瞬变电磁法反演成像算法研究

1、瞬变电磁法的测量原理 瞬变电磁法的测量原理是利用不接地回线（或电偶源）向地下发送一次脉冲磁场（或电场），在磁场的激励下，地质体内产生涡流，其大小取决于该地质体的导电能力，导电能力强则感应涡流强。当一次场消失后，涡流不能立即消失，它将有一个过渡过程（衰减过程），

双界面模式Parker算法磁性界面正反演方法

推导了双磁性界面模式正反演公式，并提出解决反演发散问题的新算法，讨论算法实现的关键技术和措施，通过模型试验分析算法的精度和可用性。结果表明：新算法能够保证反演过程稳定收敛；计算精度高，误差绝对值为0．01％-4％，且具有一定抗噪能力。用新算法处理中国某地磁测数据，得到的反演结果较为合理。

基于Parker算法的磁性双界面模式正反演研究

Parker界面反演算法中包含了一个不稳定因子——向下延拓算子,导致其不稳定,通常的做法是在反演过程中加入一个低通滤波器以限制高频振荡。这种做法在消除高频假波的同时会对有效信号进行一定的压制,造成反演精度的降低。重新推导了正反演公式,提出了双磁性界面模式正反演公式和解决反演发散问题的方法。双界面模式正反演公式在实际应用中更具合理性和普适性,解决反演发散问题的方法保证了反演过程能够稳定收敛。讨论了算法实现的关键技术和措施,通过模型实验分析算法的精度和可用性,可以发现算法计算精度很高,误差为0.8%～4%,且具有一定抗噪性。用该方法处理中国某地磁测数据,得到较好效果。

关于区域磁异常反演问题的统计分析方法

提出并全面介绍了区域磁异常反演的一种统计分析方法。包括该方法的地质和地球物理基础、统计参数、统计方法的稳定性和唯一性的讨论，以及在国内外的应用效果。该方法能够很好地反演出平均界面深度和进行地质填图工作。

低缓磁异常反演和解释的方法探讨

在对山西省五台山地区进行的1:1万高精度磁测扫面中,对圈定的低缓磁异常进行反演解释,先后对两种思路进行建模、反演和解释,最后经过钻孔验证后再对模型进一步修改,取得了较好的找矿成果。本文旨在探讨面对低缓磁异常进行分析反演的思路和方法,针对深部隐伏矿体进行研究,为今后工作面对类似异常提供经验和帮助。

基于交叉梯度函数的重磁三维联合反演

地球物理反演问题通常是不适定的,反演结果往往具有多解性和不稳定性。为了改善单一地球物理反演中面临的这些问题,本文在单一重力/磁法反演的基础上,基于结构耦合的思想,引入交叉梯度算子,实现了密度和磁化率两种物性参数的相互耦合。通过设计不同理论模型组合,应用预条件共轭梯度算法对理论模型的重力和磁法数据开展交叉梯度联合反演计算,反演结果表明,对于单一棱柱体模型和组合棱柱体模型而言,重磁联合反演算法相比于单一反演结果都具有良好的稳定性,对于异常体的空间分布的刻画具有提升效果。

磁法勘探在长春某小区城市病害埋藏物勘察中的应用

磁法勘探作为一种成熟的物探手段,在地质找矿和城市物探等领域都得到了广泛应用,并取得了良好的效果。该文介绍了利用磁法勘探对长春某小区疑似埋藏废弃炸弹进行勘察的实例,总场和梯度测量确定了异常体的存在和大致位置,三维磁法反演结果查明了磁性异常体的埋藏位置、埋深和体量等信息。后经现场开挖验证了磁法勘探结果的准确性,成功排除了该区域工程建设中的安全隐患。实践表明,磁法勘探具有操作简单、效果显著、三维反演结果立体直观等特点,值得推广应用。

磁异常化极效果的研究

在磁法数据的三维反演中,异常解释的磁异常化极法在实际运用中得到了广泛的应用。但是,化极后是否可以提高磁异常的准确性还有待研究。运用对化极后的磁异常数据进行三维反演的方法,对局部磁异常进行磁法反演;反演的结果与未进行化极的磁异常数据的三维反演结果进行对比,表明化极后的反演结果更接近异常体模型;同时运用三维可视化技术,建立3D地球物理模型。

寿光磁异常区找矿方向探讨

寿光磁异常是山东仅次于济宁的第二大磁异常。由山东省第四地质矿产勘查院实施的ZK401验证孔,在孔深856.22～1 600.87m处见中生代白垩纪青山群八亩地组地层,是一套玄武安山安山岩石组合,认为寿光磁异常是具有磁性的中生代火山岩系引起的。该文依据寿光磁异常区的重、磁异常特征,结合所处的地质构造环境,通过反演磁性体的空间分布形态,推断寿光磁性体是夹持在前古生代地层(寒武系)间的类似山顶到山谷的一个楔型火山岩盆地。套用火山机构的划分模式,把磁性体所处的潜火山岩细分为火山喷发沉积岩相、火山通道相和重熔侵入岩相等3个岩相。依据火山岩相与矿产的关系,认为寿光火山岩系的深部可能有规模较大的岩浆岩型铁矿存在。寿光磁性体的中、深部的火山通道相是金、铜、铅、锌、钼等矿产的富集场所,是今后勘查找矿的重点靶区。

山东苍山三合地区磁异常特征及地质意义

通过对山东苍山三合地区高精度磁测磁异常的揭露,利用钻孔剖面对磁化强度的大小、磁性体的形态、磁性体的厚度进行反演和分析,认为研究区的磁异常是由该区辉绿岩磁性层引起的,并且辉绿岩层的上部相对较强磁性物质的富集对磁异常的影响更大;研究区辉绿岩层可能是普遍存在的;ZK02孔相对ZK01孔部位的辉绿岩层具有埋藏浅、磁性均匀、厚度变化小的特点。研究区磁异常的原因可能是成岩后局部断裂构造的活动,部分磁性块体边端部位挠起引起的。

三维重力资料反演

我们介绍两种三维空间密度分布重力资料反演方法。在第一种方法中，我们根据重、磁间的泊松关系将重力资料转换成伪磁力资料并用三维磁法反演算法进行反演；在第二种方法中，我们研制了直接反演方法，由重力资料直接反演出密度分布的极小结构模型。在以上两种方法，三维地质体由大量长方体元密度分布构成，每一体元中密度值为常数。

PC-based artif icial neural network inversion for airborne time-domain electromagnetic data

Traditionally, airborne time-domain electromagnetic （ATEM） data are inverted to derive the earth model by iteration. However, the data are often highly correlated among channels and consequently cause ill-posed and over-determined problems in the inversion. The correlation complicates the mapping relation between the ATEM data and the earth parameters and thus increases the inversion complexity. To obviate this, we adopt principal component analysis to transform ATEM data into orthogonal principal components （PCs） to reduce the correlations and the data dimensionality and simultaneously suppress the unrelated noise. In this paper, we use an artificial neural network （ANN） to approach the PCs mapping relation with the earth model parameters, avoiding the calculation of Jacobian derivatives. The PC-based ANN algorithm is applied to synthetic data for layered models compared with data-based ANN for airborne time-domain electromagnetic inversion. The results demonstrate the PC-based ANN advantages of simpler network structure, less training steps, and better inversion results over data-based ANN, especially for contaminated data. Furthermore, the PC-based ANN algorithm effectiveness is examined by the inversion of the pseudo 2D model and comparison with data-based ANN and Zhody＇s methods. The results indicate that PC-based ANN inversion can achieve a better agreement with the true model and also proved that PC-based ANN is feasible to invert large ATEM datasets.

Application of the Adaptive Shrinkage Genetic Algorithm in the Feasible Region to TEM Conductive Thin Layer Inversion

Combining the adaptive shrinkage genetic algorithm in the feasible region with the imaging of apparent vertical conductance differential, we have inverted the TEM conductive thin layer. The result of the inversion demonstrates that by adaptive shrinkage in the feasible region, the calculation speed accelerates and the calculation precision improves. To a certain extent, in this method we surmount the transient electromagnetic sounding equivalence and reduced equivalence scope. Comparison of the inverted result with the forward curve clearly shows that we can image the conductive thin layer.

2D joint inversion of CSAMT and magnetic data based on cross-gradient theory

A two-dimensional forward and backward algorithm for the controlled-source audio-frequency magnetotelluric （CSAMT） method is developed to invert data in the entire region （near, transition, and far） and deal with the effects of artificial sources. First, a regularization factor is introduced in the 2D magnetic inversion, and the magnetic susceptibility is updated in logarithmic form so that the inversion magnetic susceptibility is always positive. Second, the joint inversion of the CSAMT and magnetic methods is completed with the introduction of the cross gradient. By searching for the weight of the cross-gradient term in the objective function, the mutual influence between two different physical properties at different locations are avoided. Model tests show that the joint inversion based on cross-gradient theory offers better results than the single-method inversion. The 2D forward and inverse algorithm for CSAMT with source can effectively deal with artificial sources and ensures the reliability of the final joint inversion algorithm.

An algorithm for multi-exponential inversion of T_2 spectrum in nuclear magnetic resonance

NMR logging can provide the permeability parameter and abundant stratigraphical information such as total porosity,oil,gas and water saturation,oil viscosity,etc. And these physical parameters can be obtained by T2 spectrum inversion. NMR inversion is an important part in logging interpretation. The authors describe a multi-exponential inversion algorithm,solid iteration redress technique( SIRT),and apply the algorithm in real data and compare the results with those based on singular value decomposition( SVD). It shows that SIRT algorithm is easier to be understood and implemented,and the time spent in SIRT is much shorter than that of SVD algorithm. And the non-negative property of T2 spectrum is much easier to be implemented. It can match the results based on SVD very well. SIRT algorithm can be used in T2 spectrum inversion for NMR analysis.

Review of snow water equivalent microwave remote sensing

Accurate quantitative global scale snow water equivalent information is crucial for meteorology, hydrology, water cycle and global change studies, and is of great importance for snow melt-runoff forecast, water resources management and flood control. With land surface process model and snow process model, the snow water equivalent can be simulated with certain accuracy, with the forcing data as input. However, the snow water equivalent simulated using the snow process models has large uncertainties spatially and temporally, and it may be far from the needs of practical applications. Thus, the large scale snow water equivalent information is mainly from remote sensing. Beginning with the launch of Nimbus-7 satellite, the research on microwave snow water equivalent remote sensing has developed for more than 30 years, researchers have made progress in many aspects, including the electromagnetic scattering and emission modeling, ground and airborne experiments, and inversion algorithms for future global high resolution snow water equivalent remote sensing program. In this paper, the research and progress in the aspects of electromagnetic scattering/emission modeling over snow covered terrain and snow water equivalent inversion algorithm will be summarized.

Magnetic Flux Leakage Signal Inversion of Corrosive Flaws Based on Modified Genetic Local Search Algorithm

In this paper,a modified genetic local search algorithm(MGLSA) is proposed.The proposed algorithm is resulted from employing the simulated annealing technique to regulate the variance of the Gaussian mutation of the genetic local search algorithm(GLSA).Then,an MGLSA-based inverse algorithm is proposed for magnetic flux leakage(MFL) signal inversion of corrosive flaws,in which the MGLSA is used to solve the optimization problem in the MFL inverse problem.Experimental results demonstrate that the MGLSA-based inverse algorithm is more robust than GLSA-based inverse algorithm in the presence of noise in the measured MFL signals.