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.

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 Regional-scale weather patterns and wildland fires in central Portugal

2009 ◽  
Vol 18 (1) ◽  
pp. 36 ◽  
Author(s):  
Klaus P. Hoinka ◽  
Anabela Carvalho ◽  
Ana Isabel Miranda
Keyword(s):  
Wildland Fire ◽  
Regional Scale ◽  
Surface Wind ◽  
Positive Anomaly ◽  
Wildland Fires ◽  
Burnt Area ◽  
Fire Event ◽  
The North ◽  
Cross Covariance ◽  
Central Portugal

The characteristic evolution of the synoptic- and meso-scale wind, temperature and humidity pattern during wildland fire events in Portugal was determined by lagged covariances for the period 1980 to 2001. The daily burnt area was chosen as the parameter to be correlated with atmospheric fields provided by the European Centre for Medium-Range Weather Forecasts Reanalysis (ERA40) data. The related time series consisted of wildland fires with a daily burnt area of more than 500 ha in central Portugal. Five days in advance of a fire event, a strong positive anomaly existed in the surface pressure and in the 500-hPa geopotential field, both appearing to the west of the Iberian Peninsula and moving towards Brittany until lag zero. In advance of the fire event, the flow above Portugal came from the north, turning to easterlies at lag time zero and finally coming from the south-east during the post-event phase. Surface wind statistics taken at Castelo Branco supported these results. Smoke plumes from wildland fires detected by satellites indicated a similar flow structure, which was quite different to the averaged summertime flow above Portugal. Cross-covariance regression between the Iberian thermal low and burnt area showed that the peak amount of burnt area occurred up to 3 days after the appearance of a thermal low. This suggested that in the pre-phase of a wildland fire, heated air is transported from the peninsula’s centre towards Portugal.

Structure du plateau continental armoricain

1975 ◽  
Vol 279 (1288) ◽  
pp. 109-121 ◽  
Keyword(s):  
Ground Level ◽  
Magnetic Anomalies ◽  
Magnetic Survey ◽  
Positive Anomaly ◽  
The South ◽  
The North ◽  
Basement Rocks ◽  
Average Accuracy ◽  
Magnetic Field Model ◽  
History Of

Between 1965 and 1970 there has been conducted, in collaboration with the hydrographic service of the French navy, a magnetic survey of the Armorican continental plateau. The zone, covered with 48000 km of profiles, stretches between the parallels of 46° 10' N and 49° 30' N and between the meridians 4° W and 7° 15' W. Position fixing was carried out by means of Toran, with an average accuracy of 50 m. Maps of the total field intensity, reduced to epoch 1967.5, and the magnetic anomalies have been drawn to the scale 1:250000. The magnetic anomalies have been calculated by means of a magnetic field model defined by Jensen and Cain. Two major zones of anomaly can be identified: a northern one, bounded to the south by the 48° N parallel, with strong relief, where the magnetic anomalies are numerous and include major ones at the entrance to the Channel; a southern zone, with considerably less relief, but where the anomalies present several major directions. Several of these anomalies have been interpreted by three different methods with the intention of determining the depth of the sources of disturbance and of specifying possible relationships between these sources and the structural geology of the Armorican plateau. From the south to the north of the region studied, the floor of the continental plateau appears to be divided into compartments by large SW-NE horst and graben structures of Hercynian age. In each compartment the depth to basement increases from east to west by step-faulting with a NW-SE orientation, such faulting has played a role throughout the geological history of the continental plateau. Finally, it emerges from this study that the magnetic anomalies are, for the most part, related to the major structural and tectonic lines of the metamorphic basement visible at ground level. Several areas of high positive anomaly may be associated with basic intrusions emplaced along the lines of major faults in the basement rocks of the Armorican platform.

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 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.

scholarly journals POLA ANOMALI MAGNET DAN NILAI SUSCEPTIBILITAS DARI BATUAN DASAR PADA PEMETAAN GEOLOGI DAN GEOFISIKA DI PERAIRAN TELUK BONE SULAWESI SELATAN

2016 ◽  
Vol 10 (1) ◽  
pp. 15
Author(s):  
Beben Rachmat ◽  
Delyuzar Ilahude
Keyword(s):  
Sedimentary Rock ◽  
Metamorphic Rock ◽  
Sedimentary Rocks ◽  
Magnetic Anomalies ◽  
Blue Color ◽  
Local Anomaly ◽  
The North ◽  
South Sulawesi ◽  
Reduction To The Pole ◽  
Local Anomalies

Pola anomali magnet dari penerapan metode reduksi kekutub dan equator menunjukkan nilai anomali lokal yang cukup signifikan. Nilai anomali magnet di perairan Teluk Bone diduga berkaitan dengan tatanan litologi batuan dasar. Nilai anomali negatif dengan notasi warna biru yang menempati bagian utara dan tenggara daerah penelitian, diduga merupakan batuan sedimen yang mendominasi daerah tersebut. Sifat kemagnitan batuan di bagian barat daerah penelitian, diduga disebabkan oleh busur magmatik dari tepian timur lengan Sulawesi Selatan. Nilai susceptibilitasnya (k) tertinggi mulai dari 0.1588 hingga 0.1596, sedangkan terendah mulai dari 0.1564 sampai 0.1572. Diperkirakan nilai susceptibilitas tertinggi, termasuk dalam kelompok batuan metamorf, sedangkan terendah termasuk dalam kelompok batuan sedimen. Kata kunci : anomali lokal, susceptibilitas The pattern of magnetic anomalies of the application the method of reduction to the pole and equator shows the value of the local anomalies are quite significant. The value of magnetic anomalies in the waters of the Gulf of Bone allegedly related to order litologi bedrock. The value of negative anomalies with blue color notation that occupy the north and southeast region research, allegedly is a sedimentary rock that dominates the area. The nature of magnetic rocks in the western part of the area of research, allegedly caused by the arc of the east arm magmatic South Sulawesi. The value of the highest susceptibilitasnya (k) ranging from 0.1588 until 0.1596, whereas the lowest starting from 0.1564 until 0.1572. Estimated value of the highest susceptibility, included in the group of metamorphic rock, while the lowest are included in the group of sedimentary rocks. Keywords: local anomaly, susceptibility

scholarly journals High-resolution aeromagnetic survey of the Teide volcano (Canary Islands): a preliminary analysis

1997 ◽  
Vol 40 (2) ◽  
Author(s):  
A. Garcìa ◽  
I. Blanco ◽  
J. M. Torta ◽  
I. Socías
Keyword(s):  
Bouguer Anomaly ◽  
Magnetic Data ◽  
Positive Anomaly ◽  
Aeromagnetic Survey ◽  
The North ◽  
First Approximation ◽  
Uniform Magnetization ◽  
Reduction To The Pole ◽  
Anomaly Map ◽  
Teide Volcano

To contribute to our understanding of the structure of the Teide volcano, a detailed aeromagnetic survey was carried out covering the area of Las Cañadas caldera and the Teide-Pico Viejo complex. Taking into account the rugged relief of the area (altitude ranges from sea level to almost 4000 m), a terrain correction has been applied. As a first approximation, the topography has been characterized by a uniform magnetization of 5 Am-1 (based on field and laboratory rock magnetic data). Several enhancement techniques have been applied to the residual map (original map minus topographic effect), such as reduction to the pole, pseudogravity integration and upward continuation. In the reduced-to-the-pole map the large positive anomaly that appears centered to the north of Pico Viejo is noteworthy and could be caused by a basaltic intrusion responsible for the last eruptions in this area. Also, a small magnetic low appears over Teide peak, which should be related to slightly-magnetized shallow phonolitic materials. The main tectonic direction of Tenerife, SW-NE, is also clearly reflected on the magnetic anomaly map. The comparison between the pseudogravity and the Bouguer anomaly maps indicates a good correlation between magnetic and gravimetric sources.

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.

scholarly journals Influence of the North Atlantic oscillation on the atmospheric levels of benzo[a]pyrene over Europe

2021 ◽  
Author(s):  
Pedro Jiménez-Guerrero ◽  
Nuno Ratola
Keyword(s):  
Spatial Pattern ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Transport Model ◽  
Regional Scale ◽  
The South ◽  
Climatic Fluctuations ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

AbstractThe atmospheric concentration of persistent organic pollutants (and of polycyclic aromatic hydrocarbons, PAHs, in particular) is closely related to climate change and climatic fluctuations, which are likely to influence contaminant’s transport pathways and transfer processes. Predicting how climate variability alters PAHs concentrations in the atmosphere still poses an exceptional challenge. In this sense, the main objective of this contribution is to assess the relationship between the North Atlantic Oscillation (NAO) index and the mean concentration of benzo[a]pyrene (BaP, the most studied PAH congener) in a domain covering Europe, with an emphasis on the effect of regional-scale processes. A numerical simulation for a present climate period of 30 years was performed using a regional chemistry transport model with a 25 km spatial resolution (horizontal), higher than those commonly applied. The results show an important seasonal behaviour, with a remarkable spatial pattern of difference between the north and the south of the domain. In winter, higher BaP ground levels are found during the NAO+ phase for the Mediterranean basin, while the spatial pattern of this feature (higher BaP levels during NAO+ phases) moves northwards in summer. These results show deviations up to and sometimes over 100% in the BaP mean concentrations, but statistically significant signals (p<0.1) of lower changes (20–40% variations in the signal) are found for the north of the domain in winter and for the south in summer.

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