View source for Earth:Induced polarization

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'''Induced polarization''' ('''IP''') is a [[Earth:Geophysical imaging|geophysical imaging]] technique used to identify the electrical chargeability of subsurface materials, such as [[Earth:Ore|ore]].<ref name="Bleil_1953"/><ref name="Zonge_2005"/>

The polarization effect was originally discovered by Conrad Schlumberger when measuring the resistivity of rock.<ref name="Allaud_1977"/>

The survey method is similar to [[Electrical resistivity tomography|electrical resistivity tomography]] (ERT), in that an [[Physics:Electric current|electric current]] is transmitted into the subsurface through two [[Physics:Electrode|electrode]]s, and [[Physics:Voltage|voltage]] is monitored through two other electrodes.

Induced polarization is a geophysical method used extensively in mineral exploration and mine operations. Resistivity and IP methods are often applied on the ground surface using multiple [[Four-terminal sensing|four-electrode]] sites. In an IP survey, in addition to resistivity measurement, capacitive properties of the subsurface materials are determined as well. As a result, IP surveys provide additional information about the spatial variation in lithology and grain-surface chemistry.

The IP survey can be made in time-domain and frequency-domain mode:

In the ''time-domain induced polarization'' method, the voltage response is observed as a function of time after the injected current is switched off or on. <ref name="Olsson_2015"/>

In the ''frequency-domain induced polarization'' mode, an alternating current is injected into the ground with variable frequencies. Voltage phase-shifts are measured to evaluate the impedance spectrum at different injection frequencies, which is commonly referred to as spectral IP.

The IP method is one of the most widely used techniques in mineral exploration and mining industry and it has other applications in hydrogeophysical surveys, environmental investigations and geotechnical engineering projects.<ref name="SSI_2018"/>

==Measurement methods==
==={{anchor|Time}}Time domain===
[[File:Theoretical current waveform and potential response for time domain resistivity and induced polarization measurements..png|thumb|Typical transmitted current waveform and potential response for time domain resistivity and induced polarization measurements.]]
Time-domain IP methods measure considers the resulting voltage following a change in the injected current. The time domain IP potential response can be evaluated by considering the mean value on the resulting voltage, known as [[Integral|integral]] chargeability<ref name="Zonge_2005"/> or by evaluating the spectral information and considering the shape of the potential response, for example describing the response with a [[Physics:Cole–Cole equation|Cole-Cole]] model.<ref name="Pelton_1978"/>

==={{anchor|Frequency}}Frequency domain===
{{Main|Earth:Spectral induced polarisation}}
Frequency-domain IP methods uses [[Physics:Alternating current|alternating current]]s (AC) to induce electric charges in the subsurface, and the apparent resistivity is measured at different AC frequencies.

== See also ==
* DC impedance spectroscopy
* AC impedance spectroscopy
* [[Physics:Electrical resistivity measurement of concrete|Electrical resistivity measurement of concrete]]
* [[Earth:Geophysical imaging|Geophysical imaging]]

==References==
{{Reflist|refs=
<ref name="Allaud_1977">{{cite book |author-last1=Allaud |author-first1=Louis A. |author-last2=Martin |author-first2=Maurice H. |translator-first=Marcel |translator-last=Schwob |title=Schlumberger - The History of a Technique |publisher=John Wiley & Sons, Inc. |location=New York, USA |date=1977-10-01 |isbn=978-047101667-0 |url-access=registration |url=https://archive.org/details/schlumbergerhist0000alla }}</ref>
<ref name="Bleil_1953">{{cite journal |author-last=Bleil |author-first=David Franklin |title=Induced Polarisation: A Method of Geophysical Prospecting |journal=Geophysics |volume=18 |issue=3 |date=July 1953 |pages=636–661 |url=https://www.researchgate.net/publication/252737250 |access-date=2018-05-15 |doi=10.1190/1.1437917}}</ref>
<ref name="Zonge_2005">{{cite book |title=Near-Surface Geophysics - Investigations in Geophysics |chapter=Chapter 9. Resistivity, Induced Polarization, and Complex Resistivity |author-first1=Ken |author-last1=Zonge |author-first2=Jeff |author-last2=Wynn |author-first3=Scott |author-last3=Urquhart |editor-first=Dwain K. |editor-last=Butler |publisher=[[Organization:Society of Exploration Geophysicists|Society of Exploration Geophysicists]] (SEG) |date=2005 |pages=265–300 |isbn=978-1-56080-130-6 |doi=10.1190/1.9781560801719.ch9}}</ref>
<ref name="SSI_2018">{{cite web |title=Induced Polarization (IP) What Is It? |date=2018 |publisher=Surface Search Inc. |url=http://surfacesearch.com/induced-polarization-ip/ |access-date=2018-05-06 |url-status=live |archive-url=https://web.archive.org/web/20180517173308/http://surfacesearch.com/induced-polarization-ip/ |archive-date=2018-05-17}}</ref>
<ref name="Pelton_1978">{{cite journal |author-last1=Pelton |author-first1=William H. |author-last2=Ward |author-first2=Stanley H. |author-last3=Hallof |author-first3=Philip G. |author-last4=Sill |author-first4=William R. |author-last5=Nelson |author-first5=Philip H. |title=Mineral discrimination and removal of inductive coupling with multifrequency IP |journal=Geophysics |date=1978-04-01 |volume=43 |issue=3 |pages=588–609 |doi=10.1190/1.1440839}}</ref>
<ref name="Olsson_2015">{{cite journal |author-last1=Olsson |author-first1=Per-Ivar |author-last2=Dahlin |author-first2=Torleif |author-last3=Fiandaca |author-first3=Gianluca |author-last4=Auken |author-first4=Esben |title=Measuring time-domain spectral induced polarization in the on-time: decreasing acquisition time and increasing signal-to-noise ratio |journal=Journal of Applied Geophysics |volume=123 |date=2015 |pages=316–321 |issn=0926-9851 |doi=10.1016/j.jappgeo.2015.08.009 |url=http://portal.research.lu.se/ws/files/11329856/Measuring_time_domain_spectral_induced_polarization_in_the_on_time_decreasing_acquisition_time_and_increasing_signal_to_noise_ratio_2_.pdf|hdl=2434/724249 |hdl-access=free}}</ref>
}}

==Further reading==
* {{cite book |author-last1=Kearey |author-first1=Philip |author-first2=Michael |author-last2=Brooks |title=An Introduction to Geophysical Exploration |date=1991 |edition=2 |publisher=Blackwell Science |isbn=978-0-632-02923-5}}

==External links==
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* [http://www.l-gm.de/English/Resistivity_Meters/resistivity_meters.html] Example IP equipment and image results

[[Category:Geophysical imaging]]

{{Sourceattribution|Induced polarization}}