共查询到20条相似文献，搜索用时 250 毫秒
1.
本文提出了一种基于模型空间压缩技术的大地电磁三维反演方法.该方法在传统大地电磁三维反演理论的基础上,通过小波变换将待反演的空间域模型参数映射到小波域进行反演,获得小波域更新模型后再通过小波逆变换得到空间域反演模型.由于小波变换具有压缩特性和多尺度分辨能力,本文反演方法可在一定程度上提高反演分辨率.为了提高反演效率,我们针对基于L_1范数的模型约束求解不易收敛的反演问题,提出了一种基于模型粗糙度的简单有效的预条件处理技术.为验证本文算法的有效性,本文首先对经典的"棋盘"模型进行三维反演测试.反演结果表明本文算法的反演效率与传统方法相当,但对于深部异常体具有更好的分辨能力.最后,我们通过对实测数据反演进一步验证本文算法的有效性. 相似文献
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《地球物理学进展》2020,(3)
全波形反演具有高精度成像能力,然而由理论走向实际应用还存在很多问题.全波形反演通过匹配波形来更新模型,数据的波形与地震子波有直接的关系.本文介绍了一种针对时间域波形反演的子波估计方法,并将其应用到全波形反演中.由于在频率域子波反演可表示为一个线性优化问题,因此本文先给定一个试探子波,在时间域通过有限差分法正演得到地震波场,并在频率域与观测数据比较分析,反演得到预测子波.此外,本文还简要地介绍了如何使用伴随状态法计算全波形反演的梯度.数值实验证明,本文方法反演得到地震子波与真实子波具有很好的吻合度,并在全波形反演中取得了不错的效果.相比不依赖于子波的方法,提前进行子波估计可提高反演效率.此外,本文方法适用于全波形反演中常使用的多尺度反演策略. 相似文献
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为压制伪随机多频电磁信号中的强干扰、提高数据质量,本文提出一种基于灰色判别准则和有理函数滤波的数据处理方法.首先通过灰色判别准则剔除各个频点频谱数据中的明显异常值,然后进行有理函数滤波得到充分接近真实值的圆滑数据曲线,进而约束数据的二次优化处理,剔除残余噪声的影响.为验证本文方法的处理效果,在实测无明显噪声数据中加入几种不同类型的强噪声,然后用本文方法进行处理.仿真处理结果表明,本文方法能高精度逼近原始数据,处理后数据误差低达8.09%.最后,将本文方法应用于重庆某工区实测伪随机多频电磁数据处理.结果表明,本文方法可以有效压制干扰,在频谱数据个数少、干扰幅值大（高达有效信号幅值的几个数量级）的情况下,仍可有效压制强干扰.处理后的数据相对误差显著下降,视电阻率曲线形态平滑,达到提高信噪比,改善实测数据质量的目的. 相似文献
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本文讨论了重磁反演中的Backus-Gilbert方法的应用.由于重磁位场公式中核函数的奇异性和观测数据有误差,给广义线性反演带来了很大的困难.为此,本文采用了正则化方法,其效果与谱展开法完全相同.而且,其法计算速度快,使用也方便.为了提高解的分辨力和降低方差,同时加快反演迭代的收敛速度,本文采用了约束条件下反演的方法.文中最后对山西运城二条剖面作了具体分析,反演了莫霍面和居里面. 相似文献
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本文运用声波导的理论讨论钻井声场的共振模式问题,特别注意稳态现象和暂态现象的区别与联系.本文考察了共振模式的存在性及其在声波测井信号中的反映. 相似文献
6.
起伏地形和关断时间对地面瞬变电磁响应影响严重,这给传统基于水平地表模型和理论阶跃波形的瞬变电磁数据解释技术带来很大困难.为此,本文开展考虑起伏地形和关断时间的地面瞬变电磁三维反演算法研究.正演采用基于非结构网格和后退欧拉隐式时间离散格式的时间域有限元算法,快速模拟起伏地表模型瞬变电磁响应.反演采用L-BFGS算法,减少每次反演迭代的计算量.针对发射线圈随地表起伏变化的特点,利用基于偶极子离散的场源处理技术模拟发射源的实际形状,采用瞬时电流脉冲技术实现考虑关断时间的地面瞬变电磁三维正演模拟.我们首先将本文开发的三维反演算法应用于理论模型的反演计算中,检验本文算法的可靠性,并分析地形和关断时间对反演结果的影响特征.在此基础上,进一步将本文算法应用于实测数据反演,验证本文算法的实用性. 相似文献
7.
本文将面向目标的自适应算法应用于三维大地电磁数值模拟.使用基于非结构网格的矢量有限单元法对起伏地表大地电磁正演模拟问题进行求解.使用利用垂向电流密度在物性界面上的连续性对后验误差进行估算的算法指导网格优化.由于全局自适应算法针对观测点优化网格的能力较差,本文通过求解正演问题的对偶问题计算后验误差的加权系数,并对相关加权系数进行改进,从而实现了面向目标的自适应算法.与传统基于结构化网格的电磁正演算法相比,采用非结构网格能够更好地拟合起伏地表和地下不规则异常体.由于使用了面向目标的自适应算法,本文能够使用更少的网格达到较高的计算精度.通过对比本文模拟结果与半空间响应和全局自适应算法计算结果,并通过对比使用改进前和改进后加权系数得到的网格剖分结果验证了本文算法的有效性. 相似文献
8.
近年来,探地雷达(GPR)凭借其快速、高效、无破损等特点,已经广泛应用于浅地层目标探测中.数值模拟是研究探地雷达电磁波在地下结构中传播规律的有效手段.辛算法是一种保持Hamilton系统总能量不变的时域数值计算方法.本文提出了基于一阶显式辛分块龙格库塔方法的探地雷达数值模拟方法.通过对比本文算法与时域有限差分方法计算结果可知,在同等计算精度下,本文算法可以节省25%的计算时间.并基于本文算法对两个复杂GPR模型进行正演模拟,得到模拟GPR探测wiggle图,这有助于更好的理解和分析实测雷达数据. 相似文献
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A simple and accurate traveltime approximation is important in many applications in seismic data processing, inversion and modelling stages. Generalized moveout approximation is an explicit equation that approximates reflection traveltimes in general two-dimensional models. Definition of its five parameters can be done from properties of finite offset rays, for general models, or by explicit calculation from model properties, for specific models. Two versions of classical finite-offset parameterization for this approximation use traveltime and traveltime derivatives of two rays to define five parameters, which makes them asymmetrical. Using a third ray, we propose a balance between the number of rays and the order of traveltime derivatives. Our tests using different models also show the higher accuracy of the proposed method. For acoustic transversely isotropic media with a vertical symmetry axis, we calculate a new moveout approximation in the generalized moveout approximation functional form, which is explicitly defined by three independent parameters of zero-offset two-way time, normal moveout velocity and anellipticity parameter. Our test shows that the maximum error of the proposed transversely isotropic moveout approximation is about 1/6 to 1/8 of that of the moveout approximation that had been reported as the most accurate approximation in these media. The higher accuracy is the result of a novel parameterization that do not add any computational complexity. We show a simple example of its application on synthetic seismic data. 相似文献
12.
《Ground Water Monitoring & Remediation》1988,8(1):83-87
The approximations implicit in Cochran's approximation to the Behrens-Fisher test are examined. This test is often used in evaluating ground water quality problems with temporal and spatial variabilities. Concern is focused on the impact of the number of samples and the magnitude of the variances at the sampling locations. Recommendations are presented for utilization of the t-test and Cochran's approximation, because Cochran's test is an approximation formula. Indications are provided for where the results may be giving answers different from those intended. 相似文献
13.
P. C. D. Milly 《Surveys in Geophysics》1991,12(1-3):145-154
Most combination equations for evaporation rely on a linear expansion of the saturation vapor-pressure curve around the air temperature. Because the temperature at the surface may differ from this temperature by several degrees, and because the saturation vapor-pressure curve is nonlinear, this approximation leads to a certain degree of error in those evaporation equations. It is possible, however, to introduce higher-order polynomial approximations for the saturation vapor-pressure curve and to derive a family of explicit equations for evaporation, having any desired degree of accuracy. Under the linear approximation, the new family of equations for evaporation reduces, in particular cases, to the combination equations of H. L. Penman (Natural evaporation from open water, bare soil and grass,Proc. R. Soc. London, Ser. A
193, 120–145, 1948) and of subsequent workers. Comparison of the linear and quadratic approximations leads to a simple approximate expression for the error associated with the linear case. Equations based on the conventional linear approximation consistently underestimate evaporation, sometimes by a substantial amount. 相似文献
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E. G. Bulakh 《Izvestiya Physics of the Solid Earth》2007,43(7):610-619
Methods of approximation occupy a significant place at the interpretation stage of gravity and magnetic surveys. Two main directions are the approximation of the initial field by an analytic function and the approximation or parametrization of a geological model. 相似文献
15.
The paper outlines the most important results of the paraxial complex geometrical optics (CGO) in respect to Gaussian beams
diffraction in the smooth inhomogeneous media and discusses interrelations between CGO and other asymptotic methods, which
reduce the problem of Gaussian beam diffraction to the solution of ordinary differential equations, namely: (i) Babich’s method,
which deals with the abridged parabolic equation and describes diffraction of the Gaussian beams; (ii) complex form of the
dynamic ray tracing method, which generalizes paraxial ray approximation on Gaussian beams and (iii) paraxial WKB approximation
by Pereverzev, which gives the results, quite close to those of Babich’s method. For Gaussian beams all the methods under
consideration lead to the similar ordinary differential equations, which are complex-valued nonlinear Riccati equation and
related system of complex-valued linear equations of paraxial ray approximation. It is pointed out that Babich’s method provides
diffraction substantiation both for the paraxial CGO and for complex-valued dynamic ray tracing method. It is emphasized also
that the latter two methods are conceptually equivalent to each other, operate with the equivalent equations and in fact are
twins, though they differ by names.
The paper illustrates abilities of the paraxial CGO method by two available analytical solutions: Gaussian beam diffraction
in the homogeneous and in the lens-like media, and by the numerical example: Gaussian beam reflection from a plane-layered
medium. 相似文献
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A new inversion method for seismic reflection data is based on impedance concepts and uses transformations to reduce the essentially non-linear problem to a linear eigenvalue formulation without approximation. A set of reflection data has been inverted using this method. The characteristic impedances of the layers so determined are compared with log data from a reference borehole. 相似文献
18.
Two stochastic models are developed to describe the BOD output (i.e. effluent) variation of facultative aerated lagoons in series. One of the models uses the uncertainty analysis (UA) technique and the other is based on the moment equation solution methodology of stochastic differential equations (SDE's). The former considers a second-order approximation of the expectation (SOAE) and a first-order approximation of the variance (FOAV). The SDE model considers that output variability is accounted for by random variations in the rate coefficient. Comparisons are provided. Calibration and verification of the two models are aciieved by using field observations from two different lagoon systems in series. The predictive performances of the two models are compared with each other and with another SDE model, presented in a previous paper, that considers input randomness. The three methods show similar predictive performances and provide good predictions of the mean and standard deviation of the lagoon effluent BOD concentrations and thus are considered as appropriate methodologies. 相似文献
19.
Summary A new approximation of the velocity-depth distribution in a vertically inhomogeneous medium is suggested. This approximation guarantees the continuity of velocity and of its first and second derivatives and does not generate false low-velocity zones. It is very suitable for the computations of seismic wave fields in vertically inhomogeneous media by ray methods and its modifications, as it removes many false anomalies from the travel-time and amplitude-distance curves of seismic body waves. The ray integrals can be evaluated in a closed form; the resulting formulae for rays, travel times and geometrical spreading are very simple. They do not contain any transcendental functions (such asln (x) orsin
–1, (x)) like other approximations; only the evaluation of one square root and of certain simple arithmetic expressions for each layer is required. From a computational point of view, the evaluation of ray integrals and of geometrical spreading is only slightly slower than for a system of homogeneous parallel layers and even faster than for a piece-wise linear approximation. 相似文献