Geophysical survey is a cost-effective and non-intrusive ground characterisation technique. Applied or exploration geophysics can be defined as mapping large scale subsurface through the remote measurement of its physical properties. Those properties observed are typically density, elasticity, magnetic susceptibility, electrical conductivity and radioactivity.
The success of any geophysical method relies on a measurable contrast between the physical properties of the target and the surrounding medium. Often a combination of methods provides the best means of solving a complex problem. Geophysical surveys are used in all areas of the geotechnical, civil engineering, mineral, groundwater and environmental industries.
EM method use a geophysical survey technique based on electromagnetic measurements of ground conductivity for imaging sub-surface structures.
As well as mapping out physical or chemical changes of sub-soil, EM imaging is often used to map sub-surface structures like remains of foundations or utilities.
Murphy Surveys can measure the electrical properties of the subsurface. and a 2D map of electrical conductivity of the ground can be produced. This is achieved by carrying the equipment along parallel lines with a sufficient spacing depending on purpose of the survey.
The depth of investigation can reach 6 meters but depending on size of objects. A single 200 litre (55 gal.) drum can be detected for example at depths greater than three meters.
As the geophysical survey is carried out with a GPS, on continuous collection mode, to ensure the most accurate location of possible targets for future exploration, it is a real fast and economic way to survey vast areas.
Electrical Resistivity Imaging
Electrical resistivity imaging is a geophysical survey method that provides a two or three dimensional resistivity image of the surface.
Electrical resistivity imaging can provide information about distinct subsurface boundaries and conditions that other geophysical methods can not.
Applications for this type of geophysical survey include:
• Landfill investigations
• Bedrock mapping
• Void mapping
• Identifying layer thickness and depths
• Site contamination surveys