Cable arrangement to reduce electromagnetic coupling effects in spectral-induced polarization studies

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. A1-A5 ◽  
Author(s):  
Myriam Schmutz ◽  
Ahmad Ghorbani ◽  
Pierre Vaudelet ◽  
Amélie Blondel
Keyword(s):  
Coupling Effect ◽  
Electromagnetic Coupling ◽  
Induced Polarization ◽  
Electrode Spacing ◽  
Coupling Effects ◽  
Array Type ◽  
Spectral Induced Polarization ◽  
Computer Codes ◽  
Lateral Offset ◽  
Phase Angles

Spectral-induced polarization (SIP) is widely used for environmental and engineering geophysical prospecting and hydrogeophysics, but one major limitation concerns the electromagnetic (EM) coupling effect. The phase angles related to EM coupling may increase even at frequencies as low as 1 Hz, depending on the ground resistivity, the array type, and the geometry. Most efforts to understand and quantify the EM coupling problem (e.g., theory and computer codes) have been developed for dipole-dipole arrays. However, we used a Schlumberger array to acquire SIP data. We found that with this array, the use of an appropriate cable arrangement during data acquisition can reduce EM coupling effects in the same proportion as for the use of a dipole-dipole array, which is the pure response of the studied earth. To measure the influence of the cable layout, four cable configurations with the same electrode spacing were compared for modeling and experimental data. We discovered that the classical DC inline array was the worst one. As soon as the cables were arranged in another shape (triangle or rectangle), the coupling effect decreased significantly. The best configuration we checked was the rectangular one with an acquisition unit located at a lateral offset of 100 m from the electrode line, even if there was still some difference between the modeled and measured data.

scholarly journals Spectral Induced Polarization Survey with Distributed Array System for Mineral Exploration: Case Study in Saudi Arabia

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 769 ◽  
Author(s):  
Fouzan A. Alfouzan ◽  
Abdulrahman M. Alotaibi ◽  
Leif H. Cox ◽  
Michael S. Zhdanov
Keyword(s):  
Effective Medium Theory ◽  
Coupling Effect ◽  
Pilot Project ◽  
Drill Hole ◽  
Induced Polarization ◽  
Effective Medium ◽  
Inductive Coupling ◽  
Geothermal Resources ◽  
Spectral Induced Polarization ◽  
Distributed Array

The Saudi Arabian Glass Earth Pilot Project is a geophysical exploration program to explore the upper crust of the Kingdom for minerals, groundwater, and geothermal resources as well as strictly academic investigations. The project began with over 8000 km2 of green-field area. Airborne geophysics including electromagnetic (EM), magnetics, and gravity were used to develop several high priority targets for ground follow-up. Based on the results of airborne survey, a spectral induced polarization (SIP) survey was completed over one of the prospective targets. The field data were collected with a distributed array system, which has the potential for strong inductive coupling. This was examined in a synthetic study, and it was determined that with the geometries and conductivities in the field survey, the inductive coupling effect may be visible in the data. In this study, we also confirmed that time domain is vastly superior to frequency domain for avoiding inductive coupling, that measuring decays from 50 ms to 2 s allow discrimination of time constants from 1 ms to 5 s, and the relaxation parameter C is strongly coupled to intrinsic chargeability. We developed a method to fully include all 3D EM effects in the inversion of induced polarization (IP) data. The field SIP data were inverted using the generalized effective-medium theory of induced polarization (GEMTIP) in conjunction with an integral equation-based modeling and inversion methods. These methods can replicate all inductive coupling and EM effects, which removes one significant barrier to inversion of large bandwidth spectral IP data. The results of this inversion were interpreted and compared with results of drill hole set up in the survey area. The drill hole intersected significant mineralization which is currently being further investigated. The project can be considered a technical success, validating the methods and effective-medium inversion technique used for the project.

Determining frequency dependence of carbon turnover in peat using spectral induced polarization

2021 ◽  
Author(s):  
Timea Katona ◽  
Benjamin Gilfedder ◽  
Sven Frei ◽  
Lukas Aigner ◽  
Matthias Bücker ◽  
...  
Keyword(s):  
Frequency Dependence ◽  
Iron Oxides ◽  
Induced Polarization ◽  
Electrode Spacing ◽  
Electrode Polarization ◽  
Biogeochemical Processes ◽  
Carbon Turnover ◽  
Spectral Induced Polarization ◽  
Polarization Response ◽  
Imaging Results

<p>Our study discusses imaging results from a spectral induced polarization (SIP) survey to identify concurring processes (such as aerobic respiration, denitrification, or sulfate- and iron reduction) in a biogeochemically active peat in a wetland located in the Lehstenbach catchment in Southeastern Germany. Terrestrial wetland ecosystems such as peatlands are a critical element in the global carbon cycle. Due to their role as natural carbon sinks and ecological importance for an array of flora and fauna, there is a growing demand to conserve and restore degraded peatlands. Biogeochemical processes occur with non-uniform reaction rates within the peat, making the environment sensitive to physical disturbances. To investigate biogeochemical processes in-situ, it is important to avoid disturbing the redox-sensitive conditions in the subsurface by bringing oxygen into anoxic areas.  Our previous study demonstrated that the induced polarization (IP) was able to identify biogeochemically active and inactive areas of the peat. The IP response was sensitive to the presence of carbon turnover and P release in the absence of iron sulfide. These highly polarizable areas have high iron concentrations, but most likely in an oxidized form. As most iron oxides are poor conductors, the strong polarization response is unlikely related to an electrode polarization process.</p><p>Here we also analyzed the frequency dependence of the SIP data to investigate whether iron oxides and carbon-iron complexes, two possible mechanisms for the high polarization response, can be distinguished. SIP imaging data sets covered the frequency range between 0.06 and 225 Hz and were collected with varying electrode spacing (20 and 50 cm) at different locations within the Waldstein catchment characterized by different properties, e.g., saturated and non-saturated soils. Our imaging results reveal variations of the IP effect within the peat layer, indicating substantial heterogeneities in the peat composition and biogeochemical activity. The frequency dependence allowed us to resolve a sharper contrast between the different features of the peat. Geochemical analyses on a freeze core and pore water samples are used to validate our results and find correlations between the Cole-Cole parameters of the SIP response and the geochemical parameters.</p>

Investigating cable effects in spectral induced polarization imaging at the field scale using multicore and coaxial cables

Geophysics ◽  
2020 ◽  
pp. 1-49
Author(s):  
Adrian Flores Orozco ◽  
Lukas Aigner ◽  
Jakob Gallistl
Keyword(s):  
Signal To Noise Ratio ◽  
Electromagnetic Coupling ◽  
Induced Polarization ◽  
Coaxial Cable ◽  
Imaging Method ◽  
Data Sets ◽  
Phase Lag ◽  
Imaging Data ◽  
Measuring Device ◽  
Spectral Induced Polarization

The Spectral Induced Polarization (SIP) method has emerged as a well-suited laboratory technique to characterize hydrogeological and biogeochemical parameters in soil samples. However, field applications of the SIP imaging method are still rare, which can be attributed to the particular care required to minimize the contamination of the data by electromagnetic coupling. To date, field procedures rely on the use of two different cables separating the current and potential dipoles to improve the quality of the SIP readings, although this increases the efforts in the field and might reduce the depth of investigation or the spatial resolution of the data. To overcome these limitations, we investigate here the use of a single coaxial cable, as an alternative to improve data quality and simplify field procedures. We present a thoughtful evaluation of SIP imaging data collected with the same measuring device using a coaxial cable and a combination of multicore cables of different length and manufacturers. Data sets collected with a single coaxial cable reveal a significantly lower number of outliers and high spatial consistency between the phase-lag readings, even for measurements collected with a coaxial cable five times longer than the length of the profile. Furthermore, the data collected with coaxial cables reveal an improved quality for deeper measurements (with lower signal-to-noise ratio) in comparison to data sets collected with separated cables. Our results demonstrate that the use of coaxial cables might permit the collection of SIP readings with high quality and similar field procedures to those used in resistivity surveys.

scholarly journals ANALYSIS OF COMPLEX APPARENT RESISTIVITY DATA CONJUGATING SPECTRAL INDUCED POLARIZATION AND ELECTROMAGNETIC COUPLING

2018 ◽  
Vol 36 (3) ◽  
pp. 1
Author(s):  
Taíla Crístia Souza Sant’Ana ◽  
Edson Emanoel Starteri Sampaio
Keyword(s):  
Apparent Resistivity ◽  
Mineral Exploration ◽  
Electromagnetic Coupling ◽  
Synthetic Data ◽  
Polarization Characteristic ◽  
Induced Polarization ◽  
Forward Modelling ◽  
New Approach ◽  
Spectral Induced Polarization ◽  
Geological Information

ABSTRACT. The induced polarization characteristic is to provide geophysical and geological information via geoelectric parameters, making possible mineral discrimination in the scope of mineral exploration. Although represents one of the main noises in measurements of this method, electromagnetic coupling between current and potential electrodes also contributes to the understanding of the geological scenario. Thus, the most appropriate way to deal with such data is an integrated study of these two phenomena, taking into account their particularities. Forward modelling and Gauss-Newton inversion of the mutual impedance in the frequency domain provide the analysis of the complex apparent resistivity considering both spectral induced polarization and electromagnetic coupling for homogeneous and one-dimensional, non-polarizable and polarizable Earth models. Besides synthetic data, this new approach was applied to data from the Copper District of Vale do Curaçá, Bahia, Brazil. The results reveal the ability of the method to distinguish between induction, dominant at the highest frequencies, and induced polarization, which varies with depth and frequency. It also may constitute a basis for mineral discrimination with the analysis of analogous circuit parameters, a fundamental tool in the search for metallic targets in mineral exploration.Keywords: Forward Modelling, Geophysical Inversion, Electromagnetic Method, Mineral Exploration.RESUMO. A polarização induzida espectral se destaca por fornecer diversas informações geofísico-geológicas através dos parâmetros geoelétricos, viabilizando a discriminação mineral no âmbito da exploração mineral. Embora constitua um dos principais ruídos nas medidas desse método, o acoplamento eletromagnético entre eletrodos de corrente e potencial também auxilia na compreensão do cenário geológico. Dessa forma, a maneira mais adequada de lidar com tais dados espectrais é o estudo integrado desses dois fenômenos, levando em conta suas particularidades. A modelagem direta e a inversão Gauss-Newton da impedância elétrica mútua no domínio da frequência proporcionam a análise da resistividade complexa aparente considerando tanto a polarização induzida espectral como o acoplamento eletromagnético para modelos de terra homogênea e uni-dimensional, polarizável e não-polarizável. Além do dado sintético, essa nova abordagem foi aplicada a dados reais do Distrito Cuprífero do Vale do Curaçá, Bahia, Brasil. Os resultados revelam a capacidade do método em distinguir o efeito indutivo, dominante nas mais altas frequências, e a variação da polarização induzida com a profundidade e frequência. Isso contitui um estudo base para a discriminação mineral por meio da análise de parâmetros de circuitos análogos, uma ferramenta fundamental na investigação de alvos em exploração mineral.Palavras-chave: Modelagem direta, Inversão Geofísica, Método Eletromagnético, Exploração Mineral. 1Universidade

Fundamental characteristics of an approximate correction method for electromagnetic coupling in frequency‐domain induced polarization

Geophysics ◽  
1985 ◽  
Vol 50 (2) ◽  
pp. 235-241 ◽  
Author(s):  
J. Wang ◽  
K. Zhan ◽  
L. Shien ◽  
L. Yan
Keyword(s):  
Coupling Effect ◽  
Theoretical Calculations ◽  
Electromagnetic Coupling ◽  
Surface Current ◽  
Correction Method ◽  
Induced Polarization ◽  
Response Curves ◽  
Surface Current Density ◽  
Model Studies ◽  
Bona Fide

Our studies have determined that both gradient and dipole‐dipole arrays may produce a rather strong electromagnetic (EM) coupling effect under certain conditions. Variations in these apparent effects are closely correlated with changes of surface current density and also influenced by topographic relief. The dipole‐dipole array can provide EM coupling anomalies with the same sign and shape as bona fide induced‐polarization (IP) anomalies. It has been shown by theoretical calculations and model studies that response curves of frequency effects of EM coupling in logarithmic coordinates have distinctive features of sectional linearization. This can provide a basic method to correct approximately EM coupling. Compared with methods being used inside and outside China, the suggested correction method has the advantage of wide application. This has been already proven by a few field examples.

scholarly journals Spectral Induced Polarization imaging to investigate an ice-rich mountain permafrost site in Switzerland

2021 ◽  
Author(s):  
Theresa Maierhofer ◽  
Christian Hauck ◽  
Christin Hilbich ◽  
Andreas Kemna ◽  
Adrián Flores-Orozco
Keyword(s):  
Electromagnetic Coupling ◽  
Spectral Response ◽  
Induced Polarization ◽  
Swiss Alps ◽  
Spatial Extent ◽  
Data Uncertainty ◽  
Monitoring Site ◽  
Imaging Data ◽  
Spectral Induced Polarization ◽  
Talus Slope

Abstract. Spectral induced polarization (SIP) measurements were collected at the Lapires talus slope, a long-term permafrost monitoring site located in the Western Swiss Alps, to assess the potential of the frequency dependence (within the frequency range of 0.1–225 Hz) of the electrical polarization response of frozen rocks for an improved permafrost characterization. The aim of our investigation was to (a) find a field protocol that provides SIP imaging data sets less affected by electromagnetic coupling and easy to deploy in rough terrains, (b) cover the spatial extent of the local permafrost distribution, and (c) evaluate the potential of the spectral data to discriminate between different substrates and spatial variations in the volumetric ice content within the talus slope. To qualitatively assess data uncertainty, we analyze the misfit between normal and reciprocal (N&R) measurements collected for all profiles and frequencies. A comparison between different cable setups reveals the lowest N&R misfits for coaxial cables and the possibility to collect high-quality SIP data in the range between 0.1–75 Hz. We observe an overall smaller spatial extent of the ice-rich permafrost body compared to its assumed distribution from previous studies. Our results further suggest that SIP data help to improve the discrimination between ice-rich permafrost and unfrozen bedrock in ambiguous cases based on their characteristic spectral behavior, with ice-rich areas showing a stronger polarization towards higher frequencies in agreement with the well-known spectral response of ice.

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