Introduction
Electromagnetic survey techniques are a popular method for determining subsurface soil conditions for structural and engineering applications. EM31 Frequency Domain Electromagnetic Survey (FDEM) is a rapidly evolving method for mapping the electrical properties of the subsurface ground, in particular sub-surface geological deposits and man-made utilities. The EM31 system, is a popular FDEM instrument for commercial use. Due to its large range of frequency response of 1 to 50,000 Hertz and the ability to interpolate data over an area, it can be used to great effect in a variety of different situations. This article will discuss the theory and application of EM31 Frequency Domain Electromagnetic Survey to determine sub-surface soil conditions.
Theory
FDEM is based on the principle of electromagnetic induction, which states that a voltage will be induced in an inductor whenever a changing magnetic field passes through it. In the case of the EM31 system, this inductor is a large circular antenna which is usually carried by a vehicle as it is driven over the survey site. The antenna emits an alternating magnetic field in the form of an azimuthal (or circular) wave and sets up a charge in the subsurface soil. This charge sets up a magnetic field which is monitored by the EM31 receiver. The receiver then calculates the total charge in the soil, the amount of charge that has been induced, the resistivity and the depth of the target.
Application
The EM31 frequency domain electromagnetic survey is used to study subsurface geological deposits, man-made utilities and any other features that may be of interest. This type of survey has a number of different applications including groundwater mapping, landfill surveys, geotechnical investigations, mineral exploration and engineering structure studies.
The EM31 system can be used for mapping the electrical properties of the subsur-face ground. The most common use is to map the electrical resistivity of soil deposits, as this information can be used to gain insight into the composition of the soil and its potential importance for engineering structures and other projects. The EM31 system can also be used to detect sub-surface metal objects such as buried utility pipes and cables. By measuring the magnetic field set out by the metal objects, the EM31 receiver can identify the location of these objects and even determine the depth at which they lie.
The EM31 frequency domain electromagnetic survey offers a great deal of flexibility and accuracy, making it an attractive option for any project requiring an accurate map of subsurface conditions. In addition, the system is relatively inexpensive and easy to use, allowing many different projects to benefit from the use of this technology.
Conclusion
The EM31 system is a powerful tool that can be used to provide insight into subsurface geological deposits, man-made utilities and other features. Utilizing the principles of electromagnetic induction, the EM31 system can map out electrical properties of the subsurface ground and identify man-made objects that may be lying beneath the surface. The EM31 frequency domain electromagnetic survey is relatively inexpensive, easy to use and highly accurate, making it an attractive option for any number of applications.
