New Methods for Interpretation of Magnetic Gradient Tensor Data

Clark, David

doi:10.1071/aseg2012ab081

Cited by 16 publications

(8 citation statements)

References 34 publications

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“…The normalized source strength (NSS) can be derived from the eigenvalues of magnetic and gravity gradient tensor data (Wilson 1985;Beiki et al 2012;Clark 2012) …”

Section: E T H O Dmentioning

confidence: 99%

“…In recent years, applications of magnetic gradient tensor (MGT) and gravity gradient tensor (GGT) data in mineral Schmidt et al 2004;Schmidt and Clark 2006;Clark 2009;Beiki and Pedersen 2010;Beiki 2010;Clark 2010;Holstein et al 2011;Beiki et al 2012;Clark, 2012;Pilkington and Beiki, 2013). However, both processing and interpretation of MGT and GGT data are still challenging and require further development.…”

Section: Introductionmentioning

confidence: 99%

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Interpretation of magnetic and gravity gradient tensor data using normalized source strength – A case study from McFaulds Lake, Northern Ontario, Canada

Beiki

Keating

Clark

2014

Geophysical Prospecting

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In this paper, we present a case study on the use of the normalized source strength (NSS) for interpretation of magnetic and gravity gradient tensors data. This application arises in exploration of nickel, copper and platinum group element (Ni‐Cu‐PGE) deposits in the McFaulds Lake area, Northern Ontario, Canada. In this study, we have used the normalized source strength function derived from recent high resolution aeromagnetic and gravity gradiometry data for locating geological bodies. In our algorithm, we use maxima of the normalized source strength for estimating the horizontal location of the causative body. Then we estimate depth to the source and structural index at that point using the ratio between the normalized source strength and its vertical derivative calculated at two levels; the measurement level and a height h above the measurement level. To discriminate more reliable solutions from spurious ones, we reject solutions with unreasonable estimated structural indices. This method uses an upward continuation filter which reduces the effect of high frequency noise. In the magnetic case, the advantage is that, in general, the normalized magnetic source strength is relatively insensitive to magnetization direction, thus it provides more reliable information than standard techniques when geologic bodies carry remanent magnetization. For dipping gravity sources, the calculated normalized source strength yields a reliable estimate of the source location by peaking right above the top surface. Application of the method on aeromagnetic and gravity gradient tensor data sets from McFaulds Lake area indicates that most of the gravity and magnetic sources are located just beneath a 20 m thick (on average) overburden and delineated magnetic and gravity sources which can be probably approximated by geological contacts and thin dikes, come up to the overburden.

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“…The normalized source strength (NSS) can be derived from the eigenvalues of magnetic and gravity gradient tensor data (Wilson 1985;Beiki et al 2012;Clark 2012) …”

Section: E T H O Dmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Interpretation of magnetic and gravity gradient tensor data using normalized source strength – A case study from McFaulds Lake, Northern Ontario, Canada

Beiki

Keating

Clark

2014

Geophysical Prospecting

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“…where λ 2 is the intermediate eigenvalue, characterized by having the smallest absolute value. It should also be noted that the normalized magnetic moment can be defined, in terms of the invariants I 1 and I 2 and the intermediate eigenvalue Clark, 2009). The magnetic moment of a compact source is the volume integral of the magnetization vector and has the units of Am 2 .…”

Section: Normalized Source Strengthmentioning

confidence: 99%

“…In the last two decades, processing and interpretation techniques of gravity and magnetic gradient tensor data have been widely improved (e.g., Pedersen and Rasmussen, 1990;Vasco and Taylor, 1991;Edwards et al, 1997;Boggs and Dransfield, 2004;Schmidt et al, 2004;Zhdanov et al, 2004;While et al, 2006While et al, , 2009Mikhailov et al, 2007;Clark, 2009Clark, , 2010Clark et al, 2009;Beiki, 2010;Beiki andPedersen, 2010, 2011;Holstein et al, 2011). In 1990, Pedersen and Rasmussen studied gradient tensors of gravity and magnetic fields and introduced scalar invariants to indicate their dimensionality (Pedersen and Rasmussen, 1990).…”

Section: Introductionmentioning

confidence: 99%

Estimating source location using normalized magnetic source strength calculated from magnetic gradient tensor data

et al. 2012

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For a number of widely used models, normalized source strength (NSS) can be derived from eigenvalues of the magnetic gradient tensor. The NSS is proportional to a constant q normalized by the nth power of the distance between observation and integration points where q is a shape factor depending upon geometry of the model and n is the structural index. The NSS is independent of magnetization direction, and its amplitude is only affected by the magnitude of magnetization. The NSS is also a homogenous function and satisfies Euler's homogeneity equation. Therefore, Euler deconvolution of the NSS can be used to estimate source location. In our algorithm, we use data points enclosed by a square window centered at maxima of the NSS for simultaneously estimating the source location and structural index. The window size is increased until it exceeds a predefined limit. Then the most reliable solution is chosen based on some statistical analysis (minimum uncertainty). One of the advantages of the presented method is that it allows automatic identification of the structural index as the constant background field is eliminated. Another advantage is reduction of interference effects from neighboring sources by differentiation of the NSS. We have compared our method with the analytic signal amplitude and when the magnetic source contains remanent magnetization with a different direction to the inducing field, the NSS provides more reliable information about source geometry. Application of the method has been demonstrated on an aeromagnetic data set from the Tuckers Igneous Complex, Queensland, Australia. The NSS has improved interpretation of magnetic anomalies for this igneous complex, for which available geologic information shows relatively strong remanent magnetization.

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“…Based on the 2D body magnetic anomaly equations, Verduzco et al (2004) stated that the horizontal derivative of Tilt gradient is independent of the magnetization direction, and it has been applied in the 3D case. In recent years, with the improvement of the magnetic gradient tensor measurement system, the appropriate treatment methods and interpretation techniques developed rapidly (Clark et al, 2009;Beiki, 2010;Beiki and Pedersen, 2010;Beiki et al, 2011;Beiki et al, 2012;Oruç et al, 2013). Previous studies have indicated that we can reduce the magnetization direction based on the tensor data, e.g.…”

Section: Introductionmentioning

confidence: 99%

The Improved Anisotropy Normalized Variance for Detecting Non‐Vertical Magnetization Anomalies

Zhang

Marangoni²,

2014

Chinese J of Geophysics

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For the magnetic field with unknown magnetization direction, it is necessary to study the edge detection for the magnetic source of oblique magnetization directly. In this study, we propose a new edge detection called anisotropy normalized variance based on magnetic gradient tensor (ANV_MGT). First we use an anisotropy scale to improve the core function of ANV to show the effect of the anisotropy Gaussian function. Then the magnetic gradient tensor mode is used in the ANV method to process the anomalies with oblique magnetization. We construct a numerical model of complex magnetic anomalies with an oblique magnetization, which is used to test the edge detection method. The model test shows that the proposed method, ANV_MGT, can detect the edge of the magnetic source with non‐vertical magnetization direction. It also shows that the proposed method is better than application of ANV on the 3D analytic signal amplitude. In the application to real data from western China, a perfect magnetite ore location is determined by performing ANV_MGT for the non‐reduction to the pole data.

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New Methods for Interpretation of Magnetic Gradient Tensor Data

Cited by 16 publications

References 34 publications

Interpretation of magnetic and gravity gradient tensor data using normalized source strength – A case study from McFaulds Lake, Northern Ontario, Canada

Interpretation of magnetic and gravity gradient tensor data using normalized source strength – A case study from McFaulds Lake, Northern Ontario, Canada

Estimating source location using normalized magnetic source strength calculated from magnetic gradient tensor data

The Improved Anisotropy Normalized Variance for Detecting Non‐Vertical Magnetization Anomalies

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