Ground Penetrating Radar Antenna Research Articles

Ultra-Wideband Bow-tie Antenna for Ground Penetrating Radar Applications

The Ground-penetrating radar (GPR) system is used for the detection of buried objects inside the earth and the classification of the subsurface structures. Ultra-wide band antenna is one of the major component of the GPR system; which is used to transmit and receive short pulse of electromagnetic nature. The performance of the GPR system in detecting buried object is mainly affected by the reflections of the GPR antenna. The reflections from the antennas itself is a basis of late-time ringing and distortion of antenna. These factors create problem in the identification of the objects. Several UWB antennas are used in the GPR system. This paper presents theoretical study for the design of ultra-wideband Bow-tie antenna as a GPR antenna. Bow-tie antenna is designed for a frequency range of 4-18 GHz. Transient and spectral behavior of the antenna is simulated. The time behavior of the antenna shows a reflected signal from the bow-tie antenna of the duration of 2.0 ns. The antenna provides a VSWR less than 2.0 and a return loss of less than -15 dB in the operating frequency range. Bow-tie antenna is then modeled and simulated in the GPR environments which includes the buried object (i.e. scatterer) and beam floor. The design, modeling and simulations are performed by using CST Microwave Studio.

Kinematic GPR-TPS Model for Infrastructure Asset Identification with High 3D Georeference Accuracy Developed in a Real Urban Test Field

This paper describes in detail the development of a ground-penetrating radar (GPR) model for the acquisition, processing and visualisation of underground utility infrastructure (UUI) in a controlled environment. The initiative was to simulate a subsurface urban environment through the construction of regional road, local road and pedestrian pavement in real urban field/testing pools (RUTPs). The RUTPs represented a controlled environment in which the most commonly used utilities were installed. The accuracy of the proposed kinematic GPR-TPS (terrestrial positioning system) model was analysed using all the available data about the materials, whilst taking into account the thickness of the pavement as well as the materials, dimensions and 3D position of the UUI as given reference values. To determine the reference 3D position of the UUI, a terrestrial geodetic surveying method based on the established positional and height geodetic network was used. In the first phase of the model, the geodetic network was used as a starting point for determining the 3D position of the GPR antenna with the efficient kinematic GPR surveying setup using a GPR and self-tracking (robotic) TPS. In the second phase, GPR-TPS system latency was quantified by matching radargram pairs with a set of fidelity measures based on a correlation coefficient and mean squared error. This was followed by the most important phase, where, by combining sets of “standard” processing routines of GPR signals with the support of advanced algorithms for signal processing, UUI were interpreted and visualised semi-automatically. As demonstrated by the results, the proposed GPR model with a kinematic GPR-TPS surveying setup for data acquisition is capable of achieving an accuracy of less than ten centimetres.

Integration of Ground- Penetrating Radar and Gamma-Ray Detectors for Nonintrusive Characterisation of Buried Radioactive Objects.

The characterisation of buried radioactive wastes is challenging because they are not readily accessible. Therefore, this study reports on the development of a method for integrating ground-penetrating radar (GPR) and gamma-ray detector measurements for nonintrusive characterisation of buried radioactive objects. The method makes use of the density relationship between soil permittivity models and the flux measured by gamma ray detectors to estimate the soil density, depth and radius of a disk-shaped buried radioactive object simultaneously. The method was validated using numerical simulations with experimentally-validated gamma-ray detector and GPR antenna models. The results showed that the method can simultaneously retrieve the soil density, depth and radius of disk-shaped radioactive objects buried in soil of varying conditions with a relative error of less than 10%. This result will enable the development of an integrated GPR and gamma ray detector tool for rapid characterisation of buried radioactive objects encountered during monitoring and decontamination of nuclear sites and facilities.

A study on surface contact effect using ground penetrating radar

In this paper, the effect of contact and non-contact antenna system of ground penetrating radar (GPR) for buried pipes are presented. The frequency for GPR antenna used in this project is 400MHz which is suitable for GPR system to detect buried pipes for the tested surfaces, since the soil involved is sand which has low electrical conductivity. The results of the radargram obtained from this experiment and the limitations occurred are discussed.

Soil Water Content Estimation Using High-Frequency Ground Penetrating Radar

The rapid high-precision and nondestructive determination of shallow soil water content (SWC) is of vital importance to precision agriculture and water resource management. However, the low-frequency ground penetrating radar (GPR) technology currently in use is insufficient for precisely determining the shallow SWC. Therefore, it is essential to develop and use a high-precision detection technology to determine SWC. In this paper, a laboratory study was conducted to evaluate the use of a high-frequency GPR antenna to determine the SWC of loamy sand, clay, and silty loam. We collected soil samples (0–20 cm) of six soil types of loamy sand, clay, and silty loam and used a high-frequency (2-GHz) GPR antenna to determine the SWC. In addition, we obtained GPR data and images as well as characteristic parameters of the electromagnetic spectrum and analyzed the quantitative relationship with SWC. The GPR reflection two-way travel times and the known depths of reflectors were used to calculate the average soil dielectric permittivities above the reflectors and establish a spatial relationship between the soil dielectric permittivity ( ε ) and SWC ( θ ), which was used to estimate the depth-averaged SWC. The results show that the SWC, which affects the attenuation of wave energy and the wave velocity of the GPR signal, is a dominant factor affecting the soil dielectric permittivity. In addition, the conductivity, magnetic soil, soil texture, soil organic matter, and soil temperature have substantial effects on the soil dielectric permittivity, which consequentially affects the prediction of SWC. The correlation coefficients R2 of the “ θ ~ ε ” cubic curve models, which were used to fit the relationships between the soil dielectric permittivity ( ε ) and SWC ( θ ), were greater than 0.89, and the root-mean-square errors were less than 2.9%, which demonstrate that high-frequency GPR technology can be applied to determine shallow SWC under variable hydrological conditions.

The contribution of geophysical prospecting to the multidisciplinary study of the Sarno Baths, Pompeii

Abstract This paper focuses on the contribution of geophysical measurements to the study of the Sarno Baths in Pompeii in the context of the MACH project funded by the University of Padua. Between 2016 and 2017, a series of geophysical measurements were carried out inside and outside the Sarno Baths in order to support the multidisciplinary study of this archaeological site. High-frequency ground penetrating radar (GPR) antennas have been applied to the characterization of horizontal and vertical structural elements (vaults and walls) of the building, where GPR acquisitions and electrical resistivity tomography (ERT) were used in the open field to identifying possible archaeological features. In general, the results made by these geophysical measurements provide new information supporting both structural analysis and preliminary archaeological excavation conducted in this area.

Real-Time Modeling of Forward-Looking Synthetic Aperture Ground Penetrating Radar Scattering From Rough Terrain

Ground penetrating radar (GPR) is a viable tool for fast and high fidelity detection of concealed explosive threats. The radar effectiveness is limited by scattering from rough terrain which considerably obscures the buried target response. To calculate the rough ground scattering, a 3-D full-wave algorithm such as finite-difference frequency-domain (FDFD) method is required but is often prohibitive for multiple frames when the GPR antennas are distant from the target region. This paper presents a real-time 3-D modeling of a moving platform forward-looking GPR scattering from rough terrain located at great electrical distances from the GPR antenna. For a synthetic aperture, the computational domain of the focal region is reduced to a very small subset of the entire observed volume, and the surface clutter is computed via a mere multiplication of a precomputed impulse response matrix of the rough ground with the matrix characterizing the GPR transmitting signal. For a vehicle-mounted GPR detection system, this results in a significant reduction of complexity and saving of computation resources. The effectiveness of the algorithm is evaluated through an implementation of 3-D Monte Carlo simulation for various rough surface parameters. Our developed model compares well with the direct FDFD results, and can be used for lossy and frequency-dispersive soils.

Algorithm development for real-time thin asphalt concrete overlay compaction monitoring using ground-penetrating radar

Ground-penetrating radar (GPR) is an effective, feasible, and non-destructive tool for real-time estimation of the density of asphalt concrete (AC) during compaction. When the AC pavement is thin, however, it is difficult to estimate the density due to the limited GPR signal resolution. In addition, the surface moisture, applied during compaction, has an effect on the GPR signal and hence impacts density prediction accuracy. In this study, a nonlinear optimization approach, based on gradient descent, was used to recover the AC pavement surface reflection. A “modified reference scan” approach was developed to remove the effect of surface moisture on GPR signals during density monitoring. The “modified reference scan” approach was first validated in a laboratory experiment setting, then validated in a field study near Chicago, IL, where GPR antennas were installed on the roller and data were collected during compaction. The results show that GPR is a prospective tool for real-time AC compaction monitoring.

Design and Implementation of Low-cost Wideband Vivaldi Antenna for Ground Penetrating Radar

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Storm response of a mixed sand gravel beach ridge plain under falling relative sea levels: A stratigraphic investigation using ground penetrating radar

AbstractBeach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore‐normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back‐barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post‐seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a palaeo‐storm initially created a washover fan into the back‐barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern‐day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern‐day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period. © 2019 John Wiley & Sons, Ltd.

Investigating the Performance of Bi-Static GPR Antennas for Near-Surface Object Detection.

Antennas are an important component in ground penetrating radar (GPR) systems. Although there has been much research reported on the design of individual antennas, there is less research reported on the design of the geometry of bi-static antennas. This paper considers the effects of key parameters in the setup of a GPR head consisting of a bi-static bow-tie pair to show the effect of these parameters on the GPR performance. The parameters investigated are the antenna separation, antenna height above the soil, and antenna input impedance. The investigation of the parameters was performed by simulation and measurements. It was found when the bi-static antennas were separated by 7 cm to 9 cm and were operated close to the soil (2 cm to 4 cm), the reflected signal from a near-surface object is relatively unaffected by height variation and object depth. An antenna input impedance of 250 Ω was chosen to feed the antennas to reduce the late-time ringing. Using these results, a new GPR system was designed and then evaluated at a test site near Benkovac, Croatia.

Using gprMax to Model Ground-Penetrating Radar (GPR) to Locate Corn Seed as an Attempt to Measure Planting Depth

Abstract. Planting depth (PD) plays an essential role in crop production by substantially impacting germination rates and yield potential. However, techniques to measure PD nondestructively have not been developed. A two-dimensional gprMax simulation study was conducted to investigate the effects of soil electromagnetic properties on ground-penetrating radar (GPR) waves. The primary objective was to examine the possibility of using GPR as a nondestructive sensor to detect subsurface corn seeds with the goal of measuring PD. A conventional fixed-offset gprMax antenna in contact with the soil surface was used in the simulations. Corn seed models of different materials and sizes were simulated, with properties of natural and synthetic (metal) corn seeds. The seed models were spherical, with radial dimensions of 0.006 and 0.024 m to simulate small and large corn seeds, respectively. Corn seed models were embedded in three homogeneous soil models (sandy loam, loam, and clay), and 1.6 and 2.6 GHz antenna models were used as excitation frequencies. A-scans and B-scans were obtained from the simulations. The A-scans showed that all targets (small natural corn and metal corn models, and large natural corm and metal corn models) successfully provided response amplitudes proportional to their dielectric properties in sandy loam and loam, but not in clay. In high bulk density soils, GPR waves failed to penetrate the soil models, and the targets were not detected. The 2.6 GHz antenna provided better response amplitudes from the targets. In the driest soil models (2.5%, and 5%), no response amplitude signatures were observed. In dry and relatively dry soil models (15%), the simulation times were much shorter to obtain a response amplitude from the targets (with feeble response amplitudes) compared to relatively wetter soils. To validate these models, laboratory experiments were conducted with three treatment factors (soil type, planting depth, and moisture content). In dry soils, corn seeds could be detected using a 2.6 GHz GPR antenna; however, the detection varied substantially within replicates of the same moisture group. Further research is necessary to understand the effects of soil moisture on the detection variability of buried corn seeds. Keywords: Corn seed, Dielectric permittivity, Electromagnetic waves, Finite difference time domain, GPR, gprMax.

Glacier bed surveying with helicopter-borne dual-polarization ground-penetrating radar

ABSTRACTTraditionally, helicopter-borne ground-penetrating radar (GPR) systems are operated with a single pair of bistatic dipole antennas to measure the thickness of glaciers. We demonstrate numerically that the directivity of the radiation pattern of single airborne dipoles do not correspond to an ideal full-space solution if the antennas are employed at typical flight heights. These directionality effects can degrade the quality of the subsurface images significantly, when the GPR antennas are orientated unfavorably. Since an adjustment of the antenna orientation is impractical during flight, we have developed a novel dual-polarization helicopter-borne GPR system consisting of two orthogonal pairs of commercial antennas in broadside configuration. To overcome the image quality deficits of the individual channels, we apply a pseudo-scalar approach in which we combine the data of both polarizations. Results of helicopter-borne GPR surveys on two alpine glaciers in Switzerland reveal more coherent bedrock reflections in the summed data compared with single dipole pair profiles. Generally, the dual-polarization setup is more suitable than a single antenna systems, because it is more versatile and less prone to directional effects caused by the placement of the dipole antennas in relation to undulating subsurface reflectors.

Realistic Expectations for Deep Ground Penetrating Radar Performance

Ground penetrating radar (GPR) is unique amongst geophysical tools in terms of its imaging resolution and the diversity of its applications. Since its commercialisation four decades ago, GPR has also been distinguished because of the prevalence of some of its purveyors to oversell the method’s capabilities, relying largely on the end users’ lack of understanding of the underlying physics. Early adopters in the 1980s and 90s were dismayed to find that environments suitable for its purported ubiquitous deep penetration capabilities were rare and that it required resistivities well into the 1000s of Ohm m. Regardless of the advances made in electronics and antenna design in the intervening decades, the fundamental limitations have not changed.Misconceptions, “specsmanship” and hype have continued to abound in the GPR marketplace, particularly in recent years. Systems purporting to penetrate hundreds of metres using “megawatt” transmitters from the former Eastern Bloc have been promoted for mineral exploration, particularly in Australia and Africa. Other pseudo-radar concepts, such as the use of beam forming to achieve kilometres of penetration with centimetre accuracy, or THz laser scanners which can detect individual diamonds deep underground, have generally targeted junior exploration groups who lack in-house geophysical guidance.This work provides an overview of the fundamentals of non-dispersive EM wave propagation in the ground and an examination of the recent published performance claims of some GPR and pseudo-GPR systems within the context of accepted EM theory. The accepted methods for potentially increasing GPR performance, given the emerging technologies such as novel transmitter and receiver designs and new GPR antennas, are also discussed.

Assessing Ground Penetrating Radar's Ability to Image Subsurface Characteristics of Icy Debris Fans in Alaska and New Zealand

Icy debris fans have recently been described as fan shaped depositional landforms associated with (or formed during) deglaciation, however, the subsurface characteristics remain essentially undocumented. We used ground penetrating radar (GPR) to non-invasively investigate the subsurface characteristics of icy debris fans (IDFs) at McCarthy Glacier, Alaska, USA and at La Perouse Glacier, South Island of New Zealand. IDFs are largely unexplored paraglacial landforms in deglaciating alpine regions at the mouths of bedrock catchments between valley glaciers and icecaps. IDFs receive deposits of mainly ice and minor lithic material through different mass-flow processes, chiefly ice avalanche and to a lesser extent debris flow, slushflow, and rockfall. We report here on the GPR signal velocity observed from 15 different wide-angle reflection/refraction (WARR) soundings on the IDFs and on the McCarthy Glacier; the effect of GPR antenna orientation relative to subsurface reflections; the effect of spreading direction of the WARR soundings relative to topographic contour; observed differences between transverse electric (TE) and transverse magnetic (TM) antenna polarization; and a GPR profile extending from the McCarthy Glacier onto an IDF. Evaluation of the WARR soundings indicates that the IDF deposits have a GPR signal velocity that is similar to the underlying glacier, and that the antenna polarization and orientation did not prevent identification of GPR reflections. The GPR profile on the McCarthy Glacier indicates that the shallowest material is layered, decreases in thickness down fan, and has evidence of brittle failure planes (crevasses). The GPR profile and WARR soundings collected in 2013 indicate that the thickness of the McCarthy Glacier is 82 m in the approximate middle of the cirque and that the IDF deposits transition with depth into flowing glacial ice.

Choke Rings for Pattern Shaping of a GPR Dipole Antenna

This paper establishes that a choke ring—a common pattern-shaping structure in GPS antennas—can also be effective when employed in ground-penetrating radar (GPR) as a shielding device to isolate GPR antennas from the above-ground environment. A choke ring shield is compared to similar cavity structures in response to a wideband pulse excitation, and it is shown that in addition to its pattern-shaping ability, good time-domain performance can be achieved through the inclusion of an absorber within the choke ring’s central cavity. Wideband performance measures are developed, and measured data are in generally very good agreement with simulations. The choke ring is shown to provide a 3–5 dB redirection of radiated power from the back to the front of the shield, while the inclusion of the absorber ensures less than −40 dB of late-time clutter.

ASSESSING THE CONDITION OF BURIED PIPE USING GROUND PENETRATING RADAR (GPR)

Abstract. The invention of Ground Penetrating Radar (GPR) technology has facilitated the possibility of detecting buried utilities and has been used primarily in civil engineering for detecting structural defects, such as voids and cavities in road pavements, slabs and bridge decks, but has not been used to assess the condition of buried pipes. Pipe deterioration can be defined as pipes where, for example, cracking, differential deflection, missing bricks, collapses, holes, fractures and corrosion exists. Assessing the deterioration of underground pipes is important for service efficiency and asset management. This paper describes a research project that focused on the use of GPR for assessing the condition of buried pipes. The research involved the construction of a suitable GPR test facility in the laboratory to conduct controlled testing in a dry sand. Plastic pipes were chosen for the experiments. A series of laboratory experiments were conducted to determine the validity and effectiveness of standard commercially available GPR technology in assessing the condition of buried utilities with common types of damage. Several types of damage to the plastic pipe were investigated with respect to different GPR antenna frequencies. The GPR surveys were carried out in order to obtain signal signatures from damaged and undamaged pipes buried at 0.5 m depth. These surveys were organised on a grid pattern across the surface of the sand in the test facility. The results presented in this paper show that GPR can identify certain types of damage associated with a buried pipe under these controlled laboratory conditions.

High gain UWB bow‐tie antenna design for ground penetrating radar application

AbstractThis article presents an elliptical shaped slot ultra‐wideband antenna with high gain (10.3 dBi) and compact size (107.7 × 68 mm2) that designed and improved by four steps. Also, it can perform in an impedance bandwidth (IBW) from 0.98 GHz to 4.5 GHz that is satisfactory IBW for ground penetrating radar (GPR) application. The proposed antenna is fabricated for experimental testing and getting GPR images in a sandbox. Simulation and measured results ensure a desirable GPR antenna.

Realistic FDTD GPR Antenna Models Optimized Using a Novel Linear/Nonlinear Full-Waveform Inversion

Finite-difference time-domain forward modeling of ground-penetrating radar (GPR) is becoming regularly used in model-based interpretation methods, such as full-waveform inversion (FWI) and machine learning schemes. Oversimplifications in such forward models can compromise the accuracy and realism with which real GPR responses can be simulated, which degrades the overall performance of interpretation techniques. A forward model must be able to accurately simulate every part of the GPR problem that affects the resulting scattered field. A key element, especially for near-field applications, is the antenna system. Therefore, the model must contain a complete description of the antenna, including the excitation source and waveform, the geometry, and the dielectric properties of any materials in the antenna. The challenge is that some of these parameters are not known or cannot be easily measured, especially for commercial GPR antennas that are used in practice. We present a novel hybrid linear/nonlinear FWI approach that can be used, with only knowledge of the basic antenna geometry, to simultaneously optimize the dielectric properties and excitation waveform of the antenna and minimize the error between real and synthetic data. The accuracy and stability of our proposed methodology are demonstrated by successfully modeling a 1.5-GHz commercial antenna from Geophysical Survey Systems, Inc. Our framework allows accurate models of GPR antennas to be developed without requiring detailed knowledge of every component of the antenna. This is significant because it allows commercial GPR antennas, regularly used in GPR surveys, to be more readily simulated.

Location of reinforcement and moisture assessment in reinforced concrete with a double receiver GPR antenna

Ground Penetrating Radar (GPR) is a popular technique in Civil Engineering for non-destructive investigations and more especially for the diagnosis of reinforced concrete structures. Its main applications are for the location of reinforcement and for measuring the thickness of elements. The advantage of GPR compared to other techniques, such as the use of a covermeter, is its rapidity of measurement, which allows large surfaces to be covered in a shorter time than with magnetic techniques. However, in a comparison with covermeters, the main disadvantage of GPR is the difficulty of accurately assessing the depth of reinforcement without advanced processing, or/and calibration.In this study, we propose a new methodology for GPR measurement and processing that allows accurate location of reinforcement in depth and an assessment of wave velocity inside the cover concrete at the same time. The new method of measurement employs a double offset configuration by using two bi-static antennas.A specific algorithm was developed for the determination of reinforcement depth and velocity inside cover concrete at the same time. The algorithm is tested on a 3 m × 3 m reinforced concrete slab with cover thickness ranging from 15 to 80 mm. With the algorithm, it is possible to measure the depth of reinforcement to within less than 2 mm, whatever concrete thickness.By using a calibration procedure specifically developed in this study, the velocity can be used to assess the water content inside cover concrete with a core conditioned at different moisture contents. A conversion model is obtained between water content and velocity measured by transmission, which can be used at different places in the structure to assess moisture.