Ground Penetrating Radar Antenna Research Articles

Thresholding Analysis and Feature Extraction from 3D Ground Penetrating Radar Data for Noninvasive Assessment of Peanut Yield

This study explores the efficacy of utilizing a novel ground penetrating radar (GPR) acquisition platform and data analysis methods to quantify peanut yield for breeding selection, agronomic research, and producer management and harvest applications. Sixty plots comprising different peanut market types were scanned with a multichannel, air-launched GPR antenna. Image thresholding analysis was performed on 3D GPR data from four of the channels to extract features that were correlated to peanut yield with the objective of developing a noninvasive high-throughput peanut phenotyping and yield-monitoring methodology. Plot-level GPR data were summarized using mean, standard deviation, sum, and the number of nonzero values (counts) below or above different percentile threshold values. Best results were obtained for data below the percentile threshold for mean, standard deviation and sum. Data both below and above the percentile threshold generated good correlations for count. Correlating individual GPR features to yield generated correlations of up to 39% explained variability, while combining GPR features in multiple linear regression models generated up to 51% explained variability. The correlations increased when regression models were developed separately for each peanut type. This research demonstrates that a systematic search of thresholding range, analysis window size, and data summary statistics is necessary for successful application of this type of analysis. The results also establish that thresholding analysis of GPR data is an appropriate methodology for noninvasive assessment of peanut yield, which could be further developed for high-throughput phenotyping and yield-monitoring, adding a new sensor and new capabilities to the growing set of digital agriculture technologies.

A Time-Domain Finite Difference Decomposition Method for Boulders in the Cultivated Layers Based on Ground-Penetrating Radar

Afinite difference time domain (FDTD) model of the electromagnetic wave of the two-dimensional Maxwell's discrete equation is established, based on the optimization of the Ground-penetrating radar (GPR) antenna frequency (recommended 100MHz), time window length, and sampling interval parameters. In our study, three test schemes are designed: The electromagnetic wave enters the boulder medium from the soil to have the first reflection (top reflection) when a boulder point appears in the homogeneous soil, and then passes through the boulder in the water and re-enters the soil. The secondary reflection (bottom reflection) is generated, and radar image interpretation shows that the size of the boulder is the same as the designed size (0.5m).Then, the interference phenomenon of the reflection waves of the two boulders can be simulated when two boulders appear in a homogeneous soil, and the spatial position and size of the two boulders can be distinguished. For the cultivated soil layer with obvious horizontal stratification, the upper soil layer does not affect the reflection of the boulder when the boulder is located in the lower layer, and the location and size of the boulder can still be accurately interpreted. Numerical test results show that the FDTD method is a very effective method to forward simulate the boulder phenomenon in the cultivated soil layer, which has the advantages of simple principle, high simulation accuracy and fast calculation speed.

Research and design of tripod-shaped UWB antenna for GPR

In recent years, GPR (Ground Penetrating Radar) has developed rapidly and has played an important role in many fields. As a key part of GPR, the antenna directly affects system performance. A suitable antenna can greatly improve the detection results. To this end, this paper introduces the design of GPR tripod-shaped ultra-wideband antenna based on bow tie antenna. The working bandwidth of the antenna is widened by means of structural loading with truncation as the main part and circular slot at the end of the antenna. Antenna optimization and simulation were performed using ANSYS HFSS (High Frequency Structure Simulator), and the effects of antenna arm truncation length on antenna performance were discussed. Simulation results show that the designed antenna has an operation bandwidth of 700MHz ~ 2GHz and good directionality. It is a miniaturized ultra-wideband antenna suitable for shallow underground pipeline detection.

Eliminating above-surface diffractions from ground-penetrating radar data using iterative Stolt migration

Above-surface diffractions (ASDs) received by unshielded ground-penetrating radar (GPR) antennas are known to contaminate subsurface reflections and diffractions. Existing ASD-removal methods either leave relatively strong residual ASDs within subsurface reflections or attenuate them excessively. We have developed an iterative migration-based ASD-removal method to address this issue that separates ASDs from subsurface reflections via surgical mute. First, we isolate ASDs within the GPR profile using an optimal window function, generated using the focal center of ASDs within the migrated domain. The remainder signifies the zeroth-order separation of subsurface reflections. Second, we perform Stolt migration on the isolated ASDs using the speed of light in air. Then, we mute out the regions dominated by ASDs from the migration results, characterized by highly focused ASDs that are well separated from the majority of subsurface reflections. Following that, we demigrate the separated ASDs and subsurface reflections back to the unmigrated domain using the speed of light in air. Next, we combine the demigrated subsurface reflections with the zeroth-order subsurface reflections, thereby completing the first iteration of the separation process. The entire aforementioned process is then repeated twice on the residual data to obtain further residual subsurface reflections from ASDs, using a lower velocity and a higher velocity in sequence. Our method is verified to suppress ASDs more effectively than existing approaches by retaining a greater proportion of subsurface reflections, and its residual error is negligible. It is robust with respect to energy levels, window widths of ASDs, and clustered ASDs.

Development of an Airborne-Based GPR System for Landmine and IED Detection: Antenna Analysis and Intercomparison

Airborne-based Ground Penetrating Radar (GPR) systems have proved to be an efficient solution for safe and accurate detection of buried threats such as Improvised Explosive Devices (IEDs) and anti-personnel and anti-tank landmines. The design of these prototypes is influenced by several parameters such as the working frequency band or the maximum weight and size of the payload to be placed on board the Unmanned Aerial Vehicle (UAV). In this sense, one of the main bottlenecks found in the design of these systems is the proper selection of the GPR antenna. This contribution focuses on the analysis of different Ultra Wideband (UWB) Vivaldi antennas and their performance in the context of an airborne-based GPR system. First, the Vivaldi antennas are characterized in terms of $S_{11}$ , radiation pattern, directivity, and phase center. Next, they are placed on board the implemented airborne-based GPR prototype to assess their impact on the detection capabilities of the system. In addition, other criteria such as the weight and size of the antennas are considered to make the final selection. Finally, the selected UWB Vivaldi antennas are tested in a realistic scenario.

Pengembangan Antena Bowtie 2,1 GHz Terintegrasi Artificial Magnetic Conductor (AMC) untuk Aplikasi Antena Transmitter pada Sistem Ground Penetrating Radar (GPR)

This study presented the development of the bowtie antenna system design as the transmitter in the Ground Penetrating Radar (GPR) system. The Artificial Magnetic Conductor (AMC) reflector was integrated into the antenna system as a ground plane to obtain a high gain, increase bandwidth and produce a low-profile antenna. The antenna is designed to work at a center frequency of 2.1 GHz with a range of 1.6 - 2.6 GHz and has ultrawideband (UWB) characteristics with a fractional bandwidth of ≥ 25%. In addition, the value of late-time ringing must also be reduced to -30 dB to prevent masking effects on the detected object. Antenna modeling and simulation was done to obtain the optimum prototype design. Bowtie antenna realization was carried out using RT Duroid 5880 as a substrate with dielectric constant (εr) = 2.2 and thickness (h) = 1.57 mm. The AMC reflector was fabricated with FR-4 Epoxy substrate with a dielectric constant (εr) = 4.4 and thickness (h) = 1.6 mm. The antenna realization results show that the antenna has bandwidth = 510 MHz, return loss = -15.17 dB and VSWR = 1.15. The AMC integrated bowtie antenna radiation pattern produces a unidirectional pattern with gain = 4.2 dB. However, the ringing level becomes high by -19.18 dB. Further development is needed to achieve ringing level values that meet the GPR antenna system specifications.

Migration of Ground Penetrating Radar With Antenna Radiation Pattern Correction

Migration can reconstruct the geometric structure of a subsurface object from the ground penetrating radar (GPR) data. However, a GPR antenna is usually simplified as an ideal point/line source of normal migration algorithms, which ignore the influence of the antenna radiation pattern in subsurface soil. In this letter, the back-propagation algorithm is corrected with the analytical half-space far-field radiation pattern of an infinite line source. The superiority of this modified migration algorithm is verified through numerical, laboratory, and field experiments. The results show that the undesired diffractive artifacts at the target edges can be suppressed, while reserving the reflection amplitude in the migrated images with antenna pattern correction, compared with the conventional back-propagation and Kirchhoff algorithms.

Reducing the Induction Footprint of Ultra-Wideband Antennas for Ground-Penetrating Radar in Dual-Modality Detectors

The combination of metal detection (MD) and ground-penetrating radar (GPR) has been successfully deployed to combat the threat from buried antipersonnel landmines. A number of issues arise from the close integration of these two sensing modalities. One issue is the proximity of the metallic GPR antennas to the MD coils, which affects the performance of the MD due to the eddy currents created within the GPR antenna structure. In this article, the effect of traditional solid bowtie antenna design on an MD is investigated, and avenues for the reduction of the eddy currents are explored. Three modifications to the solid bowtie design are proposed and evaluated. This article presents the measurements of the MD response to all four antenna designs using a magnetic induction spectroscopy sensor. It was found that the MD response to the bowtie antenna can be reduced by 91%–98% across the MD operating frequency band, without significantly altering the RF performance, such as reflection and transmission coefficient and radiation pattern.

Penetration Properties of Ground Penetrating Radar Waves Through Rebar Grids

Ground-penetrating radar (GPR) has been widely applied to the nondestructive inspection of concrete structures such as tunnel lining, bridge deck, and retaining wall, which are usually reinforced by steel bars. The scattering of electromagnetic (EM) waves caused by the dense steel rebar embedded in the concrete structures has a severe influence on the penetration capacity of GPR waves. In this letter, the scattering and penetration characteristics of EM waves propagating through rebar net are investigated via both numerical and laboratory experiments, with an aim to select the antenna nominal frequency for a different reinforcement density. The results show that the rebar, which is perpendicular to the polarization direction of GPR waves and has a very small diameter compared with the wavelength, is almost transparent to the impinged GPR waves. The scattering and interaction of GPR waves caused by the rebar that is parallel to the polarization direction result in a shielding effect, which is manifested as a blind band in the low-frequency range in the transmitted spectrum. This result violates the rule of thumb commonly used in the GPR community, i.e., the lower frequency has a deeper GPR penetration depth. In the end, a low cutoff frequency is recommended for selecting a GPR antenna with an appropriate nominal frequency when it is used in the detection of an anomaly inside and behind a reinforced concrete structure, in which the spacing of the rebar net is known.

Ground-Penetrating Radar Antenna Design for Homogeneous and Low-Loss Dielectric Multilayer Media

Abstract Non-destructive evaluation of multilayer media represents an electromagnetic inverse problem, usually solved with analysis techniques in the time and frequency domains. The time- domain analysis technique depends directly on the accurate detection of reflected peaks measured by ground-penetrating radar (GPR), which limits this technique when the reflected pulses overlap with each other or the transmitted signal. Therefore, this paper presents a new practical methodology to obtain the antenna design requirements (operating frequency and temporal response) that avoid overlapping reflected pulses. The major finding is that the proposed methodology enables the production of specific antennas for the analyzed homogeneous and low-loss dielectric multilayer problem, serving as a practical guide for GPR antenna design. A typical pavement example is analyzed to apply the methodology, and, as a result, an ultra-wideband (UWB) directive antenna with tolerable dispersion is obtained according to the design specifications. Finally, the antenna simulations were compared and validated with measurements.

3D scanner technology implementation to numerical modeling of GPR

This study presents an integration of 3D scanned objects into numerical modeling for ground-penetrating radar (GPR). The characteristics of antenna, features of surrounding medium and the realistic design of a buried object are decisive for the success of the numerical modeling. Realistic antenna design has become one of the remarkable developments of the numerical modeling by Finite-Difference Time Domain (FDTD) method. The antenna models with the specific features of commercial GPR antennas, allow researchers to obtain much closer synthetic response to measurements. In addition, lossy and inhomogeneous soil mixtures with different water content can be included in numerical models. Despite the realistic description of GPR antennas and soil types, buried objects are still roughly defined using basic geometric shapes. This article presents an alternative approach using outputs of the 3D scanner as an input into gprMax software to overcome more complex and realistic shapes of the buried objects. For this purpose, a bone fragment belonging to a bovine was firstly simulated with a basic geometric object (cylinder) and then modeled with the realistic shape of the bone, which was obtained from 3D scanner. In this way, the numerical modeling can be performed with the real shape of the object in the lossy, inhomogeneous surrounding medium by using a realistic modeled commercial antenna.

Effect on the Difference in Distances between GPR Antennas on Data Quality using Modeling

The aim of this work is studying the influence the distance between the antenna of ground penetrating radar (GPR) on quality of the signals and ability to detection the targets buried. We used for the modelling of behavior the signal by development the code on GprMax2d program. The distances different has used in this work and frequencies different. In this work we will simulate the operation of GPR using the common source point mode where the source is fixed and the receiver moved along the inspection profile for three values of the distance between the antennas. The simulations were performed for three different frequencies.

Application of Kinematic GPR-TPS Model with High 3D Georeference Accuracy for Underground Utility Infrastructure Mapping: A Case Study from Urban Sites in Celje, Slovenia

This paper describes in detail the applicability of the developed ground-penetrating radar (GPR) model with a kinematic GPR and self-tracking (robotic) terrestrial positioning system (TPS) surveying setup (GPR-TPS model) for the acquisition, processing and visualisation of underground utility infrastructure (UUI) in a real urban environment. The integration of GPR with TPS can significantly improve the accuracy of UUI positioning in a real urban environment by means of efficient control of GPR trajectories. Two areas in the urban part of Celje in Slovenia were chosen. The accuracy of the kinematic GPR-TPS model was analysed by comparing the three-dimensional (3D) position of UUI given as reference values (true 3D position) from the officially consolidated cadastre of utility infrastructure in the Republic of Slovenia and those obtained by the GPR-TPS method. To determine the reference 3D position of the GPR antenna and UUI, the same positional and height geodetic network was used. Small unmanned aerial vehicles (UAV) were used for recording to provide a better spatial display of the results of UUI obtained with the GPR-TPS method. As demonstrated by the results, the kinematic GPR-TPS model for data acquisition can achieve an accuracy of fewer than 15 centimetres in a real urban environment.

GPR laboratory tests and numerical models to characterize cracks in cement concrete specimens, exemplifying damage in rigid pavement

Cracks in road pavements are usual damages because of heavy and dense traffic. Cracks usually are hidden to visual inspections in the case of rigid pavements. In these cases, cracked cement concrete layers are located below the asphalt layer. Therefore, detection becomes a difficult task, being only possible in the case of major damage or even failure. As consequence, rehabilitation is complex due to the technical difficulty in finding those cracks.Non-destructive surveys are in many cases applied to detect those damages. However, the difficulty in data interpretation limits their use forcing the combination of different technologies and core samples. One of the most useful method, commonly applied to define the thickness of layers, is Ground Penetrating Radar (GPR). In order to understand better the GPR images obtained as consequence of damage in the case of rigid pavement, several tests were designed to determine the ability of GPR to non-destructively detect and quantify cracks in concrete samples covered by an asphalt layer. The laboratory experiment consisted of three testing configurations: (1) one concrete sample without cracks; (2) a model of a rigid pavement with the asphalt layer without cracks; (3) the same model with different crack widths. The test was performed with a 1.6 GHz centre frequency GPR antenna in two relative positions with respect the cracks, being always the radar line perpendicular to the crack axis. These measurements allowed also evaluate the effect of orientation of the crack with respect the antenna dipoles in the GPR images. In addition, numerical models were compared to the laboratory results. The results showed that the crack width was detected in most cases, even the thinnest ones (2 mm), being the higher amplitude anomaly corresponding to the case of the data acquired with the antenna parallel to the radar line.

Application of Ground Penetrating Radar to Estimate Subgrade Soil Density

Ground penetrating radar (GPR) technology has been widely used in pavement assessment over the last decade. Assessing the subgrade condition and monitoring its temporal variation provide valuable information regarding changes associated with pavement deterioration, allowing for the beneficial prediction of future road maintenance. This paper presents a method to estimate the density and water content of prepared subgrade soils of highly plastic silt using a 2 GHz GPR scan system and a simple exponential model. A bulk density prediction model was developed based on electromagnetic mixing theory to back calculate subgrade soils density. The model developed determines the soil’s dielectric constant, considering dielectric and volumetric properties of the three major components of soil: air, water, and solid particles. A series of laboratory tests was conducted on six (6) soil samples at various density levels to validate the newly developed model. For validation purposes, sand cone and dynamic cone penetration (DCP) tests were performed and compared with the estimated soils strength from GPR data. The results show that the prediction of soils density and stiffness using nondestructive technology helps efficiently forecast not only pavement deterioration, but potential risks to the subsurface pavement structure with all the advances of time saving using air coupled GPR antenna mounted on a moving vehicle.

A Compact Vivaldi Antenna With Artificial Material Lens and Sidelobe Suppressor for GPR Applications

A novel compact Vivaldi Antenna (CVA) for short-pulse ground penetrating radar (GPR) systems is presented. Artificial materials lens (AML) and sidelobe suppressor (SSR) are loaded to improve GPR Antenna’s radiation capability in the aperture and the flanks of the CVA. The simulation and experimental results indicate that the proposed CVA has a −10 dB impedance bandwidth of 100% (0.7-2.1 GHz) and a −3 dB gain bandwidth of 70.9% (1.0-2.1 GHz). Within the operating bandwidth of the CVA, AML primarily enhances the CVA’s high-frequency gain (1.4-2.1GHz), while the SSR primarily enhances the CVA’s low-frequency gain (0.7-1.4 GHz). Moreover, the CVA loaded with two kinds of artificial materials (AMs) has an average gain of 1 dB and 2 dB in the low-frequency and high-frequency parts, respectively. In addition, the transmission response with small ringing in time domain makes the proposed CVA suitable for short-pulse GPR systems. AML and SSR effectively enhance the gain of the CVA with a compact and space-saving loading method, which provides a new idea to enhance the gain of the CVA by artificial material.

An Unbalanced Sinuous Antenna for Near-Surface Polarimetric Ground-Penetrating Radar

Sinuous antennas are capable of producing ultra-wideband radiation with polarization diversity. This capability makes the sinuous antenna an attractive candidate for UWB polarimetric radar applications. Additionally, the ability of the sinuous antenna to be implemented as a planar structure makes it a good fit for close-in sensing applications such as ground-penetrating radar (GPR). In this work, each arm of a four-port sinuous antenna is operated independently to achieve a quasi-monostatic antenna system capable of polarimetry while separating transmit and receive channels-which is often desirable in GPR systems. The quasi-monostatic configuration of the sinuous antenna reduces system size as well as prevents extreme bistatic angles, which may significantly reduce sensitivity when attempting to detect near-surface targets. A prototype four-port sinuous antenna is fabricated and integrated into a GPR testbed. The polarimetric data obtained with the antenna is then used to distinguish between buried target symmetries.

GPR research on damaged road pavements built in cut and fill sections

We present the GPR (Ground Penetrating Radar) results dealing with flexible road pavements located on cut and fill sections. The aim is to evaluate the road damage (particularly the ramified cracks) taking into consideration also the cut and fill sections height and the traffic load. GPR evaluation was carried out on 14 sites selected in the secondary non-urban road network of L’Aquila, a medium-size urban area of Central Italy. Stress induced by traffic load generally affects a road section thickness of about 1.5 m. A monostatic 1600 MHz GPR antenna was used because it is quite high-resolution when inspecting road damage. GPR acquisition was carried out in damaged and adjoining undamaged road sites, to compare GPR data of the two areas. GPR data analysis was based on the sweep-rectified power approach to evaluate the radar signal attenuation curve vs. depth, which permitted to single out different road types of damage and to discuss the factors which caused them.

Low-Profile, Low-Frequency, UWB Antenna for Imaging of Deeply Buried Targets

A novel ultrawideband directive antenna for ground-penetrating radar (GPR) applications is presented in this letter. The antenna is designed for operation at frequencies below 500 MHz to allow for high-depth-resolution imaging of the deeply buried targets such as buried pipes and other deep underground man-made structures such as tunnels. The antenna is formed by a pair of coupled antennas inspired by an electrically narrow very low profile (ENVELOP) antenna with differential feeding to provide a directive pattern normal to the antenna ground over a wide bandwidth. An antenna operating in the range of 140-510 MHz is designed and fabricated using the printed circuit board (PCB) substrates. The antenna is designed and optimized for operation in the proximity of a half-space soil medium to achieve efficient coupling of power from the air to the ground. The measured reflection coefficient of the antenna near concrete and wet soil covered by sand and grass is shown to be better than -9.5 dB within the specified band. The simulated realized gain of the antenna in the presence of dry soil is better than 4.9 dBi within the range of 140-510 MHz. The antenna is low-profile with a total height of 153 mm and a lateral dimension of 600 mm × 600 mm. The performance of the antenna for GPR applications is evaluated through a field measurement of a buried object in wet soil with high losses.

Toward Core-Free Pavement Compaction Evaluation: An Innovative Method Relating Asphalt Permittivity to Density

Asphalt pavement compaction quality control and quality assurance (QC/QA) are traditionally based on destructive drilled cores and/or nuclear gauge results, which both are spot measurements representing significantly less than 1 percent of the in-service pavement. Ground penetrating radar (GPR) is emerging as a tool that can be used for nondestructive continuous assessment of asphalt pavement compaction quality through measuring the pavement dielectric constant. Previous studies have established that asphalt pavement dielectric constant measurements are inversely proportional to the air void content for a given asphalt mixture. However, field cores are currently required to calibrate the measured dielectric constant to the pavement density. In this paper, a method is proposed to eliminate the need for field calibration cores by measuring the dielectric constant of asphalt specimens compacted to various air void contents. This can be accomplished with a superpave gyratory compactor (SGC), which is routinely used in the pavement industry to fabricate 6 in. (15.2 cm.) diameter specimens. However, this poses difficulties with the GPR antenna height, direct coupling, and the Fresnel zone in relation to the asphalt specimen dimension limitation. These challenges are overcome by employing a plastic spacer with a known dielectric constant between the SGC specimen and the antenna. The purpose of the spacer is to reduce GPR wave speed so that the signal reflected from the specimen is separated from the direct coupling effects at an antenna height where the Fresnel zone of the GPR is not affected by the specimen dimension. The specimen dielectric constant can then be measured using the reflection coefficient-based surface reflection method (SR) or the pulse velocity-based time-of-flight method (TOF). Also, The Hoegh–Dai model (HD model) is demonstrated to reasonably predict pavement density based on the results of field measurements and corresponding core validation, especially as compared to the conventional exponential model. Results are presented from multiple days of paving on one project, as well as a single paving day on a project with significantly different mix properties. The agreement between the HD model, coreless prediction, and field cores shows the promise for implementation of dielectric-based asphalt compaction evaluation without the need for destructive field core calibration.