Simulations of ground-penetrating radars over lossy and heterogeneous grounds

The versatility of the three-dimensional (3-D) finite-difference time-domain (FDTD) method to model arbitrarily inhomogeneous geometries is exploited to simulate realistic groundpenetrating radar (GPR) scenarios for the purpose of assisting the subsequent designs of high-performance GPR hardware and software. The buried targets are modeled by conducting and dielectric prisms and disks. The ground model is implemented as lossy with surface roughness, and containing numerous inhomogeneities of arbitrary permittivities, conductivities, sizes, and locations. The impact of such an inhomogeneous ground model on the GPR signal is demonstrated. A simple detection algorithm is introduced and used to process these GPR signals. In addition to the transmitting and receiving antennas, the GPR unit is modeled with conducting and absorbing shield walls, which are employed to reduce the direct coupling to the receiver. Perfectly matched layer absorbing boundary condition is used for both simulating the physical absorbers inside the FDTD computational domain and terminating the lossy and layered background medium at the borders

Optimization of the transmitter-receiver separation in the ground-penetrating radar

Cataloged from PDF version of article.The finite-difference time-domain method is applied to simulate three-dimensional subsurface-scattering problems, involving a ground-penetrating-radar (GPR) model consisting of two transmitters and a receiver. The receiving antenna is located in the middle of the twos identical transmitters, which are fed 180degrees out of phase. This configuration implies the existence of a symmetry plane in the middle of two transmitters and the cancellation of the direct signals coupled from the transmitters at the receiver location. The antenna polarizations and their separations are arbitrary. The transmitter-receiver-transmitter configured GPR model is optimized in terms of the scattered energy observed at the receiver by varying the antenna separation. Many simulation results are used to demonstrate the effects of the antenna separation and the optimal separation encountered for a specific target and GPR scenario

Frequency responses of ground-penetrating radars operating over highly lossy grounds

The finite-difference time-domain (FDTD) method is used to investigate the effects of highly lossy grounds and the frequency-band selection on ground-penetrating-radar (GPR) signals. The ground is modeled as a heterogeneous half space with arbitrary background permittivity and conductivity. The heterogeneities encompass both embedded scatterers and surface holes, which model the surface roughness. The decay of the waves in relation to the conductivity of the ground is demonstrated. The detectability of the buried targets is investigated with respect to the operating frequency of the GPR, the background conductivity of the ground, the density of the conducting inhomogeneities in the ground, and the surface roughness. The GPR is modeled as transmitting and receiving antennas isolated by conducting shields, whose inner walls are coated with absorbers simulated by perfectly matched layers (PML). The feed of the transmitter is modeled by a single-cell dipole with constant current density in its volume. The time variation of the current density is selected as a smooth pulse with arbitrary center frequency, which is referred to as the operating frequency of the GPR

Transmitter-receiver-transmitter-configured ground-penetrating radars over randomly heterogeneous ground models

Ground-penetrating radar (GPR) problems are simulated using the finite-difference time-domain (FDTD) method. The GPR model is configured with arbitrarily polarized three antennas, two of which are transmitting antennas fed 180° out of phase. The receiver is placed in the middle of two transmitters, where it receives no direct coupling from the transmitting antennas. The ground is modeled as a dielectric, lossy, and heterogeneous medium. The performances of the transmitter-receiver-transmitter-configured GPRs above the heterogeneous ground models are investigated. The computational domain is terminated by perfectly matched layer (PML) absorbing boundaries. The PML is adapted to match both air and ground regions of the computation space

Three-dimensional FDTD modeling of a ground-penetrating radar

Cataloged from PDF version of article.The finite-difference time-domain (FDTD) method is used to simulate three-dimensional (3-D) geometries of realistic ground-penetrating radar (GPR) scenarios. The radar unit is modeled with two transmitters and a receiver in order to cancel the direct signals emitted by the two transmitters at the receiver. The transmitting and receiving antennas are allowed to have arbitrary polarizations. Single or multiple dielectric and conducting buried targets are simulated. The buried objects are modeled as rectangular prisms and cylindrical disks. Perfectly-matched layer absorbing boundary conditions are adapted and used to terminate the FDTD computational domain, which contains a layered medium due to the ground–air interface

Full-Wave Modelling of Ground-Penetrating Radars: Antenna Mutual Coupling Phenomena and Sub-Surface Scattering Processes

Ground-penetrating radar (GPR) technology finds applications in many areas such as geophysical prospecting, archaeology, civil engineering, environmental engineering, and defence applications as a non-invasive sensing tool [3], [6], [18]. One key component in any GPR system is the receiver/transmitter antenna. Desirable features for GPR antennas include efficient radiation of ultra-wideband pulses into the ground, good impedance matching over the operational frequency band, and small size. As the attenuation of radio waves in geophysical media increases with frequency [9], [13], ground-penetrating radars typically operate at frequencies below 1GHz [4]. For either impulse [13] or steppedfrequency continuous-wave applications [17], the wider the frequency range, the better the range resolution of the radar. Continuous wave multi-frequency radars are advantageous over impulse radars in coping with dispersion of the medium, the noise level at the receiver end, and the controllability of working frequency. It requires, however, mutual coupling between the transmit (Tx) and receive (Rx) antennas, which determines the dynamic range of the sys-tem, to be kept as small as possible [12]

Modeling of ground-penetrating-radar antennas with shields and simulated absorbers

Cataloged from PDF version of article.A three-dimensional (3-D) finite-difference time-domain (FDTD) scheme is employed to simulate ground-penetrating radars. Conducting shield walls and absorbers are used to reduce the direct coupling to the receiver. Perfectly matched layer (PML) absorbing boundary conditions are used for matching the multilayered media and simulating physical absorbers inside the FDTD computational domain. Targets are modeled by rectangular prisms of arbitrary permittivity and conductivity. The ground is modeled by homogeneous and lossless dielectric media

On the frequency-band selection for ground-penetrating radars operating over lossy and heterogeneous grounds

The frequency-band selection for ground penetrating radars operating over lossy and heterogenous grounds was discussed. The simulations were carried out using perfectly matched layer (PML) absorbing boundary conditions (ABC). The results demonstrated that for conductivities below 0.5 S/m the change in centre frequency does not influence the energy scattered from the deeper target. The selection of the center frequency thus influences the GPR measurements for the measurements performed over a highly-conducting soil

Realistic FDTD GPR antenna models optimized using a novel linear/nonlinear Full-Waveform Inversion

Finite-Difference Time-Domain (FDTD) modelling of Ground Penetrating Radar (GPR) is becoming regularly used in model-based interpretation methods like full waveform inversion (FWI), and machine learning schemes using synthetic training data. Oversimplifications in such forward models can compromise the accuracy and realism with which real GPR responses can be simulated, and this degrades the overall performance of the aforementioned interpretation techniques. Therefore, a forward model must be able to accurately simulate every part of the GPR problem that can affect the resulting scattered field. A key element is the antenna system and excitation waveform, so the model must contain a complete description of the antenna including the excitation source and waveform, the geometry, and the dielectric properties of materials in the antenna. The challenge is that some of these parameters are not known or easily measured, especially for commercial GPR antennas that are used in practice. We present a novel hybrid linear/non-linear FWI approach which can be used, with only knowledge of the basic antenna geometry, to simultaneously optimise the dielectric properties and excitation waveform of the antenna, and minimise the error between real and synthetic data. The accuracy and stability of our proposed methodology is demonstrated by successfully modelling a Geophysical Survey Systems (GSSI) Inc. 1.5~GHz commercial antenna. Our framework allows accurate models of GPR antennas to be developed without requiring detailed knowledge of every component in the antenna. This is significant because it allows commercial GPR antennas, regularly used in GPR surveys, to be more readily simulated

FDTD simulations of multiple GPR systems

A multiple-GPR detection system was simulated. The main advantage of such a system was that it saves time by detecting both the transverse and the longitudinal positions of the target by a B-scan measurement, whereas the same detection can be achieved by a C-scan with a single-GPR system. Finite-domain time-difference (FDTD) method was employed to perform the simulations, in which the ground was homogeneous and the target was perfectly conducting