基于目标区的局部角度域方向照明分析及其在偏移成像中的应用

叠前深度偏移已成为近年来地震偏移成像领域广泛应用的技术之一,其中复杂盐丘下方目标区域结构的成像始终是偏移成像中较难解决的问题.局部角度域波场分解可以提供在空间和方向上的双重局部化信息,因而这一技术被广泛地应用在方向照明分析、成像振幅校正等方面.本文在采用局部指数标架小波束进行角度域方向照明分析的基础上,研究采集系统对复杂盐丘下部层状结构成像质量的影响;同时通过分析目标区对应于相对地表采集系统分布的照明能量,确定叠前炮集数据中对盐下目标区成像起重要贡献的部分,并将这些数据用来对目标区成像,从而达到提高盐下结构成像质量的目的.本文将二维SEG-EAGE盐丘模型中盐下反射体作为目标区,分别计算其照明分析和由照明能量分布确定的炮集数据对目标区的偏移成像结果,同时通过与成像振幅校正前后的成像结果对比,说明了该方法对提高目标区结构成像质量的有效性.     

映射动力无穷元及其特性研究

本文提出了一种映射动力无穷元,这种单元不仅可以表征在均匀介质中传播的不同波数的波,而且可以模拟地基中不同介质内的波的传播特性。文中通过定义无穷元在局部坐标系中的波数(名义波数)β和在整体坐标系中的波数(介质中的实际波数)β_G,使得:1.整体坐标系中不同波数的无穷元均可用在局部坐标系中具有同一名义波数β的无穷元来模拟。这一模拟是通过改变无穷元边中点的整体坐标以及引入适当的过渡单元来实现的。2.适当地改变有限元与无穷元连接边界的法线方向与无穷元各节点在整体坐标系中的相对位置,还可以改变波在整体坐标系中的传播方向,从而为模拟不同方向传播的波提供了一种简便的技术。文中最后给出了无穷元在整体坐标系中常用的几种单元形态及其传波特性,并用算例对其精度进行了验证。     

改进高分辨率遥感影像测量断裂错动空间尺度的探讨研究

为避免在进行高空遥感影像活动断裂空间尺度测量分析时采用较多的外业控制点,降低测量过程的繁琐性,提高测量精准度,提出利用空中三角测量的遥感影像空间定位方法。通过有理多项式系数模型精准表示平面坐标系中相应像点和地面点三维空间坐标之间的数学关系,选取活动断裂区域中重叠率较高（概率较高）的控制点,忽略其他控制点以减少外业控制点的需求量;以控制点地面坐标、像点坐标作为已知值,将活动断裂区域的地面坐标以及可以精确表达卫星影像物方的几何旋转关系的定向参数作为待定量,根据有理多项式系数模型的误差方程,以最小二乘为准则确定活动断裂区域的地面坐标,定位区域遥感图像主要活动断裂解译标志包括线性标志、垂直错动和水平错动标志;依据不同标志中的两侧色调反差、阴影色调以及扭曲变形程度,将活动断裂的活动性分成强、中、弱三个等级,实现对断裂空间尺度的分析。实验结果表明,该方法测量的空间尺度精准性较高,解译和判断的断层形态与实际相符。     

曲线坐标系程函方程的求解方法研究

笛卡尔坐标系中经典的程函方程在静校正、叠前偏移、走时反演、地震定位、层析成像等许多地球物理工作都有应用,然而用其计算起伏地表的地震波走时时却比较困难.我们通过把曲线坐标系中的矩形网格映射到笛卡尔坐标系的贴体网格推导出了曲线坐标中的程函方程,此时,曲线坐标系的程函方程呈现为各向异性的程函方程(尽管在笛卡尔坐标系中介质是各向同同性的).然后尝试用求解各向同性程函方程的快速推进法和Lax-Friedrichs快速扫描算法来分别求解该方程.数值试验表明未加考虑各向异性程函方程与各向同性程函方程的差别而把求解各向同性程函方程的快速推进法直接拓展到曲线坐标中的程函方程的做法是错误的,而Lax-Friedrichs快速扫描算法总能稳定地求解曲线坐标系的程函方程,进而有效地处理了地表起伏的情况,得到稳定准确的计算结果.     

球坐标系下三维大地电磁正演研究

大地电磁正演理论研究热点一直以来主要集中在如何提高计算效率和精度,但在剖面足够长、探测深度足够大的情况下,传统的笛卡尔坐标系数值模拟方式难以准确拟合地球曲率形态.本文研究了基于球坐标系的三维大地电磁正演,推导了交错网格有限差分三维正演公式,与一维解析解和三维标准模型测试对比,验证了正演算法的正确性.通过理论模型计算,对比分析球坐标和笛卡尔坐标系正演结果表明：球坐标系模拟更合理,避免了传统笛卡尔坐标拉伸投影所引入的误差,可代替目前的笛卡尔坐标模拟方法.基于球坐标和笛卡尔坐标系的三维大地电磁正演响应值随着频率变低差异越明显.球坐标和笛卡尔坐标计算结果差异度与频率、模型结构和电阻率有关.本文模型计算结果在数万秒周期处已出现接近10%的差异,对于较大尺度的长周期大地电磁,地球曲率的影响不能忽略.     

贴体网格各向异性对坐标变换法求解起伏地表下地震初至波走时的影响

笛卡尔坐标系中的经典程函方程在静校正、叠前偏移、走时反演、地震定位、层析成像等很多地球物理工作中都有应用,然而用其计算起伏地表的地震波走时却比较困难.本文通过把曲线坐标系中的矩形网格映射到笛卡尔坐标系的贴体网格,推导出曲线坐标中的程函方程,而后,用Lax-Friedrichs快速扫描算法求解曲线坐标系的程函方程.研究表明本文方法能有效处理地表起伏的情况,得到准确稳定的计算结果.由于地表起伏,导致与之拟合的贴体网格在空间上的展布呈各向异性,且这种各向异性的强弱对坐标变换法求解地震初至波的走时具有重要影响.本文研究表明,随着贴体网格的各向异性增强,用坐标变换法求解地表起伏区域的走时计算误差增大,且计算效率降低,这在实际应用具有指导意义.     

关于手持GPS测定活断层位置中求解坐标系统转换参数的问题

测定活断层的坐标、绘制活断层空间位置分布图,是城市活断层探测的一个重要目的。手持GPS可以方便、快捷的测定目标点的WGS-84坐标,测量精度也满足1∶1万地形图的要求。本文介绍如何求解系统转换参数,将WGS-84坐标转换为我国目前使用的是1954年北京坐标系或1980年国家大地坐标系。进而可以利用GIS技术建立活断层信息管理数据库系统。     

浅水无定位拖缆观测系统定义及多次波压制效果分析

浅水无定位拖缆在近岸海洋工程及浅水多道地震勘探中应用广泛,但受无定位拖缆实际位置获取的限制,野外观测系统准确定义受影响.基于传统直线假设的观测系统定义简单易行,但计算的共反射点面元无法获得实际坐标,位置偏差较大,严重影响后续处理方法的有效应用.基于实际炮点轨迹坐标,本文提出了一种新的无定位拖缆实际坐标计算方法,新方法首先确定接收排列的相对空间位置,采用反距离比线性插值算法准确计算接收道实际坐标值,再根据实际坐标重新定义观测系统,获得了实际跑航弯曲测线观测系统图.文中对传统方法与新方法定义的不同观测系统数据,分别采用SRME(Surface-related Multiple Elimination)方法压制浅水海底鸣震类自由表面相关多次波,结果显示采用新方法定义的观测系统反射数据多次波衰减效果明显,有效反射连续,基底反射成像清晰,说明文中实际坐标计算方法符合海上弯曲测线观测系统的定义,提高了SRME方法压制多次波的效果.     

卫星重磁数据球坐标系下正反演方法研究进展

卫星重磁观测数据覆盖范围广、更新周期快是现代地球物理中重要的数据类型之一.随着卫星重磁观测技术的不断发展,卫星重磁观测数据的精度和分辨率得到了大幅提高,被广泛的应用于探索地球、月球、火星等天体内部物质分布、结构、构造等地学问题的研究.在研究过程中,对卫星重磁数据选择合适的处理和反演方法是后续能否进行精确分析解释的重要前提.基于球坐标系下的卫星重磁数据解算、正、反演方法为大尺度地学问题的球面研究为更贴近于实际地质情况提供了方法技术支持.本文针对卫星重磁数据的曲面数据和大尺度应用研究的特点,对近年来提出的球坐标系下Tesseroid单元体的正、反演方法进行了较为全面的阐述.可为国内同行深入了解卫星重磁数据在球坐标系下的研究现状和开展进一步的研究提供参考,促进卫星重磁数据在我国地球系统科学领域中发挥更大作用.     

直升机航空TEM中心回线线圈姿态校正的理论研究

在直升机航空电磁测量时,固定在吊舱内的发射-接收线圈受飞行速度、飞机颠簸、风向等影响,会发生旋转,导致线圈与大地之间的耦合发生变化,给测量的电磁数据带来姿态误差,因此,研究航空线圈姿态校正非常重要.本文在建立吊舱和大地系统双坐标系的基础上,确定了吊舱旋转时,双坐标系之间变量变换的旋转矩阵,推导出层状大地垂直圆线圈姿态变化时航空电磁响应的计算表达式,以及线圈发生摇摆、俯仰旋转时的电磁响应系数,仿真研究了线圈姿态变化对电磁测量的影响,提出了姿态误差的几何校正方法,为航空电磁测量数据的精确处理和解释奠定了理论基础.     

基于波场延拓的变换坐标转换波静校正

常规的转换波静校正的基本思想都是从地震波的运动学特征出发,基于地表一致性假设.在地表条件复杂和地表高程相差较大的地区,它不仅无法解决严重的静校正问题,反而会带来新的畸变.本文基于频率波数域波动方程偏移原理,采用波场延拓方法实现转换波静校正,其关键点在于时间空间域和频率波数域的相对应.文中通过坐标变换将起伏地表转化为新坐标系下的水平地表,把炮点和检波点映射到同一水平面上,然后在新坐标系下推导频率域波动方程延拓公式,接着对下行波P和上行转换波SV分别利用近地表速度向上延拓到基准面,恢复起伏地表到基准面之间的真实波场,最后转换到原始坐标系取出基准面数据完成转换波静校正.通过对模拟和实际数据处理,证明该方法是正确和有效的.     

大地坐标系应变张量表达及其与地心直角坐标系的相互转换

推导并给出了不同正交曲线坐标系应变张量和转动张量的普适表达和在旋转椭球坐标系下的应变张量表达,给出了不同正交曲线坐标系之间应变张量转换的普适表达式,以及在大地坐标系与地心直角坐标系这两种坐标系之间应变张量矩阵相互转换的具体表达,可供实际研究工作应用。     

MICROMETER SCALE MORPHOLOGY MEASUREMENT SYSTEM: A NEW TECHNIQUE FOR MICRO-TOPOGRAPHY MEASUREMENT ON FAULT PLANES

Earthquakes commonly occur in the sliding surface of the fault zone. The morphology of the sliding surface is the result of fault activities, and also it evolves with the activities. The irregular geometry of the fault plane affects the sliding resistance, the concentration and anisotropy of the stress distribution within the fault plane and the fault shear strength. So, the acquisition of high-precision morphological features is of great significance for studying the correlation between fault surface morphology and seismic nucleation, fracture propagation and termination. Due to the lack of reliable micron-scale morphological measurement apparatus, the study of the coherence of the fault surface morphology from large scale(unit: m-cm)to small scale(unit: μm)is subject to restrictions, as well as the study of the relationship between the micro-morphology of the experimental frictional surface and the rupture process. In order to improve the measurement accuracy of the fault plane and overcome the shortcomings of existing measurement methods, we have invented a morphology measurement system with independent intellectual property rights.
The measuring principle of this morphology measurement system is based on the laser rangefinder theory. The frame of this system consists of four parts: Braced Frame, Moving Scanner Unit, System-Controlling Unit and Data Collection Unit. Braced Frame is made up of high-adjustable frame, loading stage, dust-proof box and isolation platform, which is used to provide a vibration isolation, light proof and dust-proof measuring environment. Moving Scanner Unit contains a laser head and a two-dimensional translation stag, the laser head is used to measure vertical distance and a two-dimensional translation stage carrying a laser head moving in X-axis and Y-axis orientation to provide X, Y coordinate values. System-Controlling Unit includes two-dimensional translation stage controller, laser head controller and signal convertor. The function of this part is mainly to control operation of other parts. The Data Collection Unit is composed of computer system and software module. This part connects other parts for receiving and storing data. In order to improve the scan efficiency, we developed new software by which we can precisely control the measuring process and efficiently process the acquired data. The software is comprised of five modules: 1)Move Module, this module is used to control the original moving of the laser head relative to the two-dimension translation stage and display the 3-dimensional coordinate information in real time; 2)Set Parameters of Scan Area, the function of this module is to obtain the XY coordinate values of four corner points of the target area to scan; 3)Scan Method Module, though this part, we can control the point spacing in the X-axis orientation by inputting velocity of laser header, as well as the point spacing in X-axis orientation by inputting the Y-step parameter; 4)Pre-Scan Module, there are three functions in this module to inspect whether the z-value of the target area is beyond the range of the laser head or not, estimate consuming time for scanning the object area under the predefined parameters and to estimate the size of the result file; and 5)Scan Module, the function of this module is to store the scanning data.
We scanned the camera lens and the standard plate whose standard deviations are lower than 5μm to acquire the precision of the measurement system, and the results show that the precision of the plane positioning (X-axis and Y-axis direction)is better than 3.5μm; the vertical measurement precision is better than 4.5μm. The highest resolution of the measurement system is constrained by the performance of the laser head and two-dimension translation stage, and the horizontal resolution can reach 0.62μm, vertical resolution 0.25μm. When the needed resolution is lower than the highest, we can achieve it through adjusting the parameter of the velocity in the X-axis orientation and steps in the Y-axis orientation. To test the practical effect of the measurement system, we scanned an area of frictional surface of experimental rock using this system and obtained a high-resolution topography data. From the DEM interpolated from the cloud data, we can observe the striation on the fault plane and the variation of the roughness distribution. The roughness and slope distribution results show that the topography measurement system can meet our requirements for analyzing the microscopic morphology on the micrometer scale.
Compared with traditional measurement devices, the morphology measurement system has the following advantages: 1)The measurement system can obtain the data even in a valley region with a large dip angle on the surface because the vertically emitted beam by the laser head is practically perpendicular to the surface. So compared with other means, it can avoid producing a blank area of measurements and get a complete area; 2)the measurement system has a larger measurement range of 30cm×30cm. When the high-resolution measurement is performed on a large scale, the error caused by the registration of multiple measurement results can also be avoided.     

Matrix expression of thermal radiative characteristics for an open complex

The directionality of thermal radiance of a homogeneous isothermal non-black plane surface is totally decided by its directional emissivity, which depends on the complex dielectric constant and roughness of surface. It can be expressed by This paper proves that it is necessary to express emissivity by a matrix when a target becomes an inhomogeneous non-isothermal open complex with complicated inner geometric structure. The matrix describes the inner radiative interaction among components accurately and also expresses its thermal radiative directionality and structural characteristics completely. Advantages of matrix expression are as follows: first, the physical mechanics of effective emissivity of an open complex is described in a simple and perfect way; second, it becomes easy to understand the principle and method to retrieve components temperature from multi-angle thermal remotely sensed data; and third, the differences of directionalities between an open complex and a homogeneous isothermal non-black plane body are expressed by just using an effective emissivity matrix instead of an emissivity vector. Formula in classic physics is only the special case of matrix expression; therefore, the matrix is a universal unconditional expression to describe the directionality of thermal radiance.     

METHODS FOR CONTOURING IRREGULARLY SPACED DATA*

The sampling theorem in two dimensions univocally defines a surface, provided that its values are known at points disposed on a regular lattice. If the data are irregularly spaced, the usual procedure is first to interpolate the surface on a regular grid and then to contour the interpolated data: however, the resulting surface will not necessarily assume the prescribed values on the irregular grid. One way to obtain this result is to introduce a transformation of the coordinates such that all the original data points are transferred into part of the nodes of a regular grid. The surface is then interpolated in the points correspondent to the other crosspoints of the regular grid; the contour lines are determined in the transformed plane and then, using the inverse coordinate transformation, are transferred back to the original plane where they will certainly be congruent with the original data points. Nonetheless, the resulting surface is very sensitive to the interpolation method used: two algorithms for that are analyzed. The first (harmonization) corresponds to the determination of the potential of an electrical field whose contour conditions are those defined by the data points. The second method consists in two dimensional statistical estimation (krigeing); in particular, the effects of different choices for the data auto-covariance function are discussed. The solutions are compared and some practical results are shown.     

Results of locating the IASPEI GT(0-5) reference events using the standard ISC procedures

The International Seismological Centre (ISC) is charged with production of the definitive global bulletin of seismic events, based on the most comprehensive set of parametric data collected from all over the world. Almost every event in the bulletin retains the original hypocentral solutions reported to the ISC by contributing agencies. In addition, where possible, the ISC computes its own solution, which is intended to be the most accurate where the data from several networks are used. It is because of the requirement for consistency of the bulletin over the years that the procedures used at the centre to compute hypocentres have remained rather conservative despite considerable advances made in the field of earthquake location.The ISC has developed and put into operation a new data management system. As a result, it is now possible to review and subsequently introduce more up-to-date methods of locating seismic events into the operations. The ISC Governing Council called for a workshop dedicated to location procedures, which was held during the 2005 IASPEI General Assembly in Santiago, Chile.To compare the accuracy of different location algorithms, a list of 156 reference events (IWREF) was selected prior to the workshop. The list includes geographically well distributed earthquakes and explosions with positions known with an accuracy of up to 5 km. It covers the period of 1954-2001 and includes all station readings and hypocentral solutions of different agencies available for these events in the ISC bulletin. Although the original ISC solutions are included, these may be different from the solution obtainable now due to changes in the ISC procedures over the years. This paper presents the results of relocation of these events using standard ISC location procedures as of 2005. These new ISC locations and analysis of their shifts with respect to reference locations present a benchmark for further improvement.     

Spatial prediction of river channel topography by kriging

Topographic information is fundamental to geomorphic inquiry, and spatial prediction of bed elevation from irregular survey data is an important component of many reach‐scale studies. Kriging is a geostatistical technique for obtaining these predictions along with measures of their reliability, and this paper outlines a specialized framework intended for application to river channels. Our modular approach includes an algorithm for transforming the coordinates of data and prediction locations to a channel‐centered coordinate system, several different methods of representing the trend component of topographic variation and search strategies that incorporate geomorphic information to determine which survey data are used to make a prediction at a specific location. For example, a relationship between curvature and the lateral position of maximum depth can be used to include cross‐sectional asymmetry in a two‐dimensional trend surface model, and topographic breaklines can be used to restrict which data are retained in a local neighborhood around each prediction location. Using survey data from a restored gravel‐bed river, we demonstrate how transformation to the channel‐centered coordinate system facilitates interpretation of the variogram, a statistical model of reach‐scale spatial structure used in kriging, and how the choice of a trend model affects the variogram of the residuals from that trend. Similarly, we show how decomposing kriging predictions into their trend and residual components can yield useful information on channel morphology. Cross‐validation analyses involving different data configurations and kriging variants indicate that kriging is quite robust and that survey density is the primary control on the accuracy of bed elevation predictions. The root mean‐square error of these predictions is directly proportional to the spacing between surveyed cross‐sections, even in a reconfigured channel with a relatively simple morphology; sophisticated methods of spatial prediction are no substitute for field data. Copyright © 2007 John Wiley & Sons, Ltd.     

Dynamic loading of the boundaries in the finite-difference study of diffraction

Summary The finite-difference method can be used for obtaining the theoretical seismic response of a block structure to an incident plane wave. Computer time is saved by solving an equivalent problem of dynamic loading of the boundary of the block structure. The loading is performed by means of a set of discrete body forces, replacing the incident wave at the interface.     

CORS观测网络地壳运动监测系统研制及应用

以四川CORS观测网络为数据基础,结合GPS高精度数据处理技术及B／S技术架构,设计并实现了一套地壳运动在线监测系统。该地壳运动监测系统以GAMIT／GLOBK为数据处理引擎,实现各CORS站数据的高精度自动化解算,并通过WEB技术实现测站信息、基线序列以及坐标序列等的信息可视化表达。试验结果表明,该系统具备较好的运行稳定性和友好的人机交互性,可实现自动化的区域地壳运动监测。     

两斜交柱坐标系间谐波函数坐标变换的辅助平面方法.

针对利用波函数展开法进行三维地震响应研究中的坐标变换问题,提出了在两斜交柱坐标系间谐波函数空间坐标变换的辅助平面方法．通过建立与空间点对应的一系列辅助平面,将地震波三维散射研究中的谐波函数表达式从柱坐标系变换至辅助平面内的极坐标系,然后在辅助平面内运用Graf加法公式,将柱坐标系下的波函数表达式变换至与该柱坐标系斜交的另一柱坐标系下,从而将三维问题转换成二维问题进行处理,最终得到了斜交柱坐标系下内域问题和外域问题的坐标变换公式．