Investigating the effects of antenna coupling, wave attenuation, dispersion and scattering on GPR-based IED and landmine detection. For this purpose, we carry out systematic studies by means of realistic simulations and generate a set of sample data representing typical scenarios.
Landmines and IEDs (improvised explosive devices) are mostly made up of non-metallic materials, which is why they are only barely visible to metal detectors. This has lead to an increased use of ground-penetrating radar (GPR) sensors for detection purposes. GPR signatures vary by soil composition, material, size, form and position of the weapon device as well as the GPR system in use.
The project series Counter-IED, funded by the BMVg (german federal ministry of defence), has the goal to determine these unknown dependencies in the detection of buried weapon devices. Building upon the predecessor projects Counter-IED I + II, the influence of the antenna coupling to the subsurface is studied. Via extensive numerical simulations the distance from the antenna to the surface, as well as the antenna orientation is varied. The simulations include complex 3D antenna models and well as comprehensive, realistic soil models, whereby the soil heterogeneity and topography, as well as the frequency-dependent soil properties are considered.
To be able to study the effects of the antenna coupling via numerical simulations, complex 3D antenna models have to be implemented. The creation of such models is therefore a pillar of the project. Because numerous details of GPR antennas, like the electrical properties of the antenna materials, are unknown they are found through a full-waveform inversion of experimental calibration data.
As the results of the predecessor project Counter-IED II have shown, the successful detection of buried weapon devices depends strongly on the soil in which they are buried. In this part of the project, soil samples are analyzed with a network analyzer and characterized in their dielectric properties. Petrophysical models are fitted to this data, which are then used within the numerical simulations of the wave propagation to correctly include the attenuation and dispersion properties.
A very heterogeneous soil (with regard to the wavelength in usage, e.g. a couple of cm) will strongly hinder the identification of the target due to wave scattering. This part of the project aims at parameterising the soil heterogeneity and soil topography to implement them in the numerical simulations.
The wave propagation of an antenna array over a sand in which a shell is buried. What becomes visible is a complex wave field with the direct reflection from the tip of the shell, a reflection of the guided wave from the bottom end of the shell, as well as multiple reflections between the target and antenna array and the different single antenna elements.