共查询到20条相似文献，搜索用时 15 毫秒
1.
It is difficult to numerically solve steady-state equations for calcium, which are used to determine temperature and electron
density in a sunspot umbra chromosphere. As a result, the coefficients of equations, obtained using inversion of the measured
profiles of five Ca II lines, are to a certain degree uncertain. Never-theless, these insignificant uncertainties do not make
it possible to consider that a unique solution of the set of equations, found using classical methods, is sufficiently reliable.
Reasonable restrictions on desired variables are presented, which makes it possible to sufficiently accurately restore temperature
variations in the specified (test) model of a sunspot umbra. Temperature variations in the studied region of the chromosphere
are restored to an average relative error of ±14%. 相似文献
2.
Niels B. Christensen 《Geophysical Prospecting》2016,64(6):1620-1631
A novel, fast, and approximate forward modelling routine for time‐domain electromagnetic responses is presented. It is based on the separation of the forward problem into a configuration‐independent part, mapping conductivity as a function of depth onto apparent conductivity as a function of time, and a configuration‐dependent part, i.e., the half‐space step response. The response of a layered model is then found as the half‐space response for a half‐space conductivity equal to the apparent conductivity. The mapping is ten times faster than traditional accurate forward modelling routines, and through stochastic modelling, it is found that the standard deviation of the modelling error is 0.7 %. The forward mapping lends itself to integration in a modern state‐of‐the‐art inversion formulation in exactly the same way as traditionally computed responses, and a field example is included where inversion results using the approximate forward response are compared with those of an accurate forward response for helicopterborne transient electromagnetic data. In addition to being used in its own right in inversion of transient data, the speed and accuracy of the approximate inversion mean that it is well suited for quality control and fast turnaround data delivery of survey results to a client. It can also be used in hybrid inversion formulations by supplying initial iterations and high‐quality derivatives in an inversion based on accurate forward modelling. 相似文献
3.
有限差分法广泛应用于地震波数值模拟、成像和波形反演中,差分数值解的精度直接影响着地震成像和反演的效果.因为有限差分算子可以通过截断伪谱法的空间褶积序列得到,而截断窗函数的属性影响有限差分算子逼近微分算子的精度.具体地讲,窗函数的幅值响应的主瓣和旁瓣决定了有限差分算子逼近的精度,主瓣越窄,旁瓣衰减越大,则有限差分算子逼近微分算子的精度越高,更好地压制数值频散.基于此认识,本文提出了一种基于Chebyshev自褶积组合窗截断逼近的有限差分算子优化方法.Chebyshev自褶积组合窗的主瓣较窄,且旁瓣衰减大,其可通过只调节三个参数,更直观和可视化地控制主瓣和旁瓣的形状,改变有限差分算子逼近微分算子的精度;该窗函数截断逼近的有限差分算子不仅有较大的谱覆盖范围,而且精度误差波动较小,这表明低阶的差分算子可以达到高阶算子的精度,且逼近误差更稳定;从经济上来讲,将有效地减少模拟计算花费,提高计算效率. 相似文献
4.
G. Michael Hoversten 《Geophysical Prospecting》1996,44(6):935-961
Hydrocarbon exploration in the Papuan fold belt is made extremely difficult by mountainous terrain, equatorial jungle and thick karstified Miocene limestones at the surface. The high-velocity karstified limestones at or near the surface often render the seismic technique useless for imaging the subsurface. In such areas magnetotellurics (MT) provides a valuable capability for mapping subsurface structure. The main structural interface which can be mapped with MT, due to the large electrical contrast, is the contact between the resistive Darai limestone and the underlying conductive sediments of the Ieru Formation. In some areas the base of the Darai can be mapped with reasonable accuracy by fitting 1D models to the observed MT data. However, in many cases where 2D and 3D effects are severe, 1D interpretations can yield dramatically incorrect results. Numerical and field data examples are presented which demonstrate the severity of the 1D errors and the improvements in accuracy which can be achieved using a 2D inverse solution. Two MT lines over adjacent anticlines, both with well control and seismic data, are used to demonstrate the application of 1D and 2D inversions for structural models. In both cases the seismic data provide no aid in the interpretations. The example over the Hides anticline illustrates a situation where 1D inversion of either TE or TM mode provides essentially the same depth to base of Darai as 2D inversion of both TE and TM. Both models provide base Darai depth estimates which are within 10% of that measured in the well. The example over the Angore anticline illustrates the inadequacy of 1D inversion in structurally complex geology complicated by electrical statics. The TE mode fits a 1D Darai thickness of 800 metres while the TM mode fits a 1D Darai thickness of 3500 metres, bracketing the thickness of 2450 metres observed in the well. The final 2D inversion model provides a depth estimate of 2250 metres. Four MT lines along the Angore anticline have been interpreted using 2D inversion. A high degree of correlation exists between lineaments observed on an airborne radar image and zones of low resistivity within the high-resistivity material interpreted as Darai limestone. These low-resistivity zones are interpreted as fault zones. Three-dimensional modelling has been used to simulate 3D statics in an otherwise 2D earth. These data were used to test the Groom-Bailey (GB) decomposition for possible benefits in reducing static effects and estimating geoelectric strike in the Papua New Guinea (PNG) field data. It has been found that the GB decomposition can provide improved regional 2D strike estimates in 3D contaminated data. However, in situations such as PNG, where the regional 2D strike is well established and hence can be fixed, the GB decomposition provides apparent resistivities identical to those simply rotated to strike. 相似文献
5.
在地震勘探中,描述复杂介质的正演和反演问题通常包含许多反映介质不同特性的参数.同时获得这些参数对进行更准确的岩性描述和油藏预测具有重要的理论和现实意义.为了提高频率域黏弹性波动方程的零偏VSP多参数反演的精度,本文对多参数反演的可行性进行分析,明确了目标函数的敏感程度及参数之间的耦合情况,提出了一种基于走时约束的分频分步多参数反演策略.首先利用零偏VSP资料构建先验信息,然后分别利用高、低频数据进行两步反演,也就是"三个参数反演+五个参数反演"的过程,以提高反演的稳健性和精度.利用此方法可同时得到零偏VSP数据可靠的弹性波速度、密度和品质因子,为精确的时-深关系及含油气的解释和预测奠定基础,同时也可以为地面地震叠前反演提供可靠有效的约束,增强地面地震反演精度. 相似文献
6.
孙林洁 《CT理论与应用研究》2020,29(5):566-575
优质气层与低含气饱和度的差气层、气水同层均呈现"亮点"强振幅的地震响应特征,利用振幅类属性或者常规弹性参数难以进行有效判识。考虑到密度参数随含气饱和度的高敏感性,本文在贝叶斯叠前反演框架下,以三变量柯西分布为先验正则约束进行叠前地震反演,减小了纵波速度、横波速度与密度三参数统计相关性造成的参数估算误差,进一步提高了弹性参数的可靠性,模型测试表明新方法反演的密度精度及稳定性更高。将方法应用于马达班湾盆地X区块,在流体替代及岩石物理统计分析的指导下,利用基于三变量柯西分布的叠前地震反演方法提取密度参数,预测优质气层富集区,实钻结果与预测结果吻合度高,表明该方法具有较高的实用性。 相似文献
7.
V.B. Piip 《Geophysical Prospecting》2001,49(4):461-482
A method using simple inversion of refraction traveltimes for the determination of 2D velocity and interface structure is presented. The method is applicable to data obtained from engineering seismics and from deep seismic investigations. The advantage of simple inversion, as opposed to ray‐tracing methods, is that it enables direct calculation of a 2D velocity distribution, including information about interfaces, thus eliminating the calculation of seismic rays at every step of the iteration process. The inversion method is based on a local approximation of the real velocity cross‐section by homogeneous functions of two coordinates. Homogeneous functions are very useful for the approximation of real geological media. Homogeneous velocity functions can include straight‐line seismic boundaries. The contour lines of homogeneous functions are arbitrary curves that are similar to one another. The traveltime curves recorded at the surface of media with homogeneous velocity functions are also similar to one another. This is true for both refraction and reflection traveltime curves. For two reverse traveltime curves, non‐linear transformations exist which continuously convert the direct traveltime curve to the reverse one and vice versa. This fact has enabled us to develop an automatic procedure for the identification of waves refracted at different seismic boundaries using reverse traveltime curves. Homogeneous functions of two coordinates can describe media where the velocity depends significantly on two coordinates. However, the rays and the traveltime fields corresponding to these velocity functions can be transformed to those for media where the velocity depends on one coordinate. The 2D inverse kinematic problem, i.e. the computation of an approximate homogeneous velocity function using the data from two reverse traveltime curves of the refracted first arrival, is thus resolved. Since the solution algorithm is stable, in the case of complex shooting geometry, the common‐velocity cross‐section can be constructed by applying a local approximation. This method enables the reconstruction of practically any arbitrary velocity function of two coordinates. The computer program, known as godograf , which is based on this theory, is a universal program for the interpretation of any system of refraction traveltime curves for any refraction method for both shallow and deep seismic studies of crust and mantle. Examples using synthetic data demonstrate the accuracy of the algorithm and its sensitivity to realistic noise levels. Inversions of the refraction traveltimes from the Salair ore deposit, the Moscow region and the Kamchatka volcano seismic profiles illustrate the methodology, practical considerations and capability of seismic imaging with the inversion method. 相似文献
8.
本文实现了地面矩形大定源三维频率域反演.矩形大定源三维模型响应计算采用交错网格有限差分技术.正演的微分方程为异常电场满足的非齐次Helmholtz方程,方程右手边源项中的大定源产生的背景格林函数由虚界面法结合虚框法计算.频率域三维反演采用非线性共轭梯度反演技术.反演的数据类型为垂直磁场的频率域响应Hz的实部和虚部分量.数值结果表明,(1)三维模型正演模拟数值结果与前人一致,为三维反演奠定基础;(2)针对两个三维导电模型,分别进行了三维反演数值试算.反演结果可以清晰恢复出异常体的电阻率和位置信息,表明地面矩形大定源三维频率域非线性共轭梯度反演具有可行性.本文研究的意义在于,在电磁响应时频转换技术的基础上,如果将野外实测的瞬变电磁数据变换为对应的频率响应,则结合本文提出的三维反演技术,可以为矩形大定源瞬变电磁数据的三维解释提供一个新的思路. 相似文献
9.
Laura Carmine Elsa Aristodemou Christopher Pain Ann Muggeridge Cassiano de Oliveira 《Geophysical Prospecting》2008,56(1):115-140
The purpose of this work was to investigate a new and fast inversion methodology for the prediction of subsurface formation properties such as porosity, salinity and oil saturation, using time‐dependent nuclear well logging data. Although the ultimate aim is to apply the technique to real‐field data, an initial investigation as described in this paper, was first required; this has been carried out using simulation results from the time‐dependent radiation transport problem within a borehole. Simulated neutron and γ‐ray fluxes at two sodium iodide (NaI) detectors, one near and one far from a pulsed neutron source emitting at ～14 MeV, were used for the investigation. A total of 67 energy groups from the BUGLE96 cross section library together with 567 property combinations were employed for the original flux response generation, achieved by solving numerically the time‐dependent Boltzmann radiation transport equation in its even parity form. Material property combinations (scenarios) and their correspondent teaching outputs (flux response at detectors) are used to train the Artificial Neural Networks (ANNs) and test data is used to assess the accuracy of the ANNs. The trained networks are then used to produce a surrogate model of the expensive, in terms of computational time and resources, forward model with which a simple inversion method is applied to calculate material properties from the time evolution of flux responses at the two detectors. The inversion technique uses a fast surrogate model comprising 8026 artificial neural networks, which consist of an input layer with three input units (neurons) for porosity, salinity and oil saturation; and two hidden layers and one output neuron representing the scalar photon or neutron flux prediction at the detector. This is the first time this technique has been applied to invert pulsed neutron logging tool information and the results produced are very promising. The next step in the procedure is to apply the methodology to real data. 相似文献
10.
叠前反演技术已经成为岩性预测和流体识别的关键技术,并将在油气勘探中发挥重要作用,本文提出了模拟退火AVA同步反演方法,该方法以多个角道集地震数据体和先验纵波速度、横波速度、密度模型等为输入,综合利用地震、地质、测井等多种信息为约束,采用模拟退火全局优化方法,直接采用Knott-Zoeppritz方程求解反射系数,同步反演获得纵波阻抗、横波阻抗、纵横波速度、密度、Mu、Lambda等23种岩石弹性参数模型.其主要特点如下：１）采用Zoeppritz方程直接求解,精度高;2) 目标函数选择灵活;３）多角度提取子波;４）可获得深度域的反演结果.实际资料应用证明,该反演方法保留了地震反射振幅随偏移距不同或入射角不同而变化的特征,可有效提高储层预测和流体识别精度.实际应用表明,本方法预测结果可靠,具有较强的实用性. 相似文献
11.
套管外地层受异常地应力、油气开采的影响,在径向上表现出非均质性;采用声波测井可以对该非均质性进行探测,利用偶极子横波测井数据可以对横波速度的径向分布进行反演.本文建立了套管井外地层横波速度径向分层参考模型,采用修正的微扰法计算了该模型的偶极弯曲波频散曲线,建立了横波速度径向分布反演目标函数,采用高斯牛顿法和快速模拟退火法对目标函数进行了求解,得到了套管井外地层横波速度的径向分布.分析了偶极弯曲波频段、套管横波速度对反演结果的影响,对比了高斯牛顿法和快速模拟退火法对反演过程的影响.分析对比结果表明,采用偶极弯曲波激发强度较高的频段与采用全频段的反演结果相近;套管的横波速度准确度越高,反演结果越准确;高斯牛顿法和快速模拟退火法计算精度相同,都可以得到高精度的横波速度径向分布;快速模拟退火法的计算效率略低于高斯牛顿法,但其收敛性对初始值依赖更小,实际处理中应选择快速模拟退火法. 相似文献
12.
A. J. Zhang E. R. G. Hill B. A. Hobbs 《Physics of the Earth and Planetary Interiors》1990,60(1-4):40-52
An important stage in two-dimensional magnetotelluric modelling is the calculation of the Earth's response functions for an assumed conductivity model and the calculation of the associated Jacobian relating those response functions to the model parameters. The efficiency of the calculation of the Jacobian will affect the efficiency of the inversion modelling. Rodi (1976) produced all the Jacobian elements by inverting a single matrix and using an approximate first-order algorithm. Since only one inverse matrix required calculation the procedure speeded up the inversion. An iterative scheme to improve the approximation to the Jacobian information is presented in this paper. While this scheme takes a little longer than Rodi's algorithm, it enables a more accurate determination of the Jacobian information. It is found that the Jacobian elements can be produced in 10% of the time required to calculate an inverse matrix or to calculate a 2D starting model. A modification of the algorithm can further be used to improve the accuracy of the original inverse matrix calculated in a 2D finite difference program and hence the solution this program produces. The convergence of the iteration scheme is found to be related both to the originally calculated inverse matrix and to the change in the newly formed matrix arising from perturbation of the model parameter. A ridge regression inverse algorithm is used in conjunction with the iterative scheme for forward modelling described in this paper to produce a 2D conductivity section from field data. 相似文献
13.
利用三维感应测井交叉分量之差响应曲线在边界附近的响应行为,建立了求解大斜度井中井斜角快速反演方法.响应曲线随真实垂直深度(TVD)变化的对数衰减率与随测量距离(MD)变化的对数衰减率与之比是井斜角的余弦函数,通过简单三角函数计算可快速反演井斜角.响应曲线形态规则,在层状各向异性地层中与垂直电导率无关,主要反映水平电导率反差造成的地层边界信息.因此本文的井斜角快速反演方法既适用于各向同性地层也适用于各向异性地层.我们考察了测井环境及仪器参数对响应曲线衰减率的影响以及衰减率估算偏差对井斜角反演精度的影响.数值模拟结果验证了该反演方法在大斜度井中的有效性和实用性. 相似文献
14.
利用Ｓｈａｍｗａｙ和Ｄｅｒ的多道最大或然性反褶积原理，讨论了从单台三分量远震Ｐ波波形中分离接收函数径向与垂向分量复谱比的方法．根据Ｔａｒａｎｔｏｌａ的波形反演理论发展了接收函数复谱比的非线性反演方法．本文的反演方法除了拟合接收函数的复谱比之外，还需拟合时间域中接收函数垂向与径向分量的初至振幅比．合成波形数据反演的结果表明本文方法的反演结果不依赖初始模型．利用该方法和ＣＤＳＮ台网兰州台记录的宽频带远震Ｐ波波形数据，研究了该台站的接收函数及其随方位角的变化．接收函数复谱比非线性反演给出了该台站下方１４０ｋｍ深度岩石层的Ｓ波速度结构，得到兰州台下方地壳厚度为５４ｋｓ，岩石层厚度为９４ｋｍ． 相似文献
15.
三维电阻率探测的线性反演和非线性反演中均存在着多解性的固有难题.电阻率线性反演方法的效率较高,但反演结果对初始模型的依赖性较强,易陷入局部极小;而非线性反演方法不依赖初始模型,但搜索效率极低,尚未见到关于三维电阻率非线性反演的文献.针对上述问题,融合线性与非线性反演方法的互补优势,提出了最小二乘法(线性方法)与改进遗传算法(非线性方法)相结合的混合反演方法的概念和思想.首先,提出了将介质电阻率变化范围作为不等式约束引入反演方程的思路,以实现压制多解性、提高可靠性的目标.提出了宽松不等式约束和基于钻孔推断的局部严格不等式约束的获取及定义方法.在此基础上,分别提出了基于不等式约束的最小二乘线性反演方法和遗传算法非线性反演方法.其次,对于遗传算法在变异搜索方向控制、初始群体产生等方面进行了改进,优化了其搜索方向和初始群体多样性.然后,提出了混合反演方法及其实现方案,利用改进遗传算法进行第一阶段反演,发挥其对初始模型的依赖程度低的优势,搜索到最优解附近的空间,输出当前最优个体;利用最小二乘法进行第二阶段反演,将遗传算法得到的当前最优个体作为初始模型,在最优解附近空间执行高效率的局部线性搜索,最终实现地电结构的三维成像.最后,开展了合成数据与实际工程算例验证,与传统最小二乘方法进行了对比,发现混合反演方法在压制多解性、摆脱初始模型依赖和提高反演效果方面有较好效果. 相似文献
16.
叠前同时反演是油气探测的一种有效工具.其理论基础是平面P波Zoeppritz方程计算的反射系数的近似,是入射角的函数.叠前同时反演可以利用三项或两项Fatti方程进行反演分析.本文针对实际油田的测井数据,利用反射率法模拟了仅包含P波一次反射记录,包含P波一次反射和P波层间多次波记录以及全波场地震记录,再利用叠前同时反演对合成地震记录进行反演研究.研究结果表明,在大偏移距处P波主要反射受到其它模式波的污染,从而影响了叠前同时反演结果的精度.对于薄互层介质当转换波影响严重时,使用小角度数据的两项AVO反演比使用大角度数据的三项AVO反演更合理可靠. 相似文献
17.
Baker Hughes INTEQ的MPR是应用较广的传播电阻率测井仪器,它有4条相位差和4条幅度比测井曲线,本文以它在垂直井中的测井响应为例开展电磁传播电阻率资料的二维反演方法研究.由于其测井响应对地层纵向边界的探测灵敏度比对其他地层参数的大得多,在其资料反演中必须重视地层纵向边界位置的提取和反演精度.本文首先应用特征识别方法由分辨率最好的测井曲线提取地层纵向边界,接着对浅、深探测的两条相位差曲线分别做纵向一维反演,利用此结果来建立二维反演的初始地层模型,采用改进的阻尼型正则化高斯 牛顿优化算法,实现了MPR资料的二维全参数反演.对含23个纵向分层的两种典型地层模型的数值模拟测井资料的二维反演得到了令人满意的结果,它可显著提高MPR的资料解释水平.发现只用它的5条测井曲线就可得到与8条测井曲线几乎相同的反演效果. 相似文献
18.
Inversion of ocean-bottom seismometer (OBS) waveforms for oceanic crust structure: a synthetic study 
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下载免费PDF全文 The waveform inversion method is applied—using synthetic ocean-bottom seismometer(OBS) data—to study oceanic crust structure. A niching genetic algorithm(NGA) is used to implement the inversion for the thickness and P-wave velocity of each layer, and to update the model by minimizing the objective function, which consists of the misfit and cross-correlation of observed and synthetic waveforms. The influence of specific NGA method parameters is discussed, and suitable values are presented.The NGA method works well for various observation systems, such as those with irregular and sparse distribution of receivers as well as single receiver systems. A strategy is proposed to accelerate the convergence rate by a factor of five with no increase in computational complexity; this is achieved using a first inversion with several generations to impose a restriction on the preset range of each parameter and then conducting a second inversion with the new range. Despite the successes of this method,its usage is limited. A shallow water layer is not favored because the direct wave in water will suppress the useful reflection signals from the crust. A more precise calculation of the air-gun source signal should be considered in order to better simulate waveforms generated in realistic situations; further studies are required to investigate this issue. 相似文献
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Paolo Bergamo Cesare Comina Sebastiano Foti Margherita Maraschini 《Soil Dynamics and Earthquake Engineering》2011
Sites with a limited overburden over a stiff basement are of particular relevance for seismic site response. The characterization of such stratigraphies by means of surface wave methods poses some difficulties in interpretation. Indeed the presence of sharp seismic contrasts between the sediments and the shallow bedrock is likely to cause a relevance of higher modes in the surface wave apparent dispersion curve, which must be properly taken into account in order to provide reliable results. In this study a Monte Carlo algorithm based on a multimodal misfit function has been used for the inversion of experimental dispersion curves. Case histories related to the characterization of stations of the Italian accelerometric network are reported. Spectral ratios and amplification functions associated to each site are moreover evaluated to provide an independent benchmark test. The results show the robustness of the inversion method in such non-trivial conditions and the possibility of getting an estimate of uncertainty related to solution non-uniqueness. 相似文献
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由于地表电阻率法受到浅地表局部异常体的干扰,反演精度受到影响,井中装置数据资料参与反演虽然可以减小浅地表局部异常体的干扰,但是由于钻井位置的局限性,数据量得不到保障,也会导致反演精度降低.为此,本文开发了一套结合地表、地-井、井-地和井-井装置数据的三维联合反演算法.首先,利用有限差分法实现正演模拟,采用非线性共轭梯度法（NLCG）恢复电阻率结构;其次,调用Message Passing Interface（MPI）函数库加速正演模拟和灵敏度矩阵运算,当开辟12个进程时,反演程序获得最大加速比4.51;最后,通过合成数据和实测数据算例证明该反演算法的有效性,也证实了多种装置组合数据体反演结果明显优于单一地表装置数据体反演结果. 相似文献