wiley & Sons, Ltd.     

基于二阶预测有效度IOWGA算子的变形组合预测研究

针对一阶预测有效度未能考虑预测精度的方差以及权数不变的问题,提出一种基于二阶预测有效度IOWGA算子的变权组合预测方法。该方法以二阶预测有效度作为目标函数,根据预测精度赋权,然后将其运用于变形数据分析中。实验结果表明,该模型预测精度高,适用于变形预测与分析。     

电法勘探中异常响应特征的增强算法及其实现

地球物理电法勘探中所获得的地下地质异常体的异常响应有时存在信号不强、特征不明显或范围轮廓模糊不清,影响了地质解释与判读的正确性和精确度。通过对异常响应等值线图沿梯度带变化剧烈的方向求一次导数、二次导数及执行梯度算子和拉普拉斯算子来增强异常响应特征,能使异常响应等值线图的异常中心更加明确,异常响应范围边缘更加清晰,这对地质解释与判读的正确性和精确度有积极作用。      

广义散射层析成像反演

本文详细地给出了基于非均匀介质的体散射广义散射层析成像反演的基本理论.广义散射层析成像反演可以描述为波场的反向传播和对成像场进行局部波数域滤波的过程.在数值算例中,利用背景速度沿深度方向均匀变化的v（z）介质中的简单的方块作为速度异常体的模型,通过对该模型产生的低频的Born数据和声波的正演数据的测试,在对采集系统进行有限频率带宽和空间孔径的校正来进行局部成像矩阵谱的恢复中,可以看出模型中各点的谱在恢复后的质量无论从覆盖的面积范围还是幅值的均一性上都有着明显的提高;在对速度模型的重建中,广义散射层析成像反演能够很好地恢复速度模型的低频分量,即便是方块速度异常体相对于背景速度的平均速度扰动是23%也能很好地重建模型中的速度,且对于不同的背景速度模型基本上都能很好地恢复Marmousi速度模型的低频分量.所以该方法将基于Born模型的层析成像反演适应范围进行了一定程度的扩展.