The Influence of Subsoil on Electromagnetic Detection

Abstract

Decommissioning of exercise ranges reflects downsizing of Czech Army. That process (started in 1993) requires disposal of all remnants of military activities, namely unexploded ordnance. Methodology of explosive ordnance clearance (EOC) is based on using of metal detectors.

The world wide experience witnesses some factors limiting or even eliminating their utilisation. Metal debris diminishes EOC reliability, when conducted in the outskirts of urban areas. Apart of this, there are cases when false alarms are observed without presence of any metal waste inside ground. This phenomenon was called “mineralisation of ground” initially. Term “mineralisation” was considered either as a content of mineralized groundwater or as a content of metallic minerals dispersed in rocks. However, the content of ferromagnetic minerals in rocks occurred under scientific interest. Research works have been conducted to clarify its nature and to recommend how to practise EOC procedures under those conditions.

Electromagnetic detection is based on the Faraday’s rule of mutual induction between searching coil and a target. From this point of view the expression “mineralized soil” should be rectified. Even impregnation of ferromagnetic materials inside absolutely non-conductive rocks can cause false signal of detector. This is the right reason of “mineralisation”. Where the bedrock consists of rocks containing magnetite, the success of electromagnetic searching occurs at risk.