A generalized multibody model for inversion of magnetic anomalies

Geophysics ◽  
1980 ◽  
Vol 45 (2) ◽  
pp. 255-270 ◽  
Author(s):  
B. K. Bhattacharyya
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Magnetization Vector ◽  
Critical Dimension ◽  
Magnetic Anomalies ◽  
Field Vector ◽  
Magnetic Survey ◽  
Multibody Model ◽  
Anomalous Field ◽  
Rectangular Block

The height of the observation surface above a magnetized region primarily determines the critical dimension of the smallest inhomogeneity in magnetization that can be resolved from magnetic survey data. When a rectangular block is smaller in size than this critical dimension, it appears homogeneously magnetized in the observed magnetic field. This consideration leads to the selection of a unit rectangular block of suitable dimensions with homogeneous magnetization. The magnetized region creating the anomalous field values in the area of observation can, therefore, be broken up into several blocks having different magnetizations, each block being equal in size and uniformly magnetized. The iterative method described here assumes initially that the anomalous field values are caused by a three‐dimensional (3-D) distribution of magnetized rectangular blocks. The optimum orientation of these blocks with respect to geographic north is then determined. This orientation is particularly insensitive to adjustments in the dimensions of the blocks. The top and bottom surfaces of each of the blocks in one or more layers are adjusted in a least‐squares sense to minimize the difference between observed and calculated field values. A method is also described for constraining the magnetization vector of each block to lie within a specified angle of the normal or reversed direction of the geomagnetic field vector. The procedure for analysis of data can also be extended to the case of anomalies over a draped surface. At the conclusion of the iterations, a 3-D distribution of magnetization is generated to delineate the magnetized region responsible for the observed anomalous magnetic field. Examples including model and aeromagnetic data are provided to demonstrate the usefulness of a generalized multibody model for inversion of magnetic anomalies.

Euler’s differential equation and the identification of the magnetic point‐pole and point‐dipole sources

Geophysics ◽  
1984 ◽  
Vol 49 (9) ◽  
pp. 1549-1553 ◽  
Author(s):  
J. O. Barongo
Keyword(s):  
Magnetic Field ◽  
Differential Equation ◽  
Magnetic Anomalies ◽  
Field Vector ◽  
Magnetic Data ◽  
Dipole Source ◽  
Point Dipole ◽  
Main Subject ◽  
Depth Extent ◽  
Dipole Sources

The concept of point‐pole and point‐dipole in interpretation of magnetic data is often employed in the analysis of magnetic anomalies (or their derivatives) caused by geologic bodies whose geometric shapes approach those of (1) narrow prisms of infinite depth extent aligned, more or less, in the direction of the inducing earth’s magnetic field, and (2) spheres, respectively. The two geologic bodies are assumed to be magnetically polarized in the direction of the Earth’s total magnetic field vector (Figure 1). One problem that perhaps is not realized when interpretations are carried out on such anomalies, especially in regions of high magnetic latitudes (45–90 degrees), is that of being unable to differentiate an anomaly due to a point‐pole from that due to a point‐dipole source. The two anomalies look more or less alike at those latitudes (Figure 2). Hood (1971) presented a graphical procedure of determining depth to the top/center of the point pole/dipole in which he assumed prior knowledge of the anomaly type. While it is essential and mandatory to make an assumption such as this, it is very important to go a step further and carry out a test on the anomaly to check whether the assumption made is correct. The procedure to do this is the main subject of this note. I start off by first using some method that does not involve Euler’s differential equation to determine depth to the top/center of the suspected causative body. Then I employ the determined depth to identify the causative body from the graphical diagram of Hood (1971, Figure 26).

Study of Enhanced Self Mixing in Ferrofluid Flow in an Elbow Channel Under the Influence of Non-Uniform Magnetic Field

2019 ◽  
Author(s):  
Nadish Anand ◽  
Richard Gould
Keyword(s):  
Magnetic Field ◽  
Uniform Magnetic Field ◽  
Magnetization Vector ◽  
Field Vector ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Initial Flow ◽  
Viscosity Term ◽  
Flow Mixing ◽  
The Magnetic Field

Abstract This paper investigates numerically the various parameters dictating the vortical (self)-mixing induced by a non-uniform magnetic field in a ferrofluid flow in an elbow channel. The elbow bend region of the channel has two current carrying conductors placed symmetrically and parametrically from the channel and are used to generate a non-uniform magnetic field. The ferrofluid is assumed to be pre-magnetized, isothermal and electrically non-conductive as it enters the channel and has a prescribed inlet magnetization and temperature. The mixing efficiency is characterized by introducing different mixing scalars based on velocity of the fluid and are compared in order to determine the overall suitability of each scalar to quantify the flow vortical (self)-mixing. Parametric studies were performed by varying parameters influencing the magnetic field and the initial flow field. This resulted in variations in non-dimensional groups which control different aspects of the flow and helped establish their relationship with mixing efficiency. It was found that at higher Reynolds numbers the flow mixing induced by the lateral gradient in the Kelvin Body Force (KBF) dissipates and higher electrical inputs are required to sustain mixing in the flow. The effects of mixing enhancement on the pressure gradient across the channel was also established, along with the introduction of an enhanced viscosity term which is due to the non-collinearity of the magnetization vector and the magnetic field vector.

Calculation of magnitude magnetic transforms with high centricity and low dependence on the magnetization vector direction

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. I21-I30 ◽  
Author(s):  
Daniela Gerovska ◽  
Marcos J. Araúzo-Bravo
Keyword(s):  
Magnetic Field ◽  
Magnetization Vector ◽  
Field Vector ◽  
Data Sets ◽  
Volcanic Area ◽  
Square Root ◽  
Anomalous Magnetic Field ◽  
Total Magnitude ◽  
Vector Direction ◽  
Magnitude Magnetic Transforms

We present a Matlab tool that calculates five magnitude magnetic transforms (MMTs) from an input measured anomalous magnetic field. The MMTs are all based on the total magnitude anomaly (TMA), and consist of the TMA itself, the modulus of the gradient of the TMA, the Laplacian of the TMA, half of the square root of the Laplacian of the square of the TMA, and the square root of the product of the TMA plus the Laplacian of the TMA. These MMTs produce anomalies that are closer to the magnetic source’s true horizontal position and are simpler to interpret than the measured anomalous magnetic field itself. While the conventional magnetic transforms of reduction-to-the-pole (RTP), the pseudogravity field, and the analytic signal (AS) also have these properties, these MMTs have several additional advantages. They require only first-order, horizontal derivatives for their calculation. They are also more stable at low magnetic latitudes than the RTP, and have a pattern that is independent of the geomagnetic-field vector direction, in contrast to the AS. The Matlab tool is designed to deal with big data sets and is compatible with common data formats, GS ASCII grid files, and XYZ data files. A calculation of the MMTs of the total magnetic anomaly of a synthetic example at a low magnetic latitude and with a field example from the Kuju volcanic area, Japan demonstrate the effectiveness of the program.

A new iterative method for computing the magnetic field at high magnetic susceptibilities

Geophysics ◽  
2005 ◽  
Vol 70 (5) ◽  
pp. L53-L62 ◽  
Author(s):  
Matthew B. J. Purss ◽  
James P. Cull
Keyword(s):  
Magnetic Field ◽  
Mineral Exploration ◽  
Three Dimensional ◽  
Magnetic Survey ◽  
Magnetic Susceptibilities ◽  
Iterative Computation ◽  
Approximation Errors ◽  
High Magnetic Susceptibility ◽  
The Magnetic Field ◽  
New Iterative Method

Failure to adequately correct for the effects of self-demagnetization can lead to misinterpretation of magnetic survey data, thereby reducing the success of mineral exploration programs. Numeric methods commonly used to correct for self-demagnetization of finite three-dimensional bodies are restricted to moderate magnetic susceptibilities (χ < 1 SI) because at higher values (χ ≥ 1 SI), the approximation errors for nonellipsoidal bodies become excessive. This paper reports a new method that allows for calculation of the magnetic field from arbitrary finite bodies with high magnetic susceptibility while minimizing approximation errors caused by the use of self-demagnetization corrections for nonellipsoidal bodies. This technique uses a segmented model defined by spherical elements (or voxels) of arbitrary diameter and an iterative computation of the magnetic field at the center of each voxel in free space and then with respect to the surrounding voxels.

A geomagnetic investigation of Carboniferous igneous rocks at Tickenham, County of Avon

1980 ◽  
Vol 117 (6) ◽  
pp. 587-593 ◽  
Author(s):  
P. Kearey ◽  
J. R. Allison
Keyword(s):  
Magnetic Field ◽  
Magnetization Vector ◽  
Magnetic Anomalies ◽  
Igneous Rocks ◽  
Field Reversal ◽  
Geomagnetic Survey ◽  
Vector Orientation ◽  
Magnetic Field Reversal

SummaryA geomagnetic survey indicates that the Carboniferous igneous rocks in the Tickenham area are more extensive than previously recognized. Inversions of the magnetic anomalies suggest the causative basaltic body is tabular in form, conforms to the regional dip and has a coplanar magnetization. The magnetization vector orientation indicates emplacement during a period of magnetic field reversal and thus at a time different from other Carboniferous igneous rocks in the region.

The Perturbation of Alternating Geomagnetic Fields by an Island Near a Coastline

1973 ◽  
Vol 10 (4) ◽  
pp. 510-518 ◽  
Author(s):  
L. R. Lines ◽  
F. W. Jones
Keyword(s):  
Magnetic Field ◽  
Field Component ◽  
Method Of Lines ◽  
Three Dimensional ◽  
Field Vector ◽  
Electric Field Vector ◽  
The Earth ◽  
Electric And Magnetic Field ◽  
Contour Plots ◽  
Geomagnetic Fields

The numerical method of Lines and Jones for investigating the problem of the perturbation of alternating geomagnetic fields by three-dimensional conductivity inhomogeneities embedded in a layered Earth is extended to include models in which vertical discontinuities may extend to the grid boundaries. The case considered is that in which the electric field vector is parallel to the strike of the discontinuities at such boundaries. A model which includes an island near a coastline is studied and contour plots as well as profiles of the electric and magnetic field component amplitudes at the surface of the Earth are given.

scholarly journals Three-dimensional sensing of the magnetic-field vector by a compact planar-type Hall device

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Junichi Shiogai ◽  
Kohei Fujiwara ◽  
Tsutomu Nojima ◽  
Atsushi Tsukazaki
Keyword(s):  
Magnetic Field ◽  
Rapid Development ◽  
Three Dimensional ◽  
Field Vector ◽  
Polar Coordinates ◽  
Magnetic Field Vector ◽  
Planar Geometry ◽  
Topological Features ◽  
The Magnetic Field ◽  
Compact Planar

AbstractSmart society is forthcoming with a rapid development in the automation of electric appliances requiring abundant sensors. One of the key sensors is a three-dimensional magnetometer for detecting the motion of objects, which is usually driven by cooperative multiple sensors on three orthogonal planes. Here, we demonstrate the fundamental operation of a three-dimensional magnetometer based on a simple Fe-Sn heterostructure Hall device in a planar geometry. Polar coordinates of the magnetic-field vector are uniquely determined by the combination of the sizable anomalous Hall effect, the anisotropic magnetoresistance, and the unidirectional magnetoresistance. Thanks to the ferromagnetic topological features in the Fe-Sn heterostructure, the above-mentioned device overcomes the limitation of conventional semiconductor devices and is highly sensitive even at room temperature. The compact planar geometry will be particularly useful in versatile electrical applications requiring a low-cost three-dimensional magnetometer with space- and energy-saving features.

scholarly journals High-Precision Magnetic Survey with UAV for the Archaeological Barrows at Novaya Kurya Monument in Western Siberia

2019 ◽  
Vol 17 (4) ◽  
pp. 5-12
Author(s):  
E. V. Balkov ◽  
P. G. Dyadkov ◽  
O. A. Pozdnyakova ◽  
D. A. Kuleshov ◽  
N. D. Evmenov ◽  
...  
Keyword(s):  
High Precision ◽  
Western Siberia ◽  
Statistical Processing ◽  
Archaeological Site ◽  
Magnetic Anomalies ◽  
Primary Data ◽  
Magnetic Survey ◽  
Geomagnetic Variations ◽  
Anomalous Field ◽  
Quantum Magnetometer

The paper presents the results of high-precision magnetic surveys by a quantum magnetometer using an unmanned aerial vehicle (UAV). The object of research was an area of 10 hectares (500 × 200 m) at the archaeological site of New Kurya in Western Siberia. The accuracy of the registration of the induction module of the geomagnetic field was not lower than 0.3 nT. The spatial accuracy of GPS coordinates lies in the submeter range. Magnetic anomalies caused by ancient mounds with an amplitude of up to 5–10 nT were revealed. The technique for isolating such low-amplitude anomalies included taking into account the geomagnetic variations of the external field, the regional anomalous field, and the use of a number of algorithms for the statistical processing of primary data. Identified magnetic anomalies can reliably determine the features of the device and the size of the mounds, including those not expressed in relief. The information received makes it possible to plan a strategy for archaeological study of this monument at a qualitatively different level. The prospects of further development and use of the technology in question for solving archaeological problems are noted.

scholarly journals Magnetic field of the Western Carpathians (Slovakia): reflections on the structure of the crust

2010 ◽  
Vol 61 (5) ◽  
pp. 437-447 ◽  
Author(s):  
Peter Kubeš ◽  
Vladimír Bezák ◽  
Ľudovít Kucharič ◽  
Miroslav Filo ◽  
Jozef Vozár ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomalies ◽  
Geological Structure ◽  
Variable Magnetic Field ◽  
Present Knowledge ◽  
Western Carpathians ◽  
The West ◽  
Anomalous Field ◽  
Sizable Number

Magnetic field of the Western Carpathians (Slovakia): reflections on the structure of the crustA new digital magnetic map of Slovakia on the scale of 1: 200,000 and 1: 500,000 was compiled at the end of 2008 as the output of database magnetic objects from the whole territory of Slovakia at a scale of 1: 50,000. The variable geological structure of the West Carpathian crust is depicted in the equally variable magnetic field of this region. A sizable number of magnetic anomalies with manifold character have been recognized. The basic anomalies distribution was divided into two groups: anomalies connected with rocks of the pre-Neogene basement and anomalies which originate in Neogene and Quaternary volcanic products. Most of the significant anomalies in the pre-Neogene basement were interpreted, modelled and consequently its geological and tectonic classification was worked out. On the basis of the anomalous field features, the following sources of anomalies have been distinguished: a) known, located on the surface, or at shallow depths verified by boreholes, mainly expressed by simple morphology, b) deep-seated and expressed by complicated morphology, reinterpreted or newly interpreted and also problematic. According to our present knowledge the interpretations are insufficient and remain open for further investigation. The above mentioned sources of magnetic anomalies are classified in terms of tectonic provenience to the main tectonic units.

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