Transient electromagnetic responses of surficial, polarizable patches

Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 1098-1100 ◽  
Author(s):  
G. W. Hohmann ◽  
G. A. Newman
Keyword(s):  
Induced Polarization ◽  
Near Surface ◽  
Transient Electromagnetic ◽  
Electromagnetic Responses ◽  
Central Loop

Abnormal decay curves that are depressed or change sign often are observed in coincident‐loop and central‐loop transient electromagnetic (TEM) measurements, particularly in areas of conductive overburden. With the publication of papers by Smith and West (1989a, b) and Flis et al. (1989), the phenomenon, which is due to induced polarization (IP) in near‐surface, weakly polarizable material such as clay, is well understood.

Transient electromagnetic response of a three‐dimensional body in a layered earth

Geophysics ◽  
1986 ◽  
Vol 51 (8) ◽  
pp. 1608-1627 ◽  
Author(s):  
Gregory A. Newman ◽  
Gerald W. Hohmann ◽  
Walter L. Anderson
Keyword(s):  
Integral Equation ◽  
Frequency Domain ◽  
Digital Filters ◽  
Three Dimensional ◽  
The Body ◽  
Late Time ◽  
Near Surface ◽  
Decay Spectrum ◽  
Transient Electromagnetic ◽  
Central Loop

The three‐dimensional (3-D) electromagnetic scattering problem is first formulated in the frequency domain in terms of an electric field volume integral equation. Three‐dimensional responses are then Fourier transformed with sine and cosine digital filters or with the decay spectrum. The digital filter technique is applied to a sparsely sampled frequency sounding, which is replaced by a cubic spline interpolating function prior to convolution with the digital filters. Typically, 20 to 40 frequencies at five to eight points per decade are required for an accurate solution. A calculated transient is usually in error after it has decayed more than six orders in magnitude from early to late time. The decay spectrum usually requires ten frequencies for a satisfactory solution. However, the solution using the decay spectrum appears to be less accurate than the solution using the digital filters, particularly after early times. Checks on the 3-D solution include reciprocity and convergence checks in the frequency domain, and a comparison of Fourier‐transformed responses with results from a direct time‐domain integral equation solution. The galvanic response of a 3-D conductor energized by a large rectangular loop is substantial when host currents are strong near the conductor. The more conductive the host, the longer the galvanic responses will persist. Large galvanic responses occur if a 3-D conductor is in contact with a conductive overburden. For a thin vertical dike embedded within a conductive host, the 3-D response is similar in form but differs in magnitude and duration from the 2-D response generated by two infinite line sources positioned parallel to the strike direction of the 2-D structure. We have used the 3-D solution to study the application of the central‐loop method to structural interpretation. The results suggest variations of thickness of conductive overburden and depth to sedimentary structure beneath volcanics can be mapped with one‐dimensional inversion. Successful 1-D inversions of 3-D transient soundings replace a 3-D conductor by a conducting layer at a similar depth. However, other possibilities include reduced thickness and resistivity of the 1-D host containing the body. Many different 1-D models can be fit to a transient sounding over a 3-D structure. Near‐surface, 3-D geologic noise will not permanently contaminate a central‐loop apparent resistivity sounding. The noise is band‐limited in time and eventually vanishes at late times.

Electrical Resistivity and Induced Polarization signatures to delineate the near-surface aquifers contaminated with seawater invasion in Digha, West-Bengal, India

CATENA ◽  
2021 ◽  
Vol 207 ◽  
pp. 105596
Author(s):  
Prashant Kumar ◽  
Prarabdh Tiwari ◽  
Anand Singh ◽  
Arkoprovo Biswas ◽  
Tapas Acharya
Keyword(s):  
Electrical Resistivity ◽  
West Bengal ◽  
Induced Polarization ◽  
Near Surface

scholarly journals An overview of the spectral induced polarization method for near-surface applications

2012 ◽  
Vol 10 (6) ◽  
pp. 453-468 ◽  
Author(s):  
Andreas Kemna ◽  
Andrew Binley ◽  
Giorgio Cassiani ◽  
Ernst Niederleithinger ◽  
André Revil ◽  
...  
Keyword(s):  
Induced Polarization ◽  
Polarization Method ◽  
Near Surface ◽  
Spectral Induced Polarization

The Development of Near-source Electromagnetic Methods in China

2018 ◽  
Vol 23 (1) ◽  
pp. 115-124 ◽  
Author(s):  
Guo-qiang Xue
Keyword(s):  
High Efficiency ◽  
Academic Research ◽  
Electromagnetic Method ◽  
Detection Accuracy ◽  
Wide Field ◽  
Transient Electromagnetic Method ◽  
Transient Electromagnetic ◽  
Detection Technology ◽  
Deep Depth ◽  
Central Loop

Near-source electromagnetic technology has been developed and applied in the exploration of petroleum, metallic ore, coal, and engineering geology due to its high efficiency, high detection accuracy, and deep depth of investigation. In this paper, research and applications of the frequency-domain electromagnetic sounding method (FDEM), wide-field electromagnetic method (WFEM), modified central-loop transient electromagnetic method (TEM), and short-offset grounded-wire TEM (SOTEM) with obvious near-source characteristics, were reviewed and analyzed. From the 1960s to 1990s, the FDEM method and equipment were extensively developed in China. These methods have played important roles in the exploration of coal resources. Based on controlled source audio-frequency magnetotelluric (CSAMT) and FDEM methods, a new method has been developed by deriving a new expression to calculate apparent resistivity. This method, which is referred to as WFEM, has been studied, applied, and received great attention in China. To increase work efficiency and reduce the influence of local transverse anisotropy on the detection processes, a modified central-loop TEM detection technology based on the central loop transient electromagnetic method was developed in China. The advantages of SOTEM in near-source surveys with high resolution and increased depth detection stimulated academic research interest to further develop grounded-wire TEM techniques. [Figure: see text]

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