Geophysical Mapping: Method Details
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Method Name: DC geoelectrics - Profiling
Method Type:   Electrical Methods
Assigned Problems:
+ Aquifer pollution Groundwater
+ Contaminant plumes Hazardous Waste
+ Foundations of ancient structures Buildings and Structures
+ Gravel, clay, limestone, salt exploration Natural Resources
+ Host sediments, hydogeological settings Hazardous Waste
+ Location of Ancient Structures Cultural Heritage
+ Location of buried materials Hazardous Waste
+ Wall Construction Cultural Heritage
0 Cavity detection Civil Engineering
0 Characteristics of hazardous waste Hazardous Waste
0 Depth of Overburden-bedrock interface Civil Engineering
0 Fractures Groundwater
0 Landslides Natural Hazards
0 Monitoring Hazardous Waste
0 Permafrost and ice detection Natural Hazards
0 Porosity / Permeability Groundwater
0 Quality / Thickness of concrete Buildings and Structures
0 Quality and thickness (Natural resources) Natural Resources
0 Quantity/ Thickness Hazardous Waste
0 Soil / rock quality Civil Engineering
   '+' = Technique applicable; '0' = Application possible/limited use
Principle:   The purpose of geoelectrical profiling is to detect lateral changes in electrical resistivity within a particular depth range.
Keywords:   Electrical mapping; horizontal profiling; lateral resistivity changes; apparent resistivity; profiles or contour maps; resistivity distribution
Prerequisites:  
  • Target must be characterized by a resistivity contrast
  • Buried wires, metal pipes, metal fences influence measurements
  • Urban areas may cause high noise levels (e.g., stray currents)
  • In some areas electrode coupling may be poor (e.g. asphalt, gravel)
  • Measurements during rain should be avoided
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: Voltages [mV]. Depending on electrode configurations and currents injected values may range from a few ÁV to several V.
  • Data analysis: Voltages are plotted in form of apparent resistivities 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
  • Related add-on information: electromagnetic data
  • Independent additional information: georadar data ; seismics data
Operating Expense:  
  • Crew size: 1 key person, 1-2 assistants
  • Acquisition speed: Small arrays (< 100 m): 300 - 400 measurements per day; large arrays (> 100 m): 250 - 400 measurements per day (with new, automated data acquisition systems these numbers may be increased substantially).
  • Processing: requires 1 day 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 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
Products:  
  • Line graphs or contour plots of apparent resistivities
  • Profile data
  • Interpretation
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