Principles of probability tomography for natural‐source electromagnetic induction fields

Geophysics ◽  
1999 ◽  
Vol 64 (5) ◽  
pp. 1403-1417 ◽  
Author(s):  
Paolo Mauriello ◽  
Domenico Patella
Keyword(s):  
Electric Charge ◽  
Probability Function ◽  
Ground Surface ◽  
Magnetic Surface ◽  
Natural Source ◽  
Occurrence Probability ◽  
Suitable Parameter ◽  
Em Induction ◽  
Em Field ◽  
Induced Charge

The 3-D interpretation problem of natural‐source electromagnetic (EM) induction field data collected over a flat air‐earth boundary is dealt with using the concept of probability tomography. This paper presents a method to recognize the most probable localization of the induced electric charge accumulations across resistivity discontinuities and current channeling inside conductive bodies. We begin by writing the solutions for the electric (magnetic) ground surface EM field components in the frequency domain as a sum of elementary contributions, each resulting from a single induced‐charge (dipole) element. Then we express the total electric (magnetic) power associated with each EM field component as a sum of crosscorrelation integrals between the measured component and the homologous synthetic expression resulting from each causative induced‐charge (dipole) element. The synthetic component takes the key role of scanner function in the new imaging procedure. Moreover, using the crosscorrelation bounding inequality we introduce the concept of EM induction occurrence probability as a suitable parameter for the tomographic representation of the induced‐charge and dipole distributions underground. For each electric and magnetic surface component we define the corresponding occurrence probability function as the crosscorrelation product of the observed component and the relative scanning function, divided by the square root of the product of the respective variances. In the space domain, the 3-D tomographic procedure consists of scanning the half‐space below the survey area by the unit strength charge or dipole element, which is given a regular grid of space coordinates within the volume. At each node of the grid, the occurrence probability function is calculated. We use the complete set of calculated grid values to single out the zones of highest occurrence probability of electric charge accumulations and current channeling elements. The physical reliability of the proposed tomography is tested on synthetic and field examples.

scholarly journals COMMENTS ON THE DEPENDENCE BETWEEN ELECTRIC CHARGE AND MAGNETIC CHARGE

2002 ◽  
Vol 17 (40) ◽  
pp. 2647-2655 ◽  
Author(s):  
KANG LI
Keyword(s):  
Field Theory ◽  
Electric Charge ◽  
Magnetic Charge ◽  
Special Choice ◽  
Reduction Condition ◽  
Potential Formulation ◽  
Magnetic Source ◽  
Free Case ◽  
Em Field ◽  
Special Case

By using the two four-dimensional potential formulation of electromagnetic (EM) field theory introduced in Ref. 1, we found that the SO(2) duality symmetric EM field theory can be reduced to the magnetic source-free case by a special choice of SO(2) parameter, we called this special case nature picture of the EM field theory, the reduction condition led to a result, i.e. the electric charge and magnetic charge are no longer independent. Some comments to Ref. 10 are also mentioned.

scholarly journals An analytical expression for early electromagnetic signals generated by impulsive line-currents in conductive Earth crust, with numerical examples

2016 ◽  
Vol 59 (2) ◽  
Author(s):  
Ken'ichi Yamazaki
Keyword(s):  
Seismic Waves ◽  
Ground Surface ◽  
Space Model ◽  
Whole Space ◽  
Source Current ◽  
Em Field ◽  
Electromagnetic Signals ◽  
Analytical Expressions ◽  
The Magnetic Field ◽  
Ground Conductivity

<p>Changes in the electromagnetic (EM) field after an earthquake rupture but before the arrival of seismic waves (“early EM signals”) have sometimes been reported. Quantitative evaluations are necessary to clarify whether the observed phenomena are accounted for by known theories and to assess whether the phenomenon can be applied to earthquake early warning. Therefore, analytical expressions for the magnetic field generated by an impulsive line-current are derived for a conductive half-space model, and for a two-layer model; the somewhat simpler situation of a conductive whole-space is also considered. By analyzing the expressions obtained for the generated EM field, some expected features of the early EM signals are discussed. First, I verify that an early EM signal arrives before the seismic waves unless conductivity is relatively high. Second, I show that early EM signals are well approximated by the whole-space model when the source is near the ground surface, but not when it is at depth. Third, I show that the expected amplitudes of early EM signals are within the detection limits of commonly used EM sensors, provided that ground conductivity is not very high and that the source current is sufficiently intense. However, this does not mean that the EM signals are easily distinguishable, because detector sensitivity does not account for additive noise or false positive detections.</p>

Comparing three approaches to the ground geoelectric field modelling due to space weather events

2020 ◽  
Author(s):  
Elena Marshalko ◽  
Mikhail Kruglyakov ◽  
Alexey Kuvshinov ◽  
Elena Sokolova ◽  
Viacheslav Pilipenko ◽  
...  
Keyword(s):  
Space Weather ◽  
Design Parameters ◽  
Potential Hazard ◽  
Geoelectric Field ◽  
Geomagnetically Induced Currents ◽  
Advantages And Disadvantages ◽  
Field Modelling ◽  
Weather Events ◽  
Em Induction ◽  
Em Field

&lt;p&gt;In order to estimate the potential hazard to technological systems from space weather, it is necessary to understand the spatiotemporal evolution of the geoelectric field during geomagnetic disturbances. Once the geoelectric field is quantitively estimated, geomagnetically induced currents can be calculated from the geometry of transmission lines and system design parameters. To address the complex problem of the ground electromagnetic (EM) field modelling due to space weather events, it is necessary to consider the spatiotemporal structure of the source of the EM induction in a realistic way and take into account a realistic three&amp;#8208;dimensional (3&amp;#8208;D) distribution of the Earth's electrical conductivity.&lt;/p&gt;&lt;p&gt;In this work we compare three approaches to the geoelectric field modelling. All approaches are based on the numerical solution of Maxwell's equations in Earth's models with 3-D conductivity distribution. The difference between them lies in different setting of the EM induction source. In the first two methods the source is represented by a laterally varying sheet current flowing above the Earth. The current in the first approach is computed on the base of 3-D magnetohydrodynamic simulation of near-Earth space. In the second one the source is constructed using ground-based magnetometers' data. In the third approach the geoelectric field is calculated using plane wave excitation. We carry out geoelectric field modellings for Kola Peninsula and Karelia using these three approaches. In our simulations we utilise the 3-D conductivity model of Fennoscandia (SMAP). The geoelectric field is computed using 3-D EM forward modelling code extrEMe based on a contracting integral equation method. We compare modelling results to EM field observations and discuss advantages and disadvantages of the considered approaches.&lt;/p&gt;

Aplikasi metode tahanan jenis dalam studi geologi karst Gua Seropan di Gunung Kidul, Yogyakarta

2017 ◽  
Vol 12 (2) ◽  
pp. 105-116
Author(s):  
Pulung A. Pranantya ◽  
Nurlia Sadikin
Keyword(s):  
Fresh Water ◽  
Ground Surface ◽  
Water Source ◽  
Raw Water ◽  
Limited Information ◽  
Resistivity Method ◽  
Central Java ◽  
Underground River ◽  
Initial Exploration

In terms of geology, most areas in south of the Gunungkidul District in Central Java consist of the Wonosari formation limestone. The land is generally very dry and source of raw water is also difficult to reach. Findings on the existence of underground river in caves, however, indicate the potential amount of water within the area, especially in the eastern part of the Gunungkidul District. Although limited information available, some fishermen have discovered that Seropan cave contains fresh water source. This cave is situated at 65 m below the cliff. Initial exploration, which done using a multichannel resistivity method, confirmed the availability of freshwater in the cave and underground river. The isopach of cave depth is found in ranges of 80 200 m below the ground surface. The water of Seropan cave can be utilized by implementing pipeline or by drilling at the suggested point based on the interpretation results, i.e. 110o2223.6388 EL 8o42.874 SL. [DY1][PP2][DY1]Perbaiki grammarIn terms of geology, most areas in south of Gunungkidul District in Central Java consist of the Wonosari formation limestone. The land is generally very dry and source of raw water is also difficult to reach. Findings on the exixtence of underground river in caves, however, indicate potential amount of water within the area especially in eastern part of Gunungkidul District. Although limited information available, some fishermans has discovered that Seropan cave contain fresh water source. This cave is situated at 65 m below the cliff. Initial exploration, which done using multichannel resistivity method, confirmed the availability of freshwater in the cave and underground river. The iso pach of cave depth is found in ranges of 80 200 m below the ground surface. The water of Seropan cave can be utilized by implementing pipeline or by drilling at the suggested point based on the interpretation results i.e. 110o2223.6388 EL 8o42.874 SL.[PP2]Sudah diperbaiki

COMPARATIVE ACTION OF VARIOUS OESTROGENIC COMPOUNDS ON MOUSE VAGINAL SIALIC ACIDS (II)

1969 ◽  
Vol 62 (4) ◽  
pp. 663-670 ◽  
Author(s):  
Lars Carlborg
Keyword(s):  
Sialic Acid ◽  
Response Curve ◽  
Sialic Acids ◽  
Clear Cut ◽  
Suitable Parameter ◽  
Sufficient Degree ◽  
Comparative Action ◽  
Relative Potencies ◽  
Good Agreement

ABSTRACT Oestrogens administered in lower doses than necessary to induce full cornification of the mouse vagina induce mucification. It was shown previously that the degree of mucification could be estimated by quantitative determination of sialic acids. A suitable parameter for oestrogen assay was the measurement of vaginal sialic acid concentration which exhibited a clear cut dose response curve. Eleven assays of various oestrogens were performed with this method. Their estimated relative potencies were in good agreement with other routine oestrogen assays. A statistically sufficient degree of precision was found. The sensitivity was of the same order, or slightly higher, than the Allen-Doisy test.

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