A new method for determination of magnetization direction

The characterization and interpretation of magnetic anomalies rely upon knowledge of the total magnetization direction. Magnetization is usually assumed to consist solely, or primarily, of induced magnetization. The presence of strong remanent magnetization can alter the direction significantly and consequently adversely affect the interpretation, leading to erroneous sizes or shapes of causative bodies. Therefore, it is imperative to have some understanding of the total magnetization direction. We propose a method based upon the correlation between two quantities in magnetic data interpretation: the vertical gradient and the total gradient of the reduced-to-pole (RTP) field. This method is tested on both synthetic and field data sets. The results show that the method is effective in a variety of situations, including those with two-dimensional and three-dimensional dipping bodies and a field example that has a large deviation between the inducing field direction and the total magnetization direction.

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Plasma convection at high latitudes using the EISCAT VHF and ESR incoherent scatter radars

Annales Geophysicae ◽

10.1007/s00585-000-1088-5 ◽

2000 ◽

Vol 18 (9) ◽

pp. 1088-1096 ◽

Cited By ~ 3

Author(s):

J. M. Holt ◽

A. P. van Eyken

Keyword(s):

Three Dimensional ◽

Data Sets ◽

Plasma Convection ◽

Vhf Radar ◽

Common Assumption ◽

Incoherent Scatter ◽

Incoherent Scatter Radars ◽

The Common ◽

Convection Patterns

Abstract. The recent availability of substantial data sets taken by the EISCAT Svalbard Radar allows several important tests to be made on the determination of convection patterns from incoherent scatter radar results. During one 30-h period, the Svalbard Radar made 15 min scans combining local field aligned observations with two, low elevation positions selected to intersect the two beams of the Common Programme Four experiment being simultaneously conducted by the EISCAT VHF radar at Tromsø. The common volume results from the two radars are compared. The plasma convection velocities determined independently by the two radars are shown to agree very closely and the combined three-dimensional velocity data used to test the common assumption of negligible field-aligned flow in this regime.Key words: Ionosphere (auroral ionosphere; polar ionosphere) - Magnetospheric physics (plasma convection)

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Determination of crystallographic intensities from sparse data

IUCrJ ◽

10.1107/s2052252514022313 ◽

2015 ◽

Vol 2 (1) ◽

pp. 29-34 ◽

Cited By ~ 18

Author(s):

Kartik Ayyer ◽

Hugh T. Philipp ◽

Mark W. Tate ◽

Jennifer L. Wierman ◽

Veit Elser ◽

...

Keyword(s):

Diffraction Data ◽

Crystal Size ◽

Three Dimensional ◽

Sparse Data ◽

Data Sets ◽

X Rays ◽

Diffraction Intensity ◽

X Ray ◽

Proof Of Principle

X-ray serial microcrystallography involves the collection and merging of frames of diffraction data from randomly oriented protein microcrystals. The number of diffracted X-rays in each frame is limited by radiation damage, and this number decreases with crystal size. The data in the frame are said to be sparse if too few X-rays are collected to determine the orientation of the microcrystal. It is commonly assumed that sparse crystal diffraction frames cannot be merged, thereby setting a lower limit to the size of microcrystals that may be merged with a given source fluence. TheEMCalgorithm [Loh & Elser (2009),Phys. Rev. E,80, 026705] has previously been applied to reconstruct structures from sparse noncrystalline data of objects with unknown orientations [Philippet al.(2012),Opt. Express,20, 13129–13137; Ayyeret al.(2014),Opt. Express,22, 2403–2413]. Here, it is shown that sparse data which cannot be oriented on a per-frame basis can be used effectively as crystallographic data. As a proof-of-principle, reconstruction of the three-dimensional diffraction intensity using sparse data frames from a 1.35 kDa molecule crystal is demonstrated. The results suggest that serial microcrystallography is, in principle, not limited by the fluence of the X-ray source, and collection of complete data sets should be feasible at, for instance, storage-ring X-ray sources.

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Comprehensive approaches to 3D inversion of magnetic data affected by remanent magnetization

Geophysics ◽

10.1190/1.3294766 ◽

2010 ◽

Vol 75 (1) ◽

pp. L1-L11 ◽

Cited By ~ 94

Author(s):

Yaoguo Li ◽

Sarah E. Shearer ◽

Matthew M. Haney ◽

Neal Dannemiller

Keyword(s):

Mineral Exploration ◽

Three Dimensional ◽

Canadian Arctic ◽

Magnetization Vector ◽

Magnetic Data ◽

Inversion Algorithm ◽

3D Inversion ◽

Magnetization Direction ◽

Direct Inversion ◽

Amplitude Data

Three-dimensional (3D) inversion of magnetic data to recover a distribution of magnetic susceptibility has been successfully used for mineral exploration during the last decade. However, the unknown direction of magnetization has limited the use of this technique when significant remanence is present. We have developed a comprehensive methodology for solving this problem by examining two classes of approaches and have formulated a suite of methods of practical utility. The first class focuses on estimating total magnetization direction and then incorporating the resultant direction into an inversion algorithm that assumes a known direction. The second class focuses on direct inversion of the amplitude of the magnetic anomaly vector. Amplitude data depend weakly upon magnetization direction and are amenable to direct inversion for the magnitude of magnetization vector in 3D subsurface. Two sets of high-resolution aeromagnetic data acquired for diamond exploration in the Canadian Arctic are used to illustrate the methods’ usefulness.

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COMPUTER‐ASSISTED ANALYSIS TECHNIQUES FOR REMOTE SENSING DATA INTERPRETATION

Geophysics ◽

10.1190/1.1440719 ◽

1977 ◽

Vol 42 (3) ◽

pp. 468-481 ◽

Cited By ~ 16

Author(s):

Paul E. Anuta

Keyword(s):

Gamma Ray ◽

Remote Sensing Data ◽

Data Interpretation ◽

Magnetic Data ◽

Computer Assisted ◽

Data Sets ◽

Visual Interpretation ◽

Computer Based ◽

Interpretation Process ◽

Assisted Analysis

The development of airborne and satellite multispectral scanning radiometers has created widespread interest in the application of such sensors to mapping of earth resources. The energy sensed in each band can be used as a parameter in a computer‐based, multidimensional‐pattern‐recognition process to aid in the interpretation of the nature of elements in the scene. Images from each band can also be interpreted visually. Visual interpretation of 5 or 10 multispectral images simultaneously becomes impractical, especially as the area studied increases; hence, great emphasis has been placed on machine (computer‐assisted) techniques in the interpretation process. A number of other data sets have recently been studied and integrated by digital registration with the multispectral reflectance and radiance phenomena. Topographic data, which have been registered with four‐band Landsat multispectral scanner (MSS) data, are being studied to determine relationships between spectral and topographic variables. Geophysical variables. including gamma‐ray and magnetic data, have also been registered and studied using the multivariate analysis approach.

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Stepped inversion of magnetic data

Geophysics ◽

10.1190/1.2711661 ◽

2007 ◽

Vol 72 (3) ◽

pp. L21-L30 ◽

Cited By ~ 3

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.

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Geophysical helicopter-based magnetic methods for locating wells

Geophysics ◽

10.1190/geo2017-0181.1 ◽

2018 ◽

Vol 83 (5) ◽

pp. B269-B279 ◽

Cited By ~ 3

Author(s):

Vladislav Kaminski ◽

Richard W. Hammack ◽

William Harbert ◽

Garret A. Veloski ◽

James Sams ◽

...

Keyword(s):

Magnetic Susceptibility ◽

Accurate Determination ◽

Likelihood Estimation ◽

Vertical Gradient ◽

Magnetic Data ◽

Small Subset ◽

Data Sets ◽

Successful Recovery ◽

Tilt Derivative ◽

Airborne Magnetic

We studied the problem of determining accurately the location of abandoned and sometimes undocumented wells and the challenging and increasingly important task related to subsurface reservoir integrity and regional economic development. We reviewed a variety of semiquantitative methods based on geophysical workflows, and we tested these with airborne magnetic data collected at two field sites. Our main conclusion is that airborne magnetic surveys represent a high-value tool to aid in the accurate determination of abandoned well locations and characteristics. At one site, two surveys were collected at slightly different altitudes to compare workflow robustness and allow the observed vertical magnetic gradient to be included in well detection workflows. We also investigated using focal zone anomaly statistics (using the magnetic field intensity and its first and second horizontal derivatives), analytic signal, tilt derivative, and calculated vertical gradient. In addition, we used a 3D inversion of a small subset of data to investigate the successful recovery of well-related magnetic susceptibility distribution and estimate subsurface well topology. The recovered magnetic susceptibility volume showed distinctive vertically elongated objects that correspond to known wells. Maximum likelihood estimation and confidence calculations were then applied to these data sets and indicated that high-confidence well locations could be determined and characterized using such airborne total magnetic data.

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Automatic determination of the magnetization–density ratio and magnetization inclination from the joint interpretation of 2D gravity and magnetic anomalies

Geophysics ◽

10.1190/1.1778237 ◽

2004 ◽

Vol 69 (4) ◽

pp. 938-948 ◽

Cited By ~ 7

Author(s):

Carlos Alberto Mendonça

Keyword(s):

Vector Fields ◽

Density Ratio ◽

Magnetic Anomalies ◽

Magnetic Data ◽

Data Sets ◽

Magnetization Direction ◽

Gravity And Magnetic ◽

Geophysical Surveys ◽

Magnetization Density ◽

Gravity And Magnetic Data

The Poisson theorem establishes a linear relationship between the gravity and magnetic potentials arising from common dense and magnetized bodies with constant magnetization–density ratio and magnetization direction. For geological formations satisfying such constraints (i.e., the Poisson conditions), this theorem provides suitable relationships between the gravity and magnetic anomalies that are useful in interpreting the related data sets. In such applications, both magnetization–density ratio (MDR) and magnetization direction can be estimated, thus helping the subsurface geological mapping from potential field data acquired on the earth's surface. However, no existing method is fully automatic, which has hampered extensive use in routine applications. Such a drawback follows the adoption of equations that, although obeying the Poisson theorem, relate particular components of the gravity and magnetic fields, thus requiring either a known magnetization direction or the implementation of iterative procedures to determine it. To allow one‐pass estimates for both MDR and magnetization direction (more precisely, its inclination projected on the plane normal to the source strike), this paper presents simple analytical solutions for these parameters by relating suitable gravity and magnetic vector fields that are derived from the gravity and magnetic data sets. Because current geophysical surveys usually provide only a single‐field component, a data processing scheme is developed to determine the required components in evaluating the desired vector fields. This is done by applying suitable linear transformations on the measured components according to well‐established filtering techniques in processing gravity and magnetic data. Except for distortions from noise, the proposed method automatically determines the MDR and the projected magnetization inclination for the underlying rocks everywhere the Poisson conditions are satisfied. Two‐dimensional sources are assumed, but no constraint upon their depth and cross‐section shape is required. Distorted estimates only appear close to the sources where at least one of the Poisson conditions is violated. In this case, the proposed technique furnishes apparent values for the rock properties. The abrupt changes of apparent values over contacts detect edges, thus facilitating the mapping of geological boundaries. The proposed technique is used to interpret two profiles across the Appalachian fold belt from the eastern portion of the State of Georgia, and the results are compared with some of the geological information available for the area.

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

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.644-650.3459 ◽

2014 ◽

Vol 644-650 ◽

pp. 3459-3462 ◽

Cited By ~ 1

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.

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

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.644-650.3793 ◽

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.

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3-D inversions of magnetic gradiometer data in archeological prospecting: Possibilities and limitations

Geophysics ◽

10.1190/1.1444782 ◽

2000 ◽

Vol 65 (3) ◽

pp. 849-860 ◽

Cited By ~ 13

Author(s):

Jörg Herwanger ◽

Hansruedi Maurer ◽

Alan G. Green ◽

Jürg Leckebusch

Keyword(s):

Magnetic Susceptibility ◽

Synthetic Data ◽

Vertical Gradient ◽

Magnetic Data ◽

Data Sets ◽

Northern Switzerland ◽

Recorded Data ◽

Susceptibility Contrast ◽

Depth Extent ◽

Archeological Site

A vertical‐gradient magnetic system based on optically pumped Cesium sensors has been used to map subtle magnetic anomalies across infilled pit houses and ditches at a medieval archeological site in northern Switzerland. For estimating the locations and dimensions of these features from the recorded data, we have designed and implemented an appropriate inversion scheme. Tests of this scheme on realistic synthetic data sets suggested that suitable minimum magnetic susceptibility contrasts and smoothing parameters for the inversion may be directly extracted from the data. Inversions with minimum magnetic susceptibility contrasts generated causative bodies with maximum plausible sizes. By using higher magnetic susceptibility contrasts, a complete suite of models that matched the data equally well was produced. To constrain better the magnetic susceptibility constrast within a selected area of the archeological site, shallow samples of topsoil and sediment were analyzed in the laboratory. An inversion based on the measured magnetic susceptibility contrast yielded reliable estimates of the locations, 3-D geometries, and sizes of two small pit houses. The depth extent of one pit house was subsequently verified by shallow drilling. We concluded that inversions of vertical‐gradient magnetic data constrained by magnetic susceptibility or shallow borehole information are rapid and inexpensive means of providing key knowledge on the depth distribution of inductively magnetized bodies.

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