On: “Magnetic interpretation using the 3-D analytic signal” by W. R. Roest, J. Verhoef, and M. Pilkington (GEOPHYSICS, 1, 116–125, January 1992).

Geophysics ◽  
1993 ◽  
Vol 58 (8) ◽  
pp. 1214-1214 ◽  
Author(s):  
N. L. Mohan
Keyword(s):  
Magnetic Anomalies ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Magnetic Interpretation ◽  
Vector Addition

It is quite interesting to learn the 3-D analytic signal interpretation of Roest et al. (1992), using the vector addition. However, I am quite skeptical about their objective of determining the depth under the assumption that the magnetic anomalies are caused by vertical contacts from gridded magnetic data which, it appears to me, is nothing but an oversimplification of interpretation.

APPLICATION OF SEMI-AUTOMATED AND INTERACTIVE MAGNETIC INTERPRETATION TECHNIQUES IN PETROLEUM EXPLORATION

1977 ◽  
Vol 17 (1) ◽  
pp. 85
Author(s):  
Robert J. Whiteley ◽  
Barry F. Long ◽  
David A. Pratt
Keyword(s):  
Sedimentary Basin ◽  
Sedimentary Basins ◽  
Magnetic Anomalies ◽  
Petroleum Exploration ◽  
Magnetic Data ◽  
Magnetic Method ◽  
Magnetic Interpretation ◽  
Geological Information ◽  
Detailed Interpretation ◽  
Insight Into

The magnetic method is used at many stages of a modern petroleum exploration program. Effective interpretation techniques are required to extract maximum geological information from magnetic data. Those techniques which provide the greatest flexibility and make full use of the talents of experienced interpreters are generally of a semi-automated and interactive nature.There are several practical methods for semi-automated quantitative magnetic interpretation in sedimentary basins. Initial interpretation can be achieved by automatic calculation of characteristic anomaly parameters continuously along original or processed magnetic data profiles. Detailed interpretation of more subtle magnetic features can then follow by theoretical anomaly comparison with field anomalies using interactive portfolio modelling or by direct computation.Examples of the use of these semi-automated techniques in the interpretation of basement and intra-sedimentary magnetic anomalies show that combined magnetic and seismic interpretations can provide considerable insight into the structural processes which have operated in a sedimentary basin.

AN AUTOMATIC LEAST‐SQUARES MULTIMODEL METHOD FOR MAGNETIC INTERPRETATION

Geophysics ◽  
1973 ◽  
Vol 38 (2) ◽  
pp. 349-358 ◽  
Author(s):  
Peter H. McGrath ◽  
Peter J. Hood
Keyword(s):  
Least Squares ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Model Parameters ◽  
Hudson Bay ◽  
Northern Ontario ◽  
Magnetic Interpretation ◽  
Hudson Bay Lowlands ◽  
Sverdrup Basin ◽  
Best Fit

The magnetic anomalies caused by such diverse model shapes as the finite strike length thick dike, the vertical prism, thes loping step, the parallelepiped body, etc., may be obtained through an appropriate numerical integration of the expression for the magnetic effect produced by a finite thin plate. Using models generated in this manner, an automatic computer method has been developed at the Geological Survey of Canada for the interpretation of magnetic data. Because the magnetic anomalies produced by the various model shapes are nonlinear in parameters of shape and position, it is necessary to use an iterative procedure to obtain the values for the various model parameters which yield a least‐squares best‐fit anomaly curve to a set of discrete observed data. The interpretation method described in this paper uses the Powell algorithm for this purpose. The procedure can sometimes be made more efficient using a Marquardt modification to the Powell algorithm. Examples of the use of the method are presented for an elongated anomaly in the Moose River basin of the Hudson Bay lowlands in northern Ontario, and for an areally large elliptical anomaly in the Sverdrup basin of the Canadian Arctic Islands.

Identifying remanent magnetization effects in magnetic data

Geophysics ◽  
1993 ◽  
Vol 58 (5) ◽  
pp. 653-659 ◽  
Author(s):  
Walter R. Roest ◽  
Mark Pilkington
Keyword(s):  
Magnetic Anomaly ◽  
Remanent Magnetization ◽  
Close Agreement ◽  
Magnetic Anomalies ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Impact Structure ◽  
Magnetization Direction ◽  
Additional Constraints

Remanent magnetization can have a significant influence on the shape of magnetic anomalies in areas that are generally characterized by induced magnetization. Since modeling of magnetic anomalies is nonunique, additional constraints on the direction of magnetization are useful. A method is proposed here to study the possible contribution of remanent magnetization to a particular anomaly, by comparing two functions that are calculated directly from the observations: (1) the amplitude of the analytic signal, and (2) the horizontal gradient of pseudogravity. From the amplitude and relative position of maxima in these derived quantities, we infer the deviation of the magnetization direction from that of the ambient field. The approach is applied to the magnetic anomaly in the center of the Manicouagan impact structure (Canada). Our results, based only on the magnetic anomaly observations, are in close agreement with constraints on the direction of remanent magnetization from rock samples.

On: “Magnetic interpretation using the 3-D analytic signal” (Walter R. Roest, Jacob Verhoef, and Mark Pilkington, GEOPHYSICS, 57, 116–125)

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 667-670 ◽  
Author(s):  
Huang Lin‐ping ◽  
Guan Zhi‐ning
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Vertical Gradient ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Magnetic Interpretation ◽  
Vertical Derivative ◽  
Horizontal Gradients ◽  
High Resolution Technique ◽  
Basic Concepts

Over the last decades increasing interest has been expressed for determining boundaries and depths by using the analytic signal. The basic concepts of the analytic signal in 2-D case for magnetic data were extensively discussed by Nabighian (1972, 1974). Roest et al. (1992) discussed a new method for magnetic interpretation based on the generalization of analytic signal concept to 3-D. They considered that the analytic signal exhibits maxima over magnetization contrasts, independent of the ambient magnetic field, and source magnetization directions and locations of these maxima thus determine the outlines of magnetic sources. Afterward, Hsu et al. (1996) adopted a high‐resolution technique (also related to analytic signal) to image geologic boundaries such as contacts and faults. The outlines of the geologic boundaries can be determined by tracing the maximum amplitudes of an enhanced analytic signal composed of the nth‐order vertical derivative values of two horizontal gradients and one vertical gradient.

Automatic 3-D interpretation of potential field data using analytic signal derivatives

Geophysics ◽  
1997 ◽  
Vol 62 (1) ◽  
pp. 87-96 ◽  
Author(s):  
Nicole Debeglia ◽  
Jacques Corpel
Keyword(s):  
Signal Amplitude ◽  
Vertical Gradient ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Practical Implementation ◽  
Potential Field Data ◽  
Gravity And Magnetic ◽  
Second Derivatives ◽  
Gravity And Magnetic Data ◽  
Derivatives Of

A new method has been developed for the automatic and general interpretation of gravity and magnetic data. This technique, based on the analysis of 3-D analytic signal derivatives, involves as few assumptions as possible on the magnetization or density properties and on the geometry of the structures. It is therefore particularly well suited to preliminary interpretation and model initialization. Processing the derivatives of the analytic signal amplitude, instead of the original analytic signal amplitude, gives a more efficient separation of anomalies caused by close structures. Moreover, gravity and magnetic data can be taken into account by the same procedure merely through using the gravity vertical gradient. The main advantage of derivatives, however, is that any source geometry can be considered as the sum of only two types of model: contact and thin‐dike models. In a first step, depths are estimated using a double interpretation of the analytic signal amplitude function for these two basic models. Second, the most suitable solution is defined at each estimation location through analysis of the vertical and horizontal gradients. Practical implementation of the method involves accurate frequency‐domain algorithms for computing derivatives with an automatic control of noise effects by appropriate filtering and upward continuation operations. Tests on theoretical magnetic fields give good depth evaluations for derivative orders ranging from 0 to 3. For actual magnetic data with borehole controls, the first and second derivatives seem to provide the most satisfactory depth estimations.

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).

scholarly journals Estimating Effectiveness of Some Methods for Detecting Edge of Potential Field Sources

2020 ◽  
Vol 36 (4) ◽  
Author(s):  
Pham Thanh Luan ◽  
Le Thi Sang ◽  
Vu Duc Minh ◽  
Ngo Thi To Nhu ◽  
Do Duc Thanh ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Tilt Angle ◽  
Northeast China ◽  
Signal Amplitude ◽  
Analytic Signal ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
North Vietnam ◽  
Gradient Amplitude

This paper presents a comparative study of effectiveness of edge detection methods such as total horizontal gradient, analytic signal amplitude, tilt angle, gradient amplitude of tilt angle, theta map, horizontal tilt angle, tilt angle of total horizontal gradient, tilt angle of analytic signal, improved theta map, and total horizontal gradient of improved tilt angle. The effectiveness of each method was estimated on synthetic magnetic data and synthetic gravity anomaly data with and without noise. The obtained results show that the tilt angle of gradient amplitude can detect all the edges more clearly and precisely. The applicability of each method is demonstrated on the aeromagnetic anomaly data from the Zhurihe region of Northeast China, and Bouguer gravity anomaly data from a region of North Vietnam. The results computed by the tilt angle of horizontal gradient were also in accord with the geologic structures of the areas.

Magnetization vector imaging for borehole magnetic data based on magnitude magnetic anomaly

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. D429-D444 ◽  
Author(s):  
Shuang Liu ◽  
Xiangyun Hu ◽  
Tianyou Liu ◽  
Jie Feng ◽  
Wenli Gao ◽  
...  
Keyword(s):  
Conjugate Gradient Method ◽  
Conjugate Gradient ◽  
Gradient Method ◽  
Magnetization Vector ◽  
Real Data ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Preconditioned Conjugate Gradient ◽  
Magnetization Direction ◽  
Magnetization Intensity

Remanent magnetization and self-demagnetization change the magnitude and direction of the magnetization vector, which complicates the interpretation of magnetic data. To deal with this problem, we evaluated a method for inverting the distributions of 2D magnetization vector or effective susceptibility using 3C borehole magnetic data. The basis for this method is the fact that 2D magnitude magnetic anomalies are not sensitive to the magnetization direction. We calculated magnitude anomalies from the measured borehole magnetic data in a spatial domain. The vector distributions of magnetization were inverted methodically in two steps. The distributions of magnetization magnitude were initially solved based on magnitude magnetic anomalies using the preconditioned conjugate gradient method. The preconditioner determined by the distances between the cells and the borehole observation points greatly improved the quality of the magnetization magnitude imaging. With the calculated magnetization magnitude, the distributions of magnetization direction were computed by fitting the component anomalies secondly using the conjugate gradient method. The two-step approach made full use of the amplitude and phase anomalies of the borehole magnetic data. We studied the influence of remanence and demagnetization based on the recovered magnetization intensity and direction distributions. Finally, we tested our method using synthetic and real data from scenarios that involved high susceptibility and complicated remanence, and all tests returned favorable results.

2D potential theory using complex algebra: New equations and visualization for the interpretation of potential field data

Geophysics ◽  
2018 ◽  
Vol 83 (2) ◽  
pp. J1-J13 ◽  
Author(s):  
Pauline Le Maire ◽  
Marc Munschy
Keyword(s):  
Magnetic Field ◽  
Complex Plane ◽  
Potential Field ◽  
Single Point ◽  
Magnetic Anomalies ◽  
Analytic Signal ◽  
Power Functions ◽  
Field Equations ◽  
Complex Algebra ◽  
Location Depth

The shape of an anomaly (magnetic or gravity) along a profile provides information on the geometry, horizontal location, depth, and magnetization of the source. For a 2D source, the horizontal location, depth, and geometry of a source are determined through the analysis of the curve of the analytic signal. However, the amplitude of the analytic signal is independent of the dips of the structure, the apparent inclination of magnetization, and the regional magnetic field. To better characterize the parameters of the source, we have developed a new approach for studying 2D potential field equations using complex algebra. Complex equations for different geometries of the sources are obtained for gravity and magnetic anomalies in the spatial and spectral domains. In the spatial domain, these new equations are compact and correspond to logarithmic or power functions with a negative integer exponent. We found that modifying the shape of the source changes the exponent of the power function, which is equivalent to differentiation or integration. We developed anomaly profiles using plots in the complex plane, which is called mapping. The obtained complex curves are loops passing through the origin of the plane. The shape of these loops depends only on the geometry and not on the horizontal location of the source. For source geometries defined by a single point, the loop shape is also independent of the source depth. The orientation of the curves in the complex plane is related to the order of differentiation or integration, the geometry and dips of the structures, and the apparent inclination of magnetization and of the regional magnetic field. The application of these equations and mapping on total field magnetic anomalies across a magmatic dike in Norway shows coherent results, allowing us to determine the geometry and the apparent inclination of magnetization.

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