Ground Penetrating Radar Scenarios Research Articles

An Efficient Full Wave Model for Investigating Layered Media Using Bi-Static Ground Penetrating Radar

Ground penetrating radar (GPR) is a popular non-destructive sensor for subsurface media investigation. Modelling of the GPR system has a significant role in the successful estimation of sub-surface media properties, imaging, and detection of buried object. A model should provide good accuracy and computational efficiency while taking care of numerous GPR scenarios. However, achieving accuracy and speed of computation is a difficult task. In this respect, analytical modellings are promising techniques to represent a specific GPR scenario. In this work, a simplified full wave model (FWM) for bi-static GPR has been developed to represent radar transceivers with layered media. The model has been derived from an existing full wave model (FWM) solution. The accuracy of the proposed model has been verified by comparing it with existing FWMs, and by laboratory experiments based on stepped frequency continuous wave (SFCW) GPR. The corresponding results show that the proposed bi-static model is as accurate as FWM and its computational efficiency is enormous in estimating the sub-surface media properties.

Efficacious GPR Implementations of Z-Transform-Based Hybrid LOD-FDTD with Subgridding Scheme: Theoretical Formalism and Numerical Study

Ground penetrating radar (GPR) forward modeling is one of the core geophysical research topics and also the primary task of simulating ground penetrating radar system. It is a process of simulating the propagation laws and characteristics of electromagnetic waves in simulated space when the distribution of internal parameters in the exploration region is known. And the finite-difference-time-domain (FDTD) method has the characteristics of simulating the space-time transient evolution of electromagnetic wave, whose numerical method is simple and easy to program, so it has become one of the most extensively utilized methods in GPR forward modeling. It is generally known that the conventional FDTD approach requires finer uniform Yee cell all the time to produce satisfactory accuracies from numerical simulations of the GPR. However, the smaller temporal incremental has to be adopted due to the lower spatial incremental, which would dramatically weaken the advantage of the FDTD method. To solve this issue, the subgridding-technique-based hybrid local-one-dimensional FDTD (LOD-FDTD) is applied in this work to modeling the classical GPR scenarios. In this method, the unconditional-stable LOD-FDTD is employed in the fine-grid domain, while the traditional FDTD is used in the coarse-grid domain, which could avoid the oversampling problem in the local domain if the uniform fine-grid scheme is adopted. Meanwhile due to the unconditional stability of the LOD-FDTD, the larger time step, derived from the coarse grid which satisfies the Courant-Friedrichs-Lewy (CFL) stability condition, could be utilized in the whole domain so that the long-time interpolation process could be circumvented. Additionally, the proposed approach could be arbitrarily adjusted by means of different ratio of both coarse- and fine-grid, and hence it holds much higher generality. As compared with the auxiliary differential equation (ADE) technique, the Z-transform method is integrated into FDTD methods for modeling multi-pole Debye-based dispersive media in this method, resulting in more direct numerical implementations and fewer computing steps. Finally, three different classical GPR problems are carried out to validate accuracies and efficiencies of the proposed method.

Hybrid sub-gridded ADE-FDTD method for modeling ground-penetrating radar on dispersive soils

Based on the sub-gridding scheme, a hybrid method with explicit finite-difference time-domain (FDTD) and implicit Crank–Nicolson (CN) FDTD is presented for ground-penetrating radar (GPR) simulations on dispersive and conductive soils in this paper. The time step of CN-FDTD can be set to a large value so that the whole region can be run with a common time step determined by the coarse grid in a stable fashion. The missing information in the sub-gridded border region is obtained with an interpolation in space. The dispersion of the soil is modeled by a multi-pole Debye model and is solved with auxiliary differential equations (ADEs) for both FDTD and CN-FDTD. Additionally, examples of the GPR scenario are calculated to verify the accuracy and efficiency of the hybrid sub-gridded ADE-FDTD method.

Hybrid Sub-Gridded Time-Domain Method for Ground Penetrating Radar Simulations Including Dispersive Materials

Based on the explicit finite-difference time-domain (FDTD) and implicit Crank–Nicolson (CN) FDTD methods, this paper presents a hybrid sub-gridded scheme whose time step size depends on the coarse grid size for numerically simulating the 3-D ground penetrating radar (GPR) scenarios in lossy, dispersive, and inhomogeneous soils. The time step size of CN-FDTD is independent of the grid size in the dense grid region due to its unconditional stability. Thus, the whole region can be run with a time step size determined by the coarse grid in an absolutely stable fashion. Moreover, a multi-pole Debye dispersion model, solved with auxiliary differential equations (ADEs) for both FDTD and CN-FDTD, is incorporated to simulate realistic GPR scenarios, including the detection of different objects buried in dispersive soils. In order to reduce the matrix size of the 3-D implicit CN-FDTD method, the domain decomposition technique is originally employed to achieve fast calculation. Several numerical examples of the GPR scenarios are provided to demonstrate the accuracy and efficiency of the hybrid sub-gridded ADE-FDTD method.

Subgridded FDTD Modeling of Ground Penetrating Radar Scenarios Beyond the Courant Stability Limit

This paper presents an efficient 3-D finite-difference time-domain (FDTD) subgridding scheme that is free of the Courant-Friedrichs-Lewy stability condition, for the modeling of ground-penetrating radar (GPR) scenarios in lossy dispersive media. Spatial filtering of FDTD fields within the subgrid is employed to render the time step independent of the cell size in the fine-cell subgrids. This process is applied with minimal modification of the original FDTD code, no implicit operations, and very modest computational overhead. Moreover, multiterm dispersion is included to model practical GPR scenarios involving the detection of realistic scatterers within dispersive soil. Several numerical examples are provided to demonstrate the potential of the proposed method as a powerful GPR modeling tool.

Resistive Loaded Antenna for Ground Penetrating Radar Inside a Bottom Hole Assembly

Resistive loaded antennas are widely used in ground penetrating radar scenarios due to their good pulse radiation behavior and small size. Despite these facts their implementation into an antenna housing with absorber material and shielding leads to a quite cumbersome ground penetrating radar component not suitable for integration into a bottom hole assembly (BHA). Furthermore, the metallic bottom hole assembly influences the pulse radiation behavior in a negative way. This article describes an antenna design optimized for integration into a bottom hole assembly, incorporating simulation and measurement. As a result, ground penetrating radar usage may now be extended to the field of logging/measuring while drilling, maximizing the information about the surrounding media during the drilling process.

Discretization of the CFS‐PML for computational electromagnetics using discrete differential forms

AbstractA new numerical discretization of the complex frequency shifted‐perfectly matched layer (CFS‐PML) is presented for truncation of open domains. This discretization is based on the theory of discrete differential forms applied to electromagnetism, which guarantees both the simplification of the algorithms and a more elegant formulation of expression. The curl Maxwell's equations are solved in time domain in terms of electric e magnetic fields. The Ampere‐Maxwell law with, the constitutive relations included through the Hodge operator, is discretized in space by applying the Galerkin method. Conversely, the Faraday law is represented by topological relations via incidence matrix. The time domain discretization uses the leap‐frog scheme with a recursive convolution inside PML region. Two examples are shown, the first one to validate the CFS‐PML procedure and the second one to solve a typical ground penetrating radar scenario which include a lossy media. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:351–357, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27298

Sparse Reconstruction From GPR Data With Applications to Rebar Detection

The problem of detecting and localizing 2-D thin scatterers (i.e., elongated scatterers whose cross sections are small in terms of the probing wavelength) from scattered field measurements is considered. To this end, a linear model that neglects mutual scattering and is based on a distributional representation of the unknown is established. An improved imaging technique based on a minimization algorithm, which takes advantage of the inherent sparseness of the considered ground-penetrating radar scenario, is presented and compared to a classical migration algorithm. The comparison is achieved for both synthetically generated and experimental data collected in realistic conditions under a multimonostatic/multifrequency configuration.

Early-stage leaking pipes GPR monitoring via microwave tomographic inversion

Ground penetrating radar (GPR) is one of the most suitable technological solutions for timely detection of damage and leakage from pipelines, an issue of extreme importance both environmentally and from an economic perspective. However, for GPR to be effective, there is the need of designing appropriate imaging strategies such to provide reliable information. In this paper, we address the problem of imaging leaking pipes from single-fold, multi-receiver GPR data by means of a novel microwave tomographic method based on a 2D “distorted” scattering model which incorporates the available knowledge on the investigated scenario (i.e., pipe position and size). In order to properly design the features of the approach and test its capabilities in controlled but realistic conditions, we exploit an advanced, full-wave, 2.5D Finite-Difference Time-Domain forward modeling solver capable of accurately simulating real-world GPR scenarios in electromagnetically dispersive materials. By means of this latter approach, we show that the imaging procedure is reliable, allows us to detect the presence of a leakage already in its first stages of development, is robust against uncertainties and provides information which cannot be inferred from raw-data radargrams or “conventional” tomographic methods based on a half-space background.

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

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 two identical transmitters, which are fed 180/spl deg/ 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.