scholarly journals Transient Electromagnetic Surveys for the Determination of Talik Depth and Geometry Beneath Thermokarst Lakes

2018 ◽  
Vol 123 (11) ◽  
pp. 9310-9323 ◽  
Author(s):  
A. L. Creighton ◽  
A. D. Parsekian ◽  
M. Angelopoulos ◽  
B. M. Jones ◽  
A. Bondurant ◽  
...  
Keyword(s):  
Thermokarst Lakes ◽  
Transient Electromagnetic ◽  
Electromagnetic Surveys

The harmonic and transient electromagnetic response of a thin dipping dike

Geophysics ◽  
1983 ◽  
Vol 48 (7) ◽  
pp. 934-952 ◽  
Author(s):  
P. Weidelt
Keyword(s):  
Formal Solution ◽  
Harmonic Excitation ◽  
Electromagnetic Response ◽  
Approximate Determination ◽  
Finite Conductivity ◽  
Circular Loop ◽  
Decay Modes ◽  
Transient Electromagnetic ◽  
Free Decay

An exact solution is given for the electromagnetic induction in a dipping dike of finite conductivity, represented as a thin half‐sheet in a nonconducting surrounding. The problem is formulated for arbitrary dipole or circular loop [Formula: see text] configurations. The formal solution obtained by the Wiener‐Hopf technique is cast into a rapidly convergent triple integral suitable for an effective numerical treatment. A good agreement is found between numerical results and analog measurements available for harmonic excitation. The transient response is obtained as a superposition of the half‐sheet free‐decay modes and is illustrated by some numerical examples for coincident loops, including a diagram for the approximate determination of conductance and depth of a vertical dike.

Transient electromagnetic fields of a buried horizontal magnetic dipole

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. E481-E491 ◽  
Author(s):  
Andrei Swidinsky ◽  
Misac Nabighian
Keyword(s):  
Electric Field ◽  
Magnetic Dipole ◽  
Time Domain ◽  
Major Axis ◽  
Secondary Response ◽  
Burial Depth ◽  
Transient Electromagnetic ◽  
The Earth ◽  
Smoke Ring ◽  
Electromagnetic Surveys

Electromagnetic surveys using a vertical transmitter loop are common in land, marine, and airborne geophysical exploration. Most of these horizontal magnetic dipole (HMD) systems operate in the frequency domain, measuring the time derivative of the induced magnetic fields, and therefore a majority of studies have focused on this subset of field measurements. We examine the time-domain electromagnetic response of a HMD including the electric fields and corresponding smoke rings produced in a conductive half-space. Cases of a dipole at the surface and buried within the earth are considered. Results indicate that when the current in the transmitter is rapidly switched off, a single smoke ring is produced within the plane of the vertical transmitter loop, which is then distorted by the air-earth interface. In this situation, the circular smoke ring, which would normally diffuse symmetrically away from the source in a whole space, is approximately transformed into an ellipse, with a vertical major axis at an early time and a horizontal major axis at a late time. As measured from the location of the transmitter, the depth of investigation and lateral footprint of such a system increases with burial depth. It is also observed that the electric field measured in the direction of the magnetic dipole only contains a secondary response related to the charge accumulation on any horizontal conductivity boundaries because the primary field is always absent. This field component can be expressed analytically in terms of a static and time-varying field, the latter term adding spatial complexity to the total horizontal electric field at the earth surface at early times. Applications of this theoretical study include the design of time-domain induction-logging tools, crossborehole electromagnetic surveys, underground mine expansion work, mine rescue procedures, and novel marine electromagnetic experiments.

Use of water indices in the determination of thermokarst lakes according to remote sensing data

2021 ◽  
pp. 67-74
Author(s):  
Artem Pshenichnikov
Keyword(s):  
Visual Analysis ◽  
Remote Sensing Data ◽  
Water Bodies ◽  
Identical Result ◽  
Spectral Indices ◽  
Quadratic Error ◽  
Thermokarst Lakes ◽  
Ndvi Index ◽  
Water Indices

The results of application of six spectral indices (AWEI, MNDWI, NDVI, NDWI, TCW, WRI) for the isolation of thermokarst lakes in tundra landscapes of northern Yakutia are presented. To assess the accuracy of decryption of lakes, an average quadratic error (MSE) was calculated. The minimum MSE value is 0.11 km2 and corresponds to the NDWI index. An almost identical result (0.12 km2) is found in the WRI index, slightly worse (0.15 km2) one — in the NDVI index. An MNDWI index has the highest mean square error (7.02 km2). Visual analysis also showed better decryption of water bodies using the NDWI, WRI and NDVI indices, which allows the use of these indices for automatical isolatation water bodies.

Coincident loop transient electromagnetic master curves for interpretation of two‐layer earths

Geophysics ◽  
1981 ◽  
Vol 46 (1) ◽  
pp. 53-64 ◽  
Author(s):  
A. P. Raiche ◽  
B. R. Spies
Keyword(s):  
Time Range ◽  
Late Time ◽  
Sufficient Time ◽  
Master Curves ◽  
Layer Depth ◽  
Apparent Conductivity ◽  
Transient Electromagnetic ◽  
Tem Method ◽  
Earth Conductivity

A set of apparent conductivity master curves has been calculated for the coincident loop transient electromagnetic (TEM) method used over a two‐layer earth. Conductivity contrasts range from 0.001 to 1000. Loop radius/layer depth ratios range from 0.01 to 100. The time range is sufficient to see the entire shape of the curves from the early to the late time asymptotes. These curves allow the determination of the parameters of a two‐layer earth for accurate data over a sufficient time range. Examples using the curves to interpret multilayered earths are given. The curves are also used to show the limitations placed on interpretation by existing TEM equipment.

scholarly journals SkyTEM helicopter transient electromagnetic surveys of tailings dams

2012 ◽  
Vol 2012 (1) ◽  
pp. 1-4 ◽  
Author(s):  
James Reid ◽  
Niels Christensen ◽  
Kate Godber
Keyword(s):  
Transient Electromagnetic ◽  
Tailings Dams ◽  
Electromagnetic Surveys

Transient electromagnetic surveys for highresolution near-surface exploration: basics and case studies

First Break ◽  
2017 ◽  
Vol 35 (9) ◽  
Author(s):  
M.V. Sharlov ◽  
I.V. Buddo ◽  
N.V. Misyurkeeva ◽  
I.A. Shelokhov ◽  
Yu.A. Agafonov
Keyword(s):  
Case Studies ◽  
Near Surface ◽  
Transient Electromagnetic ◽  
Surface Exploration ◽  
Electromagnetic Surveys
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