Geophysical Mapping: Method Details
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Method Name: Induced polarization - Profiling
Method Type:   Electrical Methods
Assigned Problems:
+ Location of Ancient Structures Cultural Heritage
+ Location of buried materials Hazardous Waste
0 Aquifer pollution Groundwater
0 Characteristics of hazardous waste Hazardous Waste
0 Contaminant plumes Hazardous Waste
0 Gravel, clay, limestone, salt exploration Natural Resources
0 Host sediments, hydogeological settings Hazardous Waste
   '+' = Technique applicable; '0' = Application possible/limited use
Principle:   The purpose of induced polarization surveys is to determine the lateral subsurface chargeability distribution.
Keywords:   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)
Resolution:   Horizontal resolution scales with electrode spacing (horizontal resolution is equal or less than average electrode spacing).

Typical depth of investigation ranges from less than a meter to several tens of meters.

Expected Results:  
  • Measured parameter: chargeability [mV/V] (and usually also the apparent resistivity [Ωm]).
  • Data analysis: chargeability is plotted in form of apparent chargeability as profiles or contour maps.
  • Interpretation: 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
Operating Expense:  
  • Crew size: 1 key person; 1 - 2 assistants
  • Acquisition speed: 100 - 400 per day
  • Processing: requires 1 - 2 days per acquisition day
  • Equipment rental costs: intermediate
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.
QC Documents:  
  • 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.
  • Interpretation
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