Reduction‐to‐the‐pole of low latitude magnetic anomalies

1982 ◽  
Author(s):  
William C. Pearson ◽  
Christopher M. Skinner
Keyword(s):  
Magnetic Anomalies ◽  
Low Latitude ◽  
Reduction To The Pole

Differential reduction‐to‐the‐pole of regional magnetic anomalies

Geophysics ◽  
1988 ◽  
Vol 53 (12) ◽  
pp. 1592-1600 ◽  
Author(s):  
J. Arkani‐Hamed
Keyword(s):  
Frequency Domain ◽  
Regional Scale ◽  
Magnetic Anomalies ◽  
Positive Anomaly ◽  
Low Latitude ◽  
Mean Values ◽  
The North ◽  
Differential Reduction ◽  
Reduction To The Pole ◽  
Spectral Frequency

I present a differential reduction‐to‐the‐pole technique that reduces regional scale magnetic anomalies to the geomagnetic pole, while taking into account the variations in the direction of the geomagnetic field and that of the magnetization of the crust over the region. The technique is developed in the spectral frequency domain as an inverse problem solved iteratively using a perturbation method. I regard the variations in the directions as finite perturbations about the mean values of the directions over the region and evaluate the nonlinear coupling terms due to these perturbations in the space domain at each iteration before transforming them into the spectral frequency domain. The technique is applied to the magnetic anomalies of three semiinfinite prisms, which are inductively magnetized and located at high, mid, and low latitudes in a region where the inclination of the ambient field changes from 10 to 90 degrees and its declination changes from −30 to +30 degrees. The differential reduction to the pole shifts the positive anomaly of the low‐latitude prism toward the north more than it shifts that of the mid‐latitude prism, which in turn is shifted northward more than that of the high‐latitude prism. The reduction also suppresses the negative lobes to the north of the mid and low‐latitude prisms and moves the positive anomalies to points directly over the prisms. I also apply the technique to the marine magnetic anomalies off the east coast of Canada. The positive magnetic anomalies in the southern part of the area are displaced northward by about 30 km, whereas those in the northern part are not moved significantly.

Preliminary Interpretation of the magnetic anomalies of the Eastern Vietnam sea and adjacent region a

2018 ◽  
Vol 25 (2) ◽  
pp. 173-181
Author(s):  
Lê Huy Minh ◽  
Lưu Việt Hùng
Keyword(s):  
Magnetic Anomalies ◽  
Seafloor Spreading ◽  
Wiener Filtering ◽  
Adjacent Region ◽  
Low Latitude ◽  
Tectonic History ◽  
Geological Features ◽  
History Of ◽  
Reduction To The Pole ◽  
Filtering Approach

In this paper we showed that the reduction to the pole at low latitude based on a Wiener filtering approach of Hansen and Pawlowski could be applied on the magnetic equator if the magnetic boundaries are not paralel to magnetic meridians. Using this reduced-to-the-pole method, we have found that the geologic boundaries determined from the reduced-tothe-pole magnetic anomalies of the Eastern Vietnam sea and adjacent regions correlate remarkably well with the major geological features, including majorfaults, seafloor spreading segments, volcanic or intrusive blocks ... These results could be considered as very important informations to reconstruct the tectonic history of the region.

Differential reduction of magnetic anomalies to the pole on a massively parallel computer

Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1945-1951 ◽  
Author(s):  
Richard S. Lu ◽  
John Mariano ◽  
Dennis E. Willen
Keyword(s):  
Filter Design ◽  
Finite Impulse Response ◽  
Mineral Exploration ◽  
Magnetic Anomalies ◽  
Parallel Computer ◽  
Massively Parallel ◽  
Central Location ◽  
Differential Reduction ◽  
Reduction To The Pole ◽  
The Difference

A finite‐impulse‐response filter was implemented on a computer with massively parallel processors to reduce a magnetic anomaly map to the magnetic pole, allowing each grid node to have a different inclination and declination (differential reduction to the pole, DRTP). The dramatic speed improvement of such an implementation for the filter design and application via space‐domain convolution makes DRTP a practical tool for hydrocarbon and mineral exploration. Application of this tool to magnetic anomalies in east China reveals that the northward shift in position of the anomaly maximum generated by DRTP is 6 km for anomalies with dominant wavelengths of approximately 25 km in the northernmost part of the study area. The shift increases as the anomaly wavelength increases. Shifts for all anomaly wavelengths are even larger in the southern part of the study area, where the magnetic inclination is lower. The shift in position of the anomaly maximum for anomalies of wavelengths 25 km in the northernmost area produced by DRTP is 2 km less than that produced by a conventional reduction to the pole using the inclination and declination at the central location of the study area. Once again, such differences in shifts are larger for anomalies of longer wavelengths. The farther away from the central location, the greater is the absolute value of the difference.

scholarly journals Potensi Endapan Pasir Besi di Daerah Grabag dan Sekitarnya Berdasarkan Data Geomagnet

2019 ◽  
Vol 20 (2) ◽  
pp. 75 ◽  
Author(s):  
G.M. Lucki Junursyah ◽  
Wanda Rahmat
Keyword(s):  
Cross Sections ◽  
River Flow ◽  
Magnetic Anomalies ◽  
Research Area ◽  
Environmental Damage ◽  
Mining Activities ◽  
River Bank ◽  
Central Java ◽  
Reduction To The Pole ◽  
Potential Area

The potential of iron sand in Grabag area and its surrounding, Central Java Province, is not fully known yet because it is covered by thick alluvium, so that mining activities are done unmanaged without seeing the effect of environmental damage caused. This study uses reduction to the pole and upward continuation processing and analysis for Geomagnetic data in order to spread of lateral magnetic anomalies (map) and forward modelling for vertical magnetic anomalies (2D cross-sections). Based on the dispersion of magnetic anomaly, it is known that iron sand potential in the research area is located on old alluvium deposits with depth around 60 m and young coast alluvium sedimentation with depth around of 20 m, forming a lens as sand dump or river bank, followed by lane of ancient river flow pattern with thickness reaching ±10 m. The potential area is estimated to reach 26,329,188 m² with the calculation of hypothetical reserves reaching 69,575 Ton on the southwest and 5,880, 213 Ton in the northwest of the research area. The results of this study are expected to be used as reference for further research, so that it can menage iron sand mining activities more regularly and not caused environmental damaged.Keywords: Geomagnetic, Iron Sand, Alluvium. 

Differential reduction to the pole: Revisited

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. L13-L20 ◽  
Author(s):  
Jafar Arkani-Hamed
Keyword(s):  
Random Noise ◽  
Magnetic Anomalies ◽  
Space Domain ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Domain Reduction ◽  
Low Latitudes ◽  
Differential Reduction ◽  
Low Pass ◽  
Reduction To The Pole

Following a detailed investigation of the Fourier-domain differential reduction-to-the-pole (DRTP) algorithm I compared the results to those obtained using a space-domain reduction-to-the-pole algorithm. I demonstrate that DRTP reduces magnetic anomalies to the pole more effectively than the space-domain algorithm. The DRTP operator has singularities at the geomagnetic equator and enhances north-south trending features at low latitudes. The operator is modified by slightly increasing the inclination of the core field at low latitudes to suppress the singularity. This space-domain modification only affects the anomalies very close to the equator. The modified DRTP operator successfully reduces the magnetic anomalies at low latitudes to the pole. The effects of random noise added to the original magnetic anomalies are investigated in some detail, and an appropriate directional low-pass filter is used to remove the resulting enhanced noise in the reduced-to-the-pole magnetic anomalies. Very simple bodies (uniformly magnetized, cubic, or rectangular) are considered to clearly illustrate the effects of the DRTP, its modified version, and the directional low-pass filter.

Reduction to the pole as an inverse problem and its application to low‐latitude anomalies

Geophysics ◽  
1986 ◽  
Vol 51 (2) ◽  
pp. 369-382 ◽  
Author(s):  
João B. C. Silva
Keyword(s):  
Inverse Problem ◽  
Geomagnetic Field ◽  
Three Dimensional ◽  
Theoretical Data ◽  
Dimensional Case ◽  
Low Latitude ◽  
Horizontal Projection ◽  
Magnetization Direction ◽  
Reduction To The Pole ◽  
Dimensional Instability

Traditionally, reduction to the pole has been accomplished either by space‐ or wavenumber‐domain filtering. In the two‐dimensional case, this procedure is stable regardless of the latitude, as long as the source strike is not parallel to the horizontal projection of the geomagnetic field. In the three‐dimensional case, however, reduction‐to‐the‐pole filtering is stable only at high magnetic latitudes. At latitudes lower than 15 degrees, it is of no practical use due to a sharply increasing instability toward the magnetic equator. The three‐dimensional instability of this filtering technique is demonstrated, and the reduction‐to‐the‐pole problem is formulated in the context of a general linear inverse problem. As a result, stable solutions are found by using well‐known stabilizing procedures developed for the inverse linear problem. The distribution of magnetization of an equivalent layer of doublets that reproduces the observed data is computed. The magnetic doublets are parallel to the magnetization direction which is assumed constant throughout the sources. The magnetic field reduced to the pole is then obtained by changing the inclinations of the geomagnetic field and the doublets to 90 degrees and recalculating the total field. The usefulness and limitations of the method at low magnetic latitudes are assessed using theoretical data. The effects of noise and anomaly truncation are also investigated for both high and low latitudes. In all cases, application of the proposed method produced meaningful results regardless of the latitude. The method is applied to field data from two different low‐latitude anomalies. The first anomaly is due to a seamount in the Gulf of Guinea with reversed magnetization. The geomagnetic field at this location is about −23 degrees. The second anomaly is an intrabasement anomaly from Parnaiba Basin, Brazil, where the magnetization is assumed to be induced by a geomagnetic field with −1.4 degree inclination. The results obtained confirm that the proposed method produces stable, meaningful, reduced‐to‐the‐pole maps.

Using an equivalent source with positivity for low-latitude reduction to the pole without striation

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. J81-J90 ◽  
Author(s):  
Yaoguo Li ◽  
Misac Nabighian ◽  
Douglas W. Oldenburg
Keyword(s):  
Large Scale ◽  
Computational Cost ◽  
Equatorial Region ◽  
Magnetic Data ◽  
Data Sets ◽  
Low Latitude ◽  
Equivalent Source ◽  
Large Scale Data ◽  
Reduction To The Pole ◽  
Equivalent Sources

We present a reformulation of reduction to the pole (RTP) of magnetic data at low latitudes and the equator using equivalent sources. The proposed method addresses both the theoretical difficulty of low-latitude instability and the practical issue of computational cost. We prove that a positive equivalent source exists when the magnetic data are produced by normal induced magnetization, and we show that the positivity is sufficient to overcome the low-latitude instability in the space domain. We further apply a regularization term directly to the recovered RTP field to improve the solution. The use of equivalent source also naturally enables the processing of data acquired on uneven surface. The result is a practical algorithm that is effective at the equatorial region and can process large-scale data sets with uneven observation heights.

Reduction to the pole at low latitudes by Wiener filtering

Geophysics ◽  
1989 ◽  
Vol 54 (12) ◽  
pp. 1607-1613 ◽  
Author(s):  
R. O. Hansen ◽  
R. S. Pawlowski
Keyword(s):  
Frequency Domain ◽  
Synthetic Data ◽  
Wiener Filtering ◽  
Magnetic Data ◽  
Noise Power ◽  
Low Latitude ◽  
High Quality ◽  
Computational Load ◽  
Low Latitudes ◽  
Reduction To The Pole

Using simple estimates of the signal and noise power from gridded magnetic data, we design regulated frequency‐domain operators for reduction to the pole at low magnetic latitudes. These operators suppress the artifacts along the direction of the magnetic declination associated with the conventional reduction‐to‐the‐pole procedure, with negligible increase in computational load. The new procedure is applied to produce high‐quality reductions to the pole for noisy low‐latitude synthetic data and for magnetic data from the Dixon Seamount.

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