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1.
波形反演是近年来较热门的反演方法,其分辨率可以达到亚波长级别.在波形反演的实际应用中,源子波的估计十分重要.传统方法使用反褶积来估计源子波并随着反演过程更新,该方法在合成数据波形反演中效果较好,但在实际数据反演过程中存在一系列的问题.由于实际数据信噪比较低,在源子波估计过程中需要大量的人为干涉,且结果并不一定可靠.本文使用一种基于褶积波场的新型目标函数,令反演过程不再依赖源子波.详细推导了针对跨孔雷达波形反演的梯度及步长公式,实现介电常数和电导率的同步反演.针对一个合成数据模型同时反演介电常数和电导率,结果表明该方法能够反演出亚波长尺寸异常体的形状和位置.接着,将该方法应用到两组实际数据中,并与基于估计源子波的时间域波形反演结果进行比较.结果表明不依赖源子波的时间域波形反演结果分辨率更高,也更准确. 相似文献
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速度是地震偏移成像准确与否的关键所在.全波形反演综合利用地震波场运动学和动力学信息,能够得到相比传统速度建模方法更高频的成分.全波形反演的理论比较成熟,但实际应用成功的例子相对较少,特别是对于陆上地震资料.塔里木盆地地震地质条件复杂,为了实现缝洞型储层的准确成像,本文开展了针对目标靶区的全波形反演精细速度建场研究.采用一种时间域分层多尺度全波形反演流程:首先通过层析成像建立初始速度模型;其次利用折射波反演浅层速度模型;最后利用反射波反演中深层速度模型.偏移成像结果表明基于全波形反演的速度建模技术能有效改善火成岩下伏构造的成像精度,显示了全波形反演在常规陆上采集资料的应用潜力. 相似文献
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为了提高表层速度反演精度,本文提出了一种新的波形反演方法.该方法只利用初至波波形信息以减少波形反演对初始模型的依赖性,降低反演多解性与稳定性.由于只利用初至波波形信息,所以该方法利用高斯束计算格林函数和正演波场,以减少正演计算量.为了避免庞大核函数的存储,该方法基于Born波路径,利用矩阵分解算法实现方向与步长的累加计算.将此基于Born波路径的初至波波形反演方法应用于理论模型实验,并与声波方程全波形反演和初至波射线走时层析方法相对比,发现该方法的反演效果略低于全波形反演方法,但明显优于传统初至波射线走时层析方法,而计算效率却与射线走时层析相当.同时,相对于全波形反演,本文方法对初始模型的依赖性也有所降低. 相似文献
4.
《应用地球物理》2016,(3)
棱柱波的特点是它有三段主要反射路径和两个反射点,一个反射点位于反射界面上,另一个位于陡倾角反射层上。从而含有了很多一次波无法获取的地下高陡反射界面信息,我们应用Born近似对常规逆时偏移成像剖面处理可以将棱柱波信息提取出来,然后用棱柱波进行速度更新以提高盐体悬伸侧翼等高陡构造的反演速度。基于此想法下提出了棱柱波形反演(prismatic waveform inversion),简称PWI方法,但棱柱波形反演方法存在明显的弱点:一次迭代的时间是全波形反演(FWI)的两倍,而且不能充分利用全波场信息。为此,我们将全波形反演与棱柱波形反演方法两者结合起来进行联合反演,FWI与PWI方法交替使用更新速度场。模型的试算表明,这种联合反演方法对初始模型中高陡构造信息是否缺失依赖性较低,对高陡构造的反演精度和效率都更高。 相似文献
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伴随层析成像（Adjoint Tomography）通过求解全波方程来准确模拟地震波在复杂介质中的传播,并利用波形信息来反演地下结构,是新一代的高分辨率成像方法.其中3-D伴随层析成像需要庞大的计算资源,而2-D反演相对更具计算效率.面波和远震体波是研究地壳上地幔速度结构的重要方法,它们对S波速度及Moho面的敏感度不同,通过联合反演,可以得到更为准确的S波速度结构及Moho面.通过两种数据的高度互补性,本文提出基于伴随方法的线性台阵背景噪声面波和远震体波联合成像方法,同时约束台阵下方S波速度结构及Moho面形态.我们将该方法应用到符合华北克拉通岩石圈典型结构特征的理论模型上,测试结果表明联合反演方法优势明显,相比于面波伴随层析成像,能获得更高分辨率的S波速度结构,同时能精准约束Moho面形态.相比于体波伴随层析成像,联合反演能有效压制高频假象,降低波形反演过程中的非线性化程度.本研究有望提供一种更为高效精准的线性台阵成像方法,搭建联合伴随层析成像理论框架,提升岩石圈成像分辨率,并为后续其他类型波形数据的引入提供思路和方法. 相似文献
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探地雷达（GPR）时间域全波形反演计算量巨大,内存要求高,在微机上计算难度大.本文中作者基于GPU并行加速的维度提升反演策略,采用优化的共轭梯度法,避免了Hessian矩阵的计算,在普通微机上实现了时间域全波形二维GPR双参数（介电常数和电导率）快速反演.论文首先推导了二维TM波的时域有限差分法（FDTD）的交错网格离散差分格式及波场更新策略.然后,基于Lagrange乘数法,将约束问题转化为无约束最小问题,构建了共轭梯度法反演目标函数,采用Fletcher-Reeves公式与非精确线搜索Wolfe准则,确保了梯度方向修正因子及迭代步长选取的合理性.而GPU并行计算及维度提升反演策略的应用,数倍地提升了反演速度.最后,开展了3个模型的合成数据的反演实验,分别从观测方式、梯度优化及天线频率等方面,分析了这些因素对雷达全波形反演的影响,说明双参数的反演较单一的介电常数反演,能提供更丰富的信息约束,有效提高模型重建的精度. 相似文献
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近地表地层与人类生产生活密切相关,利用地震层析成像方法准确重建浅部地壳速度结构有助于开展高精度地震勘探、探查浅部矿产资源、规避潜在自然灾害,并利于城市地下空间建设.中国大陆地表条件复杂,尤其中西部盆岭结合带地形起伏剧烈,对浅部地壳精确速度建模构成严重挑战.本文系统论述了地震层析成像领域基于高频近似理论的走时成像方法和有限频层析成像方法,阐明两类方法的基本原理、存在问题和发展方向等.依据正演走时有无显式射线追踪,基于高频近似理论的走时成像方法分为传统走时层析成像方法和无射线路径的走时层析成像方法.基于射线追踪的传统走时层析成像方法,在浅层速度强烈变化时,因存在阴影区或多路径现象引起成像失真,严重影响成像效率;而无射线路径的层析成像方法通过程函方程走时场的正传和逆传直接计算敏感核,并利用伴随状态法获得目标函数的梯度,具有快速、稳健的优点.以上两种基于地震射线高频近似理论的走时成像方法由于未考虑地震波频率的带限性,存在波散射、波前愈合及反演约束差等问题.有限频层析成像方法克服了射线理论"无限高频"假设所带来的弊端,已成为重要的研究方向之一.该类方法主要分为射线有限频层析成像方法和基于波动方程的有限频层析成像方法.射线有限频层析成像方法能够提高成像的分辨率,但在方法本质上仍依赖于射线理论,较难处理较复杂的波现象问题;基于波动方程的有限频层析成像方法能准确处理复杂地质问题,提高成像可靠性并能以图像形式直观展示地球内部地震波的速度结构分布,但是该方法在实际应用中强烈依赖于数据中的低频信息及较精确的初始速度模型,其推广应用仍需进一步探索. 相似文献
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地面电磁法在实际工作中在很大程度上受到了探测深度和分辨率的限制.为了克服这些缺点,出现了井间电磁法.井间电磁法指的是在两个(或多个)钻孔中分别发射或接收电磁波信号,利用电磁波信号进行成像并探测井间物理性质的地球物理方法.由于发射机和接收机可以分别放置在很深钻孔中,其具有大透距、大探测深度的特点,因而广泛应用于工程环境物探、矿产勘查、石油勘探等中.针对不同的应用,产生了各具特点的一些特殊方法,包括井间无线电波成像、跨孔雷达、井间电磁成像.井间无线电波成像仪目前只测量电场强度数据,工作频率低,一般是单频的电磁波,频率范围通常在1 kHz至10 MHz.由于缺少走时数据修正射线路径,井间无线电波成像主要是进行基于直射线追踪的衰减层析成像.井间无线电波成像既可用于工程与环境地球物理也可用于找矿.跨孔雷达是钻孔雷达的一种探测方式,用高频电磁脉冲探测两个井孔间介电常数和电导率的变化.跨孔雷达层析成像也叫地质雷达CT,既可进行走时成像,还可进行衰减成像.一般来说,地质雷达CT的电磁波工作频率较高,中心频率通常在10 MHz和1 GHz之间,因此在分辨率指标上占有优势,跨孔雷达主要用于工程与环境地球物理.井间电磁成像采用更低的频率,测量复电磁信号,适合油气储集层监测,是一种地球物理前沿技术.经过在多个试验区初步试验表明,井间电磁成像是油藏研究的有效手段,可用于分析剩余油分布,寻找油气富集区,进而达到提高钻探高效井成功率和提高采收率的目的.本文详细介绍对比了这三种方法在理论和实践中的一些特点,并对未来的发展进行了展望. 相似文献
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本文使用最小二乘线性迭代反演方法对跨孔雷达直达波初至时数据进行反演,每次迭代过程中,用有限差分法求解走时程函方程,并用高精度快速推进方法(HAFMM)进行波前扩展,通过追踪波前避免了进行射线追踪.为了验证该方案,我们对三组合成数据进行了测试,分析了单位矩阵算子、一阶差分算子和拉普拉斯算子等三种不同模型参数加权算子对模型的约束和平滑效果;讨论了FMM和HAFMM对反演精度的影响;测试了LSQR,GMRES和BICGSTAB等三种矩阵反演算法的反演效果.此外,我们还对一组野外实测数据进行了反演,对比了基于本方案以及基于平直射线追踪和弯曲射线追踪的走时层析成像反演效果.对比分析结果表明,使用拉普拉斯算子和HAFMM进行反演能较好地进行目标体重建,而三种矩阵反演方法对反演效果的影响差别不大;并且通过对波前等时线图的分析可以定性地判断异常体的性质和位置;而在对实测数据目标体的重建上,本方案能达到甚至优于弯曲射线算法的重建效果. 相似文献
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地球介质的物理属性(如速度)隐含了地球内部结构和演化信息,因而获取高精度的地下介质模型是探测内部结构的重要目标之一.全波形反演方法利用地震观测记录的振幅、相位等全波信息来重建速度和密度等介质参数模型,被认为是建立高精度地下介质模型的最有潜力的研究方法之一,其不但是石油勘探地震成像的主要研究方向,而且在结构地震学获得了较高关注和初步应用.随着该理论的完善以及计算机技术的发展,全波形反演方法已被应用于大陆尺度以及全球尺度的壳-幔结构探测,并成为探测地球深部结构的研究方向之一.本文首先简述了全波形反演理论研究及应用进展,包括地震波场正演模拟方法、目标函数构建、迭代优化方法、初始模型建立等;然后介绍了全波形反演方法在澳大利亚、东亚、欧亚大陆以及全球尺度的上地幔结构研究,并分析其探测壳-幔结构的效果;最后给出算法的优化策略(例如地震波场正演模拟、目标函数、寻优算法等),时间域或频率域的多尺度反演策略,结合其他反演方法(如走时反演)的多手段联合反演策略以及高性能计算技术将是全波形反演方法突破计算瓶颈并在内部结构成像广泛应用的可能途径. 相似文献
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In this study, we focus on a hydrogeological inverse problem specifically targeting monitoring soil moisture variations using tomographic ground penetrating radar (GPR) travel time data. Technical challenges exist in the inversion of GPR tomographic data for handling non-uniqueness, nonlinearity and high-dimensionality of unknowns. We have developed a new method for estimating soil moisture fields from crosshole GPR data. It uses a pilot-point method to provide a low-dimensional representation of the relative dielectric permittivity field of the soil, which is the primary object of inference: the field can be converted to soil moisture using a petrophysical model. We integrate a multi-chain Markov chain Monte Carlo (MCMC)–Bayesian inversion framework with the pilot point concept, a curved-ray GPR travel time model, and a sequential Gaussian simulation algorithm, for estimating the dielectric permittivity at pilot point locations distributed within the tomogram, as well as the corresponding geostatistical parameters (i.e., spatial correlation range). We infer the dielectric permittivity as a probability density function, thus capturing the uncertainty in the inference. The multi-chain MCMC enables addressing high-dimensional inverse problems as required in the inversion setup. The method is scalable in terms of number of chains and processors, and is useful for computationally demanding Bayesian model calibration in scientific and engineering problems. The proposed inversion approach can successfully approximate the posterior density distributions of the pilot points, and capture the true values. The computational efficiency, accuracy, and convergence behaviors of the inversion approach were also systematically evaluated, by comparing the inversion results obtained with different levels of noises in the observations, increased observational data, as well as increased number of pilot points. 相似文献
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波形反演在探地雷达领域的应用已有十余年历史,但绝大部分算例属于时间域波形反演.频率域波形反演由于能够灵活地选择迭代频率并可以使用不同类型的目标函数,因而更加多样化.本文的频率域波形反演基于时间域有限差分(FDTD)法,采用对数目标函数,可在每一次迭代过程中同时或者单独反演介电常数和电导率.文中详细推导了频率域波形反演的理论公式,给出对数目标函数下的梯度表达式,并使用离散傅氏变换(DFT)实现数据的时频变换,能够有效地减少大模型反演的内存需求.在后向残场源的时频域转换过程中,提出仅使用以当前频点为中心的一个窄带数据,可以消除高频无用信号的干扰,获得可靠的反演结果.为加速收敛,采用每迭代十次则反演频率跳跃一定频带宽度的反演策略.实验证明适当的频率跳跃能够在不降低分辨率的基础上有效地提高反演效率.通过两组不同情形下合成数据反演的分析对比,证明基于对数目标函数的波形反演结果准确可靠.最后,将该方法应用到一组实际数据,得到较好的反演结果. 相似文献
14.
The travel time and amplitude of ground-penetrating radar (GPR) waves are closely related to medium parameters such as water content, porosity, and dielectric permittivity. However, conventional estimation methods, which are mostly based on wave velocity, are not suitable for real complex media because of limited resolution. Impedance inversion uses the reflection coefficient of radar waves to directly calculate GPR impedance and other parameters of subsurface media. We construct a 3D multiscale stochastic medium model and use the mixed Gaussian and exponential autocorrelation function to describe the distribution of parameters in real subsurface media. We introduce an elliptical Gaussian function to describe local random anomalies. The tapering function is also introduced to reduce calculation errors caused by the numerical simulation of discrete grids. We derive the impedance inversion workflow and test the calculation precision in complex media. Finally, we use impedance inversion to process GPR field data in a polluted site in Mongolia. The inversion results were constrained using borehole data and validated by resistivity data. 相似文献
15.
2.5维井间电磁反演在中国东部孤岛油田的应用 总被引：3，自引：1，他引：2
In this study, we present a practical technique of transforming cross-hole EM data into the inter-well resistivity distribution. The a priori information constraint is incorporated into an iterative regularized inversion procedure and a variable roughness is added into the inversion process. Finite element approximation based on a two and a half-dimensional （2.5D） model has been developed for the forward problem and the ＂pseudo-forward＂ problem needed for constructing the sensitivity matrix and synthetic data set. The regularized least-squares inversion scheme, constrained with the a priori information obtained from well logs, was adopted to reconstruct the inter-well resistivity profile from two synthetic electromagnetic data sets and field data acquired in the Gudao Oil Field, East China. The partial derivatives of the sensitivity matrix were computed by the adjoint equation based on the reciprocity principle. Inversion results of the synthetic and field data examples suggest that our method is robust and stable in the presence of random noise in the field data and can be used for cross-hole EM field data interpretation. 相似文献
16.
从二维麦克斯韦方程组出发推导出反演介电常数和电导率等二维介质物性参数的反演公式.反演的步骤是: 建立初始猜测模型，利用电磁波时间域有限差分法模拟正演数据，用正演数据与观测数据之间的数据残差建立目标函数，通过引入一个由麦克斯韦方程计算的伴随场，将目标函数对介质参数的导数表示成显式形式，应用最优化理论得出对初始猜测模型的修改，用共轭梯度法迭代，最终得到反演结果.用合成数据反演具有粗糙地表的非导电介质的介电常数，用实验数据同时反演介电常数和电导率，并比较了麦克斯韦方程反演结果与声波方程反演结果、波动方程偏移剖面的差异. 相似文献
17.
Crosshole ground penetrating radar (GPR) tomography has been widely used and has the potential to improve the obtained subsurface models due to its high spatial resolution compared to other methods. Recent advances in full-waveform inversion of crosshole GPR data show that higher resolution images can be obtained compared to conventional ray-based GPR inversion because it can exploit all information present in the observed data. Since the first application of full-waveform inversion on synthetic and experimental GPR data, the algorithm has been significantly improved by extending the scalar to a vectorial approach, and changing the stepped permittivity and conductivity update into a simultaneous update. Here, we introduce new normalized gradients that do not depend on the number of sources and receivers which enable a comparison of the gradients and step lengths for different crosshole survey layouts. An experimental data set acquired at the Boise Hydrogeophysics Research Site is inverted using different source–receiver setups and the obtained permittivity and conductivity images, remaining gradients and final misfits are compared for the different versions of the full-waveform inversion. Moreover, different versions of the full-waveform inversion are applied to obtain an overview of all improvements. Most improvements result in a reducing final misfit between the measured and synthetic data and a reducing remaining gradient at the final iteration. Regions with relatively high remaining gradient amplitudes indicate less reliable inversion results. Comparison of the final full-waveform inversion results with Neutron–Neutron porosity log data and capacitive resistivity log data show considerably higher spatial frequencies for the logging data compared to the full-waveform inversion results. To enable a better comparison, we estimated a simple wavenumber filter and the full-waveform inversion results show an improved fit with the logging data. This work shows the potential of full-waveform inversion as an advanced method that can provide high resolution images to improve hydrological models. 相似文献
18.
Cross-hole imaging method using Time Domain (TD) and Frequency Domain (FD) parts of cross-hole radar tomography data acquired using Step Frequency Ground Penetrating Radar (SFGPR) was implemented. This method was adopted for imaging foundation of a dam to check if the foundation was free of geological weak zones. The dam site is characterised by massive and jointed-phyllites associated with major and minor shears. The cross-hole radar tomography data was acquired in the frequency bandwidth of 250 MHz, from the deepest level gallery up to a depth of 40 m in the foundation. In TD, first arrival time and amplitudes of radio waves were inverted using Simultaneous Iterative Reconstruction Technique (SIRT) resulting in velocity and attenuation tomograms. The tomograms showed nearly uniform velocity or attenuation structure in the respective tomographic plane. Subsequently, cross-hole radar tomography data was analysed in FD for a variation of spectrum-amplitude at different frequencies. Amplitudes picked at each single frequency were then inverted using SIRT for obtaining frequency domain attenuation tomogram (FDAT). The FDAT clearly showed presence of anomalous high attenuation zones in the depth range of 23–33 m of the tomographic plane. The anomalous zones in the attenuation tomogram are weak zones in the foundation. To validate the above observations, cross-hole seismic tomography was also done in the same boreholes. Cross-hole seismic tomography results showed low velocity (p-wave) zones around the same location corresponding to the high attenuation zone in FDAT, bringing the dormant weak zone to light. This enabled fine-tuning of the reinforcement design and strengthening the weak zone. This paper discusses the cross-hole radar tomography imaging method, the results of its application in imaging weak zones in the foundation and the comparison of cross-hole radar tomography results (in TD and FD) with the cross-hole seismic tomography results. 相似文献
19.
Pre-stack depth migration velocity analysis is one of the key techniques influencing image quality. As for areas with a rugged surface and complex subsurface, conventional prestack depth migration velocity analysis corrects the rugged surface to a known datum or designed surface velocity model on which to perform migration and update the velocity. We propose a rugged surface tomographic velocity inversion method based on angle-domain common image gathers by which the velocity field can be updated directly from the rugged surface without static correction for pre-stack data and improve inversion precision and efficiency. First, we introduce a method to acquire angle-domain common image gathers (ADCIGs) in rugged surface areas and then perform rugged surface tomographic velocity inversion. Tests with model and field data prove the method to be correct and effective. 相似文献