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Nonlinear, nonlocal and adaptive optimization algorithms, now readily available, as applied to parameter estimation problems,
require that the data to be inverted should not be very noisy. If they are so, the algorithm tends to fit them, rather than
smoothening the noise component out. Here, use of Bernstein polynomials is proposed to prefilter noise out, before inversion
with the help of a sophisticated optimization algorithm. Their properties are described. Inversion of gravity and magnetic
data for basement depth estimation, singly and jointly, and without and after Bernstein-preprocessing is conducted to illustrate
that the inversion of Bernstein-preprocessed gravity data alone may be slightly superior to the joint inversion of gravity
and magnetic data. 相似文献
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南海重力异常特征及其显著的构造意义 总被引：1，自引：0，他引：1
在南海地区地震测深数据有限的情况下,利用重力异常可以研究南海大范围的深部地壳结构及地质构造展布特征。基于空间重力异常,结合最新的地形、沉积物厚度及地震测深等数据,分别从地震约束的莫霍面反演和无约束的三维相关成像两个视角研究南海的地壳结构,利用壳幔界面起伏、地壳厚度及三维等效密度分布来探讨地壳结构的纵横向变化。同时,联合采用延拓、水平梯度及线性构造增强滤波方法聚焦重力异常中的区域线性特征,突出显示了反映地壳横向变化的深断裂、洋陆转换边界、海盆扩张轴等线性构造的展布。重力解释与贯穿南海南北的广州-巴拉望地学断面对比表明,重力异常反演及异常的区域线性特征,较好地揭示了南海海域大范围的地壳结构与区域构造展布。 相似文献
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A method to model 3D sedimentary basins with parabolic density contrast is applied to Büyük Menderes basin in Western Anatolia. The measured gravity fields, reduced to a horizontal plane, are assumed to be available at grid nodes of a rectangular/square mesh. Juxtaposed 3D vertical prisms with their geometrical epicenters on top coincide with grid nodes of a mesh to approximate a sedimentary basin. The algorithm based on Newton’s forward difference formula automatically calculates the initial depth estimates of a sedimentary basin assuming that 2D infinite horizontal slabs can generate the measured gravity fields and among these slabs the density contrast varies with depth. The lower boundary of a sedimentary basin is formulated by estimating the depth values of the 3D prisms with in predetermined limits. Measured gravity fields pertaining to the Büyük Menderes basin, Turkey, where the density contrast varies with depth, are interpreted to show the applicability of the method. 相似文献
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Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gradients. At present, vertical, horizontal, and triaxial aeromagnetic gradiometers are in operation throughout the world, while the first two are used more widely. Transformations between horizontal and vertical gradients are needed for acquiring three gradient components or for checking the vali... 相似文献
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The decrease of density contrast with depth in sedimentary basins is approximated by an exponential function. The anomaly
equation, in frequency domain, of a prismatic model with an exponential density function is derived. The method has been extended
to derive the Fourier transforms of the gravity anomalies of the sedimentary basin, wherein the basin is viewed as vertical
prisms placed in juxtaposition. The gravity anomalies of the sedimentary basin are obtained by taking the inverse Fourier
transforms. Filon’s method has been extended for calculating accurate inverse Fourier transforms. The accuracy of the method
has been tested using a synthetic example. A combination of space and frequency domain methods have been developed for inversion
of gravity anomalies over the sedimentary basin. The method has been applied to interpret one synthetic profile and one field
profile over the Godavari basin. The method developed in this paper to calculate the inverse Fourier transforms yields continuous
spectrum with accurate values. The maximum depth deduced from the gravity anomalies is of the same order as the depth encountered
to the basement at the Aswaraopeta borewell. 相似文献
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Least squares collocation is a very comprehensive method for gravity field modelling, since it may use known noise characteristics of the data. In many earlier applications the errors affecting the data were considered uncorrelated, mainly due to the difficulty in estimating the systematic character of such kind of errors. In this study, error covariance functions of airborne gravity gradiometer data are estimated by comparing model covariance functions with empirical covariance functions of the gravity gradiometer data. The model covariance functions were estimated from accurate surface gravity data and continuated upward to the height of the airborne measurements using the covariance propagation law. The estimated error covariance functions were modeled as finite ones and used as an additional information for the prediction of gravity anomalies from gravity gradiometer data. The assessment of the prediction results was made by comparing the gravity values predicted from the airborne gradient data and showed up to 25% improvement compared to not using correlated errors. 相似文献
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The Rapid Inversion of 3-D Potential Field and Program Design 总被引：1，自引：0，他引：1
The application of three-dimensional inversion of gravity and magnetic fields is very important not only in geophysical researches, but also in the study of geological structures. A formula of potential field in frequency-domain, developed by Parker in 1973, can be used as a rapid and effective algorithm in gravity and magnetic inversion. The technique has been improved then by Oldenburg, Sprenke, Feng and others.In addition to a brief introduction of Parker's algorithm and its applications, this paper includes the following five parts: basic computational techniques, inversion of single layer, convergence and constraints, simultaneous inversion for density and topography as well as inversion of multilayers. The authors present relevant practical iterative formulas and its varieties when density distribution varies with depth in linear or exponential relation. In order to maintain computation stability and speed up iteration convergence, some approaches are taken in the program design, for instance shifting lower interface of the studied layer, inverting corrections of topography, reducing grid boundary effects and utilizing low-pass filter. With the consideration of the nonuniqueness of the inversion, a method of using seismic data to constrain the range ofpossible models is discussed. It is pointed out that the density variation generates less effects than those of topography on the spectrum of gravity anomaly in second order. Therefore density contrast and topography can be inverted simultaneously by an alternative weighting iteration. By analogy, the inversion of multilayer model can be done in the above procedure. An approach of model decomposition is useful in the computation of multilayer model. The techniques discussed in the present paper for gravitational field are also valid for magnetic field. 相似文献
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复小波变换反演重力异常 总被引：6，自引：2，他引：6
对国外最新研究位场连续复小波变换理论的一系列文章进行了系统归纳、推导与总结,推出了板状体重力场的小波变换系数解析式.对齐次场源形成的重力场进行柯西小波变换,等效于重力场向上延拓和求导两种运算相结合,并服从小波变换双尺度定律.利用小波变换系数模沿极值轴线的变化特征同时反演重力场源的几何形状、埋深、倾角.独立编写了所有程序,并对不同理论模型进行了大量计算,对所有结果进行了分析与讨论.此法为重力场反演提供了一条新的途径,实用于重磁资料自动化处理、反演与解释. 相似文献
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场源中心位置的计算是重磁数据反演的主要任务之一,现主要通过异常与场源位置之间的数学物理方程来估算地质体的位置.为了快速、准确获得地质体的位置信息,提出基于重磁梯度比值的深度学习技术实现场源位置的获取;其利用深度学习技术所建立的重磁梯度比值水平分布与地质体埋深、构造指数的关系,快速实现异常场源位置计算,且提出利用多个值的相互关系来更加准确、稳定地计算出地质体的信息.该方法可以计算复杂地质体的中心位置,且避免了以往线性方程反演方法需对结果进行筛选的复杂过程,对于存在剩磁的磁异常则采用解析信号的深度学习方法来进行位置反演.理论模型试验证明利用梯度比值的深度学习方法可以准确获得地质体的深度,且通过对比更多点的深度学习计算结果发现,采用多个不同比例极值点可以减弱噪声带来的干扰,从而得到更加准确的位置.最后将该方法应用于实测磁异常的反演工作,获得了地下磁性物体的中心位置,且计算结果与欧拉反褶积法相接近,因此该方法具有良好的实用性. 相似文献
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The resolution of self-potential anomalies due to closely spaced multiple sheet-like bodies by the potential difference and potential gradient is studied in this paper. Self-potential anomalies due to several synthetic models were inverted through a very fast simulated annealing (VFSA) global optimization. Increase in depth to the top, polarization constant and depth extent of the body decreases resolution at a particular target separation. It has been observed that depth to the top and separation between two targets play an important role in the resolution. Vertical sheets at equal depth can be resolved in the potential difference measurement only if they are separated by at least four times their depth, while they can be resolved in the gradient method, if they are separated by twice the depth. Resolution using potential difference becomes more difficult for dipping sheets, although the potential gradient method can resolve them efficiently. Efficacy of potential gradient data in the inversion is demonstrated in the study using synthetic data as well as field measurement from South Purulia Shear Zone related with uranium investigation. 相似文献
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An evolutionary approach is applied to solve the nonlinear well logging inverse problem. In the framework of the proposed interval inversion method, nuclear, sonic, and laterolog resistivity data measured at an arbitrary depth interval are jointly inverted, where the depth variation of porosity, water saturation, and shale volume is expanded into series using Legendre polynomials as basis functions. In the interval inversion procedure, the series expansion coefficients are estimated by using an adaptive float-encoded genetic algorithm. Since the solution of the inverse problem using traditional linear optimization tools highly depends on the selection of the initial model, a heuristic search is necessary to reduce the initial model dependence of the interval inversion procedure. The genetic inversion strategy used in interval inversion seeks the global extreme of the objective function and provides an estimate of the vertical distribution of petrophysical parameters, even starting the inversion procedure from extremely high distances from the optimum. For a faster computational process, after a couple of thousand generations, the genetic algorithm is replaced by some linear optimization steps. The added advantage of using the Marquardt algorithm is the possibility to characterize the accuracy of the series expansion coefficients and derived petrophysical properties. A Hungarian oil field example demonstrates the feasibility and stability of the improved interval inversion method. As a significance, the genetic inversion method does not require prior knowledge or strong restrictions on the values of petrophysical properties and gives highly reliable estimation results practically independent of the initial model and core information.
相似文献14.
We investigate the pressure distribution with depth in regions undergoing horizontal shortening and experiencing crustal thickening both analytically and numerically. Our results show that, in a convergent tectonic setting, pressure can be considerably higher than lithostatic (the pressure resulting from the weight of the overburden). Increases in pressure with respect to lithostatic conditions result from both the contribution of horizontal stresses and the flexural vertical loads, the latter generated by the deflection of the upper crust and of the mantle because of the presence of topographic relief and a root, respectively. The contribution of horizontal stresses is particularly relevant to the upper crust and uppermost mantle, where rocks are thought to deform brittlely. In these domains, pressure gradients twice lithostatic can be achieved. The contribution of horizontal stresses is less important in the ductile domains as differential stresses are progressively relaxed; nevertheless, the effects are still noteworthy especially close to the brittle–ductile transition. Flexural vertical loads generated by the deflection of the upper crust and lithospheric mantle are relevant for rocks of the weaker lower crust. As a result of the combination of the two mechanisms, the pressure gradient varies vertically through the lithosphere, ranging from negative (inverted) gradients to gradients up to several times the lithostatic gradient. The pressure values range from one to two times the lithostatic values (1ρ gz to 2ρ gz ). 相似文献
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航空重力梯度勘探中，载体自身产生的重力梯度效应对于超高精度的重力梯度仪而言是一种严重的干扰。由于载体结构复杂，用常规的载体建模并正演难以精确去除这种干扰。本文从统计学角度出发，用多元线性回归来处理自身梯度效应，不需要对载体模型做出任何假设与近似，用纯数据驱动的方式来校正自身梯度的干扰。回归诊断与模型仿真验证了这种校正方式有较高的准确性，并且当实际的转角落在地面标定的范围内时具备预测能力。 相似文献
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A new method was developed for the inversion reconstruction of gravity potential. This method offers the possibility to determine
the potential function and all of its important derivatives using the common inversion of gravity gradients and the first
derivatives of potential. Gravity gradients can be originated from Torsion balance measurements, while the first derivatives
of potential can be derived from the deflections of the vertical data. Different fields having great importance can be originated
from this reconstructed potential function at any points of the investigated area. The advantage of this method is that the
solution can be performed by a significantly over-determined inverse problem. Test computations were performed for the inversion
reconstruction of gravity potential. There were 248 torsion balance measurements and 13 points where the deflections of the
vertical are known in our test area. This inversion algorithm is rather stable. Gravity potential, the first and the second
derivatives of the potential were determined for the test area by this suggested method. This method gives a good possibility
for a useful geodetic application; deflections of the vertical based on torsion balance measurements can be determined for
the whole area for each torsion balance stations. 相似文献
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针对重力勘探中光滑反演存在的分辨率较低的问题,本文提出一种基于地质体埋深、地层倾向等一定先验信息的局部光滑约束三维反演算法,并提出了一种光滑反演中粗糙度矩阵的存储方式,该存储方式可以将M×N维粗糙度矩阵存储为M×2维,减少了计算机计算内存,且详细介绍了该存储方式下粗糙度矩阵与其他矩阵相乘时,粗糙度矩阵所存储的位置信息的读取方式以及与其他矩阵逐列逐步相乘最终得到计算结果的过程。最后,利用文中提出的算法对理论模型和实测数据进行反演试算,结果表明局部光滑反演算法相比于全局光滑反演结果更加准确,且该算法在一定噪声水平下依然稳定,在实际生产中有效可行。 相似文献
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内蒙古拉布达林盆地面积大、油气勘探程度很低.由于浅层广泛分布的火山岩的强反射屏蔽作用造成地震勘探对深层成像差，难以评价盆地油气勘探潜力.为了解决盆地主要目的层上库力组底界深度及沉积岩分布不清的问题，对盆地南部二维地震资料开展重力-地震联合反演解释.通过在GM-SYS重磁剖面解释软件中加载地震剖面，建立重力模型，利用地震浅层可靠解释成果做约束条件，消除上覆火山岩的重力干扰，减少了重力反演深层构造界面的多解性，成功地反演了盆地上库力组底界深度、沉积岩厚度，指出巴彦哈达断陷为有利勘探区，在此基础上估算出油气资源量. 相似文献
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高精度重力资料在胜利油区油气藏探测中的应用 总被引：2，自引：0，他引：2
摘要：应用改进的重力归一化总梯度法（ＧＨ法）对胜利油田ＤＢ区的高精度重力测量资料进行了处理。计算了ＧＨ值在地下的三维分布。某一深度ＧＨ平面等值线图中的闭合极小值（ＧＨ低）反映了低密度体的存在及其水平位置,而不同深度等值线图中ＧＨ低的数目的变化可以近似表示低密度体集中的深度范围。ＧＨ平面等值线图还可以为选择ＧＨ铅垂断面图的方向提供依据。ＧＨ铅垂断面等值线图中的闭合极小值更清楚地显示出低密度体的形态及其近似深度。计算出的ＧＨ值的三维分布与钻井资料的比较表明,ＧＨ的闭合极小值与已知油气藏在位置上有较明显的相关关系。 相似文献