A New Method of Cross-Correlation by Magnetic Dipole for Estimating Magnetization Direction under the Influence of Remanent Magnetization

2014 ◽  
Vol 644-650 ◽  
pp. 3459-3462 ◽  
Author(s):  
Lei Shi ◽  
Liang Hui Guo ◽  
Feng Yi Guo
Keyword(s):  
Correlation Coefficient ◽  
Magnetic Dipole ◽  
Remanent Magnetization ◽  
Cross Correlation ◽  
New Method ◽  
Magnetic Data ◽  
Dipole Source ◽  
Total Field ◽  
Magnetization Direction ◽  
Total Magnetization

Processing and interpretation of magnetic data usually require information of total magnetization direction. However, under the effects of remanent magnetization, total magnetization direction is different from induced magnetization direction, which makes data processing and interpretation complexity. In this paper, we present a new method by cross-correlation of magnetic dipole source for determination of magnetization direction from relatively isolated and approximate equiaxial-shape magnetic total field anomaly. This method calculates cross-correlation coefficient between observed magnetic total field anomaly and theoretical magnetic total field anomaly caused by a magnetic dipole source, by using a set of varying parameters of positions and total magnetization direction of dipole source for trial and error. The corresponding magnetization direction of maximum correlation coefficient is regarded as estimated total magnetization direction. Test on synthetic data indicates that this method reliably and effectively estimates the magnetization direction from relatively isolated and approximate equiaxial-shape magnetic total field anomaly.

Estimating the Magnetization Direction of Sources through Correlation between Reduced-to-Pole Anomaly and Normalized Source Strength

2014 ◽  
Vol 644-650 ◽  
pp. 3793-3796
Author(s):  
Liang Hui Guo ◽  
Rui Gao ◽  
Guo Li Zhang
Keyword(s):  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Cross Correlation ◽  
Synthetic Data ◽  
Field Direction ◽  
Magnetic Data ◽  
Source Strength ◽  
Magnetization Direction ◽  
New Approach ◽  
Total Magnetization

Under the effects of remanent magnetization, total magnetization direction is different from geomagnetic field direction, which makes magnetic data processing and interpretation complexity. In this paper, we present a new approach for estimating the total magnetization direction of sources via cross-correlation between the reduced-to-pole anomaly and the normalized source strength (who is less sensitive to remanent magnetization). The geomagnetic field direction is used to calculated the normalized source strength, while various assumed total magnetization directions are used to calculated the RTP anomalies. The maximum correlation between the RTP anomalies and the normalized corresponds to the estimated total magnetization direction. Test on synthetic data showed that the new approach is simple and effective.

Inversion of magnetic anomaly on rugged observation surface in the presence of strong remanent magnetization

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. J11-J19 ◽  
Author(s):  
Shu-Ling Li ◽  
Yaoguo Li
Keyword(s):  
Remanent Magnetization ◽  
Country Rock ◽  
Magnetization Vector ◽  
Magnetic Data ◽  
Magnetization Direction ◽  
Equivalent Source ◽  
Total Magnetization ◽  
Amplitude Inversion ◽  
Amplitude Data ◽  
And Inversion

We study the inversion of magnetic data acquired over a rugged observation surface and where the buried source bodies have strong remanent magnetization that leads to unknown total magnetization directions. These factors pose significant challenges for processing and inversion of such data. To tackle the challenges from both a rugged observation surface and an unknown magnetization direction, we propose a strategy through the joint use of the equivalent source technique and 3D amplitude inversion to obtain 3D magnetization strength. We use equivalent source processing to calculate the amplitude data in the space domain because the use of the wavenumber-domain method is invalid due to large variations in the data elevation. We then carried out an amplitude inversion to generate a 3D subsurface distribution of the magnitude of the total magnetization vector. The results from a synthetic example and aeromagnetic data in Daye Mine in China showed that this approach is effective and images the magnetic units whose contact zones with the limestone country rock host the mineralization. The method is general and can be applied to a variety of cases with similar challenges.

Constrained 3D inversion of magnetic data with structural orientation and borehole lithology: A case study in the Macheng iron deposit, Hebei, China

Geophysics ◽  
2019 ◽  
Vol 84 (2) ◽  
pp. B121-B133 ◽  
Author(s):  
Shida Sun ◽  
Chao Chen ◽  
Yiming Liu
Keyword(s):  
Remanent Magnetization ◽  
Magnetic Data ◽  
Iron Deposit ◽  
Reference Field ◽  
Total Field ◽  
Equivalent Source ◽  
Structural Orientation ◽  
Amplitude Data ◽  
Ore Bodies

We have developed a case study on the use of constrained inversion of magnetic data for recovering ore bodies quantitatively in the Macheng iron deposit, China. The inversion is constrained by the structural orientation and the borehole lithology in the presence of high magnetic susceptibility and strong remanent magnetization. Either the self-demagnetization effect caused by high susceptibility or strong remanent magnetization would lead to an unknown total magnetization direction. Here, we chose inversion of amplitude data that indicate low sensitivity to the direction of magnetization of the sources when constructing the underground model of effective susceptibility. To reduce the errors that arise when treating the total-field anomaly as the projection of an anomalous field vector in the direction of the geomagnetic reference field, we develop an equivalent source technique to calculate the amplitude data from the total-field anomaly. This equivalent source technique is based on the acquisition of the total-field anomaly, which uses the total-field intensity minus the magnitude of the reference field. We first design a synthetic model from a simplified real case to test the new approach, involving the amplitude data calculation and the constrained amplitude inversion. Then, we apply this approach to the real data. The results indicate that the structural orientation and borehole susceptibility bounds are compatible with each other and are able to improve the quality of the recovered model to obtain the distribution of ore bodies quantitatively and effectively.

Using airborne vector magnetic data to calculate the projection of magnetic anomaly vector onto normal geomagnetic field

Geophysics ◽  
2021 ◽  
pp. 1-47
Author(s):  
Rukuan Xie ◽  
Shengqing Xiong ◽  
Shuling Duan ◽  
Jinlong Wang ◽  
Ping Wang ◽  
...  
Keyword(s):  
Magnetic Anomaly ◽  
Geomagnetic Field ◽  
Approximation Error ◽  
Magnetic Data ◽  
Total Field ◽  
Projection Formula ◽  
Total Magnetization ◽  
Vector Formula ◽  
Relationship Of ◽  
Anomaly Formula

The total-field magnetic anomaly [Formula: see text] is an approximation of the projection [Formula: see text] of the magnetic anomaly vector [Formula: see text] onto the normal geomagnetic field [Formula: see text]. However, for highly magnetic sources, the approximation error of [Formula: see text] cannot be ignored. To reduce the error, we have developed a method for calculating [Formula: see text] by using airborne vector magnetic data based on the vector relationship of geomagnetic field [Formula: see text]. The calculation uses the magnitude of the vectors [Formula: see text], [Formula: see text], and [Formula: see text] through a simple approach. To ensure that each magnitude has the same level, we normalize the magnitude of [Formula: see text] using the total-field magnetic data measured by the scalar magnetic sensor. The method is applied to the measured airborne vector magnetic data at the Qixin area of the East Tianshan Mountains in China. The results indicate that the calculated [Formula: see text] has high precision and can distinguish the approximation error less than 3.5 nT. We also analyze the characteristics of the approximation error that are caused by the effects of different total magnetization inclinations. These error characteristics are used to predict the total magnetization inclination of a 2D magnetic source based on the measured airborne vector magnetic data.

Improving the crosscorrelation method to estimate the total magnetization direction vector of isolated sources: A space-domain approach for unstable inclination values

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. J59-J70 ◽  
Author(s):  
Nelson Ribeiro-Filho ◽  
Rodrigo Bijani ◽  
Cosme Ponte-Neto
Keyword(s):  
Magnetic Field ◽  
Real Data ◽  
Magnetic Anomalies ◽  
Direction Vector ◽  
Total Field ◽  
Magnetization Direction ◽  
Ambient Magnetic Field ◽  
Total Magnetization ◽  
Synthetic Test ◽  
Equivalent Sources

Knowledge of the total magnetization direction of geologic sources is valuable for interpretation of magnetic anomalies. Although the magnetization direction of causative sources is assumed to be induced by the ambient magnetic field, the presence of remanence should not be neglected. An existing method of correlating total and vertical gradients of the reduced-to-the-pole (RTP) anomaly estimates the total magnetization direction well. However, due to the numerical instability of RTP transformation in the Fourier domain, an assumption should be considered for dealing with inclination values at approximately 0°. We have adopted an extension to the standard crosscorrelation method for estimating the total magnetization direction vector, computing the RTP anomaly by means of the classic equivalent layer technique for low inclination values. Additionally, an ideal number of equivalent sources within the layer is considered for reducing the computational demands. To investigate the relevant aspects of the adopted method, two simple synthetic scenarios are presented. First, a magnetic anomaly produced by a homogeneous and isolated vertical dike is considered. This test illustrates the good performance of the adopted approach, finding the true magnetization direction, even for low inclination values. In the second synthetic test, a long-wavelength component is added to the previous magnetic total-field anomaly. In this case, the method adopted here fails to estimate a reliable magnetization direction vector, showing weak performance for strong interfering magnetic anomalies. On the real data example, the application tests an isolated total-field anomaly of the Carajás Mineral Province, in northern Brazil, where the inclination of the ambient magnetic field is close to zero. The obtained results indicate weak remanence in the estimated total magnetization direction vector, which would never be reached in the standard formulation of the crosscorrelation technique.

Stepped inversion of magnetic data

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. L21-L30 ◽  
Author(s):  
Soraya Lozada Tuma ◽  
Carlos Alberto Mendonça
Keyword(s):  
Magnetic Anomaly ◽  
Shape Function ◽  
Source Parameters ◽  
Real Data ◽  
Magnetic Data ◽  
Total Field ◽  
Magnetization Direction ◽  
Magnetization Intensity ◽  
Magnetic Inversion ◽  
Total Gradient

We present a three-step magnetic inversion procedure in which invariant quantities with respect to source parameters are inverted sequentially to give (1) shape cross section, (2) magnetization intensity, and (3) magnetization direction for a 2D (elongated) magnetic source. The quantity first inverted (called here the shape function) is obtained from the ratio of the gradient intensity of the total-field anomaly to the intensity of the anomalous vector field. For homogenous sources, the shape function is invariant with source magnetization and allows reconstruction of the source geometry by attributing an arbitrary magnetization to trial solutions. Once determined, the source shape is fixed and magnetization intensity is estimated by fitting the total gradient of the total-field anomaly (equivalent to the amplitude of the analytic signal of magnetic anomaly). Finally, the source shape and magnetization intensity are fixed and the magnetization direction is determined by fitting the magnetic anomaly. As suggested by numerical modeling and real data application, stepped inversion allows checking whether causative sources are homogeneous. This is possible because the shape function from inhomogeneous sources can be fitted by homogeneous models, but a model obtained in this way fits neither the total gradient of the magnetic anomaly nor the magnetic anomaly itself. Such a criterion seems effective in recognizing strongly inhomogeneous sources. Stepped inversion is tested with numerical experiments, and is used to model a magnetic anomaly from intrusive basic rocks from the Paraná Basin, Brazil.

Simultaneous estimation of total magnetization direction and 3-D spatial orientation

Geophysics ◽  
1995 ◽  
Vol 60 (5) ◽  
pp. 1365-1377 ◽  
Author(s):  
Walter E. Medeiros ◽  
João B.C. Silva
Keyword(s):  
Dipole Moment ◽  
Spatial Orientation ◽  
A Priori ◽  
Magnetic Data ◽  
Simultaneous Estimation ◽  
Magnetization Direction ◽  
Observation Plane ◽  
Total Magnetization ◽  
Spatially Correlated ◽  
Principal Axes

Magnetic interpretations are usually carried out either by assuming induced magnetization and estimating the model geometry, or by presuming a known source spatial orientation to estimate the total magnetization. We present a 3-D magnetic interpretation method that estimates simultaneously the total magnetization direction and the spatial orientation of the source. It is based on the approximation of the anomaly by the series derived from expanding the magnetic potential into multipoles and retaining source moments up to second order. The moments and linear combinations of moments appearing in the series are then inverted from the magnetic anomaly. The total magnetization is assumed constant in direction but not in magnitude. It is also presumed implicitly that the anomalous distribution of magnetization intensity has nonzero values in a finite‐volume region, is far from the observation points, and presents three othogonal planes of symmetry intersecting at the center of the dipole moment. The method is essentially linear and requires no a priori explicit assumption of a fixed geometry for the sources. The method is particularly suited to interpret compact, isolated or disjoint, but spatially correlated sources. If the source satisfies all assumptions presumed by the method, it is possible to obtain accurate, stable estimates of the total dipole moment vector, the position of the center of dipole moment, and the directions of all three principal axes of symmetry. If the source is not far from the observation plane and/or if the total magnetization direction is not constant, it is still possible to obtain accurate and stable estimates of the direction of the mean total magnetization and the projection, on the observation plane, of the center of dipole moment. The method is applied to magnetic data from the Gulf of Guinea Seamount. The estimated magnetic palaeopole is at 50°48′S and 74°54′E which is in good agreement with estimates published by other authors.

scholarly journals 3D magnetic amplitude inversion in the presence of self-demagnetization and remanent magnetization

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. J69-J82 ◽  
Author(s):  
Boxin Zuo ◽  
Xiangyun Hu ◽  
Yi Cai ◽  
Shuang Liu
Keyword(s):  
Remanent Magnetization ◽  
Large Scale ◽  
Magnetic Data ◽  
Inversion Problem ◽  
Aeromagnetic Data ◽  
Inversion Algorithm ◽  
Rapid Convergence ◽  
Magnetization Direction ◽  
Amplitude Inversion ◽  
Nonlinear Conjugate Gradient

We have developed a general 3D amplitude inversion algorithm for magnetic data in the presence of self-demagnetization and remanent magnetization. The algorithm uses a nonlinear conjugate gradient (NLCG) scheme to invert the amplitude of the magnetic anomaly vector within a partial differential equation framework. Three quantities— the amplitude of the anomalous magnetic field, the analytic signal, and the normalized source strength, defined as the amplitudes of magnetic data that are weakly dependent on the magnetization direction — are inverted to recover the 3D distribution of the subsurface magnetic susceptibility. Numerical experiments indicate that our NLCG amplitude inversion algorithm has a rapid convergence rate that provides a reasonable inversion solution in the absence of knowing the total magnetization direction. High-resolution aeromagnetic data collected from the Pea Ridge iron oxide-apatite-rare earth element deposit, southeast Missouri, USA, are used to illustrate the efficacy of our amplitude inversion algorithm. This algorithm is generally applicable for tackling the large-scale inversion problem in the presence of self-demagnetization and remanent magnetization.

A paradigm shift in magnetic data interpretation: Increased value through magnetization inversions

2021 ◽  
Vol 40 (2) ◽  
pp. 89-98
Author(s):  
Yaoguo Li ◽  
Jiajia Sun ◽  
Shu-Ling Li ◽  
Marcelo Leão-Santos
Keyword(s):  
Paradigm Shift ◽  
Remanent Magnetization ◽  
Mineral Content ◽  
Mineral Exploration ◽  
Magnetization Vector ◽  
Data Interpretation ◽  
Magnetic Data ◽  
Data Set ◽  
Total Magnetization ◽  
Informational Value

Magnetic data are sensitive to both the induced magnetization in rock units caused by the present earth's magnetic field and the remanent magnetization acquired by rock units in past geologic time. Susceptibility is a direct indicator of the magnetic mineral content, whereas remanent magnetization carries information about the formation process and subsequent structural movement of geologic units. The ability to recover and use total magnetization, defined as the vectorial sum of the induced and remanent magnetization, therefore enables us to take full advantage of magnetic data. The exploration geophysics community has achieved significant advances in inverting magnetic data affected by remanent magnetization. It is now feasible to invert any magnetic data set for total magnetization. We provide an overview of the state of the art in magnetization inversion and demonstrate the informational value of inverted magnetization through a set of case studies from mineral exploration problems. We focus on the methods that recover either the magnitude of the total magnetization or the total magnetization vector itself.

scholarly journals Higher-Order Multifractal Detrended Partial Cross-Correlation Analysis for the Correlation Estimator

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Keqiang Dong ◽  
Xiaojie Gao
Keyword(s):  
Time Series ◽  
Correlation Analysis ◽  
Correlation Coefficient ◽  
Nonlinear Interaction ◽  
Cross Correlation ◽  
Nonstationary Time Series ◽  
New Method ◽  
Nonlinear Interactions ◽  
Cross Correlation Analysis ◽  
The Cross

In this paper, we develop a new method to measure the nonlinear interactions between nonstationary time series based on the detrended cross-correlation coefficient analysis. We describe how a nonlinear interaction may be obtained by eliminating the influence of other variables on two simultaneous time series. By applying two artificially generated signals, we show that the new method is working reliably for determining the cross-correlation behavior of two signals. We also illustrate the application of this method in finance and aeroengine systems. These analyses suggest that the proposed measure, derived from the detrended cross-correlation coefficient analysis, may be used to remove the influence of other variables on the cross-correlation between two simultaneous time series.

Sign in / Sign up

Export Citation Format

Share Document