Development of a soil rating system for GPR-based IED detection
For some years, the application of ground-penetrating radar (GPR) in the field of detecting explosive remnants of war has expanded from the detection of landmines and unexploded ordnances (UXOs), to the detection of improvised explosive devices (IEDs) in active areas of conflict. Since IEDs are often made from non-metallic material, stand-alone metal detectors often fail and GPR sensors are complementary used in dual sensors. GPR enables to discriminate between any buried material and the surrounding medium, provided a contrast in their electrical or dielectric properties exists. However, under certain soil conditions and physical properties of the soil, GPR can fail and buried targets will be overseen. Since the knowledge of the limitations of a technique is of vital importance in the field, a method is needed that enables to predict the performance of a certain GPR sensor with respect to the soil.
The performance of GPR is influenced by the electromag¬netic (EM) wave attenuation, the contrast in the electrical proper¬ties between the target and the soil and heterogeneities in the soil. UXOs and IEDs generally are located deeper than landmines, such that the attenuation of the EM waves becomes a limiting factor. The attenuation is strongly dependent on the soil material and increases for example with salinity, clay content and water saturation of the soil. Furthermore, attenuation is frequency-dependent, which can cause distortion of the radar signature.
The aim of the project is to develop a system for predicting GPR performance. We use a technique based on time-domain reflectometry (TDR) to measure in-situ intrinsic attenuation and dielectric permittivity. The TDR system is easy to use and therefore suitable for deminers to predict the GPR performance for a specific soil in the field.
In contrast to IEDs and UXOs, landmines are commonly buried near the surface, i.e. within the upper 10 cm of the soil. Therefore, attenuation is usually not the limiting factor, but soil heterogeneity and micro-topography cause noise in the data that can mask the landmine signal. This is especially the case if the target contrast is low and the resulting amplitude of the according GPR reflection is weak.
To systematically investigate the impact of soil heterogeneity, we carry out extensive numerical simulations with varying spatial distributions of electromagnetic soil properties. The generated synthetic data can be used to specify the limits of GPR sensors in heterogeneous soils. One challenge is to deduce a prognosis system, which is robust and easy to use, and thereby applicable by deminers in the field.