Ultra-wideband Ground Penetrating Radar Research Articles

Full-Wave Modeling and Inversion of UWB Radar Data for Wave Propagation in Cylindrical Objects

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.

GPR Monitoring of Artificial Debonded Pavement Structures throughout Its Life Cycle during Accelerated Pavement Testing

The paper gives an overview of a ground penetrating radar (GPR) experiment to survey debonding areas within pavement structure during accelerated pavement tests (APT) conducted on the university Gustave Eiffel’s fatigue carrousel. Thirteen artificial defect sections composed of three types of defects (Tack-free, Geotextile, and Sand-based) were embedded during the construction phase between the top and the base layers. The data were collected in two stages covering the entire life cycle of the pavement structure using four GPR systems: An air-coupled ultra-wideband GPR (SF-GPR), two wideband 2D ground coupled GPRs (a SIR-4000 with a 1.5 GHz antenna and a 2.6 GHz-StructureScan from GSSI manufacturer), and a wideband 3D GPR (from 3D-radar manufacturer). The first stage of the experiments took place in 2012–2013 and lasted up to 300 K loadings. During this stage, the pavement structure presented no clear degradation. The second stage of experiments was conducted in 2019 and continued until the pavement surface demonstrated a strong degradation, which was observed at 800 K loadings. At the end of the GPR experiments, several trenches were cut at various sections to get the ground truth of the pavement structure. Finally, the GPR data are processed using the conventional amplitude ratio test to study the evolution of the echoes coming from the debonded areas.

Integrated synchronous data acquisition subsystem for high‐speed GPR system

In this study, an integrated synchronous data acquisition subsystem for high-speed dual-channel ultra-wideband ground penetrating radar (GPR) system is designed and tested. Factors that could cause data missing and asynchronisation are analyzed. According to timing sequence, a field-programmable gate array-based onboard digital control module is integrated to synchronise the data acquisition and data storage subsystems. By applying simultaneous multi-buffer acquisition and readout mode and multi-threading configuration, as well as the critical section control and queue storage structure, the GPR data throughput is considerably improved. For the practicality of this system, a smart End-of-Job control design is performed between different threads to control data acquisition. By using different performance indexes, receiver operation characteristic curve, maximum scan rate, and the rebar detection experiment demonstrate the superiority of author's method.

GPR Image Enhancement Based on Frequency Shifting and Histogram Dissimilarity

In the ground-penetrating radar (GPR) B-scan images, various noise sources are superimposed due to the ruggedness of the surface, sensor vibration, and multiple reflections. Additionally, the intensity of the received signals from small-size or low-metal-content landmines is low. Thus, it is difficult to accurately detect buried mines. In this letter, we propose an effective method to improve the B-scan image so that accurate landmine detection is possible even in such conditions. The proposed B-scan image enhancement method is comprised of two main techniques: an A-scan transformation based on frequency shifting and a background-landmine dissimilarity measurement using cumulative intensity distribution (CID). Based on frequency shifting, an A-scan transformation is devised to attenuate the strong ac component contained by the received A-scan signal. The CID-based dissimilarity is introduced to measure how an A-scan differs from a background model in the presence of a landmine. The proposed dissimilarity measure provides a robust response to a rugged ground surface and sensor vibration. For performance analysis, we compared our method with some conventional methods using the GPR data set acquired by an ultra wide band GPR sensor manufactured by Hanwha Systems Co., Ltd. We carried out various experiments and verified that the proposed method has a better performance than the conventional methods.

Potentialities of ultrawideband GPR in low-resistivity geoenvironments

We assess the potentia4lities of ultrawideband (UWB) electromagnetic pulse sounding of low-resistivity geoenvironments using the ground-penetrating radar (GPR) system developed by us and compare the obtained results with 2D electrical resistivity tomography and standard GPR data. The research was performed in an area of Quaternary clay deposits with a resistivity of 20-50 Ohmm. For an OKO-2 GPR antenna with a center frequency of 150 MHz, the sounding depth is 2-4 m, whereas UWB sounding provides penetration of the GPR pulse to a depth of 30-40 m. Deep UWB sounding of low-resistivity environments is possible under the following conditions: use of generators based on drift step recovery diodes (DSRDs), high matching of the UWB receiving and transmitting antennas to the environment, and an increase in the noise immunity of the recording system, in particular, due to a decrease in the intensity of air waves.

Simulation and imaging using ultrawideband ground penetrating radar and finite-difference time-domain method

The whole electromagnetic field simulation model of the near-field ultrawideband ground penetrating radar imaging is established using the two-dimensional finite-difference time-domain method. According to the back-projection method, this paper focuses on the underground target imaging. The feasibility of the technology for underground target imaging is confirmed by specific examples. Some problems existing in imaging are also discussed. The result shows that the correction of electromagnetic wave propagation time is the basis of obtaining right and clear imaging. In addition, the underground target, which is close to the transmitting and receiving antenna, costs less electromagnetic wave energy, as long as the underground target is detected. The whole process can make the image more clear. (C) 2017 SPIE and IS&T

Monostatic ultra-wideband GPR antenna for through wall detection

The aim of this paper is to present a monostatic arc-shaped ultra-wideband (UWB) printed monopole antenna system with 3-16 GHz frequency bandwidth suitable for through-wall detection. Ground penetrating radar (GPR) technique is used for detection with the gain of 6.2 dB achieved for the proposed antenna using defected ground structure (DGS) method. To serve the purpose, a simulation experiment of through-wall detection model is constructed which consists of a monostatic antenna act as transmitter and receiver, concrete wall and human skin model. The time domain reflection of obtained result is then analysed for target detection.

Ultra-Wideband Antenna Design for GPR Applications: A Review

This paper presents a comparative review study on ultra-wideband (UWB) antenna technology for Ground Penetrating Radar (GPR) applications. The proposed antenna designs for UWB ground penetrating radar include a bow-tie antennas, Vivaldi antennas, horn antennas, planar antennas, tapered slot antennas, dipole antennas, and spiral antennas. Furthermore a comprehensive study in terms of operating frequency range, gain and impedance bandwidth on each antenna is performed in order to select a suitable antenna structure to analyze it for GPR systems. Based on the design comparison, the antenna with a significant gain and enhanced bandwidth has been selected for future perspective to examine the penetration depth and resolution imaging, simultaneously suitable for GPR detection applications. Three different types of antennas are chosen to be more suitable from the final comparison which includes Vivaldi, horn and tapered slot antennas. On further analysis a tapered slot antenna is a promising candidate as it has the ability to address the problems such as penetration depth and resolution imaging in GPR system due to its directional property, high gain and greater bandwidth operation, both in the lower and higher frequency range.

Supervised Automatic Detection of UWB Ground-Penetrating Radar Targets Using the Regression SSIM Measure

This letter introduces the concept of regression structural similarity index measure (regression SSIM) and builds a supervised graph framework of automatic detection of small-size ultrawideband (UWB) radar targets. The twofold contribution made in this letter includes the following: 1) The regression SSIM is proposed to measure the similarity of the local pattern between a test image and a reference image; and 2) the framework of a supervised graph, together with the regression SSIM, has been developed to address the automatic detection of UWB radar objects. As opposed to other detection techniques reported in the literature, our methodology does not rely on statistical modeling or imposing typical shape parameters. Selected results of processing simulated and real UWB ground-penetrating radar data are provided, which verifies the state-of-the-art performance of the proposed methodology and provides important potential for a wide class of target detection.

Autofocusing of UWB MIMO GPR Images by Using MZO and Entropy Minimization

In this letter, an autofocusing method for ultra-wideband ground-penetrating radar imaging with multiple-input multiple-output (MIMO) configuration is proposed. The proposed method is based on the minimization of the entropy of the images that have been migrated by frequency-wavenumber migration. A particular migration to zero-offset (MZO) operator is applied to reduce the processing complexity for MIMO data. The results on the simulation data show that the computation time of the autofocusing process is reduced significantly with the MZO operator, while some advantages of the MIMO configuration are successfully preserved.

Detection of Implanted Devices In Underground By Using UWB Penetrating Radar with Support of PN Code

Ground Penetrating Radar (GPR) is a method for estimation of underground structures by sending and receiving electromagnetic. With Ultra Wideband (UWB) signal, GPR is expected to improve resolution for detection of objects in underground. But there are problems that attenuation of waves from deep objects and confusion of waves from different objects. We propose a signal processing for UWB GPR to improve detection accuracy by applying interference cancellation technique for wireless communication. To obtain gains, we use a long transmitting signal with PN codes remain in low instantaneous power. Then estimating and cancelling reflect waves from received signals, we detect objects recursively. Position estimation of medical implanted devices can be also improved by using the technique. With comparing GPR and medical devices, we study a signal processing for position estimation for objects in dielectric substances.

Non-Invasive Forest Litter Characterization Using Full-Wave Inversion of Microwave Radar Data

Litter is acknowledged to affect microwave remote sensing data over forests, and accurate quantification of litter radiative properties is essential for proper retrieval of forest soil water content and forest canopy biophysical characteristics from satellite or airborne sensors. Furthermore, detailed characterization of forest soil organic horizons is of paramount importance for ecological studies and for carbon cycle and global changerelated studies. Ultrawideband ground-penetrating radar (GPR) data acquired above beech forest litter were used to analyze the effects of litter on the backscattering and investigate the ability of GPR to quantitatively characterize the properties of the forest floor. Radar measurements were performed over different litter configurations (i.e., single layers of recently fallen litter (OL) or of fragmented litter (OF), and combined OL-OF layers) and thicknesses. Radar data were processed through full-wave inversion. Over the considered frequency range (0.8–4.0 GHz), attenuation of the radar signal increased as both frequency and litter thickness increase, due to scattering and dielectric losses. These effects were accounted for in the radar model through frequency dependence of litter apparent electrical conductivity. Good agreement(RMSE = 9.5 × 10−3 m) was observed between estimatedand measured litter thicknesses. Radar data inversions provided reliable estimates of litter electromagnetic properties, with relative dielectric permittivity values around 1.2 and 3.9 for OL and OF litters, respectively, and corresponding values of 0.032 and 0.080 Sm−1 for litter apparent electrical conductivity at 4.0 GHz. These results show great promise for the use of GPR for noninvasive characterization of forest litter.

Using polarization diversity in the detection of small discontinuities by an ultra-wide band ground-penetrating radar

A ground-penetrating radar (GPR) has been developed for civil engineering applications. Ultra-wide band (UWB) bowtie slot antennas operating at frequencies from 460MHz to beyond 4GHz have been designed to be integrated in a ground-penetrating radar (GPR) positioned very close to the soil surface. FDTD modeling has allowed to define the optimal geometrical parameters associated with the ground-coupled radar system that has been studied in two polarization configurations TE and TM. The ability of the GPR system in detecting small discontinuities using polarization diversity has been analyzed considering several buried canonical objects with different dielectric characteristics. Measurements in a sand box have been compared to full-wave simulations.

Buried Object Characterization Using Ultra-Wideband Ground Penetrating Radar

In this paper, a method to characterize buried nonmagnetic objects in ground using ultra-wideband (UWB) ground penetrating radar (GPR) is proposed. In this method, UWB pulses are radiated by the radar, while scattered signals from the ground with the buried object are received. The received signals are then post-processed to estimate the depth, thickness, and electrical properties of the buried object. A constant depth and thickness is enforced at all frequencies while the signals are processed to extract the buried object characteristics, resulting in more accurate estimations and reduced processing time. In addition, path loss due to the close proximity of the radar to the ground is compensated analytically. The applicability of the proposed method is validated with several planar objects and a boulder that we typically encounter in the construction industry. The proposed method can achieve sufficient reliability in estimating the permittivity of buried objects for the purpose of material identification. Incorporating the proposed method into the GPRs enhances their existing imaging ability by adding material identification capability.

Development of High-Speed Ultrawideband Ground-Penetrating Radar for Rebar Detection

This paper describes the development of new air-coupled ultrawideband ground-penetrating radar (GPR) for highway pavement and bridge deck inspections that can achieve high spatial resolution and high inspection performance while operating on vehicles driving at regular highway speeds. The major design features include dual-frequency band operation, 8 gigasamples per second high-speed real-time data acquisition, high-speed large volume data transmission and storage, and customized signal-processing algorithms for GPR image enhancement and feature extractions. For design validations, steel reinforcing bar detection experiments in various setups are conducted. The measurement results show good agreement with the subsurface feature configurations.

Accounting for soil surface roughness in the inversion of ultrawideband off-ground GPR signal for soil moisture retrieval

We combined a full-waveform ground-penetrating radar (GPR) model with a roughness model to retrieve surface soil moisture through signal inversion. The proposed approach was validated under laboratory conditions with measurements performed above a sand layer subjected to seven different water contents and four different surface roughness conditions. The radar measurements were performed in the frequency domain in the range of 1–3 GHz and the roughness amplitude standard deviation was varied from 0 to 1 cm. Two inversion strategies were investigated: (1) Full-waveform inversion using the correct model configuration, and (2) inversion focused on the surface reflection only. The roughness model provided a good description of the frequency-dependent roughness effect. For the full-waveform analysis, accounting for roughness permitted us to simultaneously retrieve water content and roughness amplitude. However, in this approach, information on soil layering was assumed to be known. For the surface reflection analysis, which is applicable under field conditions, accounting for roughness only enabled water content to be reconstructed, but with a root mean square error (RMS) in terms of water content of [Formula: see text] compared to an RMS of [Formula: see text] for an analysis where roughness is neglected. However, this inversion strategy required a priori information on soil surface roughness, estimated, e.g., from laser profiler measurements.

Development of a time–frequency approach to quantify railroad ballast fouling condition using ultra-wide band ground-penetrating radar data

This paper discusses the use of ground-penetrating radar (GPR) to assess railroad track substructure conditions. An ultra-wide band (UWB) GPR system, having a centre frequency at or higher than 2 GHz, can be used to detect the scattering pattern and to predict air void volume in railroad ballast. A time–frequency technique was implemented to characterise the signal in time and frequency domains simultaneously. Because electromagnetic energy attenuation is highly frequency dependent, the frequency sub-bands of the reflected UWB GPR signal can be analysed separately to quantify the fouling material and quantify moisture content. Additionally, to validate the GPR system capability, a ground truth field survey was conducted. Using ballast samples collected from the field for validation, this paper shows that a time–frequency analysis may provide a new method to measure the thickness of clean ballast, detect the trapped water and assess the ballast fouling and moisture content along the track.

Design of a resistively loaded vee dipole for ultrawide-band ground-penetrating Radar applications

A new resistively loaded vee dipole (RVD) is designed and implemented for ultrawide-band short-pulse ground-penetrating radar (GPR) applications. The new RVD is improved in terms of voltage standing wave ratio, gain, and front-to-back ratio while maintaining many advantages of the typical RVD, such as the ability to radiate a short-pulse into a small spot on the ground, a low radar cross section, applicability in an array, etc. The improvements are achieved by curving the arms and modifying the Wu-King loading profile. The curve and the loading profile are designed to decrease the reflection at the drive point of the antenna while increasing the forward gain. The new RVD is manufactured by printing the curved arms on a thin Kapton film and loading them with chip resistors, which approximate the continuous loading profile. The number of resistors is chosen such that the resonant frequency due to the resistor spacing occurs at a frequency higher than the operation bandwidth. The antenna and balun are made in a module by sandwiching them between two blocks of polystyrene foam, attaching a plastic support, and encasing the foam blocks in heat-sealable plastic. The antenna module is mechanically reliable without significant performance degradation. The use of the new RVD module in a GPR system is also demonstrated with an experiment.

Development of ground‐penetrating image radar using a novel compact ultra‐wideband monopole antenna

AbstractA compact ultra‐wideband ground‐penetrating radar (UWB GPR) using an impulse waveform is developed. A proper impulse generator is designed and then a novel compact UWB monopole antenna is developed for transmitting the impulse and receiving the reflected signals. For visualization of buried targets, image processing is performed. For verification, a UWB GPR prototype is built. The experimental results show that the system has very good depth and spatial resolution. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 521–524, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20522

Modeling and Investigation of a Geometrically Complex UWB GPR Antenna Using FDTD

A detailed analysis of ultrawide-band (UWB), dual-polarized, dielectric-loaded horn-fed bow-tie (HFB) antennas is carried out using the finite-difference time-domain (FDTD) method. The FDTD model includes realistic features of the antenna structure such as the feeding cables, wave launchers, dielectric loading, and resistive-film loading. Important antenna characteristics that are usually difficult to obtain via measurements can be obtained more directly from this FDTD model. Since the HFB antennas under consideration are intended for ground penetrating radar (GPR) applications, the effects of the half-space medium are also investigated. The simulated results serve to verify the performance of the HFB antenna design, and to optimize various antenna parameters.