Introduction
Radiological exploration is a technique used to analyze and assess the composition of soils and bedrock underlying the surface. It is a non-destructive method that can be used to identify the hydrological, geological and geophysical characteristics of the subsurface. There are various geophysical techniques that can be used to conduct radiographic exploration of a site, including Electrical Resistivity (ER), Ground Penetrating Radar (GPR), Seismic Refraction (SR), Seismic Reflection (SR), and Gamma-ray Spectrometry (GRS). Each of these techniques relies on the principle of measuring changes in a magnetic or electrical field, which can be used to identify and map subsurface features that can include fractures, fault zones, cavities, and easier, among others. This paper provides an overview of how each technique works, the advantages and limitations, and potential applications.
Electrical Resistivity
Electrical resistivity (ER) is the measure of electrical field resistance of the subsurface. This is measured by placing two or more electrodes into the ground and passing an electrical current between them. ER measurements are used to detect changes in permeability, porosity, lithology, and structural features. The result is a detailed visual representation of subsurface features.
Advantages
ER is highly cost-effective, fast, and non-destructive. Furthermore, it can monitor changes over time, as well as depths far beyond those of traditional methods, often up to several hundred meters.
Limitations
ER can only detect changes in a small range of physical properties in the subsurface, and accuracy is limited by the number of electrodes used.
Applications
ER can be used to detect bedrock, fault zones, and fractures, as well as other structural features. It can also be used to measure moisture content and detect regulatory contaminants.
Ground Penetrating Radar
Ground penetrating radar (GPR) is a geophysical method that uses high frequency electromagnetic waves to penetrate the subsurface and detect features and stratigraphic changes. It is used to detect changes in the subsurface composition, such as impedance, porosity, saturation, and lithology.
Advantages
GPR can detect changes in the subsurface in real-time, and can detect subsurface features at depths far beyond those of conventional methods, often up to several hundred meters.
Limitations
GPR is highly sensitive to electromagnetic interference and is not suitable for use in areas with high levels of background noise.
Applications
GPR is used to detect artifacts, geological features, and mapping features, such as faults and fractures. It can also be used to detect subsurface water or mineral resources.
Seismic Refraction
Seismic refraction (SR) is a geophysical technique that uses sound waves of high frequencies to detect changes in the subsurface. Sound waves sent into the subsurface will be reflected back to the surface, and this information can be used to identify changes in the geologic composition and density of the subsurface.
Advantages
SR can detect changes in the subsurface in real-time, and is capable of penetrating depths greater than those of ER methods.
Limitations
SR is highly sensitive to background noise, which can interfere with the accuracy of results. It is also an expensive technique.
Applications
SR is used to identify faults and fractures, as well as subsurface geologic features, such as buried sedimentary structures.
Seismic Reflection
Seismic reflection (SR) is a geophysical technique used to detect changes in the subsurface. SR works by generating sound waves that travel through the subsurface, which are then reflected back to the surface. This information is used to identify changes in the subsurface composition, as well as to detect irregularities in sedimentary layers.
Advantages
SR is capable of penetrating deep into the subsurface, and can be used to detect even small irregularities.
Limitations
SR is expensive and requires significant event-building time.
Applications
SR is used to detect subsurface faults, fractures, and geologic features, such as stratigraphic boundaries.
Gamma-Ray Spectrometry
Gamma-ray spectrometry (GRS) is a geophysical technique used to measure gamma-ray radiation emitted from the subsurface. The source of this radiation can be either natural or artificial, and can be used to identify changes in the geologic composition and density of the subsurface.
Advantages
GRS is relatively fast and non-destructive, and can detect subtle changes in structure, such as strata and lithology.
Limitations
GRS is not suitable for use in areas with high levels of background noise, as this can interfere with the accuracy of results.
Applications
GRS is used to identify subsurface faults, fractures and geologic features, such as stratigraphic boundaries. It can also be used to detect subsurface water and mineral resources.
Conclusion
Radiological exploration is a non-destructive technique used to analyze and assess the composition of soils and bedrock underlying the surface. There are various geophysical techniques that can be used to conduct radiographic exploration of a site, including Electrical Resistivity, Ground Penetrating Radar, Seismic Refraction, Seismic Reflection, and Gamma-ray Spectrometry. Each technique has its own unique advantages, limitations, and applications.
