A helicopter time-domain EM system applied to mineral exploration: system and data

First Break ◽  
2005 ◽  
Vol 23 (11) ◽  
Author(s):  
D. Fountain ◽  
R. Smith ◽  
T. Payne ◽  
J. Limieux
Keyword(s):  
Time Domain ◽  
Mineral Exploration

Time-domain-induced polarization: Full-decay forward modeling and 1D laterally constrained inversion of Cole-Cole parameters

Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. E213-E225 ◽  
Author(s):  
Gianluca Fiandaca ◽  
Esben Auken ◽  
Anders Vest Christiansen ◽  
Aurélie Gazoty
Keyword(s):  
Time Domain ◽  
Mineral Exploration ◽  
Induced Polarization ◽  
Significant Loss ◽  
Step Response ◽  
Model Parameters ◽  
Full Time ◽  
Inversion Algorithm ◽  
Modeling Tools ◽  
Polarization Response

Time-domain-induced polarization has significantly broadened its field of reference during the last decade, from mineral exploration to environmental geophysics, e.g., for clay and peat identification and landfill characterization. Though, insufficient modeling tools have hitherto limited the use of time-domain-induced polarization for wider purposes. For these reasons, a new forward code and inversion algorithm have been developed using the full-time decay of the induced polarization response, together with an accurate description of the transmitter waveform and of the receiver transfer function, to reconstruct the distribution of the Cole-Cole parameters of the earth. The accurate modeling of the transmitter waveform had a strong influence on the forward response, and we showed that the difference between a solution using a step response and a solution using the accurate modeling often is above 100%. Furthermore, the presence of low-pass filters in time-domain-induced polarization instruments affects the early times of the acquired decays (typically up to 100 ms) and has to be modeled in the forward response to avoid significant loss of resolution. The developed forward code has been implemented in a 1D laterally constrained inversion algorithm that extracts the spectral content of the induced polarization phenomenon in terms of the Cole-Cole parameters. Synthetic examples and field examples from Denmark showed a significant improvement in the resolution of the parameters that control the induced polarization response when compared to traditional integral chargeability inversion. The quality of the inversion results has been assessed by a complete uncertainty analysis of the model parameters; furthermore, borehole information confirm the outcomes of the field interpretations. With this new accurate code in situ time-domain-induced polarization measurements give access to new applications in environmental and hydrogeophysical investigations, e.g., accurate landfill delineation or on the relation between Cole-Cole and hydraulic parameters.

scholarly journals Application of electric polarization to contaminant detection in soils

1989 ◽  
Vol 26 (4) ◽  
pp. 536-550 ◽  
Author(s):  
Raymond N. Yong ◽  
Edward J. Hoppe
Keyword(s):  
Contaminant Transport ◽  
Time Domain ◽  
Mineral Exploration ◽  
Electric Polarization ◽  
Induced Polarization ◽  
Time Domain Reflectometry ◽  
Dielectric Measurements ◽  
Polarization Method ◽  
Contaminant Detection ◽  
Nonpolar Liquids

Preliminary experiments indicate the feasibility of constructing for field use a contaminant-detection instrumentation based on dielectric measurements. This study applies the technique of time-domain reflectometry to assess characteristic "signatures" of some selected contaminants and soil–contaminant mixtures. The results imply that a proper differentiation between various signatures can be attained, allowing an assessment in regard to soil–contaminant status. The proposed technique is similar in principle to the induced-polarization method applied in mineral exploration. Key words: electric polarization, contaminant transport, dielectrics, induced polarization, nonpolar liquids, time-domain reflectometry, relaxation, contaminant–soil interaction.

Modeling induced polarization effects in helicopter time-domain electromagnetic data: Field case studies

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. B49-B61 ◽  
Author(s):  
Vladislav Kaminski ◽  
Andrea Viezzoli
Keyword(s):  
Time Domain ◽  
Signal To Noise Ratio ◽  
Mineral Exploration ◽  
Induced Polarization ◽  
Electromagnetic Transients ◽  
Additional Information ◽  
Time Domain Electromagnetic ◽  
Airborne Electromagnetic ◽  
Cole Model ◽  
Inversion Techniques

Induced polarization (IP) effects are becoming more evident in time-domain helicopter airborne electromagnetic (AEM) data thanks to advances in instrumentation, mainly due to improvements in the signal-to-noise ratio and hence better data quality. Although the IP effects are often manifested as negative receiver voltage values, which are easy to detect, in some cases, IP effects can distort recovered transients in other ways so they may be less obvious and require careful data analysis and processing. These effects represent a challenge for modeling and inversion of the AEM data. For proper modeling of electromagnetic transients, the chargeability of the subsurface and other parameters describing the dispersion also need to be taken into consideration. We use the Cole-Cole model to characterize the dispersion and for modeling of the IP effects in field AEM data, collected by different airborne systems over different geologies and exploration targets, including examples from diamond, gold, and base metal exploration. We determined how multiparametric inversion techniques can simultaneously recover all four Cole-Cole parameters, including resistivity [Formula: see text], chargeability [Formula: see text], relaxation time [Formula: see text], and frequency parameter [Formula: see text]. The results obtained are in good agreement with the ancillary information available. Interpretation of the IP effects in AEM data is therefore seen by the authors as providing corrected electrical resistivity distributions, as well as additional information that could assist in mineral exploration.

scholarly journals (Quasi-)Real-Time Inversion of Airborne Time-Domain Electromagnetic Data via Artificial Neural Network

2020 ◽  
Vol 12 (20) ◽  
pp. 3440
Author(s):  
Peng Bai ◽  
Giulio Vignoli ◽  
Andrea Viezzoli ◽  
Jouni Nevalainen ◽  
Giuseppina Vacca
Keyword(s):  
Neural Network ◽  
Time Domain ◽  
Mineral Exploration ◽  
Time Inversion ◽  
Computationally Efficient ◽  
Electromagnetic Data ◽  
Time Domain Data ◽  
Novel Approach ◽  
True Resistivity ◽  
Time Domain Electromagnetic

The possibility to have results very quickly after, or even during, the collection of electromagnetic data would be important, not only for quality check purposes, but also for adjusting the location of the proposed flight lines during an airborne time-domain acquisition. This kind of readiness could have a large impact in terms of optimization of the Value of Information of the measurements to be acquired. In addition, the importance of having fast tools for retrieving resistivity models from airborne time-domain data is demonstrated by the fact that Conductivity-Depth Imaging methodologies are still the standard in mineral exploration. In fact, they are extremely computationally efficient, and, at the same time, they preserve a very high lateral resolution. For these reasons, they are often preferred to inversion strategies even if the latter approaches are generally more accurate in terms of proper reconstruction of the depth of the targets and of reliable retrieval of true resistivity values of the subsurface. In this research, we discuss a novel approach, based on neural network techniques, capable of retrieving resistivity models with a quality comparable with the inversion strategy, but in a fraction of the time. We demonstrate the advantages of the proposed novel approach on synthetic and field datasets.

scholarly journals Influence of Clay on Time Domain Induced Polarization

2018 ◽  
Vol 3 (1) ◽  
pp. 1
Author(s):  
Yatini Yatini
Keyword(s):  
Time Domain ◽  
Physical Modeling ◽  
Mineral Exploration ◽  
Total Content ◽  
Spherical Model ◽  
Induced Polarization ◽  
Soil Medium ◽  
Spherical Target ◽  
Target Value ◽  
Modeling Data

The main problem in mineral exploration is how to determine the existence of deposits at subsurface based on resistivity and chargeability parameters. Clay almost exists in rocks. Here, this study was to understand the influence of clay on time domain induced polarization. To clarify the clay parameters, field physical modeling was conducted. The results showed physical modeling data of 20-cm diameter spherical target with a total content of 28.3% of iron did not show any significant response. The high content of clays on the medium used in field physical modeling seems to be the main reason for the change in sample. In the case of the subsurface spherical model that is near to the soil medium, the presence of clay leads to the medium resistivity value to be identical to the target value. As a consequence, the resistivity response can not be identified clearly. The chargeability between the medium and the target remains small but the chargeability response remains constant.

On closed-form expressions for the approximate electromagnetic response of a sphere interacting with a thin sheet — Part 1: Theory in the frequency and time domain

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. E189-E198 ◽  
Author(s):  
Jacques K. Desmarais
Keyword(s):  
Closed Form ◽  
Time Domain ◽  
Mineral Exploration ◽  
Thin Sheet ◽  
Electromagnetic Response ◽  
Uniform Field ◽  
Electromagnetic Modeling ◽  
The Time Domain ◽  
Glacial Clays ◽  
Metamorphic Terranes

In mineral exploration and geologic mapping of igneous and metamorphic terranes, the background is often dominantly resistive. The most important electromagnetic interaction is between a discrete conductor and an overlying sheet of conductive overburden (e.g., glacial clays or weathering products of the basement rocks). To enable the electromagnetic modeling of these common situations, here I provide closed-form expressions for the approximate electromagnetic response of a sphere embedded in highly resistive rocks and interacting with an overlying thin sheet. The sphere is assumed to be dipolar and excited by a locally uniform field. The expressions in the time and frequency domains are represented as sums of complete and incomplete cylindrical functions. New asymptotic approximations are provided for the efficient evaluation of the required incomplete cylindrical functions. The frequency-domain formulas are validated by numerical transformation to the time domain and comparison to the time-domain solution.

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