Coherence algorithm with a high-resolution time–time transform and feature matrix for seismic data     

Fengyuan Sun  Jinghuai Gao  Bing Zhang  Naihao Liu 《Geophysical Prospecting》2020,68(4):1113-1125

Traditional coherence algorithms are often based on the assumption that seismic traces are stationary and Gaussian. However, seismic traces are actually non-stationary and non-Gaussian. A constant time window and the canonical correlation analysis in traditional coherence algorithms are not optimal for non-stationary seismic traces and cannot describe the similarity between adjacent seismic traces in detail. To overcome this problem, a new coherence algorithm using the high-resolution time–time transform and the feature matrix is designed. The high-resolution time–time transform used to replace the constant time window can produce a frequency-dependent time local series to analyse non-stationary seismic traces. The feature matrix, constructed by the frequency-dependent time local series and the related local gradients, defines a new correlation metric that enhances more details of the geological discontinuities in seismic images than does the canonical correlation analysis. Additionally, the Riemannian metric is introduced for related calculations because the feature matrices are not defined in a Euclidean space but rather in a manifold space. Application to field data illustrates that the proposed method reveals more details of structural and stratigraphic features.  相似文献   

一种实时场地校正方法及其在地震预警中的应用     

王辅臣  马强  陶冬旺  刘赫奕 《地震工程与工程振动》2020,(1):171-184

地震预警系统对地震数据处理的实时性要求极高。其系统数据来源除布设在基岩的测震台站外,还有大量非基岩场地的强震动台站和地震烈度仪台站,其场地影响不容忽视。为了考虑震级估算和地震动场预测中的场地影响,需实时对各种场地条件下的地震波形进行校正。目前处理一般使用某个标量来表征场地放大效应。本文采用一种实时的场地校正方法,首先计算目标场地与参考场地的谱比,然后通过最小二乘法、双线性变换将谱比转化为因果递归的无限冲激响应(IIR)时域滤波器,之后可以应用该滤波器进行实时场地校正。该方法考虑了场地放大系数的频率依赖性,相比于标量校正提高了准确度。应用我国四川和日本部分强震动台站记录,验证并讨论了这种实时场地校正方法在地震预警中的应用效果。  相似文献   

空间波数混合域磁异常场积分解三维数值模拟          下载免费PDF全文

李昆  戴世坤  陈轻蕊  张钱江  赵东东  王顺国  凌嘉宣 《地球物理学报》2019,62(11):4437-4450

本文提出一种空间波数混合域磁异常场三维数值模拟方法.该方法利用磁位三维空间域积分为卷积的特点，沿水平方向进行二维傅里叶变换，把空间域磁位满足的三维积分问题转化为不同波数之间相互独立的垂向一维积分问题.保留垂向为空间域，优势之一在于便于浅层单元剖分可适当加密，随着深度增加，单元剖分适当稀疏，可以准确模拟任意复杂地形和磁性体的磁异常，兼顾了计算精度与计算效率；优势之二在于一维积分垂向可离散为多个单元积分之和，每个单元采用二次形函数表征磁化强度，可得出单元积分的解析表达式，计算精度高、效率高.该方法充分利用一维形函数积分的高效和高精度、快速傅里叶变换的高效性及算法高度并行性，实现了磁异常场高效、高精度的数值模拟.设计棱柱体模型，将模型解析解与空间波数混合域法的数值解对比，结果表明该方法计算精度高、效率高.设计了组合棱柱体复杂模型，对比分析了标准FFT扩边法与Gauss-FFT法的计算精度与计算效率，总结了标准FFT的扩边系数选取策略.针对任意复杂地形条件下的磁异常模拟问题，本文提出一种适用于起伏地形条件下的磁异常场快速计算方法，并对其有效性进行了验证.  相似文献   

基于广义模型约束的时间域航空电磁反演研究   总被引：1，自引：0，他引：1       下载免费PDF全文

苏扬  殷长春  刘云鹤  张博  任秀艳 《地球物理学报》2019,62(2):743-751

由于航空电磁具有海量数据,因此快速有效的成像和反演手段至关重要.本文针对层状介质模型推导与实现了广义模型约束条件下时间域航空电磁一维反演.从正则化反演的目标函数出发,通过改变模型约束项构造Lp范数反演和聚焦反演,进而通过改变模型求解域构造出基于小波变换的稀疏约束反演.针对不同反演方法目标函数的构建方式,本文进一步从数学原理上分析不同反演方法的预期效果,并通过理论模型和实测数据进行验证.结果表明L0.8范数反演、聚焦反演和基于小波变换的稀疏约束反演可以得到更符合地下层状介质陡变界面的反演结果.  相似文献   

Semi‐analytical solution to one‐dimensional consolidation for unsaturated soils with semi‐permeable drainage boundary under time‐dependent loading          下载免费PDF全文

L. Wang  D. A. Sun  A. F. Qin  Y. F. Xu 《国际地质力学数值与分析法杂志》2017,41(16):1636-1655

This paper presents semi‐analytical solutions to Fredlund and Hasan's one‐dimensional consolidation of unsaturated soils with semi‐permeable drainage boundary under time‐dependent loadings. Two variables are introduced to transform two coupled governing equations of pore‐water and pore‐air pressures into an equivalent set of partial differential equations, which are easily solved by the Laplace transform. The pore‐water pressure, pore‐air pressure and settlement are obtained in the Laplace domain. Crump's method is adopted to perform the inverse Laplace transform in order to obtain semi‐analytical solutions in time domain. It is shown that the present solutions are more general and have a good agreement with the existing solutions from literatures. Furthermore, the current solutions can also be degenerated into conventional solutions to one‐dimensional consolidation of unsaturated soils with homogeneous boundaries. Finally, several numerical examples are provided to illustrate consolidation behavior of unsaturated soils under four types of time‐dependent loadings, including instantaneous loading, ramp loading, exponential loading and sinusoidal loading. Parametric studies are illustrated by variations of pore‐air pressure, pore‐water pressure and settlement at different values of the ratio of air–water permeability coefficient, depth and loading parameters. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Likely effects of climate change on groundwater availability in a Mediterranean region of Southeastern Spain          下载免费PDF全文

Hassane Moutahir  Pau Bellot  Robert Monjo  Juan Bellot  Miguel Garcia  Issam Touhami 《水文研究》2017,31(1):161-176

Groundwater resources are typically the main fresh water source in arid and semi‐arid regions. Natural recharge of aquifers is mainly based on precipitation; however, only heavy precipitation events (HPEs) are expected to produce appreciable aquifer recharge in these environments. In this work, we used daily precipitation and monthly water level time series from different locations over a Mediterranean region of Southeastern Spain to identify the critical threshold value to define HPEs that lead to appreciable aquifer recharge in this region. Wavelet and trend analyses were used to study the changes in the temporal distribution of the chosen HPEs (≥20 mm day^?1) over the observed period 1953–2012 and its projected evolution by using 18 downscaled climate projections over the projected period 2040–2099. The used precipitation time series were grouped in 10 clusters according to similarities between them assessed by using Pearson correlations. Results showed that the critical HPE threshold for the study area is 20 mm day^?1. Wavelet analysis showed that observed significant seasonal and annual peaks in global wavelet spectrum in the first sub‐period (1953–1982) are no longer significant in the second sub‐period (1983–2012) in the major part of the ten clusters. This change is because of the reduction of the mean HPEs number, which showed a negative trend over the observed period in nine clusters and was significant in five of them. However, the mean size of HPEs showed a positive trend in six clusters. A similar tendency of change is expected over the projected period. The expected reduction of the mean HPEs number is two times higher under the high climate scenario (RCP8.5) than under the moderate scenario (RCP4.5). The mean size of these events is expected to increase under the two scenarios. The groundwater availability will be affected by the reduction of HPE number which will increase the length of no aquifer recharge periods (NARP) accentuating the groundwater drought in the region. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Steady‐state analytical solutions of flow and deformation coupling due to a point sink within a finite fluid‐saturated poroelastic layer          下载免费PDF全文

P. Li  K. Wang  G. Fang  D. Lu 《国际地质力学数值与分析法杂志》2017,41(8):1093-1107

An exact steady‐state closed‐form solution is presented for coupled flow and deformation of an axisymmetric isotropic homogeneous fluid‐saturated poroelastic layer with a finite radius due to a point sink. The hydromechanical behavior of the poroelastic layer is governed by Biot's consolidation theory. Boundary conditions on the lateral surface are specifically chosen to match the appropriate finite Hankel transforms and simplify the transforms of the governing equations. Ordinary differential equations in the transformed domain are solved, and then the analytical solutions in the physical space for the pore pressure and the displacements are finally obtained by using finite Hankel inversions. The analytical solutions at some special locations such as the top and bottom surfaces, lateral surface, and the symmetrical axis are given and analyzed. And a case study for the consolidation of a water‐saturated soft clay layer due to pumping is conducted. The analytical solution is verified against the finite element solution. Meanwhile, an analysis of coupled hydromechanical behavior is carried out herein. The presented analytical solution is an exact solution to the practical poroelastic problem within an axisymmetric finite layer. It can provide us a better understanding of the poroelastic behavior of the finite layer due to fluid extraction. Besides, it can be applied to calibrate numerical schemes of axisymmetric poroelasticity within finite domains. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Elastic fields in two joined transversely isotropic media of infinite extent as a result of rectangular loading     

H. T. Xiao  Z. Q. Yue 《国际地质力学数值与分析法杂志》2013,37(3):247-277

This paper presents the closed‐form solutions for the elastic fields in two bonded rocks induced by rectangular loadings. Each of the two bonded rocks behaves as a transversely isotropic linear elastic solid of semi‐infinite extent. They are completely bonded together at a horizontal surface. The rectangular loadings are body forces along either vertical or horizontal directions and are uniformly applied on a rectangular area. The rectangular area is embedded in the two bonded rocks and is parallel to the horizontal interface. The classical integral transforms are used in the solution formulation, and the elastic solutions are expressed in the forms of elementary harmonic functions for the rectangular loadings. The stresses and displacements in the rocks induced by both the horizontal and vertical body forces are also presented. The numerical results illustrate the important effect of the anisotropic bimaterial properties on the stress and displacement fields. The solutions can be easily implemented for numerical calculations and applied to problems encountered in rock mechanics and engineering. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

高分辨率航空影像建筑物垂直边缘线提取技术研究   总被引：1，自引：0，他引：1  

李二森  张保明  邱志斌  李宝峰 《测绘工程》2010,19(5):15-19

高分辨率航空影像建筑物垂直边缘线的提取在获取建筑物高度信息和检测建筑物过程中可以发挥重要的作用。分析建筑物垂直边缘线在遥感影像上的特性,在遥感影像边缘检测和细化基础上,利用带约束条件的Hough变换实现建筑物垂直边缘线的提取,通过实验验证该方法的可行性。  相似文献   

第二次土地调查底图生产监理中若干技术的探讨     

陈晓雪  马小计  周亦  武娟 《北京测绘》2010,(3):48-50

第二次全国土地调查底图生产是一项重大的系统工程,认真做好二次调查底图生产监理工作可有效保证成果的质量。文章对二次土地调查底图生产的监理流程进行了简单介绍,同时对工作中出现的正射纠正、投影变换以及影像质量检查等若干技术方法进行了一些探讨。  相似文献