Ground Penetrating Radar Applications Research Articles

GPR Application on Geothermal Studies: The Case Study of the Thermal Baths of San Xusto (Pontevedra, Spain)

Geophysical studies are frequently used on the geothermal field to define and characterize deep structures. However, shallow investigations are also needed for understanding the origin and local potential structures of a promising geothermal site. In this research, it is intended to present a review of the possibilities of the application of ground-penetrating radar (GPR) on the study of geothermal resources and how this geophysical technique can contribute to improving the energy use of these thermal resources. For this, the specific case of application to the investigation of the thermal baths of San Xusto (Pontevedra, Spain) is included in this work, whose interest for the region makes it necessary to perform an in-depth analysis of the original thermal structure. A GPR survey with frequency antennas of 200 and 500 MHz was conducted. Additionally, chemical analyses were performed to characterize the thermal water in the San Xusto site. As a result, a hot spring was detected by identifying reverberation phenomena in GPR imaging due to the presence of metal compounds and silica. Locating the origin of the thermal springs could allow for a more efficient use of the thermal resources as well as the hydrothermal possibilities of the area.

Assessment of ballast layer under multiple field conditions in China

Ballast layer condition should be more regularly and accurately inspected to ensure safe train operation; however, traditional inspection methods cannot sufficiently fulfil this task. This paper presents a method of ground penetrating radar (GPR) application to reflect ballast layer fouling levels under diverse field conditions (annual gross passing load, cleaning and renewal year, fouling composition and transportation type). The results show that the GPR-based inspection method can assess the ballast layer fouling level with a 1–7% difference from the traditional sieving results. Fouling composition (especially metal materials) has a great effect on the GPR signals, thus affecting the inspection accuracy of ballast layer fouling level. Developing diverse GPR-based fouling indicators (by distinguishing different GPR signal features) can improve the GPR inspection applicability to the diverse field conditions.

Parameter Inversion by a Modified Reflected Signal Reconstruction Method for Thin-Layered Media

Parameter estimation of layered media is an important application of ground penetrating radar (GPR). However, in the case of thin-layer detection, the limitation of GPR vertical resolution can lead to overlapping reflected signals, which seriously deteriorates the detection results. To solve this problem, a modified reflected signal reconstruction method based on reflected signal reconstruction is proposed in this letter. First, a forward model of the GPR reflected signal is constructed using the generalized reflection coefficient definition. Then, the parameter inversion is transformed into an optimization problem. The residue cost function is defined as the error square between the model and the actual reflected signal, which is minimized by using genetic algorithm. Furthermore, the generalized reflection coefficient spectrum is feasible to estimate the parameters of each layer as the initial values of the parameters required by the algorithm, thus improving the accuracy and convergence speed of the algorithm. Numerical, experimental, and field tests demonstrate that the method has a high time resolution and antinoise capability in the inversion of layered media parameters.

A 1‐bit reconfigurable metasurface antenna for ground penetrating radar application

A 1-bit reconfigurable metasurface antenna for Ground penetrating radar (GPR) application is proposed. The element is loaded with one PIN diode, which can be electronically controlled to generate two states with 200° reflection phase difference at 2.0 GHz. The two states are regarded as “1” and “0.” Based on the proposed element, a 10 × 10 reconfigurable metasurface is designed. Besides, a digital control board is used to control the state of element. A reconfigurable metasurface antenna is simulated and fabricated. The simulated and experimented results indicate that the proposed antenna can achieve ±40° beam scanning with a gain tolerance of 3 dB and the maximum gain of 16.7 dBi. In addition, the beam-forming performance can be achieved, such as multibeam. These properties ensure the proposed antenna has great potential in GPR and microwave imaging systems.

Application of Ground Penetrating Radar in Monitoring Land Subsidence

Application of Ground Penetrating Radar in Monitoring Land Subsidence

State-of-the-Art Review of Ground Penetrating Radar (GPR) Applications for Railway Ballast Inspection

In the past 20 years, many studies have been performed on ballast layer inspection and condition evaluation with ground penetrating radar (GPR). GPR is a non-destructive means that can reflect the ballast layer condition (fouling, moisture) by analysing the received signal variation. Even though GPR detection/inspection for ballast layers has become mature, some challenges still need to be stressed and solved, e.g., GPR indicator (for reflecting fouling level) development, quantitative evaluation for ballast fouling levels under diverse field conditions, rapid GPR inspection, and combining analysis of GPR results with other data (e.g., track stiffness, rail acceleration, etc.). Therefore, this paper summarised earlier studies on GPR application for ballast layer condition evaluation. How the GPR was used in the earlier studies was classified and discussed. In addition, how to correlate GPR results with ballast fouling level was also examined. Based on the summary, future developments can be seen, which is helpful for supplementing standards of ballast layer evaluation and maintenance.

Asymmetrical Coplanar Vivaldi Antenna Design

In recent years, studies about miniaturization of wideband antennas had become popular with rapid development of antenna design technologies. Vivaldi antenna is one of these antennas which can be used in different areas such as microwave imaging, antenna arrays, ground penetrating radar applications. In this paper it is intended to approach with a novel method to reduce dimensions of Vivaldi Antennas because of its advantages such as simple configuration, wide bandwidth characteristics, low profile and low cost at fabrication process. Unlike traditional forms of Vivaldi Antennas it is used asymmetrical curves in this study. These curves have a different exponential coefficient to make the antenna have an asymmetrical shape. In this study the simulation results of the designed structure and a Coplanar Vivaldi Antenna were compared and the designed antenna showed similar characteristics. To verify the results a prototype of the Asymmetrical Vivaldi Antenna was fabricated on FR4 substrate with 4.6 dielectric constant. Measurement results illustrated that return loss of the designed antenna is below -10dB between 0.177GHz and 2.74GHz frequencies and the antenna have 93% fractional bandwidth. The measurement results match simulation results. Wideband frequency range, simple configuration andreduced dimensions make the designed antenna a good candidate for wideband antenna applications in future.

Ultrawide band cage dipole antenna for ultra high frequency band ground penetrating radar system

This paper presents ultrawide band (UWB) Cage Dipole Antenna, designed and developed for ultra high frequency band ground penetrating radar (GPR) system. The presented cage antenna consists of two thick diverging cages composed of 10 cylindrical metallic rods. It operates at 500 MHz center frequency and provides 105% impedance bandwidth for |S11| <−10 dB. Antenna has donut-shaped radiation pattern and provides 2.6-dBi gain at center frequency. Impedance variation of designed Cage dipole antenna has been matched using wideband lumped component-based balanced to unbalanced (Balun) network. Integrated analysis of cage dipole antenna and Balun network has been carried out in 3D electromagnetic simulator and analyzed results are presented. Moreover, metallic mount with Teflon bush has been designed to support the cage dipole antenna during far-field characterization and its effect has also been taken into account during the analysis. Time-domain analysis of proposed Cage dipole has been carried out and its results are presented in detail. Presented cage dipole antenna provides suppressed late ringing, making it best suitable for GPR applications.

A GPR-Based Test Study on the Influencing Factors of the Dielectric Constant of Cement-Stabilized Macadam Bases

Dielectric constant is an important parameter for the nondestructive test of cement stabilized macadam base (CSMB) on road by ground-penetrating radar (GPR). However, few studies have been reported on the quantitative relationship between the dielectric constant and the compaction degree, strength indicators, and influencing factors of CSMB. To address the problem, groups of CSMB specimens, which were different in gradation of aggregate (fine or coarse), compaction degree, and curing time, were made and tested for dielectric constant and influencing factors with the help of the Swedish MALA GPR. The relationship between the dielectric constant of CSMB and the influencing factors such as the compaction degree, moisture content, percent residues of aggregate on the sieve of maximum particle size and curing age, and the relationship between the dielectric constant and the unconfined compressive strength were investigated based on several test data and theoretical analysis. The major findings are as follows. There is a good logarithmic correlation between the dielectric constant and the compaction degree of CSMB, and quantitative functions have been established. There is a good linear relationship between the dielectric constant and the unconfined compressive strength of CSMB, and quantitative functions have been established. A comprehensive equation between the dielectric constant of CSMB and the influencing factors such as the compaction degree, moisture content, percent residues of aggregate on the sieve of maximum particle size, and curing age has been established and validated with high significance and small error. The findings are a theoretical basis for the application of GPR to the test and quality assessment of CSMB on roads.

Optimizing GPR time‐zero adjustment and two‐way travel time wavelet measurements using a realistic three‐dimensional numerical model

ABSTRACTTime‐zero adjustment or the true ground surface for ground penetrating radar (GPR) applications is a very important aspect and an essential factor in order to position subsurface targets, especially those located at shallow depths, at their true position in depth. As the transmitted and received signals from GPR antennas are affected by the presence of different materials with varying electromagnetic properties, adjusting the time zero appropriately is important, but often not straightforward to position accurately. This paper uses a realistic three‐dimensional numerical model of a GPR transducer in order to examine where is the best location for time zero on a GPR trace. It is shown that, in order to establish a robust and consistent time‐zero position, careful consideration is also needed around how the two‐way travel time of the reflected GPR wavelet is estimated. Starting with a simple homogeneous model with a set of different targets, a better process of time‐zero adjustment and time picking of the GPR wavelets is put forward, that is verified using further more complex and realistic heterogeneous models. Further verification is obtained by using experimental data.

GPR application for the characterization of sinkholes in Teresina, Brazil

The town of Teresina, in the state of Piauí, Brazil, presents a history of land sinking processes. Two sinking events deserve to be highlighted, the first occurred in 1999 at Simplício Mendes Street and the other occurred on July 31, 2008, at Francisco Mendes Street. To identify possible shallow caves and associated structures, the Geological Survey of Brazil/CPRM developed a Ground Penetrating Radar (GPR) study to verify the occurrence of reflection patterns characteristic of these dissolution structures. In the field, the team conducted GPR sections along streets with a history of collapse. The GPR results obtained with shielded antennas of 200 MHz allowed the identification of old areas of collapse of the terrain, to a maximum depth of 3 m. In addition, the results obtained by this study show the potential of applying the GPR method in the characterization of the subsoil of paved streets, making it possible to identify various layers: asphalt, actual pavement, subgrade pavement, soil, saprolite, and mixed material. The high clay content of the subsoil does not allow the GPR to investigate further depths in the research area. The interpretation of aero-magnetometric data shows that the occurrence of sinkholes is associated with magnetic lineaments mainly in the NW–SE direction and enhances the understanding of the structural framework of the study area.

Construction waste landfill volume estimation using ground penetrating radar.

Underground landfill, the primary disposal method of construction waste in several areas, negatively affects the surrounding environments. Suitably locating and estimating waste volume in an underground landfill are vital for adequate disposal and recycling of construction wastes. In this study, we investigated the applicability of ground penetrating radar (GPR) technology to estimate waste depth and volume of a construction waste landfill. The results revealed the following. (1) The GPR technology effectively delineated boundaries between underground waste and the surrounding strata; the topographic structure obtained from the analysis of the associated images was consistent with the actual topography. (2) Layer information from GPR images and electromagnetic wave velocity calculated using the complex refractive index model for construction waste burial depth inversion produced highly accurate results. Waste depth in the landfill was estimated using the GPR inversion results and spatial interpolation. Kriging interpolation exhibited the highest accuracy. (3) The trapezoid, Simpson and Simpson 3/8 rules were suitable for estimating construction waste volume. A three-dimensional model created using the spatial interpolation grid precisely depicted the structure of the buried landfill. Our study provides references for the management, recycling and environmental impact assessment of construction waste.

Super UWB Grooved and Corrugated Antenna for GPR Application

A novel super Ultra-Wideband (UWB) monopole antenna for Ground Penetrating Radar (GPR) application is investigated in this paper. The designed antenna is constructed by a grooved elliptical patch and a corrugated semi-elliptical ground plane. The designed antenna is fabricated on the FR4-substrate that has a compact size of 0.195 λ0 × 0.1625 λ0 × 0.00975 λ0 at 1.95 GHz. The measurements are performed by using a well calibrated R&amp;S®ZNB Vector Network Analyzer. The measured results show that the fabricated prototype covers a super UWB extending from 1.95 GHz to upper than 20 GHz (&gt;164.46 %). Additionally, the voltage standing wave ratio (VSWR) and the gain responses of the antenna are simulated in close proximity to a dry/wet sand box to verify the penetration ability of the antenna. The results are acceptable which guarantee the aptitude of this antenna to operate as a GPR antenna.

Circularly polarized quasi-rectangular patch UWB antenna for GPR applications

In this paper, a Circularly Polarized (CP) rectangular patch Ultra-Wideband (UWB) antenna is presented for Ground Penetrating Radar (GPR) applications. The designed geometry is constructed of a quasi-rectangular radiator and a partial ground plane. It is printed on the low-cost FR-4 substrate that has a compact size of 25?30?1.5 mm3. The calculated Impedance Bandwidth (IBW) of the proposed CP quasi-rectangular patch antenna is spanning from 3.16 GHz to 13.7 GHz (125.03%). Moreover, the measured IBW of the fabricated prototype is spanning from 3.2 GHz to greater than 14 GHz (&gt;125.58%) which covers the entire UWB range. Besides, the designed antenna reveals a wide Axial Ratio Band-Width (ARBW) extending from 4.23 GHz to 7.02 GHz (49.6%). Therefore, stable radiation patterns with an agreeable peak gain and high radiation efficiency are simulated over the whole working bandwidth.

Learning to Remove Clutter in Real-World GPR Images Using Hybrid Data

The clutter in the ground-penetrating radar (GPR) radargram disguises or distorts subsurface target responses, which severely affects the accuracy of target detection and identification. Existing clutter removal methods either leave residual clutter or deform target responses when facing complex and irregular clutter in the real-world radargram. To tackle the challenge of clutter removal in real scenarios, a clutter-removal neural network (CR-Net) trained on a large-scale hybrid dataset is presented in this study. The CR-Net integrates residual dense blocks into the U-Net architecture to enhance its capability in clutter suppression and target reflection restoration. The combination of the mean absolute error (MAE) loss and the multi-scale structural similarity (MS-SSIM) loss is used to effectively drive the optimization of the network. To train the proposed CR-Net to remove complex and diverse clutter in real-world radargrams, the first large-scale hybrid dataset named CLT-GPR dataset containing clutter collected by different GPR systems in multiple scenarios is built. The CLT-GPR dataset significantly improves the generalizability of the network to remove clutter in real-world GPR radargrams. Extensive experimental results demonstrate that the CR-Net achieves superior performance over existing methods in removing clutter and restoring target responses in diverse real-world scenarios. Moreover, the CR-Net with its end-to-end design does not require manual parameter tuning, making it highly suitable for automatically producing clutter-free radargrams in GPR applications. The CLT-GPR dataset and the code implemented in the paper can be found at https://haihan-sun.github.io/GPR.html.

Design of a Circular Patch Antenna with a reflector for GPR applications

In this paper, a structure of a patch antenna operating at 0.5 GHz is proposed for ground-penetrating radar (GPR) applications, with an optimized performance at low frequencies. The structure was designed using FR4 substrate, with a 4.4 permittivity value, and a tangent loss equivalent to 0.021. The prototype design is backed by an optimized rectangular reflector, which has improved the antenna gain and directivity. The performance of the antenna is evaluated in terms of the return loss, gain, and the radiation pattern for two cases, with and without a reflector. When using the reflector, a good radiation pattern is obtained, a wide operational bandwidth ranging from 0.4GHz and 1.25 GHz is achieved, and an increased gain from 4.3 to 7.43dB was realized.

Artifacts Suppression Using Correlation-Weighted Back Projection Imaging Algorithm for Chaotic GPR

A correlation weighted back projection (CWBP) imaging algorithm is proposed to suppress artifacts introduced by the classic back projection (BP) algorithm in the application of chaotic ground-penetrating radar (GPR). In the proposed CWBP algorithm, the backscattering response to each point in the imaging region is first reconstructed through the weighting, which is used to highlight the backscattering response of targets. Then the quadratic cross correlation is calculated to reduce the nontargets’ backscattering. The experimental results show that the artifacts are significantly suppressed. In addition, the ghosts generated by overlapped of multitargets artifacts in the classic BP are removed. Our results also show that the proposed CWBP can be applied for the stepped frequency continuous wave radar.

The Orientation Estimation of Elongated Underground Objects via Multipolarization Aggregation and Selection Neural Network

The horizontal orientation angle and the vertical inclination angle of an elongated subsurface object are key parameters for object identification and imaging in ground-penetrating radar (GPR) applications. Conventional methods can only extract the horizontal orientation angle or estimate both angles in narrow ranges due to limited polarimetric information and detection capability. To address these issues, this letter, for the first time, explores the possibility of leveraging neural networks with multipolarimetric GPR data to estimate both angles of an elongated subsurface object in the entire spatial range. Based on the polarization-sensitive characteristic of an elongated object, we propose a multipolarization aggregation and selection network (MASNet), which takes the multipolarimetric radargrams as inputs, integrates their characteristics in the feature space, and selects discriminative features of reflected signal patterns for accurate orientation estimation. Numerical results show that our proposed MASNet achieves high estimation accuracy with an angle estimation error of less than 5°. The promising results obtained by the proposed method encourage one to think of new solutions for GPR-related tasks by integrating multipolarization information with deep learning techniques. The data and code implemented in the letter can be found at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://haihan-sun.github.io/GPR.html</uri> .

Recent Advances in the GPR Detection of Grouting Defects behind Shield Tunnel Segments

Injecting grout into the gaps between tunnel shield segments and surrounding rocks can reduce ground subsidence and prevent ground water penetration. However, insufficient grouting and grouting defects may cause serious geological disasters. Ground penetrating radar (GPR) is widely used as a nondestructive testing (NDT) method to evaluate grouting quality and determine the existence of defects. This paper provides an overview of GPR applications for grouting defect detection behind tunnel shield segments. State-of-the-art methodologies, field cases, experimental tests and signal processing methods are discussed. The reported field cases and model test results show that GPR can detect grouting defects behind shield tunnel segments by identifying reflected waves. However, some subsequent problems still exist, including the interference of steel bars and small differences in the dielectric constants among media. Recent studies have focused on enhancing the signal-to-noise ratio and imaging methods. Advanced GPR signal processing methods, including full waveform inversion and machine learning methods, are promising for detecting imaging defects. Additionally, we conduct a preliminary experiment to investigate environmental noise, antenna configuration and coupling condition influences. Some promising topics, including multichannel configuration, rapid evaluation methods, elastic wave method scanning equipment for evaluating grout quality and comprehensive NDT methods, are recommended for future studies.

A Wideband Reflector-Backed Antenna for Applications in GPR

A resistively loaded wideband slotted patch antenna with optimized performance on lower frequencies is proposed for ground-penetrating radar (GPR) applications. The proposed design is backed by an optimized reflector composed of a periodic array of square loop elements, which enhances the antenna’s gain and directivity. The antenna shows good radiation characteristics and ease of integration with the GPR systems. The proposed structure features a compact size and wide bandwidth covering from 0.6 to 4.6 GHz. The peak gain of 7 dBi is achieved. The fabricated prototype of the antenna along with an integrated optimized reflective surface has overall dimensions of 18 × 22 × 5 cm3. The measured results validate the antenna’s performance in both free space and sandy medium, which enlighten its use for GPR applications.