The effectiveness of very low-frequency electromagnetics (VLF-EM) method in detecting buried targets at a controlled site

Abstract

The ever-increasing anthropogenic activities that pose a significant threat to environmental security and sustainability have spurred geophysicists to review enhance geophysical techniques for shallow geophysical investigations, especially in identifying illegal buried materials. This article applied very low-frequency electromagnetic (VLF-EM) at an experimental geophysical site (EGS) to examine the geophysical response over various buried targets. The VLF-EM data acquired on the site with and without buried targets demonstrate the nature of the anomalies and the characteristic signals of the buried targets. There are significant variations in the anomalies source-bodied between the site with and without buried targets. The result of the pre-burial investigation shows no major contrast in the equivalent current density values across the site without targets. Minors and major anomalies were encountered after burying the targets corresponding to the buried targets. Some signals become stronger over a large buried target. However, there were a few undetected targets and some cases of unsatisfied results, which were also discussed. The performance of the VLF-EM method in terms of depth estimation was also examined. A significant variation was noted due to the presence of the buried targets and it was noted that the current density seems to always emerge maximally and minimally around the conductor targets and non-conductive targets, respectively. The failure of the VLF-EM to detect the buried pipes in various orientations was examined. The VLF-EM method is more consistent at small spacing and it can be very useful for identifying underground metallic and non-metallic targets. The study successfully provides useful information to complement the complexity of the use of geophysical methods while enhancing the subsurface information and understanding of VLF-EM anomalies or responses generated by various targets such as subsurface geological structures, buried waste contaminants and underground utilities to boost environmental studies and engineering investigations.