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Method Name: |
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Ground penetrating radar (surface-based) |
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Method Type: |
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Electromagnetic Methods
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Assigned Problems: |
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Principle: |
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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. |
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Keywords: |
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Georadar; electromagnetic reflection method (EMR); dielectric permittivity;electrical conductivity ;2-D georadar sections; 3-D georadar cubes |
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Prerequisites: |
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- 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.
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Resolution: |
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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. |
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Expected Results: |
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- 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.
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Combination with other Methods: |
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- 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
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Operating Expense: |
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- 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
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Parameters to specify: |
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- 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)
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QC Documents: |
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- Field notes (e.g., all activities, effective time schedule, present personnel)
- Optional: Map of buried cables, roads
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Products: |
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- 2-D georadar sections
- 3-D georadar cubes
- Interpretation
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