The frequency and the time‐domain responses of a buried axial conductor

Geophysics ◽  
1980 ◽  
Vol 45 (5) ◽  
pp. 941-951 ◽  
Author(s):  
Koji Tsubota ◽  
James R. Wait
Keyword(s):  
Magnetic Dipole ◽  
Time Domain ◽  
Dipole Source ◽  
Earth Model ◽  
Layered Earth ◽  
Vertical Magnetic Dipole ◽  
Lateral Inhomogeneity ◽  
Impedance Condition ◽  
The Time Domain ◽  
Lower Medium

Our objective is to analyze the frequency and the time‐domain responses of a two‐dimensional lateral inhomogeneity such as an axial conductor which is buried in a stratified earth. Such inhomogeneities in the earth’s structure give complex transients that cannot be interpreted using just a uniformly layered earth model. To proceed, we determine the fields of a thin axial conductor carrying a filamental current situated in the lower medium of a two‐layered earth. This infinitely long axial conductor is characterized by a specific axial impedance. The impedance condition can be used to determine the total field response when the source is a magnetic dipole. Some results are presented that show the waveform at the induced current in a buried axial conductor excited by an impulsive current in a vertical magnetic dipole source located on the earth’s surface. A feature of the waveform is the reversal of the polarity that would not occur in the absence of the buried cable.

scholarly journals Megasource time-domain electromagnetic sounding at Poggi del Sasso - Cinigiano (GR)

1994 ◽  
Vol 37 (5 Sup.) ◽  
Author(s):  
G. V. Keller ◽  
P. Cantini ◽  
R. Carrara ◽  
O. Faggioni ◽  
E. Pinna
Keyword(s):  
Depth Profile ◽  
Time Domain ◽  
Environmental Conditions ◽  
Dipole Source ◽  
Electromagnetic Noise ◽  
Electromagnetic Sounding ◽  
Piecewise Constant ◽  
Time Domain Electromagnetic ◽  
The Time Domain ◽  
Single Set

An experiment was carried out in the vicinity of the “I Terzi” area in Southeastern Tuscany (fig. 1) to evaluate the applicability of the Time Domain Electromagnetic (TDEM) sounding method under the geological and environmental conditions prevailing in that area. An electromagnetic source was established using a motor-generator set and heavy cable. Measurements were attempted at four sites. Numerous samples of electromagnetic noise were recorded at each of these sites. At one site, signals transmitted for a grounded dipole source at 1.6 km distance were also recorded with the noise. The single set of observations has been processed and inverted to yield a six-layer piecewise constant resistivity depth-profile to a depth of about 2 km. The primary achievement of the experiment was demonstration of the praeticability of TDEM methods under the conditions prevailing in the site.

Time-domain study of transient fields for a thin circular loop antenna

2002 ◽  
Vol 80 (9) ◽  
pp. 995-1003 ◽  
Author(s):  
S T Bishay ◽  
G M Sami
Keyword(s):  
Time Domain ◽  
Analytical Form ◽  
Loop Antenna ◽  
Inverse Laplace Transform ◽  
Wave Number ◽  
Earth Model ◽  
Circular Loop ◽  
Wave Forms ◽  
Displacement Currents ◽  
The Time Domain

The transient fields in the time-domain of a thin circular loop antenna on a two-layer conducting earth model are expressed in analytical form. In these expressions, the displacement currents both in the two-layer ground and in the air region are taken into consideration. The closed-form expressions of the time-domain are obtained as the inverse Laplace transform of the derived full-wave time-harmonic solution. These time-domain solutions are obtained as a summation of wave-guide modes plus contributions from branch cuts in the complex plane of the longitudinal wave number. Numerical examples are given to indicate the important features in the wave forms of the surface fields due to step and pulsed current excitation. These features provide the means of detecting the earth's stratification, measuring the overburden height, and determining the ratio of the conductivities of the layers. PACS Nos.: 41.20Jb, 42.25Bs, 42.25Gy, 44.05+e

On: “Apparent resistivity curves in controlled‐source electromagnetic sounding directly reflecting true resistivities in a layered earth”, by U. C. Das (January‐February 1995 GEOPHYSICS, 60, 53–60).

Geophysics ◽  
1996 ◽  
Vol 61 (3) ◽  
pp. 918-918 ◽  
Author(s):  
Pierre Valla
Keyword(s):  
Magnetic Dipole ◽  
Apparent Resistivity ◽  
Electromagnetic Sounding ◽  
Controlled Source ◽  
Layered Earth ◽  
Vertical Magnetic Dipole ◽  
Em Field ◽  
Depth Sounding

Using a clever mix of two components of the EM field caused by a vertical magnetic dipole, U. C. Das derives what he claims to be an exact apparent resistivity for use in EM depth sounding.

Detectability of Intermediate conductive and resistive layers by time‐domain electromagnetic sounding

Geophysics ◽  
1979 ◽  
Vol 44 (11) ◽  
pp. 1862-1878 ◽  
Author(s):  
Rajni K. Verma ◽  
Kumarendra Mallick
Keyword(s):  
Time Domain ◽  
Intermediate Layer ◽  
Mutual Coupling ◽  
Pulse Excitation ◽  
Layered Earth ◽  
Layer Sequence ◽  
Wide Range ◽  
Earth Models ◽  
Element System ◽  
The Time Domain

An analysis in the time domain has been made of the detectability of an intermediate layer in a three‐layer earth model by the horizontal coplanar loops (system I) and loop‐wire element (system V) electromagnetic (EM) sounding systems for a train of half‐sinusoidal and square waveforms of alternating polarity. The studies involve conversion into the time domain by a Fourier series summation of the matched complex mutual coupling ratios, computed by the digital linear filter method, of the layered‐earth models. The three‐layer earth models considered here have the following resistivity distribution: [Formula: see text], [Formula: see text] for the conductive case, and [Formula: see text], [Formula: see text] for the resistive case (subscripts 1, 2, and 3 represent the first, second, and third layer in the three‐layer sequence; ρ is the resistivity). The intermediate‐layer thickness varies over a wide range. The responses of the three‐layer earth models have been compared with that of a homogeneous earth with the resistivity of the top layer in the three‐layer sequence. The measurement error is assumed to be of the order of 3 percent, and an rms difference of 10 percent between the responses for the three‐layer and the homogenous earth is defined as the detectability level. On the basis of this definition, it is observed that the horizontal coplanar loops system (system I) is better than the loop‐wire element system (system V) in detecting the thin intermediate layer, which may be either conductive or resistive. For a transmitter‐receiver separation (R) of 1000 m by square‐pulse excitation, a conductive intermediate layer as thin as 1/14 of the top layer can be detected by system I and as thin as 1/6 by system V. For the resistive intermediate layer, the corresponding thickness ratios are 0.6 for system I and 1.25 for system V. The detectability is lower in the case of half‐sinusoidal pulse excitation. Instead of normalizing the mutual coupling of the layered earth to the free‐space coupling, the detectability is enhanced markedly if the normalization is done to the coupling over a homogeneous ground. For system V, it is observed that an intermediate layer as thin as 1/100 in the conductive case and 1/4 in the resistive case of the top layer can be detected easily by this approach. Some direct comparisons between the time‐domain and the frequency‐domain results also are given.

scholarly journals A STUDY OF THE ELECTROMAGNETIC FIELD FROM THE MCSEM DIPOLE SOURCE IN AN ANISOTROPIC LAYERED EARTH

2015 ◽  
Vol 33 (2) ◽  
Author(s):  
Walleson Gomes Dos Santos ◽  
Cícero Roberto Teixeira Régis
Keyword(s):  
Electromagnetic Field ◽  
Finite Thickness ◽  
Electrical Anisotropy ◽  
Dipole Source ◽  
Earth Model ◽  
Electromagnetic Modeling ◽  
Technical Literature ◽  
Layered Earth ◽  
Geometric Patterns ◽  
Ocean Layer

ABSTRACT. This paper studies the electromagnetic field from a horizontal electrical dipole inside a layered earth model with TIV anisotropy, including a visualization of the geometric patterns of the field through the medium. The objective here is to present a detailed formulation of the problem, as an aid to those who have an interest in modeling data from the Marine Controlled-Source ElectroMagnetic method – mCSEM, but find it hard to follow the usually abridged, often incomplete, descriptions found in the technical literature. We present a detailed vector potential formulation, with a semi-analytical solution, that allows the calculation of the fields with the source located in a finite thickness ocean layer over N-layered earth models. As an application, we use the implemented solution to study the geometrical distribution of the electric field generated by the dipole source in anisotropic layered media.Keywords: mCSEM, TIV electrical anisotropy, 1D electromagnetic modeling. RESUMO. Este artigo estuda o campo eletromagnético de um dipolo elétrico horizontal no interior de um modelo estratificado com anisotropia TIV, incluindo uma visualização da geometria das linhas de campo através do meio. O objetivo é apresentar a formulação detalhada do problema, para aqueles que têm interesse na modelagem de dados do método eletromagnético de fonte controlada marinho – mCSEM, mas encontram dificuldades em seguir as descrições geralmente muito resumidas, diversas vezes incompletas, na literatura técnica. Apresentamos uma formulação detalhada em termos do potencial vetorial, com uma solução semi-analítica que permite o cálculo dos campos com a fonte localizada em um oceano de espessura finita sobre uma terra estratificada com Ncamadas. Como aplicações, usamos a solução implementada para estudar a distribuição geométrica do campo elétrico gerado pelo dipolo fonte em meios estratificados anisotrópicos.Palavras-chave: mCSEM, anisotropia elétrica TIV, modelagem eletromagnética 1D.

On the propagation of a pulse through an antipode

1969 ◽  
Vol 47 (12) ◽  
pp. 1327-1330 ◽  
Author(s):  
James R. Wait
Keyword(s):  
Time Domain ◽  
Pulse Shape ◽  
Dipole Source ◽  
Transient Field ◽  
Idealized Model ◽  
Time Domain Response ◽  
The Time Domain ◽  
Strong Distortion

The time domain response of the fields in the vicinity of an axial caustic is calculated. The idealized model is a spherical concentric cavity with perfectly conducting walls. It is shown that the transient field, in the vicinity of the antipode of a dipole source, exhibits a strong distortion in the pulse shape.

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