Ground-coupled Electromagnetic Method
In recent years, the application of the ground-coupled electromagnetic (EM) method (GCEMM) for subsurface exploration has become increasingly popular. The GCEMM can be used for various purposes, including geophysical studies of environmental or engineering site conditions, subsurface surveying for the purpose of groundwater monitoring or waste disposal, or exploration for oil or mineral deposits. As its name implies, the GCEMM uses an electromagnetically-excited current in the earths subsurface to detect subsurface targets.
Before a GCEMM survey can be conducted, it is important to understand the nature of the target environment and how it is likely to affect the results. The most important factor to consider is the electrical conductivity of the subsurface. Conductivity has a major effect on the EM signal and its ability to penetrate the subsurface to detect subsurface targets. In addition, the presence of subsurface structures such as faults, fractures, and soil layering, can also have an effect.
Once the subsurface environment is understood, a survey can be conducted using the GCEMM. The method involves pulsing an electromagnetic field into the earths subsurface using an electromagnetically-excited current. This current interacts with subsurface targets, producing detectable EM responses that can be recorded. These responses can be used to map the subsurface in three dimensions, revealing its structure and any potential resources that may lie beneath.
The most common type of GCEMM survey is a three-dimensional (3D) survey. It involves scanning a line along the surface of the earth and varies the depth of the scan depending on the depth of the target area to be explored. The signals are then analyzed and the data is used to create a 3D image of the subsurface. In some cases, multiple lines may be scanned and the data combined to form an even more detailed 3D image.
The GCEMM has several advantages over traditional subsurface exploration methods. First, it is non-invasive; there is no need to disrupt the surface of the earth. Second, it can provide results in a relatively short time frame, depending on the surveys area of focus. Finally, the GCEMM can provide incredibly detailed images of subsurface features, potentially allowing for more accurate subsurface exploration than other methods.
In summary, the ground-coupled electromagnetic (EM) method is a powerful tool for subsurface exploration. By using an electromagnetic field to detect subsurface targets, the GCEMM can provide detailed information quickly and without the need to disrupt surface areas. It is especially useful when exploring sites where risk or cost may be of concern, such as oil and mineral surveys. With continued improvements in the accuracy and sophistication of the method, the GCEMM is likely to remain a popular choice for many applications.
