Abstract
The nondestructive characterization of cylindrical objects is needed in many fields, such as medical diagnostics, tree trunk inspection, or concrete column testing. In this study, the radar equation of Lambot et al. is combined with cylindrical Green’s functions to fully model and invert ultra-wideband (UWB) ground-penetrating radar (GPR) data and retrieve the properties of cylindrical objects. Inversion is carried out using a lookup table (LUT) approach followed by local optimization to ensure retrieval of the global minimum of the objective function. Numerical experiments were conducted to analyze the capabilities of the developed inversion procedure to estimate the radius, permittivity, and conductivity of the cylinders. The full-wave model was validated in laboratory conditions on metallic and plastic pipes of different sizes. The adopted radar system consists of a lightweight vector network analyzer (VNA) connected to a single transmitting and receiving horn antenna. The numerical experiments highlighted the complexity of the inverse problem, mainly originating from the multiple propagation modes within cylindrical objects. The laboratory measurements demonstrated the accuracy of the forward modeling and reconstructions in far-field conditions.
Highlights
Published: 17 June 2021Ground-penetrating radar (GPR) is a nondestructive measurement technique, which uses high frequency electromagnetic waves to locate targets within dielectric materials
Inversion is carried out using a lookup table (LUT) approach followed by local optimization using the Nelder−Mead simplex algorithm to ensure robust and efficient retrieval of the global minimum of the objective function
To determine the complex values of the antenna characteristic coefficients for the model described by Equation (10), we set up an experiment to measure the ground-penetrating radar (GPR) signals over a 3 × 3 m2 copper sheet, assumed as a perfect electrical conductor (PEC), at different distancesWe ranging unevenly from m tosignals
Summary
Ground-penetrating radar (GPR) is a nondestructive measurement technique, which uses high frequency electromagnetic waves to locate targets within dielectric materials. Due to its fast data acquisition capability, its high resolving ability and the fact that it responds to metallic as well as non-metallic targets, GPR has been widely used in agricultural and environmental engineering [1], civil engineering [2], glacier and permafrost geology [3,4], archaeological prospecting [5,6], landmine detection [7,8,9], etc. To encourage better applications of GPR and MWI to these new fields, a deeper understanding of their ability to retrieve relevant electrical parameters of cylindrical media is necessary. There are two major modes of analysis when using GPR to visualize the cross section of a (nearly) cylindrical medium, namely, ray-based and full-wave inversion approaches. The ray-based method mainly consists of determining the dielectric
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