Transforming Total‐Field Magnetic Anomalies Into Three Components Using Dual‐Layer Equivalent Sources

2020 ◽  
Vol 47 (3) ◽  
Author(s):  
Duan Li ◽  
Qing Liang ◽  
Jinsong Du ◽  
Shida Sun ◽  
Yi Zhang ◽  
...  
Keyword(s):  
Magnetic Anomalies ◽  
Total Field ◽  
Equivalent Sources ◽  
Three Components

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.

scholarly journals Experimental Study on the Localization of Moving Object by Total Geomagnetic Field

2017 ◽  
Vol 2017 ◽  
pp. 1-7
Author(s):  
Chong Kang ◽  
Liming Fan ◽  
Quan Zheng ◽  
Xiyuan Kang ◽  
Jian Zhou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
High Sensitivity ◽  
Magnetic Anomalies ◽  
Target Localization ◽  
Total Field ◽  
Detection Range ◽  
Vector Sensors ◽  
Field Localization ◽  
Low Sensitivity

In the method of target localization based on magnetic anomalies, the scheme of vector field localization and experimental research are significant. Because more information of magnetic field can be measured by vector sensors, the position of the target can be directly calculated by the equations. However, the vector magnetic anomaly generated by the target is difficult to measure. And the detection range is small due to the low sensitivity of vector sensors. A method for target localization based on the total geomagnetic field is proposed. Its advantages are that the measurement of total magnetic field is not affected by the orientation of the total field sensors and the detection range is large due to their high sensitivity. In this paper, we focus on the localization using the array with the total field magnetometers. And we design an array structure with the total field magnetometers. Then, we obtain the higher order nonlinear equations for the target localization based on this array. The numerical method is used to solve the equations. Meanwhile, we present a method for eliminating the effect of geomagnetic field variations and uneven spatial distribution. In suburban roads, localization experiments were carried out. And the results showed that the relative error of target localization is less than 5% by using the proposed method.

An inverse scattering technique for electromagnetic bistatic scattering

1969 ◽  
Vol 47 (11) ◽  
pp. 1177-1184 ◽  
Author(s):  
V. H. Weston ◽  
W. M. Boerner
Keyword(s):  
Plane Wave ◽  
Scattered Field ◽  
Convex Surface ◽  
The Body ◽  
Total Field ◽  
Convex Shape ◽  
Plane Wave Incident ◽  
Smooth Body ◽  
Equivalent Sources ◽  
The Fourier Transform

It is shown that the total field produced by a plane wave incident upon a scattering body can be expressed at all points in space as the sum of the incident field and the Fourier transform of a quantity which is related to the scattering matrix. For points exterior to the minimum convex surface enclosing the body, the scattered field is reducible to a plane-wave representation which requires knowledge of the bistatic scattered field, for a fixed frequency and direction of incidence. It is shown that for certain cases, the resulting expression for the bistatic scattered field may be employed in interior portions of the minimum convex shape (including the body) in which case it represents the field arising from a set of equivalent sources. Alternative representations are also given. A technique is presented which yields the surface of a perfectly-conducting piecewise-smooth body from knowledge of the local total field. To achieve uniqueness, the technique must be applied for at least two different frequencies. Numerical results are presented which illustrate the technique.

scholarly journals Interpolation of magnetic anomalies over an oceanic ridge region using an equivalent source technique and crust age model constraint

2021 ◽  
Author(s):  
Duan Li ◽  
Jinsong Du ◽  
Chao Chen ◽  
Qing Liang ◽  
Shida Sun
Keyword(s):  
Plate Tectonics ◽  
Magnetic Anomalies ◽  
Background Field ◽  
Source Model ◽  
Magnetic Data ◽  
Magnetization Distribution ◽  
Equivalent Source ◽  
Oceanic Ridge ◽  
Age Model ◽  
Equivalent Sources

Abstract. Marine magnetic surveys over oceanic ridge regions are of great interest for investigations of structure and evolution of oceanic crust, and have played a key role in developing the theory of plate tectonics (Dyment, 1993; Maus et al, 2007; Vine and Matthews, 1963). In this study, we propose an interpolation approach based on the dual-layer equivalent source model for the generation of a magnetic anomaly map based on sparse survey line data over oceanic ridge areas. In this approach, information from an ocean crust age model is utilized as constraint for the inversion procedure. The constraints can affect the magnetization distribution of equivalent sources following crust age. The results of synthetic tests show that the obtained magnetic anomalies have higher accuracy than those obtained by other interpolation methods. Meanwhile, considering the unclear on the true magnetization directions of sources and the background field in the synthetic model, well interpolation result can still be obtained. We applied the approach to magnetic data obtained from five survey lines east of the Southeast Indian Ridge. This prediction result is useful to improve the lithospheric magnetic field models WDMAMv2 and EMAG2v3, in the terms of spatial resolution and the consistency with observed data.

Generalized positivity constraint on magnetic equivalent layers

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. J99-J110
Author(s):  
André L. A. Reis ◽  
Vanderlei C. Oliveira Jr. ◽  
Valéria C. F. Barbosa
Keyword(s):  
Inverse Problem ◽  
Magnetic Moment ◽  
A Priori ◽  
Synthetic Data ◽  
Total Field ◽  
Magnetization Direction ◽  
Moment Distribution ◽  
Equivalent Sources ◽  
Priori Information ◽  
Equivalent Layer

It is known from the potential theory that a continuous and planar layer of dipoles can exactly reproduce the total-field anomaly produced by arbitrary 3D sources. We have proven the existence of an equivalent layer having an all-positive magnetic-moment distribution for the case in which the magnetization direction of this layer is the same as that of the true sources, regardless of whether the magnetization of the true sources is purely induced or not. By using this generalized positivity constraint, we have developed a new iterative method for estimating the total magnetization direction of 3D magnetic sources based on the equivalent-layer technique. Our method does not impose a priori information about the shape or the depth of the sources, does not require regularly spaced data, and presumes that the sources have a uniform magnetization direction. At each iteration, our method performs two steps. The first step solves a constrained linear inverse problem to estimate a positive magnetic-moment distribution over a discrete equivalent layer of dipoles. We consider that the equivalent sources are located on a plane and have a uniform and fixed magnetization direction. In the second step, we use the estimated magnetic-moment distribution and solve a nonlinear inverse problem for estimating a new magnetization direction for the dipoles. The algorithm stops when the equivalent layer yields a total-field anomaly that fits the observed data. Tests with synthetic data simulating different geologic scenarios show that the final estimated magnetization direction is close to the true one. We apply our method to field data from the Goiás alkaline province, over the Montes Claros complex, in the center of Brazil. The results suggest the presence of intrusions with remarkable remanent magnetization, in agreement with the current literature for this region.

The zero-line method of interpreting total field magnetic anomalies of spherical ore-bodies

1978 ◽  
Vol 116 (6) ◽  
pp. 1191-1199 ◽  
Author(s):  
I. V. Radhakrishna Murthy ◽  
D. Bhaskara Rao
Keyword(s):  
Magnetic Anomalies ◽  
Total Field ◽  
Line Method ◽  
Zero Line ◽  
Ore Bodies

3D forward and inverse modeling of total-field magnetic anomalies caused by a uniformly magnetized layer defined by a linear combination of 2D Gaussian functions

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. L11-L18 ◽  
Author(s):  
Juan García-Abdeslem
Keyword(s):  
Linear Combination ◽  
Magnetic Anomaly ◽  
Synthetic Data ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Nonlinear Inversion ◽  
Total Field ◽  
Gaussian Functions ◽  
Estimated Parameters ◽  
Forward And Inverse Modeling

I develop a method for 3D forward modeling and nonlinear inversion of the total-field magnetic anomaly caused by a uniformly magnetized layer with its top and bottom surfaces represented by a linear combination of 2D Gaussian functions. The solution of the forward problem is found through both analytic and numerical methods of integration to calculate the theoretical magnetic anomaly. The magnetic anomalies computed by the present numerical method compare well with the ones calculated by using an analytic solution. To test the robustness of the algorithm, the inversion is performed with noisy synthetic data. The estimated parameters in the case of a synthetic model were found to deviate only modestly from the true parameters in the presence of noise. The algorithm is used to interpret a dipolar magnetic anomaly of high amplitude attributable to a laccolith of intermediate composition in northern Mexico.

Sign in / Sign up

Export Citation Format

Share Document