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 enhance geophysical techniques for shallow geophysical investigations, especially in identifying illegal buried materials. This article applied very low-frequency electromagnetic (VLF-EM) at a controlled geophysical site (CGS) where several targets were buried to examine the geophysical response for environmental and engineering simulation. The VLF-EM data obtained on the natural ground (without buried targets) and buried ground along the same profiles demonstrate the nature of the anomalies and the characteristic signals generated by the site's natural ground and after various buried targets are installed. There are clear and significant anomalies source-bodied between the natural and buried ground. The result shows no major high equivalent current density (conductive media) or low equivalent current density (non-conductive media) across the natural ground. Several minors and major conductive and non-conductive zones were encountered after the installations of the buried targets corresponding to conductive and non-conductive buried targets. Some anomalies become stronger over the large conductivity and non-conductive buried targets. A reasonable position of the buried targets was determined by the VLF-EM method with positive matches and few significant mismatches in the actual depths of buried targets. However, there are some unexpected emergencies, where some non-conductive buried target generates high equivalent current density values indicating conductive media, while some conductive buried target produces low equivalent current density values indicating non-conductive body, especially for large spacing. Major and minor characteristic VLF-EM anomalies were obtained across all the survey profiles. The VLF-EM method is more consistent at small spacing and it can be very useful for identifying underground metallic and non-metallic targets.