Excitation process under the ramp-step waveform of inductive source-induced polarization method

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. E57-E65
Author(s):  
Yanju Ji ◽  
Yanqi Wu ◽  
Yuheng Wu ◽  
Yi Zhang
Keyword(s):  
Debye Model ◽  
Induced Polarization ◽  
Frozen Soil ◽  
Polarization Field ◽  
High Resistivity ◽  
Excitation Process ◽  
Transient Electromagnetic ◽  
Source Contributions ◽  
Polarizable Body ◽  
Off Time

Most previous studies explain the induced polarization (IP) effects in transient electromagnetic (TEM) data using an idealized but unrealizable step-waveform transmitter current. However, the ramp-step waveform, which is commonly applied in TEM measurement, has been given less attention. To explore the effects of the switch-off time, we have compared the IP responses induced by two waveforms: the step and the ramp step. We apply a wire-filament circuit composed of a Debye model and an inductor to identify the differences in the aspect of the energy transfer process. Furthermore, we extend the analysis to illustrate the IP effects in a frozen-soil zone, metallic sulfide ore, and graphite ore and to analyze the relationship between the switch-off time, IP effects, and the polarization parameters. The results indicate that the primary and secondary fields act as excitation sources of the polarization field. In the step waveform case, the excitation source of the polarization field is the secondary field. As the switch-off time increases, the contribution rate of the primary field gradually increases, especially in the high-resistivity media. The finding provides a new understanding of the excitation process of the IP effects and indicates that source contributions are variable in different situations. Moreover, a longer switch-off time weakens the IP effects severely, and in the high-resistivity, high-polarizable media, the IP effects are more sensitive to the switch-off time. Therefore, a suitable switch-off time should be chosen based on the properties of the polarizable media, such as resistivity and time constant. To detect a relatively high-resistivity, high-polarizable body, the switch-off time should be as short as possible. Nevertheless, to detect a relatively low-resistivity polarizable body, the IP effects are fairly insensitive to the switch-off time, so the transmitter waveform can easily meet the requirements.

scholarly journals Double Trapezoidal Wave Transmitting System with Controllable Turn-Off Edge

2020 ◽  
Vol 10 (21) ◽  
pp. 7932
Author(s):  
Yuan Jiang ◽  
Yanju Ji ◽  
Yibing Yu ◽  
Shipeng Wang ◽  
Yuan Wang
Keyword(s):  
Polarization Effect ◽  
Induced Polarization ◽  
Emission Current ◽  
Wire Loop ◽  
Transient Electromagnetic ◽  
Charging Time ◽  
The Earth ◽  
Electromagnetic Measurement ◽  
Induced Polarization Effect ◽  
Off Time

For time domain transient electromagnetic measurement, the negative sign often appears in the polarization region, which contains the induced polarization information. It is considered that the polarization effect is caused by the capacitance charge of the earth. Extending the turn-off time of the emission current means increasing the charging time, and reducing the charging voltage, which makes the polarization effect easier to observe. Therefore, a double trapezoidal wave transmitting system with a controllable turn-off edge is designed in this paper. In the process of current transmitting, the turn-off time can be controlled by changing the clamping voltage depending on the passive clamping technology. By cutting into the absorption resistance, the current oscillation can be eliminated under the condition of ensuring linearity. To verify the effectiveness of the system, we designed a polarized wire loop based on the filament model simulating the polarized earth. Comparing the response of the wire loop, the emission current with short and long turn-off times contributes to inducing the induction and polarization fields respectively. The double trapezoidal wave transmitting system with a controllable turn-off edge is suitable for measuring the induced polarization effect.

Induced polarization effect on grounded-wire transient electromagnetic data from transverse electric and magnetic fields

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. E111-E120 ◽  
Author(s):  
Nan-Nan Zhou ◽  
Lei Kangxin ◽  
Guoqiang Xue ◽  
Wen Chen
Keyword(s):  
Transverse Electric ◽  
Transverse Magnetic ◽  
Induced Polarization ◽  
Double Line ◽  
Electromagnetic Data ◽  
Transient Electromagnetic ◽  
Electric And Magnetic Fields ◽  
The Difference ◽  
Polarizable Body ◽  
Induced Polarization Effect

Transient electromagnetic (TEM) data can be seriously distorted by induced polarization (IP) phenomena when a polarizable body is present. The TEM field generated by a grounded-wire source contains transverse electric (TE) and transverse magnetic (TM) modes. The IP effect is most commonly studied with the TEM total field, rather than considering the difference between TE and TM fields. To investigate the effect of IP phenomena on the TE and TM fields, we have performed a detailed analysis on IP-distorted TEM data based on numerical and field examples. We first compare the IP effect on the TE and TM fields when polarizable bodies with different polarizable parameters are present. The TM field is more severely affected by the IP effect than the TE field. Compared to a single grounded-wire source, a double-line grounded-wire source can generate a larger TM field in the horizontal electric field. We compare the IP effect on TEM data from single- and double-line grounded-wire TEM configurations, and find that the data from the double-line configuration have a higher TM/TE ratio and are more severely affected by IP phenomena than in the single-line case. Thus, it would be easier to identify and extract the IP response from field data acquired with a double-line grounded-wire source configuration. These results have been verified by a field survey of the Kalatongke copper-nickel ore district, which has predominantly layered geology, in Xinjiang, China.

scholarly journals An enhanced correlation identification algorithm and its application on spread spectrum induced polarization data

2021 ◽  
Vol 28 (2) ◽  
pp. 247-256
Author(s):  
Siming He ◽  
Jian Guan ◽  
Xiu Ji ◽  
Hang Xu ◽  
Yi Wang
Keyword(s):  
Data Processing ◽  
Spread Spectrum ◽  
Background Noise ◽  
Signal To Noise Ratio ◽  
Induced Polarization ◽  
High Resistivity ◽  
Observation System ◽  
Pseudorandom Sequence ◽  
Identification Algorithm ◽  
The Time Domain

Abstract. In spread spectrum induced polarization (SSIP) data processing, attenuation of background noise from the observed data is the essential step that improves the signal-to-noise ratio (SNR) of SSIP data. The time-domain spectral induced polarization based on pseudorandom sequence (TSIP) algorithm has been proposed to improve the SNR of these data. However, signal processing in background noise is still a challenging problem. We propose an enhanced correlation identification (ECI) algorithm to attenuate the background noise. In this algorithm, the cross-correlation matching method is helpful for the extraction of useful components of the raw SSIP data and suppression of background noise. Then the frequency-domain IP (FDIP) method is used for extracting the frequency response of the observation system. Experiments on both synthetic and real SSIP data show that the ECI algorithm will not only suppress the background noise but also better preserve the valid information of the raw SSIP data to display the actual location and shape of adjacent high-resistivity anomalies, which can improve subsequent steps in SSIP data processing and imaging.

scholarly journals Characterisation of subglacial water using a constrained transdimensional Bayesian transient electromagnetic inversion

Solid Earth ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 75-94 ◽  
Author(s):  
Siobhan F. Killingbeck ◽  
Adam D. Booth ◽  
Philip W. Livermore ◽  
C. Richard Bates ◽  
Landis J. West
Keyword(s):  
Electrical Resistivity ◽  
Saline Water ◽  
Radar Data ◽  
High Resistivity ◽  
Transient Time ◽  
Fractured Bedrock ◽  
Transient Electromagnetic ◽  
Seismic Shear ◽  
Time Domain Electromagnetic ◽  
Ground Penetrating

Abstract. Subglacial water modulates glacier-bed friction and therefore is of fundamental importance when characterising the dynamics of ice masses. The state of subglacial pore water, whether liquid or frozen, is associated with differences in electrical resistivity that span several orders of magnitude; hence, liquid water can be inferred from electrical resistivity depth profiles. Such profiles can be obtained from inversions of transient (time-domain) electromagnetic (TEM) soundings, but these are often non-unique. Here, we adapt an existing Bayesian transdimensional algorithm (Multimodal Layered Transdimensional Inversion – MuLTI) to the inversion of TEM data using independent depth constraints to provide statistical properties and uncertainty analysis of the resistivity profile with depth. The method was applied to ground-based TEM data acquired on the terminus of the Norwegian glacier, Midtdalsbreen, with depth constraints provided by co-located ground-penetrating radar data. Our inversion shows that the glacier bed is directly underlain by material of resistivity 102 Ωm ± 1000 %, with thickness 5–40 m, in turn underlain by a highly conductive basement (100 Ωm ± 15 %). High-resistivity material, 5×104 Ωm ± 25 %, exists at the front of the glacier. All uncertainties are defined by the interquartile range of the posterior resistivity distribution. Combining these resistivity profiles with those from co-located seismic shear-wave velocity inversions to further reduce ambiguity in the hydrogeological interpretation of the subsurface, we propose a new 3-D interpretation in which the Midtdalsbreen subglacial material is partitioned into partially frozen sediment, frozen sediment/permafrost and weathered/fractured bedrock with saline water.

Transient electromagnetic response of a polarizable ground

Geophysics ◽  
1981 ◽  
Vol 46 (7) ◽  
pp. 1037-1041 ◽  
Author(s):  
T. Lee
Keyword(s):  
Time Constant ◽  
Transient Response ◽  
Induced Polarization ◽  
Electromagnetic Response ◽  
Relaxation Model ◽  
Reverse Polarity ◽  
Transient Electromagnetic ◽  
Show Evidence ◽  
Positive Time

When a uniform ground has a conductivity which may be described by a Cole‐Cole relaxation model with a positive time constant, then the transient response of such a ground will show evidence of induced polarization (IP) effects. The IP effects cause the transient initially to decay quite rapidly and to reverse polarity. After this reversal the transient decays much more slowly, the decay at this stage being about the same rate as a nonpolarizable ground.

scholarly journals Geophysical Delineation of Barite-Galena Mineralization Using Coupled Electrical Resistivity (ER) and Induced Polarization (IP) Techniques. A Case Study of Iyamitet, Cross River State, South-South, Nigeria

2021 ◽  
pp. 11-18
Author(s):  
O. J. Airen ◽  
D. A. Babaiwa
Keyword(s):  
Electrical Resistivity ◽  
Joint Inversion ◽  
Induced Polarization ◽  
High Resistivity ◽  
Cross River ◽  
Cross River State ◽  
Geophysical Techniques ◽  
Mineralized Zone ◽  
2D Resistivity

A combined Electrical Resistivity (ER) and Induced Polarization (IP) techniques were carried out at Iyamitet, Cross-River State Nigeria with the aim of mapping the Barite-Galena mineralization zone within the area. Five traverses were established in orthogonal directions with length of 100 m. The traverses were established in grid format for better coverage of the study area and Dipole-Dipole electrode configuration was adopted for the data acquisition for both ER and IP. Res2Dinvx software was employed for the joint inversion of the data and the resulting 2D resistivity and chargeability images of the subsurface were interpreted qualitatively and semi-quantitatively to locate the mineralized zone. The result of the investigation revealed that the resistivity values of the suspected mineralized zones fall between 1023 ohm-m to 377599 ohm-m and the chargeability falls between 232 msec and 727 msec. The depth to the top of some of the mineralized zones is as shallow as 1.25 m and as deep as 19.8 m in other places. The results of the investigation have indicated the presence of the Barite-Galena ore within the area and this manifested as high resistivity and high chargeability zones along the traverses. The result of this investigation highlights the efficiency of combined geophysical techniques in locating mineralized zones in a basement area.

scholarly journals Effects of full transmitting-current waveforms on transient electromagnetics: Insights from modeling the Albany graphite deposit

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. E255-E268 ◽  
Author(s):  
Sihong Zeng ◽  
Xiangyun Hu ◽  
Jianhui Li ◽  
Colin G. Farquharson ◽  
Peter C. Wood ◽  
...  
Keyword(s):  
Real Data ◽  
Forward Modeling ◽  
Northern Ontario ◽  
Data Set ◽  
Rock Types ◽  
Full Waveform ◽  
Transient Electromagnetic ◽  
Steady Stage ◽  
Geologic Model ◽  
Off Time

In transient electromagnetic (TEM) methods, the full transmitting-current waveform, not just the abrupt turn-off, can have effects on the measured responses. A 3D finite-element time-domain forward-modeling solver was used to investigate these effects. This was motivated by an attempt to match, via forward-modeling, real data from the Albany graphite deposit in northern Ontario, Canada. Initial modeling results for homogeneous half-spaces illustrate the effects that a full waveform can have on TEM responses, especially the durations of the steady stage and turn-off time. For the Albany data set, a geophysical conductivity model was developed from a geologic model that itself had been constructed predominantly from drillhole information. The conductivities of the various geologic units in the model were first estimated based on typical conductivity values for the respective rock types, then adjusted to fit the measured TEM data as closely as possible. We found that the TEM responses differed significantly from the pure step-off response and that incorporating the effects of the full waveform (particularly the linear ramp turn-off) greatly improved the match between observed and computed responses, especially for the early measurement times. In addition, this Albany example illustrates the presence of sign changes in TEM data caused primarily by localized conductivity targets.

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