Geophysics - Induced Polarization

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Induced Polarization
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Two types of IP data are acquired: frequency domain and time domain. Time domain IP surveys involve measurement of the magnitude of the polarization voltage (Vp) that results from the injection of pulsed current into the ground. Polarization voltages primarily result from electrochemical action (ionic exchange) within the pores and pore fluids of the material being energized. The current is applied in the form of a square waveform, with the polarization voltage being measured over a series of time intervals after each current cut-off using non-polarizing electrodes. The measured value of Vp is divided by the steady voltage (observed whilst the current is on) to give the apparent chargeability of the ground. This provides qualitative information on the subsurface geology. TD-IP is primarily used in mineral exploration surveys.
 
Spectral IP surveys involve measurement of the magnitude and relative phase of the polarization voltage that results from the injection of an alternating current into the ground. Polarization voltages primarily result from electrochemical action (ionic exchange) within the pores and pore fluids of the material being energized. Measurements of the relative phase shift between the transmitted current and the measured signal and the magnitude of the polarization voltage are taken over a range of different frequencies. This results in a distinct IP response spectrum or 'dispersion' at each measurement position that can be used to determine capacitive parameters such as relaxation time and chargeability, and can be interpreted qualitatively or modeled quantitatively in 2D and 3D to estimate the distribution of clay or metallic mineralization


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