安徽省铜陵县严冲地区高精度磁法的成果解释及研究

安徽省铜陵县严冲矿区位于长江中下游的铁、铜、金、硫、钨钼、铅锌成矿带。该地区受到矽卡岩影响,因此采用高精度磁法进行物探,以圈定成矿靶区并推测隐伏岩体(矿体)的空间分布。通过对该矿区进行地面高精度磁法工作和多种数据处理方法的研究和解释,可以提高对该地区隐伏岩体(矿体)的认知水平。

简述高精度磁法在地质找矿中的应用

磁法勘探是一种地球物理勘探方法,指的是通过观测探测对象的磁性差异导致的磁异常情况来分析探测地区的地质构造特点和矿产资源分布。磁法勘探是一种发展最早、应用时间最久、应用范围最广的地球物理勘探方法,如今这一技术已经非常成熟。本文首先简单介绍了高精度磁法数据处理技术,然后结合地质找矿实例分析了该技术的应用方法。

利用重磁对应分析法对负磁异常区内油页岩的推断

汉中地区的油页岩是陆相沉积的侏罗纪沉积岩,成分以石英砂岩、高岭土为主,具有油页岩普遍特征,相对密度中等,磁性弱,不适合重磁处理。但由于研究区的造山运动,被火成岩入侵,含有金属矿物带和褶皱带,油页岩层被其切割。因此,反其道而行,首先利用常规重磁处理手段,剔除金属矿脉和褶皱,圈出负磁异常区;其次,改造重力对应分析法,提出新相关系数R',把负磁异常区内的符合要求的R'断定为油页岩存在的区域。为油页岩的探测提供了一种新的探测方法。

磁异常模量垂向一阶导数的特征及应用

磁异常转换模量(magnitude magnetic transforms,简称MMTs)相比传统的数据处理方法如化极、总梯度模等,其产生的异常更接近实际磁性异常体的水平位置,以便进行磁法解释.本文基于转换模量,提出了磁异常模量的垂向一阶导数的处理方法.进一步分析模量垂向一阶导数的特征可知,对于2D异常体其完全不依赖于异常体的磁化方向;对于3D异常体其弱依赖于异常体的磁化方向.模量垂向一阶导数相比磁异常模量具有更小的中心偏移量和相对峰值;相比其他磁异常转换模量而言,具有计算量小、计算方便等优点.因此,在磁法解释中,磁异常模量垂向一阶导数能更好地确定异常体的水平投影位置以及分布规模.

Multiobjective particle swarm inversion algorithm for two-dimensional magnetic data

Regularization inversion uses constraints and a regularization factor to solve ill- posed inversion problems in geophysics. The choice of the regularization factor and of the initial model is critical in regularization inversion. To deal with these problems, we propose a multiobjective particle swarm inversion （MOPSOI） algorithm to simultaneously minimize the data misfit and model constraints, and obtain a multiobjective inversion solution set without the gradient information of the objective function and the regularization factor. We then choose the optimum solution from the solution set based on the trade-off between data misfit and constraints that substitute for the regularization factor. The inversion of synthetic two-dimensional magnetic data suggests that the MOPSOI algorithm can obtain as many feasible solutions as possible; thus, deeper insights of the inversion process can be gained and more reasonable solutions can be obtained by balancing the data misfit and constraints. The proposed MOPSOI algorithm can deal with the problems of choosing the right regularization factor and the initial model.

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.

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.

Experimental analysis on bolt interference during advanced water detection with the mine transient electromagnetic method

During advanced water detection using the transient electromagnetic method, the exploration effect for water-rich area is often poor due to the interference of bolts that are distributed in different positions in working face. Thus, the study on the interference characteristics of bolts in different states has important directive significance for improving the acquisition quality and data processing method in water detection. Based on the analysis of the distribution laws of magnetic field excited by small multi-turn coincident loop in full space of homogeneity, the test on the interference of bolts has been designed in the mine. Through drilling 18 holes around the overlapping coil in the working face, mass data are collected in order with the posi- tion change and the exposed bolt length. The results of comprehensive data analysis show that the transient electromagnetic field is strongly interfered as the distance between the bolt and the center of the coil is less than 3 m, and the interference varies greatly as the distance varies. On the other hand, the field induced by the bolts can be ignored as the distance exceeds 3 m. The findings can help to improve data acquisition and correction during advanced water detection when using the transient electromagnetic method.

Research on modeling source effect of 3D CSAMT based on staggered-grid finite difference method

There is usually source effect in the field work of controlled-source audio-frequency magnetotelluric method.Source effect is a thorny problem during field working,data processing and interpretation.Therefore,it is very important for the results of field prospecting to model source effect and summarize its influence rules.Based on the previous research,the authors use 3D finite difference method to simulate the electromagnetic field and set different anomaly situation to study the source effect in near-field measurement,then conclude the influence rules of source effect.Simulations provide the reference for the actual field work and data processing to correct the influence of source effect,so the information of the underground will be more approaching to the real.

High precision magnetometer for geomagnetic exploration onboard of the China Seismo-Electromagnetic Satellite

The China Seismo-Electromagnetic Satellite(CSES) is the first platform of China's earthquake observation system in space and the first satellite of China's geophysical field detection missions. The high precision magnetometer(HPM), which contains two fluxgate sensors and a coupled dark state magnetometer(CDSM), measures the vector of the Earth's magnetic field with a bandwidth from DC to 15 Hz. The two fluxgate sensors are in a gradiometer configuration in order to reduce satellite interferences. Additionally, the CDSM sensor measures the scalar value of the magnetic field with higher accuracy and stability.Several data processing and calibration methods have been prepared to get accurate vector magnetic field data. This includes the calibration of each of the three sensors, the absolute vector correction algorithm, the spacecraft magnetic interference elimination and the coordinate transformation method. Also the instrument performances based on ground calibration activities are shown in this article.

First experimental demonstration of an exact quantum search algorithm in nuclear magnetic resonance system

The success probability of searching an objective item from an unsorted database using standard Grover's algorithm is usually not exactly 1. It is exactly 1 only when it is used to find the target state from a database with four items. Exact search is always important in theoretical and practical applications. The failure rate of Grover's algorithm becomes big when the database is small, and this hinders the use of the commonly used divide-and-verify strategy. Even for large database, the failure rate becomes considerably large when there are many marked items. This has put a serious limitation on the usability of the Grover's algorithm. An important improved version of the Grover's algorithm, also known as the improved Grover algorithm, solves this problem. The improved Grover algorithm searches arbitrary number of target states from an unsorted database with full success rate. Here, we give the first experimental realization of the improved Grover algorithm, which finds a marked state with certainty, in a nuclear magnetic resonance system. The optimal control theory is used to obtain an optimized control sequence. The experimental results agree well with the theoretical predictions.