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

1999 ◽  
Author(s):  
Richard S. Lu ◽  
John Mariano ◽  
Dennis E. Willen
Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1945-1951 ◽  
Author(s):  
Richard S. Lu ◽  
John Mariano ◽  
Dennis E. Willen

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.


Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. L13-L20 ◽  
Author(s):  
Jafar Arkani-Hamed

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.


Geophysics ◽  
1988 ◽  
Vol 53 (12) ◽  
pp. 1592-1600 ◽  
Author(s):  
J. Arkani‐Hamed

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.


1987 ◽  
Author(s):  
Jafar Arkani‐Hamed ◽  
David W. Strangway

Author(s):  
Jose-Maria Carazo ◽  
I. Benavides ◽  
S. Marco ◽  
J.L. Carrascosa ◽  
E.L. Zapata

Obtaining the three-dimensional (3D) structure of negatively stained biological specimens at a resolution of, typically, 2 - 4 nm is becoming a relatively common practice in an increasing number of laboratories. A combination of new conceptual approaches, new software tools, and faster computers have made this situation possible. However, all these 3D reconstruction processes are quite computer intensive, and the middle term future is full of suggestions entailing an even greater need of computing power. Up to now all published 3D reconstructions in this field have been performed on conventional (sequential) computers, but it is a fact that new parallel computer architectures represent the potential of order-of-magnitude increases in computing power and should, therefore, be considered for their possible application in the most computing intensive tasks.We have studied both shared-memory-based computer architectures, like the BBN Butterfly, and local-memory-based architectures, mainly hypercubes implemented on transputers, where we have used the algorithmic mapping method proposed by Zapata el at. In this work we have developed the basic software tools needed to obtain a 3D reconstruction from non-crystalline specimens (“single particles”) using the so-called Random Conical Tilt Series Method. We start from a pair of images presenting the same field, first tilted (by ≃55°) and then untilted. It is then assumed that we can supply the system with the image of the particle we are looking for (ideally, a 2D average from a previous study) and with a matrix describing the geometrical relationships between the tilted and untilted fields (this step is now accomplished by interactively marking a few pairs of corresponding features in the two fields). From here on the 3D reconstruction process may be run automatically.


1991 ◽  
Author(s):  
J. M. McDonough ◽  
E. C. Hylin ◽  
Tony F. Chan ◽  
Matthew T. Chan ◽  
Y. Yang ◽  
...  

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