High Frequency Ground Penetrating Radar Research Articles

Bayesian optimization based extreme gradient boosting and GPR time-frequency features for the recognition of moisture damage in asphalt pavement

Moisture damage is one of the major defects in asphalt pavement, and will evolve into potholes in a short time which will affect traffic safety. Ground Penetrating Radar (GPR) is an effective non-destructive testing (NDT) method for detecting moisture damage but its data explanation replies on human experience and subjects to labor intensive. To address this issue, an automatic detection method based on extreme gradient boosting (XGBoost) combined with Bayesian hyper-parameter optimization (BHPO) was proposed to detect moisture damage area from GPR traces. High frequency GPR antenna with 2.3 GHz was used to detect the moisture damage area from simulation, laboratory and field tests, and moisture damage dataset with 7960 traces was collected. Thirty time-frequency parameters were extracted from each GPR trace, normalized to unify the three data source, and then optimized into 12 sensitive parameters by feature importance method. These 12 parameters were used to build the recognition model with XGBoost, and the model tuning parameters were optimized by BHPO. To obtain optimization model, random forest (RF) and artificial neural network (ANN) were also trained with BHPO, and compared with XGBoost model. The results indicate that performance of XGBoost model with BHPO achieves the highest accuracy and lowest time cost both in moisture damage and normal trace classification, the accuracies for moisture damage are XGBoost (96.9%) > ANN (95.6%) > RF (95.4%), respectively, and normal are XGBoost (96.5%) > RF (96.1%) and ANN (96.0%), respectively. On this basis, field tests were conducted by core samples, which verified the correct result of XGBoost model. Our method provides a swift and accurate method to locate subsurface targets directly from GPR signals.

Evidence of shallow basaltic lava layers in Von Kármán crater from Yutu-2 Lunar Penetrating Radar

Yutu-2 – the rover from the Chang’E-4 mission – is the longest operational Lunar rover, and the first rover to land on the far side of the Moon. It is the second planetary rover to be equipped with ground-penetrating radar (GPR), one of the few in-situ geophysical techniques used in planetary exploration. Since landing in 2019, Yutu-2 has travelled more than 1 kilometre in the Von Kármán (VK) crater, and has been able to investigate the dielectric properties of the shallow Lunar ejecta using its on-board high frequency GPR channels. In this paper, we use advanced signal processing and frequency attributes to infer a detailed dielectric structure of the first ≈30 metres of the subsurface, providing valuable information on the ilmenite content of the landing site. Both the dielectric properties and the ilmenite content suggest a shallow sequence of Imbrian basaltic layers overlaying a low-ilmenite ejecta blanket.

Quantifying the impact of parameters of chloride-induced reinforcement corrosion on the GPR signal

The sensitivity of the high-frequency ground penetrating radar (GPR) signal to changes within the reinforced concrete (RC) makes it a valuable tool for corrosion assessment of RC structures. The most important parameters in chloride-induced corrosion are moisture content, chloride content, and reinforcement diameter loss. The objective of this laboratory study was to investigate and quantify the influence of these parameters on the GPR signal. Of particular interest was to determine which of the observed parameters the GPR is most sensitive to. Furthermore, particular emphasis was placed on understanding the influence of corrosion products, which has not met the consensus in the existing literature. The parameters were studied on a total of forty-two specimens where the reflector of the GPR waves was the reinforcement embedded in the concrete specimen. Based on the experimental data, values of normalized amplitude related to the evaluation of corrosion by GPR were proposed.

Evaluation of starting model approaches and effective source wavelet variations for high-frequency ground-penetrating radar full-waveform inversion

High-frequency ground-penetrating radar (GPR) full-waveform inversion (FWI) can enhance the characterization of small-scale structures in the subsurface below the decimeter scale. We have investigated the potential and requirements to use FWI for higher-frequency data. Thereby, we focus on the two most important criteria to achieve reliable FWI results: adequate starting models that fulfill the half-wavelength criterion and the accuracy of the effective source wavelet. Therefore, we have defined a realistic reference model, generated synthetic GPR data sets (200, 450, and 700 MHz), and tested different standard ray-based starting model methods and frequency-hopping approaches to derive results close to our reference model. Although standard starting models provide good parameter reconstruction for lower-frequency data, a frequency-hopping approach is required for the 700 MHz data. In addition, we have seen that the reconstruction of the conductivity results is more sensitive to the presence of noise (25 dB) than the permittivity tomograms. The definition of the effective source wavelets is directly linked to the accuracy of the starting models; therefore, we investigate the effect on the FWI results for high-frequency data by varying the source wavelets in terms of starting time and/or amplitude. Considering the multiparameter nature of FWI, we observe that time shifts have a greater influence on the performance of the FWI than amplitude variations. Large time shifts of approximately 0.1 ns for the 700 MHz data may lead to the failure of the inversion, whereas amplitude variations (±5% of the maximum amplitude) affect the quantitative conductivity results only (no effect on permittivity) with an increased root-mean-square error of the data of up to 20%. Using a stochastically perturbed synthetic model, we determine an improved parameter reconstruction for higher frequencies. On the basis of our findings, we develop a workflow to obtain reliable results for high-frequency GPR FWI for future users.

Transport Infrastructure Monitoring by InSAR and GPR Data Fusion

This study reviews research developments in non-destructive assessment of linear transport infrastructures. The main focus will be on the integration between satellite remote sensing and ground-based techniques. Specifically, the potential of using interferometric synthetic aperture radar (InSAR) and high-frequency ground penetrating radar (GPR) techniques as self-standing and integrated survey methodologies will be discussed. To this effect, an overview on data fusion techniques will be given. The last section of the paper reports recent results achieved by using both GPR systems and the permanent scatterers InSAR technique on a real-life railway.

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.

Multi-frequencies GPR measurements for delineating the shallow subsurface features of the Yushu strike slip fault

In order to assess Ground penetrating radar (GPR) for imaging the shallow subsurface geometry and characteristics of the fault in Yushu area, details GPR measurements with 25 MHz, 100 MHz and 250 MHz frequencies antenna were firstly conducted in four sites along the Yushu fault after geomorphologic and geological investigation. The 25 MHz profiles delineated an excellent general view of deformation zones at a much wider area and greater depth. While the 100 MHz and 250 MHz data provided more detailed analysis of the shallow subsurface deformation about the geologic structure and the fault, including the stratigraphic structures, the dip angle and direction of the fault plane. The remarkable variation in the pattern and relative amplitude of electromagnetic waveform on the two-dimensional GPR profiles are all obvious and it is considered as the main fault zone with a nearly vertical fault with the dip angle of 70°–85°. High frequency GPR profiles show a good consistency with the trench sections at three sites. The geometry of the main fault zone can be depicted and deduced up to ~ 12 m deep or even deeper on the 25 MHz GPR profile in Yushu area and it is considered to be the result of the movement of active faults. What’s more, the geophysical features on GPR profile associated to the strike-slip fault are further summarized in different geological and geomorphological environment in Yushu area, the study also provides further evidence that GPR is valuable for fault investigation and palaeoseismic study in the Qinghai-Tibet Plateau area.

High frequency impulse ground penetrating radar application in assessment of interlayer connections

Ground Penetrating Radar (GPR) technique is commonly used in the nondestructive evaluation of pavement structures. In particular, this method is used to estimate thicknesses of pavement layers as well as it can be utilized in advanced studies of pavement structures. The device presented in this paper comprise the high frequency impulse antennas that allow for investigating the interlayer zones in terms of their electromagnetic properties (e.g. dielectric constant). In some cases these electromagnetic responses can be suitable in the assessment of layer bonding in the pavement structure. This paper discusses the assessment of the quality of asphalt pavement interlayer bonding with the use of high frequency GPR techniques. The preliminary laboratory measurements were performed using an impulse antenna in the zero-offset configuration combined with the large-scale models simulating an idealized horizontal delamination. These measurements allowed to estimate the antenna sensitivity to detect interlayer connection under dry and wet conditions. Analysis of collected results led to formulating practical conclusions regarding critical limitations of the measuring system and adequate methods of signal processing and interpretation. The field investigations consisted of the GPR measurements along selected road sections and collection of the core samples at the locations associated with the specific reflexes. Inspection of the cores provided some real insights into the structure of different delaminations associated with characteristic reflexes. Analysis showed the reflection properties are able to expresses some important features of the interlayer zone, such as delaminations, presence of alien material at the interface, insufficient compaction occurring at the base of layer, and water penetration.

Пастухов А.В. Высокочастотное георадиолокационное зондирова- ние почвогрунтов многолетнемерзлых бугристых болот (европейский Северо-Восток России).

Пастухов А.В. Высокочастотное георадиолокационное зондирова- ние почвогрунтов многолетнемерзлых бугристых болот (европейский Северо-Восток России).

MAPPING AND MODELLING FRACTURES USING GROUND PENETRATING RADAR FOR ORNAMENTAL STONE ASSESSMENT AND RECOVERY OPTIMIZATION: TWO CASE STUDIES

Rock mass is typically characterized by inherent fractures that cause natural blocks of rocks. Unplanned cutting of stone deposits in quarries may lead to over-producing waste (rock debris) or extracting unfi t (fractured) stone blocks. This paper presents two case studies through the use of low and high frequency Ground Penetrating Radar (GPR) antennas to detect fractures in two benches of a quarry. In the fi rst case study, a high frequency GPR antenna was used aiming to: (i) compare the GPR results with a map of the out-cropping fracture intensity in the bench surface, developed using the data of the GPR survey marks and interpolated by the Ordinary Kriging technique, and (ii) present how sub-vertical fractures can be numerically modelled in three dimensions from the GPR results. The second case study was focused on using a low frequency antenna to detect large aperture size of fracture surfaces as deep as possible in order to evaluate a deposit stratum before quarrying. This could be done through studying the refl ections from a 3D cross-sectional GPR model anda 3D transparent GPR model. In the discussion section, an exploitation planning approach, based on modelling fractures as 3D surfaces, is theoretically and graphically proposed to optimize the stone production recovery. The two case studies showed that GPR is a successful tool for the assessment of ornamental stone deposits and a promising tool for recovery optimization.

Tracing and imaging minor water seepage of concealed PVC pipe in a reinforced concrete wall by high-frequency ground penetrating radar

This paper studies the perturbation patterns of GPR images as a tool for tracing water seepage pathway in a plastic and concealed water pipe in a full-scale concrete wall specimen. Water seepage was triggered with a water circulation system and a pre-drilled hole (as seepage point) in a PVC pipe concealed in a concrete wall. Making use of a 2GHz antenna, different GPR perturbations patterns on the PVC pipe (as weak scatterers) and several steel bars (as strong scatterers) in concrete, were mapped. The time-lapse changes of spatial spread and degree of water seepage were monitored for 59days to trace the water seepage path. The perturbation patterns enable the observation of the wave attenuation explained by the well-established theories of water in construction materials. Analysis in the validation experiment pushed the limit of GPR that the use of high-frequency GPR is potentially useful to trace and image minor degree of water seepage in concrete.

A High-Order Time Domain Discontinuous Galerkin Method with Orthogonal Tetrahedral Basis for Electromagnetic Simulations in 3-D Heterogeneous Conductive Media

AbstractWe present a high-order discontinuous Galerkin (DG) method for the time domain Maxwell's equations in three-dimensional heterogeneous media. New hierarchical orthonormal basis functions on unstructured tetrahedral meshes are used for spatial discretization while Runge-Kutta methods for time discretization. A uniaxial perfectly matched layer (UPML) is employed to terminate the computational domain. Exponential convergence with respect to the order of the basis functions is observed and large parallel speedup is obtained for a plane-wave scattering model. The rapid decay of the out-going wave in the UPML is shown in a dipole radiation simulation. Moreover, the low frequency electromagnetic fields excited by a horizontal electric dipole (HED) and a vertical magnetic dipole (VMD) over a layered conductive half-space and a high frequency ground penetrating radar (GPR) detection for an underground structure are investigated, showing the high accuracy and broadband simulation capability of the proposed method.

An Experimental and Numerical Study on Embedded Rebar Diameter in Concrete Using Ground Penetrating Radar

High frequency ground penetrating radar (GPR) has been widely used to detect and locate rebars in concrete. In this paper, a method of estimating the diameter of steel rebars in concrete with GPR is investigated. The relationship between the maximum normalized positive GPR amplitude from embedded rebars and the rebar diameter was established. Concrete samples with rebars of different diameters were cast and the maximum normalized amplitudes were recorded using a 2.6 GHz GPR antenna. Numerical models using GPRMAX software were developed and verified with the experimental data. The numerical models were then used to investigate the effect of dielectric constant of concrete and concrete cover on the maximum normalized amplitude. The results showed that there is an approximate linear relationship between the rebar diameter and the maximum GPR normalized amplitude. The developed models can be conveniently used to estimate the embedded rebar diameters in existing concrete with GPR scanning; if the concrete is homogeneous, the cover depth is known and the concrete dielectric constant is also known. The models will be highly beneficial in forensic investigations of existing concrete structures with unknown rebar sizes and locations.

Perturbation mapping of water leak in buried water pipes via laboratory validation experiments with high-frequency ground penetrating radar (GPR)

This paper studies the perturbation patterns of GPR images as a tool for water leakage detection in buried water pipes with laboratory experiments. Different perturbations patterns on GPR signals due to a water leak of metallic and PVC pipes buried in a sand box, were mapped and studied with controlled water injection and leak volume, as well as a fixed leak position in the pipes. These perturbation patterns of signal strength include the tale-tell signs of a central leak point and propagation of the radial wetting front vortex centered around the leak point at different injection times. These patterns, compared to the no-leak dry condition, were interpreted with the conventional principles of dielectric contrast and reflection coefficients, and the associated reflection and absorption mechanisms. It is believed that this set of data will serve as an image matching fingerprint to identify and map water leaks in the field.

Ground penetrating radar examination of thin tsunami beds — A case study from Phra Thong Island, Thailand

Coastal overwash deposits from tsunamis and storms have been identified and characterised from many coastal environments. To date, these investigations have utilised ad-hoc time, energy and cost intensive invasive techniques, such as, pits and trenches or taking core samples. Here, we present the application of high-frequency ground penetrating radar (GPR) to identify and characterise the 2004 Indian Ocean Tsunami (IOT) and palaeotsunami deposits from Phra Thong Island, Thailand. This site is one of the most intensively studied palaeotsunami sites globally and preserves a series of late-Holocene stacked sandy tsunami deposits within an organic, muddy low-energy backbeach environment.Using 100, 500 and 1000MHz GPR antennas, 29 reflection profiles were collected from two swales (X and Y) inland of the modern beach, and two common mid-point (CMP) profiles using the 200MHz antennas were collected from Swale Y. Detailed examination of the CMPs allowed accurate velocity estimates to be applied to each profile. The reflection profiles included across-swale profiles and a high-resolution grid in Swale X, and were collected to investigate the feasibility of GPR to image the palaeotsunami deposits, and two profiles from Swale Y where the tsunami deposits are poorly known. The 500MHz antennas provided the best stratigraphic resolution which was independently validated from the stratigraphy and sedimentology recovered from 17 auger cores collected along the profiles. It is clear from the augers and GPR data, that the different dielectric properties of the individual layers allow the identification of the IOT and earlier tsunami deposits on Phra Thong Island. Although applied in a coastal setting here, this technique can be applied to other environments where thin sand beds are preserved, in order to prioritise sites for detailed examination.

GPR System for Monitoring Paddy Moisture Content in a Drying Process

High-frequency ground penetrating radar (GPR) was used in this study to monitor the moisture content of paddy in a drying process. The reflected radar pulses were used to calculate the dielectric constant of paddy. Owing to the temperature increase, Nelson and Noh's quadratic model was extended by introducing a temperature correction factor adapted to predict the dielectric constants at different temperatures. The calculated paddy moisture content was in good agreement with the values measured by the conventional oven method. Our results demonstrate the potential use of GPR systems as an online tool for monitoring the paddy moisture content in the drying process.

Application of high-frequency ground penetrating radar to the reconstruction of 3D sedimentary architecture in a flume model of a fluvial system

Ground penetrating radar (GPR) offers a fast and efficient method for visualizing three-dimensional (3D) images of shallow subsurface structures. We investigated the application of GPR to nondestructive imaging of deposits formed in a small experimental flume using a high-frequency GPR antenna. The GPR measurements, made with a 1.6GHz antenna, were conducted on flume models of sandy fluvial systems. We conducted two experiments, one to reveal the penetration depth and resolution of the GPR antenna and to reconstruct the 3D architecture of fluvial deposits created in a flume, and the other to examine the characteristics of reflection boundaries. The experimental materials were mainly loamy soil. The first experiment showed that a 1.6GHz antenna was suited to laboratory use, offering a depth resolution of 2–3cm in full penetration of a bed 15–24cm thick. GPR scanning yielded an accurate reconstruction of the 3D architecture of a fluvial channel using magnetite marker beds. The second experiment also successfully imaged a 3D architecture using quartz sand instead of magnetite, and loamy soil, which have different relative permittivities. This research shows that GPR is a feasible technique for 3D analysis of experimental flume deposits.

Analysis of the capabilities of low frequency ground penetrating radar for cavities detection in rough terrain conditions: The case of Divača cave, Slovenia

High frequency ground penetrating radar (GPR) is usually applied for cavities detection in a shallow subsurface of karst areas to prevent geotechnical hazards. For specific projects, such as tunnel construction, it is important to detect also larger voids at medium depth range. However, dimensions of classical rigid low frequency antennas seriously limit their applicability in a rough terrain with dense vegetation commonly encountered in a karst. In this study recently developed 50 MHz antennas designed in a tube form were tested to detect cave gallery at the depth between 12 m and 60 m. The Divaca cave was selected because of a wide range of depths under the surface, possibility of unknown galleries in the vicinity and a rough terrain surface typical for Slovenian karst. Seven GPR profiles were measured across the main gallery of the cave and additional four profiles NE of the cave entrance where no galleries are known. Different acquisition and processing parameters were analysed together with the data resolution issues. The main gallery of the cave was clearly imaged in the part where the roof of the gallery is located at the depth from 10 m to 30 m. The width of the open space is mainly around 10 m. Applied system was not able to detect the gallery in the part where it is located deeper than 40 m, but several shallower cavities were discovered which were unknown before. The most important result is that the profiles acquired NE of the cave entrance revealed very clearly the existence of an unknown gallery which is located at the depth between 15 m and 22 m and represents the continuation of the Divaca cave. Access to this gallery is blocked by the sediment fill in the entrance shaft of the cave. The results of the study are important also for future infrastructure projects which will involve construction of tunnels through karstified limestone and for speleological investigations to direct the research efforts.Keywords: ground penetrating radar, cavity detection, spatial resolution, limestone, Divača cave.

Integrated non-invasive sensing techniques and geophysical methods for the study and conservation of architectural, archaeological and artistic heritage

Integrated non-invasive sensing techniques and geophysical methods for the study and conservation of architectural, archaeological and artistic heritage

Time‐Lapse Geophysical Investigations over a Simulated Urban Clandestine Grave*

A simulated clandestine shallow grave was created within a heterogeneous, made-ground, urban environment where a clothed, plastic resin, human skeleton, animal products, and physiological saline were placed in anatomically correct positions and re-covered to ground level. A series of repeat (time-lapse), near-surface geophysical surveys were undertaken: (1) prior to burial (to act as control), (2) 1 month, and (3) 3 months post-burial. A range of different geophysical techniques was employed including: bulk ground resistivity and conductivity, fluxgate gradiometry and high-frequency ground penetrating radar (GPR), soil magnetic susceptibility, electrical resistivity tomography (ERT), and self potential (SP). Bulk ground resistivity and SP proved optimal for initial grave location whilst ERT profiles and GPR horizontal "time-slices" showed the best spatial resolutions. Research suggests that in complex urban made-ground environments, initial resistivity surveys be collected before GPR and ERT follow-up surveys are collected over the identified geophysical anomalies.