scholarly journals Wavelet characterization of external magnetic sources as observed by CHAMP satellite: evidence for unmodelled signals in geomagnetic field models

2013 ◽  
Vol 192 (3) ◽  
pp. 946-950 ◽  
Author(s):  
Praveen Kunagu ◽  
Georgios Balasis ◽  
Vincent Lesur ◽  
E. Chandrasekhar ◽  
C. Papadimitriou
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Induction ◽  
External Source ◽  
Source Model ◽  
Magnetic Data ◽  
Satellite Mission ◽  
Champ Satellite ◽  
Geomagnetic Field Models ◽  
Source Signals

Abstract We apply continuous wavelet transform technique to the full decade (2001–2010) of CHAMP vector magnetic data from 55417 tracks, to search for evidences of external source field signatures that are either misunderstood or ignored in modern magnetic field models. We show that satellite magnetic time-series, after subtracting the main and lithospheric field contributions, exhibit several external source signals. Other than the diurnal, 27-day, and annual periodicities, we also have observed the 210-day periodicity, in the external magnetic field. Central to these observations is the local time dependency of 27-day variations, which suggests that the purely zonal source model, generally considered for the estimation of electromagnetic induction response is inadequate. We discuss the origin and characteristics of 210-day periodicity, although its geophysical significance needs to be fully ascertained. A better understanding of the external fields as seen at satellite altitude is a prerequisite for an optimum exploitation of Swarm multi-satellite mission, which is scheduled for launch in 2013.

scholarly journals Estimating ocean tide model uncertainties for electromagnetic inversion studies

2018 ◽  
Vol 36 (4) ◽  
pp. 1009-1014 ◽  
Author(s):  
Jan Saynisch ◽  
Christopher Irrgang ◽  
Maik Thomas
Keyword(s):  
Upper Mantle ◽  
Electromagnetic Induction ◽  
Point Of View ◽  
Ocean Tide ◽  
Model Uncertainties ◽  
Satellite Mission ◽  
Champ Satellite ◽  
Ocean Tide Model ◽  
Magnetometer Data ◽  
Electromagnetic Signals

Abstract. Over a decade ago the semidiurnal lunar M2 ocean tide was identified in CHAMP satellite magnetometer data. Since then and especially since the launch of the satellite mission Swarm, electromagnetic tidal observations from satellites are increasingly used to infer electric properties of the upper mantle. In most of these inversions, ocean tidal models are used to generate oceanic tidal electromagnetic signals via electromagnetic induction. The modeled signals are subsequently compared to the satellite observations. During the inversion, since the tidal models are considered error free, discrepancies between forward models and observations are projected only onto the induction part of the modeling, e.g., Earth's conductivity distribution. Our study analyzes uncertainties in oceanic tidal models from an electromagnetic point of view. Velocities from hydrodynamic and assimilative tidal models are converted into tidal electromagnetic signals and compared. Respective uncertainties are estimated. The studies main goal is to provide errors for electromagnetic inversion studies. At satellite height, the differences between the hydrodynamic tidal models are found to reach up to 2 nT, i.e., over 100 % of the local M2 signal. Assimilative tidal models show smaller differences of up to 0.1 nT, which in some locations still corresponds to over 30 % of the M2 signal.

An Augmented Iteratively Re-weighted and Refined Least Squares Method for lp Minimization Problem in Inverse Modeling of Potential Field Magnetic Data

2020 ◽  
Vol 1 (3) ◽  
Author(s):  
Maysam Abedi
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Least Squares ◽  
Minimization Problem ◽  
Potential Field ◽  
Field Data ◽  
Least Squares Method ◽  
Porphyry Copper ◽  
Magnetic Data ◽  
Magnetic Field Data

The presented work examines application of an Augmented Iteratively Re-weighted and Refined Least Squares method (AIRRLS) to construct a 3D magnetic susceptibility property from potential field magnetic anomalies. This algorithm replaces an lp minimization problem by a sequence of weighted linear systems in which the retrieved magnetic susceptibility model is successively converged to an optimum solution, while the regularization parameter is the stopping iteration numbers. To avoid the natural tendency of causative magnetic sources to concentrate at shallow depth, a prior depth weighting function is incorporated in the original formulation of the objective function. The speed of lp minimization problem is increased by inserting a pre-conditioner conjugate gradient method (PCCG) to solve the central system of equation in cases of large scale magnetic field data. It is assumed that there is no remanent magnetization since this study focuses on inversion of a geological structure with low magnetic susceptibility property. The method is applied on a multi-source noise-corrupted synthetic magnetic field data to demonstrate its suitability for 3D inversion, and then is applied to a real data pertaining to a geologically plausible porphyry copper unit.  The real case study located in  Semnan province of  Iran  consists  of  an arc-shaped  porphyry  andesite  covered  by  sedimentary  units  which  may  have  potential  of  mineral  occurrences, especially  porphyry copper. It is demonstrated that such structure extends down at depth, and consequently exploratory drilling is highly recommended for acquiring more pieces of information about its potential for ore-bearing mineralization.

scholarly journals Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sabrina Sanchez ◽  
Johannes Wicht ◽  
Julien Bärenzung
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Wave Number ◽  
Main Magnetic Field ◽  
Candidate Model ◽  
Uncertainty Estimates ◽  
Geomagnetic Field Models ◽  
Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

scholarly journals Characterization of tillage effects on the spatial variation of soil properties using ground-penetrating radar and electromagnetic induction

Geoderma ◽  
2013 ◽  
Vol 207-208 ◽  
pp. 310-322 ◽  
Author(s):  
François Jonard ◽  
Mohammad Mahmoudzadeh ◽  
Christian Roisin ◽  
Lutz Weihermüller ◽  
Frédéric André ◽  
...  
Keyword(s):  
Soil Properties ◽  
Spatial Variation ◽  
Ground Penetrating Radar ◽  
Electromagnetic Induction ◽  
Ground Penetrating

Characterization of ablation plumes and carbon nitride films produced by reactive pulsed laser deposition in the presence of a magnetic field

1998 ◽  
Vol 66 (4) ◽  
pp. 403-406 ◽  
Author(s):  
F. Kokai ◽  
K. Yamamoto ◽  
Y. Koga ◽  
S. Fujiwara ◽  
R.B. Heimann
Keyword(s):  
Magnetic Field ◽  
Pulsed Laser Deposition ◽  
Carbon Nitride ◽  
Pulsed Laser ◽  
Laser Deposition

Fabrication and characterization of highly textured (Bi,Pb)2Sr2Ca2Cu3Ox superconducting ceramics using high magnetic field and cold isostatic pressing

1995 ◽  
Vol 10 (10) ◽  
pp. 2433-2443 ◽  
Author(s):  
Wai Lo ◽  
R. Stevens ◽  
R. Doyle ◽  
A.M. Campbell ◽  
W.Y. Liang
Keyword(s):  
Magnetic Field ◽  
Electron Microscopy ◽  
Cold Isostatic Pressing ◽  
Sintered Ceramic ◽  
Grain Alignment ◽  
Isostatic Pressing ◽  
Transmission Electron ◽  
Superconducting Ceramics ◽  
High Degree

High textured (Bi,Pb)2Sr2Ca2Cu3Ox ceramics have been fabricated by aligning deflocculated flakes of (Bi,Pb)2Sr2Ca2Cu3Ox suspended in an organic medium by means of a high de magnetic field (6 T) at room temperature followed by cold isostatic pressing. The proportion of the (Bi,Pb)2Sr2Ca2Cu3Ox phase in the precursor powder was carefully controlled, and the characteristics of the powder, such as size distribution and morphology, were determined. A high degree of grain alignment was found in the specimens after the magnetic alignment, although the bulk density of the materials was low. Cold isostatic pressing substantially increased the density of the magnetically prealigned specimens which also resulted in a slight decrease in the degree of grain alignment. This minor realignment was found to be due to the various kinds of processing defects that appeared in the specimens during compaction due to the grinding and cracking of the grains and their interlocking. The microstructural and superconducting properties of the sintered ceramic have been studied using texture goniometry, high resolution scanning electron microscopy, transmission electron microscopy, ac magnetic susceptometry, and critical current measurements.

scholarly journals Compton and Raman free electron laser stability properties for a cold electron beam propagating through a helical magnetic wiggler

1985 ◽  
Vol 33 (3) ◽  
pp. 387-423 ◽  
Author(s):  
John A. Davies ◽  
Ronald C. Davidson ◽  
George L. Johnston
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Dispersion Relation ◽  
Free Electron ◽  
Free Electron Laser ◽  
Relativistic Electron Beam ◽  
Cold Electron ◽  
Wiggler Magnetic Field ◽  
Laser Stability

This paper gives an extensive characterization of the range of validity of the Compton and Raman approximations to the exact free electron laser dispersion relation for a cold, relativistic electron beam propagating through a constantamplitude helical wiggler magnetic field. The electron beam is treated as infinite in transverse extent. Specific properties of the exact and approximate dispersion relations are investigated analytically and numerically. In particular, a detailed numerical analysis is carried out to determine the range of validity of the Compton approximation.

scholarly journals A simple method for characterization of the magnetic field in an ion trap using Be+ ions

2014 ◽  
Vol 68 (12) ◽  
Author(s):  
Jianwei Shen ◽  
Andrii Borodin ◽  
Stephan Schiller
Keyword(s):  
Magnetic Field ◽  
Ion Trap ◽  
Simple Method ◽  
The Magnetic Field

Magnetic field characterization of Macolod Corridor (Luzon, Philippines): New perspectives on rifting in a volcanic arc setting

2021 ◽  
pp. 229179
Author(s):  
Rurik S.P. Austria ◽  
Nathaniel E. Parcutela ◽  
Edd Marc L. Reyes ◽  
Leo T. Armada ◽  
Carla B. Dimalanta ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Volcanic Arc ◽  
Arc Setting
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