Geophysical Mapping: Method Details
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Method Name: Ground penetrating radar (surface-based)
Method Type:   Electromagnetic Methods
Assigned Problems:
+ Aquifer pollution Groundwater
+ Building stability Buildings and Structures
+ Cavity detection Civil Engineering
+ Contaminant plumes Hazardous Waste
+ Dead body Forsenic Investigations
+ Depth of Overburden-bedrock interface Civil Engineering
+ Earthquakes / paleoseismology Natural Hazards
+ Foundations of ancient structures Buildings and Structures
+ Fractures Groundwater
+ Gravel, clay, limestone, salt exploration Natural Resources
+ Groundwater table Groundwater
+ Host sediments, hydogeological settings Hazardous Waste
+ Ice thickness Natural Hazards
+ Landslides Natural Hazards
+ Location of Ancient Structures Cultural Heritage
+ Location of buried materials Hazardous Waste
+ Monitoring Hazardous Waste
+ Permafrost and ice detection Natural Hazards
+ Quality / Thickness of aquifer/aquitard Groundwater
+ Quality / Thickness of concrete Buildings and Structures
+ Quality of roads/ airfields Buildings and Structures
+ Soil / rock quality Civil Engineering
+ Temporal variations Groundwater
+ Wall Construction Cultural Heritage
+ Weapon Forsenic Investigations
0 Characteristics of hazardous waste Hazardous Waste
0 Porosity / Permeability Groundwater
0 Quality and thickness (Natural resources) Natural Resources
0 Quantity/ Thickness Hazardous Waste
0 UXO detection Hazardous Waste
   '+' = Technique applicable; '0' = Application possible/limited use
Principle:   Ground penetrating radar is a technique that uses high frequency electromagnetic waves to acquire subsurface information. Georadar responds to changes in electromagnetic properties that are related to characteristics of soil, rock and interstitial fluids.
Keywords:   Georadar; electromagnetic reflection method (EMR); dielectric permittivity;electrical conductivity ;2-D georadar sections; 3-D georadar cubes
Prerequisites:  
  • Target must be characterized by a contrast in electromagnetic properties (dielectric permittivity, electrical conductivity)
  • Buried wires, metal pipes, metal fences (not with shielded antenna) may influence measurements
  • Metal fences, trees or vehicles may produce strong and disturbing surface reflections
  • Penetration of georadar signals in conductive material, such as clays / clay-rich sediments and in materials having conductive pore fluid, may be limited or even impossible.
Resolution:   Resolution depends primarily on the frequency of the emitted signals and ranges from a few centimeters (2 GHz antennae), to approx. 1 m (100 MHz antennae) to a few meters (25 MHz antennae). The horizontal resolution is additionally constrained by the spatial sampling intervals. The Fresnel zone is dependent on the velocity and the frequency-content of the electromagnetic wave determines the resolution decreases with depth.

Depth of investigation is strongly site-dependent. It ranges from more than 100 m in ice to 30 m or more in un-fractured crystalline rocks to about 10 m in typical quaternary sediments.

Expected Results:  
  • Measured parameter: electromagnetic signals reflected at discontinuities within the Earth (radargram).
  • Data analysis: application of digital signal processing techniques. Representation of processed radargrams in sections (2-D) or cubes (3-D)
  • Interpretation: identification of continuous reflectors (discontinuities) or diffractions (objects). Pitfalls: reflectors dipping with angles greater than 45 on unmigrated (not corrected) georadar sections are unlikely to be real reflections.
Combination with other Methods:  
  • Required additional information: Geological information for reliable interpretation (for geological applications, not for applications in civil engineering)
  • Related add-on information: NA
  • Independent additional information: electromagnetic data ; magnetic data; very high-resolution seismics
Operating Expense:  
  • Crew size: 1 key person, 1-2 assistants
  • Acquisition speed: depending on the measurement distance and topography: 200 - 50'000 m per day
  • Processing: requires 1 -4 days per acquisition day; real-time plotting and interpretation is possible
  • Equipment rental costs: intermediate
Parameters to specify:  
  • Antenna orientation (parallel)
  • Spatial sampling interval (depends on antennae frequency)
  • Signal stacking (depends on ambient electromagnetic noise)
  • Dominant antenna frequency
  • Source and receiver intervals (usually a few dm)
QC Documents:  
  • Field notes (e.g., all activities, effective time schedule, present personnel)
  • Optional: Map of buried cables, roads
Products:  
  • 2-D georadar sections
  • 3-D georadar cubes
  • Interpretation
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