Geophysical Mapping: Method Details
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Induced polarization - Profiling
Location of Ancient Structures
Location of buried materials
Characteristics of hazardous waste
Gravel, clay, limestone, salt exploration
Host sediments, hydogeological settings
'+' = Technique applicable; '0' = Application possible/limited use
The purpose of induced polarization surveys is to determine the lateral subsurface
Induced polarization; Horizontal profiling; Self potential; Chargeability; Apparent chargeability profiles; Apparent chargeability contour maps
Target must be characterized by a chargeabilty contrast
Depth of target must be known approximately
Buried wires, metal pipes, metal fences may influence measurements
Urban areas may cause high noise levels (e.g. stray currents)
Measurements during rain should be avoided
In some areas electrode coupling may be poor (e.g., asphalt, gravel, dry sand)
scales with electrode spacing (horizontal resolution is equal or less than average electrode spacing).
depth of investigation
ranges from less than a meter to several tens of meters.
chargeability [mV/V] (and usually also the apparent resistivity [Ωm]).
chargeability is plotted in form of apparent chargeability as profiles or contour maps.
often qualitative. Areas displaying anomalously high or low values, or anomalous patterns can be identified. Depth of objects can be roughly estimated. Additional geological or geophysical surface data may be required for reliable interpretation. A priori information (layer thickness and / or resistivity values) are helpful to constrain the models.
Combination with other Methods:
Required additional information:
rough estimates of target depths; Resistivity distribution should be approximately known.
Related add-on information:
electromagnetic data; electrical data
Independent additional information:
georadar data; seismics data
1 key person; 1 - 2 assistants
100 - 400 per day
requires 1 - 2 days per acquisition day
Equipment rental costs:
Parameters to specify:
Array type: Usually Wenner- or Schlumberger-type arrays are employed.
Array size: Total length of array: 3 to 10 times the depth of investigation; typically more then six times the depth of investigation.
Array orientation: Should be perpendicular to the strike for a maximum response of geological structures (if only measured along profiles).
Electrode spacing: Usually between 1 and 10 m.
Documentation of accuracy of transmitted currents.
Documentation of accuracy of transmitted currents and voltages.
Measurements of natural potentials and transition resistances between electrodes and ground.
Measurements of reproducibility (measurements of reciprocal or redundant configurations).
Optional: Map of buried cables, roads.
Apparent chargeability along profiles.
Areal distribution of apparent chargeability displayed in form of contour plots.
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