GPR (Ground Penetrating Radar) Method
Purpose: Ground Penetrating Radar (GPR) is a versatile method for shallow subsurface imaging, widely used in applications from mineral exploration to environmental and construction studies. GPR provides high-resolution data on subsurface features, especially in low-conductivity materials, making it valuable for locating specific targets and mapping stratigraphy.
Applications:
- Mineral and Diamond Exploration: GPR helps in shallow mineral exploration, providing depth information about overburden and bedrock.
- Environmental and Utility Mapping: It locates underground storage tanks (UST), water table depth, and utility lines, and can detect contaminants under suitable conditions.
- Geotechnical Uses: GPR assists in mapping roadbeds, grave sites, and geological layers, offering critical insights for construction and archaeological studies.
Technical Process: GPR works best in dry, resistive materials, with signal penetration and resolution adjusted by varying the frequency. High frequencies (e.g., 500-1000 MHz) are used for shallow, high-resolution targets like rebar or utility lines, while lower frequencies (e.g., 50-100 MHz) provide deeper penetration for bedrock detection. The method is often supplemented with EM tools like Geonics EM61 for comprehensive site analysis, especially in challenging conditions.
Key Uses: GPR’s adaptability for both environmental and exploration tasks makes it an essential tool for detailed, shallow-depth imaging, offering precise results across varied applications.
some GPR applications include:
- diamond exploration
- UST (underground storage tanks) locates
- depth to water table
- depth to bedrock
- Private Locates
- stratigraphy mapping
- contaminant mapping (in special cases)
- road-bed studies
- grave site mapping
- See also:
The GPR geophysical method works best in low conductivity (high resistivity) areas. Conductive materials (e.g., clay) attenuate the GPR signal to the point that very little depth penetration is achieved. Penetration is greatest in unsaturated sands and fine gravels. When possible, additional geophysical methods, such as the Geonics EM61 metal detector for UST locates, or the Geonics EM31 for depth to bedrock mapping, are used. Physical evidence from boreholes and test pits are commonly used to complement the geophysical data to provide a more robust quantitative interpretation of the broad coverage geophysical results.
GPR can also be used to detect contaminants and water main leaks, if the conditions are right. The reflection delay time is controlled by the dielectric properties of the material. The signal velocity (m/ns) is approximately equal to one third the value of the dielectric constant. Some contaminants have different dielectric properties compared to the host geology. For example, GPR signals travel at 0.01 m/ns through sea water compared to 0.06 m/ns through clean, saturated sand.
The penetration depth of the instrument is also dependent on the chosen base frequency. The higher the frequency, the less the penetration. The trade-off is that the lower frequencies lose target resolution. Typically, 100 MHz and 50 MHz are used for bedrock detection, 500 MHz and 250 MHz antennae are used for tank locates, and 1000 MHz is used for rebar checking.
- We use Sensors & Software Noggin 100 MHz, 250 MHz, 500 MHz and Conquest 100 instruments.
- PulseEKKO gear use lower frequencies (e.g., 50 MHz and 25 MHz) required for diamond exploration, overburden studies, etc.
- often run in ATV- and Snowmobile-mode to better cover large areas of ground.
- production rates of a few km per day are typical.
