Ground Penetrating Radar Measurements Research Articles

Mapping Arctic Bottomfast Sea Ice Using SAR Interferometry

Bottomfast sea ice is an integral part of many near-coastal Arctic ecosystems with implications for subsea permafrost, coastal stability and morphology. Bottomfast sea ice is also of great relevance to over-ice travel by coastal communities, industrial ice roads, and marine habitats. There are currently large uncertainties around where and how much bottomfast ice is present in the Arctic due to the lack of effective approaches for detecting bottomfast sea ice on large spatial scales. Here, we suggest a robust method capable of detecting bottomfast sea ice using spaceborne synthetic aperture radar interferometry. This approach is used to discriminate between slowly deforming floating ice and completely stationary bottomfast ice based on the interferometric phase. We validate the approach over freshwater ice in the Mackenzie Delta, Canada, and over sea ice in the Colville Delta and Elson Lagoon, Alaska. For these areas, bottomfast ice, as interpreted from the interferometric phase, shows high correlation with local bathymetry and in-situ ice auger and ground penetrating radar measurements. The technique is further used to track the seasonal evolution of bottomfast ice in the Kasegaluk Lagoon, Alaska, by identifying freeze-up progression and areas of liquid water throughout winter.

The application of non-destructive methods in the diagnostics of the approach pavement at the bridges

The article presents the possibility of using non-destructive methods of road pavement diagnostics as an alternative to traditional means to assess the reasons for premature cracks adjacent to bridge objects. Two scanning methods were used: laser scanning to measure geometric surface deformation and ground penetrating radar (GPR) inspection to assess the road pavement condition. With the use of a laser scanner, an effective tool for road deformation assessment several approach pavement surfaces next to the bridges were scanned. As the result, a point cloud was obtained including spatial information about the pavement deformation. The data accuracy was about 3 mm, the deformations were presented in the form of deviation maps between the reference surface and the actual surface. Moreover characteristic pavement surface cross-sections were presented. The in situ measurements of the GPR method were performed and analysed in order to detect non-homogeneity in the density of structural layers of the pavement. Due to the analysis of the permittivity of individual layers, it was possible to detect non-homogeneity areas. The performed GPR measurements were verified by standard invasive tests carried out by drilling boreholes and taking cores from the pavement and testing the compaction and air voids content in asphalt layers. As a result of the measurements made by both methods significant differences in layer compacting factor values were diagnosed. The factor was much smaller in the area directly next to the bridgehead and much larger in the zone located a few meters away. The research showed the occurrence of both design and erection errors as well as those related to the maintenance of engineering structures.

Identification of deep-rooted transverse cracks using Ground Penetrating Radar

Executive summaryTransverse cracking is a surface distress resulting from various mechanisms appearing in the pavement and their occurrence proves improper action of the structure, which, in a long run will be subject to accelerated degradation. The proper evaluation of the progress of cracking is certainly helpful in finding out the origin of this type of damage; therefore, also in the correct selection of the repair technology.The use of GPR (Ground Penetrating Radar) as an auxiliary tool in assessing the structural condition of the pavement in terms of identification of transverse cracking is not a new practice. However, it is still a complicated task due to many external factors which may distort the result or even prevent analysis of data, especially in terms of interpretation of the obtained radar images.This article presents the case study for the practical use of the method of GPR inspection of the transverse cracks structure to analyse the process of restoring transverse cracks in bituminous pavement. This procedure is based on the earlier catalogue of the GPR manifestations of the elements of deep cracking structure and requires precise synchronization of the GPR measurement with cracks observed on the pavement. Explicit manifestations are only visible in expanded cracks, where the zone of material changes in the vicinity of the cracking surface has a width of at least one decimetre. Such defects usually result from the long-lasting operating process, and their presence in the deeper layers of the structure is an evidence of breaking continuity of mechanical consistency of the foundation under the cracking line.

SEA ICE THICKNESS MEASUREMENT BY GROUND PENETRATING RADAR FOR GROUND TRUTH OF MICROWAVE REMOTE SENSING DATA

Abstract. Observation of sea ice thickness is one of key issues to understand regional effect of global warming. One of approaches to monitor sea ice in large area is microwave remote sensing data analysis. However, ground truth must be necessary to discuss the effectivity of this kind of approach. The conventional method to acquire ground truth of ice thickness is drilling ice layer and directly measuring the thickness by a ruler. However, this method is destructive, time-consuming and limited spatial resolution. Although there are several methods to acquire ice thickness in non-destructive way, ground penetrating radar (GPR) can be effective solution because it can discriminate snow-ice and ice-sea water interface. In this paper, we carried out GPR measurement in Lake Saroma for relatively large area (200 m by 300 m, approximately) aiming to obtain grand truth for remote sensing data. GPR survey was conducted at 5 locations in the area. The direct measurement was also conducted simultaneously in order to calibrate GPR data for thickness estimation and to validate the result. Although GPR Bscan image obtained from 600MHz contains the reflection which may come from a structure under snow, the origin of the reflection is not obvious. Therefore, further analysis and interpretation of the GPR image, such as numerical simulation, additional signal processing and use of 200 MHz antenna, are required to move on thickness estimation.

Application of Ground Penetrating Radar Supported by Mineralogical-Geochemical Methods for Mapping Unroofed Cave Sediments

Ground penetrating radar (GPR) using a special unshielded 50 MHz Rough Terrain Antenna (RTA) in combination with a shielded 250 MHz antenna was used to study the capability of this geophysical method for detecting cave sediments. Allochthonous cave sediments found in the study area of Lanski vrh (W Slovenia) are now exposed on the karst surface in the so-called “unroofed caves” due to a general lowering of the surface (denudation of carbonate rocks) and can provide valuable evidence of the karst development. In the first phase, GPR profiles were measured at three test locations, where cave sediments are clearly evident on the surface and appear with flowstone. It turned out that cave sediments are clearly visible on GPR radargrams as areas of strong signal attenuation. Based on this finding, GPR profiling was used in several other places where direct indicators of unroofed caves or other indicators for speleogenesis are not present due to strong surface reshaping. The influence of various field conditions, especially water content, on GPR measurements was also analysed by comparing radargrams measured in various field conditions. Further mineralogical-geochemical analyses were conducted to better understand the factors that influence the attenuation in the area of cave sediments. Samples of cave sediments and soils on carbonate rocks (rendzina) were taken for X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses to compare the mineral and geochemical compositions of both sediments. Results show that cave sediments contain higher amounts of clay minerals and iron/aluminium oxides/hydroxides which, in addition to the thickness of cave sediments, can play an important role in the depth of penetration. Differences in the mineral composition also lead to water retention in cave sediments even through dry periods which additionally contribute to increased attenuation with respect to surrounding soils. The GPR method has proven to be reliable for locating areas of cave sediments at the surface and to determine their spatial extent, which is very important in delineating the geometry of unroofed cave systems. GPR thus proved to be a very valuable method in supporting geological and geomorphological mapping for a more comprehensive recognition of unroofed cave systems. These are important for understanding karstification and speleogenetic processes that influenced the formation of former underground caves and can help us reconstruct the direction of former underground water flows.

Site characterization and evaluation of the stability of the Yesilyurt Landslide (Trabzon, NE Turkey) using back analysis method

The aim of this study was to determine the soil profile of the Yesilyurt Landslide Area (NE Turkey) and to investigate the stability of the landslide area after the excavation planned by back analysis for support design. For these purposes, after the 1/1000 scaled engineering geological map was prepared, seismic refraction, electrical resistivity tomography and ground penetrating radar measurements were performed on different profiles to understand vertical and horizontal homogeneity of the landslide materials and undisturbed/disturbed soil samples were obtained from the test pits to determine the geotechnical properties of the soil. The results of the geophysical measurements showed that the landslide material was composed of two different soil zones. While the maximum thickness of the upper zone is 2.5, the thickness of the lower zone is about 5 m. The depth of dasidic rock mass is about 7 m. Residual cohesions of the soil samples obtained upper and lower zones were determined as 38 kPa and 44 kPa, and their residual friction angles were determined as 18° and 15° respectively. Unit weight values of the soil samples obtained from both zones were 16.9 kN m−3. The data obtained from laboratory tests showed that the landslide material is a uniform lithology. The geophysical measurements indicate that the wave velocity and resistivity values of these profiles differ from each other due to groundwater at a depth of 2.5 m. Limit equilibrium analysis were carried out with Slide v5.0 software using data obtained from the field measurements and laboratory tests to evaluate current and supported cases of the studied area. Because the safety factor of the slope obtained from the LE analyses is 0.99 and the studied soil environment is considered as unstable, the reliable and economical reinforcement was suggested using the retaining wall. The back-analysis method was evaluated to ensure the stability for a 1.5 safety factor and finally the lateral active forces for the retaining wall were calculated in the LE analysis as 718 kN and 1839 kN for without and with seismic load respectively.

Volumetric water content estimation of C-30 concrete using GPR

In this research, we consider a laboratory specimen of C-30 concrete block using a geophysical technique called GPR (Ground-Penetrating Radar). The volumetric water content of the C-30 concrete block can be estimated using a central frequency of 2 GHz shielded GPR antenna in a non-destructive way. In this purpose, time-lapse GPR measurements were applied over the C-30 concrete block that took about 150 days. We estimated relative dielectric permittivity of concrete block from the scatters on GPR profiles that caused by an iron bar in the concrete block. Data were acquired consecutively 5 times in each day to calculate the arithmetic mean of relative dielectric permittivity. To estimate the volumetric water content of a sample, we used previously suggested formula for various concrete classes. Based on information from the factory, the volumetric water content of the sample was 7.31% according to its composition. However, based on our estimation by the formula, the volumetric water content was estimated 7.19% at the 3rd day after the concrete block was prepared in the factory. This experiment suggests that the water content variation of the corresponding concrete sample can be monitored using the GPR method in a non-destructive way. The result may be extended to other classes of concrete as well. The suggested method is a fast, economic and simple way to estimate the volumetric water content of a concrete sample. Our time-lapse measurements can be a guide to estimate volumetric water content of C-30 concrete class.

The spatial correlation between track roughness and ground-penetrating radar inferred ballast degradation

Ballast degradation is considered to be a primary factor that contributes to the development of track roughness, and as such it is important to develop efficient techniques to assess the condition of the ballast. Ground-penetrating radar is one method that has been applied in a variety of railway foundation studies including those attempting to non-destructively assess ballast degradation. However, there has yet to be a large-scale study that attempts to correlate the ground-penetrating radar-based estimates of ballast degradation with the observed track roughness. This study investigates this correlation along a 335 km-long heavy-haul railway subdivision in Alberta, Canada. Track roughness is quantified from repeated track alignment and surface measurements spanning 15 months prior to the ground-penetrating radar data acquisition. Three sets of 400 MHz ground-penetrating radar measurements were performed in August 2012, one along each ballast shoulder and one along the track centreline. The results of this study reveal that significant correlations between the observed track roughness and the ground-penetrating radar-based interpretation of ballast degradation are rare and only exist when the data are compared at very small spatial scales. The absence of significant correlations between track roughness and the estimates of ballast degradation is primarily interpreted as being the result of ambiguous ground-penetrating radar data caused by local-scale variations in the track foundation unrelated to ballast degradation. To address these issues, potential improvements in the application of ground-penetrating radar as a ballast degradation detection tool are proposed.

The bedrock topography of Gries- and Findelengletscher

Abstract. Knowledge of the ice thickness distribution of glaciers is important for glaciological and hydrological applications. In this contribution, we present two updated bedrock topographies and ice thickness distributions for Gries- and Findelengletscher, Switzerland. The results are based on ground-penetrating radar (GPR) measurements collected in spring 2015 and already-existing data. The GPR data are analysed using ReflexW software and interpolated by using the ice thickness estimation method (ITEM). ITEM calculates the thickness distribution by using principles of ice flow dynamics and characteristics of the glacier surface. We show that using such a technique has a significance advantage compared to a direct interpolation of the measurements, especially for glacier areas that are sparsely covered by GPR data. The uncertainties deriving from both the interpretation of the GPR signal and the spatial interpolation through ITEM are quantified separately, showing that, in our case, GPR signal interpretation is a major source of uncertainty. The results show a total glacier volume of 0.28±0.06 and 1.00±0.34 km3 for Gries- and Findelengletscher, respectively, with corresponding average ice thicknesses of 56.8±12.7 and 56.3±19.6 m.

Measuring Soil Water Content with Ground Penetrating Radar: A Decade of Progress

Core Ideas There has been tremendous progress in GPR as a tool for soil water content determination. Numerous studies have shown the potential of GPR to detect and map SWC. We highlight new possibilities and achievements for GPR acquisition and processing strategies. Quantitative SWC detection and hydrological parameter estimation are possible using GPR. We encourages other communities to embrace GPR as a tool for SWC determination. Tremendous progress has been made with respect to ground penetrating radar (GPR) equipment, data acquisition, and processing since the establishment of GPR as a tool for soil water content determination in vadose zone hydrology about 25 yr ago. In this update, we aim to provide a critical overview of recent advances in vadose zone applications of GPR with a particular focus on new possibilities for multi‐offset and borehole GPR measurements, the development of quantitative off‐ground GPR methods, full‐waveform inversion of GPR measurements, the potential of time‐lapse GPR measurements for process investigations and hydrological parameter estimation, and recent improvements in GPR instrumentation. We hope that this update encourages the soil hydrology, groundwater, and critical zone community to embrace GPR as a viable tool for soil water content determination and the elucidation of subsurface hydrological processes.

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.

Random Subsampling and Data Preconditioning for Ground Penetrating Radars

Ground penetrating radars (GPRs) for mine detection can profit from the many advantages that compressed sensing can offer through random subsampling in terms of hardware simplification, reduced data volume and measurement time, or imagery simplification. An intrinsic antenna-ground model is used, canceling the undesired reverberation effects and the very strong reflection from the air–soil interface, producing higher detection rates, or even unmasking shallowly buried mines. Extensive Monte Carlo simulations on real GPR measurements (800–2200 MHz) show an increase in the probability of detection, yielding globally promising exploitable results, whenever the principal component analysis technique is used a as preconditioner, as well as providing lower random subsampling bounds for frequency and spatial measurements (cross range), whether applied individually or combined.

Zerstörungsfreie archäologische Prospektion des römischen Carnuntum – erste Ergebnisse des Forschungsprojekts „ArchPro Carnuntum“

Over the course of four years (2012–2015) the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archeology (LBI ArchPro), in collaboration with the Central Institute for Meteorology and Geodynamics (ZAMG) and on behalf of the provincial government of Lower Austria, has conducted the comprehensive, non-invasive archaeological prospection project entitled “ArchPro Carnuntum”. The purpose of this project has been to generate a basis for future archaeological research and the sustainable spatial planning and cultural heritage management in the area. By combining new information on buried archaeology using different aerial and ground-based archaeological prospection methods and a thorough archaeological interpretation of the combined data within the framework of a GIS environment, it was possible to document Carnuntum’s archaeological heritage, which is threatened by a dramatic increase in erosion and destruction through ploughing, infrastructure development and looting by treasure hunters. In total, an area covering eight square kilometres was explored at very high sampling resolution using magnetic prospection methods, while 2.5 square kilometres were mapped with ultra-high resolution ground-penetrating radar measurements. The results of the project and the spatio-temporal analysis and interpretation of the prospection data are presented here as a preliminary report.

The research on the buried public monumental complexes of Lupiae (Lecce) by geophysical prospecting

Ongoing and extensive urbanisation may threaten important archaeological structures that are still buried in urban areas. The ground penetrating radar (GPR) method is the most promising alternative for resolving buried archaeological structures in urban territories. This paper presents a case study that involves a geophysical survey employing the surface three-dimensional (3D) GPR techniques, in order to archaeologically characterise the investigated areas. The site is located in the south-western sector of the historical centre of Lecce (Apulia, Italy), where the modern city overlaps the main public monuments of the Roman municipium of Lupiae, only partially preserved or excavated: the amphitheatre, the theatre, the baths and maybe also the Forum. GPR measurements, integrated with the results of archaeological excavations and the topographical surveys of the preserved remains, were carried out in several areas regarding sectors of the ancient roman city. The GPR data were collected along a dense network of parallel profiles. The GPR sections were processed applying specific filters to the data in order to enhance their information content. The GPR images significantly contributed in reconstructing the complex subsurface properties in these modern urban areas. Strong GPR reflections features were correlated with possible ancient structures and they were integrated in the digital archaeological map of the city.

Estimating active layer thickness and volumetric water content from ground penetrating radar measurements in Barrow, Alaska.

Ground penetrating radar (GPR) has emerged as an effective tool for estimating active layer thickness (ALT) and volumetric water content (VWC) within the active layer. In August 2013, we conducted a series of GPR and probing surveys using a 500 MHz antenna and metallic probe around Barrow, Alaska. We collected about 15 km of GPR data and 1.5 km of probing data. Here, we describe the GPR data processing workflow from raw GPR data to the estimated ALT and VWC. We include the corresponding uncertainties for each measured and estimated parameter. The estimated average GPR‐derived ALT was 41 cm, with a standard deviation of 9 cm. The average probed ALT was 40 cm, with a standard deviation of 12 cm. The average GPR‐derived VWC was 0.65, with a standard deviation of 0.14.

Estimating Belowground Carbon Stocks in Isolated Wetlands of the Northern Everglades Watershed, Central Florida, Using Ground Penetrating Radar and Aerial Imagery

AbstractPeat soils store a large fraction of the global soil carbon (C) pool and comprise 95% of wetland C stocks. While isolated freshwater wetlands in temperate and tropical biomes account for more than 20% of the global peatland C stock, most studies of wetland soil C have occurred in expansive peatlands in northern boreal and subarctic biomes. Furthermore, the contribution of small depressional wetlands in comparison to larger wetland systems in these environments is very uncertain. Given the fact that these wetlands are numerous and variable in terms of their internal geometry, innovative methods are needed for properly estimating belowground C stocks and their overall C contribution to the landscape. In this study, we use a combination of ground penetrating radar (GPR), aerial imagery, and direct measurements (coring) in conjunction with C core analysis to develop a relation between C stock and surface area, and estimate the contribution of subtropical depressional wetlands to the total C stock of pine flatwoods at the Disney Wilderness Preserve (DWP), Florida. Additionally, GPR surveys were able to image collapse structures underneath the peat basin of depressional wetlands, depicting lithological controls on the formation of depressional wetlands at the DWP. Results indicate the importance of depressional wetlands as critical contributors to the landscape C budget at the DWP and the potential of GPR‐based approaches for (1) rapidly and noninvasively estimating the contribution of depressional wetlands to regional C stocks and (2) evaluating the formational processes of depressional wetlands.

Quantification of Arctic Soil and Permafrost Properties Using Ground-Penetrating Radar and Electrical Resistivity Tomography Datasets

Improving understanding of Arctic ecosystem climate feedback and parameterization of models that simulate freeze-thaw dynamics require advances in quantifying soil and snow properties. Due to the significant spatiotemporal variability of soil properties and the limited information provided by point-scale measurements (e.g., cores), geophysical methods hold potential for improving soil and permafrost characterization. In this study, we evaluate the use of a ground-penetrating radar (GPR) to estimate thaw layer thickness, snow depth, and ice-wedge characteristics in an ice-wedge-dominated tundra region near Barrow, AK, USA. To this end, we analyze GPR and point-scale measurements collected along several parallel transects at the end of the growing season and the end of frozen season. In addition, we compare the structural information extracted from the GPR data with electrical resistivity tomography (ERT) information about ice-wedge characteristics. Our study generally highlights the value of GPR data collected in the frozen season, when conditions lead to the improved GPR signal-to-noise ratio, facilitate data acquisition, and reduce acquisition-related ecosystem disturbance relative to growing season. We document for the first time that GPR data collected during the frozen season can provide reliable estimates of active layer thickness and geometry of ice wedges. We find that the ice-wedge geometry extracted from GPR data collected during the frozen season is consistent with ERT data, and that GPR data can be used to constrain the ERT inversion. Consistent with recent studies, we also find that GPR data collected during the frozen season can provide good estimates of snow thickness, and that GPR data collected during the growing season can provide reliable estimate thaw depth. Our quantification of the value of the GPR and ERT data collected during growing and frozen seasons paves the way for coupled inversion of the datasets to improve understanding of permafrost variability.

A compressive sensing-based computational method for the inversion of wide-band ground penetrating radar data

This work presents an innovative computational approach for the inversion of wideband ground penetrating radar (GPR) data. The retrieval of the dielectric characteristics of sparse scatterers buried in a lossy soil is performed by combining a multi-task Bayesian compressive sensing (MT-BCS) solver and a frequency hopping (FH) strategy. The developed methodology is able to benefit from the regularization capabilities of the MT-BCS as well as to exploit the multi-chromatic informative content of GPR measurements. A set of numerical results is reported in order to assess the effectiveness of the proposed GPR inverse scattering technique, as well as to compare it to a simpler single-task implementation.

The Jettencave, Southern Harz Mountains, Germany: Geophysical observations and a structural model of a shallow cave in gypsum/anhydrite-bearing rocks

Gypsum and anhydrite are soluble rocks, where fissures and bedding partings can be enlarged with time by the dissolution of the mineral species through water. The selective enlargement results in sub-surface voids acting as preferential flow path for the drainage of the rock. With time, larger cavities develop, and a network of cave passages can evolve. If the enlarged cave voids are not too deep under the surface, geophysical measurements can be used to detect, identify and trace these structures. We have used gravity measurements (GRAV), electrical resistivity imaging (ERI), self-potential measurements (SP), electrical conductivity measurements (EC), and ground-penetrating radar (GPR) above the cave Jettenhöhle, a cave located in the southern Harz Mountains in Germany. The Jettencave is developed in the Hauptanhydrit formation of the Permian Zechstein sequence, characterised by large breakdown rooms and an exposed water table. The overburden of the cave is only around 10–15m, and dolomitic rocks are located in close vicinity. We present results from our geophysical surveys in vicinity of the cave. We are able to identify the cave geometry from GRAV, ERI, and GPR measurements, which distinguish the local lithology of the Permian Zechstein rocks in the area. From the ERI and EC measurements, we derive information on the void volume in the soluble rocks. We finally present a three-dimensional structural model of the Jettencave and its surroundings, based on our geophysical results and the hydrological interpretation.

Incorporation of GPR data into genetic algorithms for assessing recycled pavements

The current paper outlines the necessity to incorporate Ground Penetrating Radar (GPR) during assessment procedures in order to increase the accuracy of backcalculated results through the increased accuracy provided for test location thickness data. The focus is on the assessment of a pavement that has undergone full depth reclamation with foamed asphalt (FDR-FA). The examined pavement structure was rebuilt and in operation for a total of five years at which point a scheduled monitoring program was undertaken. The monitoring of the investigated section was carried out in-situ by both Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR) measurements and the asphalt pavement layers moduli were estimated utilizing genetic algorithms and evaluated. GPR data was vital for the investigation as the coring data along the section exhibited an increased variability along the test section. Results of the investigation are found in the paper and they indicate increased accuracy from the inclusion of GPR data and point to the long term sustainability of the FDR-FA process.