High-resolution Ground-penetrating Radar Research Articles

Determination of Grave Locations with High Resolution Ground-penetrating Radar (GPR) in War Cemeteries: Sample Study of Biga (Çanakkale) War Graves

The most important turning point in Turkish history of the Çanakkale War, known in English as the Dardanelles Campaign, the Battle of Gallipoli, or the Battle of Çanakkale, involves many omissions in terms of historical records due to the situation facing the country at the time and the threats from both internal and external enemies. Though there is very valuable information like notes and maps left by officers in the Ottoman army (Col. Şevki Paşa etc.), due to the intense severity of the war much important information has not been transferred directly to the present day. Most probably, one of the areas with greatest omissions is the location of war grave sites (martyr’s cemeteries). The main reason for this is considered to be the excessive number of fallen soldiers or martyrs and the extreme loss of life in a very short period. In spite of these negative aspects, the locations of many war grave sites have been determined by detailed research by historians and the use of maps drawn during wartime. However, in these cemetery areas, approximate locations were defined for war graves and in line with this, areas were fenced off as war cemeteries. Using the same logic, an area close to the location used as Biga War hospital during the Çanakkale War was renovated and opened to visitors as Biga War Cemetery with gravestones in certain locations. The high-resolution, non-destructive shallow geophysical method of ground-penetrating radar (GPR) has long been used with the aim of identifying structural elements that are buried (graves, tunnels, archeological remains, etc.). In line with this, its use to research war grave sites in areas known as war cemeteries will illuminate the past and contribute to reorganizing war cemeteries according to war grave locations and providing the necessary importance and respect that war cemeteries deserve.

Beach-ridge architecture constrained by beach topography and ground-penetrating radar, Itilleq (Laksebugt), south-west Disko, Greenland – implications for sea-level reconstructions.

Detailed topographic data and high-resolution ground-penetrating radar (GPR) reflection data are presented from the present-day beach and across successive raised beach ridges at Itilleq, south-west Disko, West Greenland. In the western part of the study area, the present low-tide level is well defined by an abrupt change in sediment grain size between the sandy foreshore and the upper shoreface that is characterised by frequently occurring large clasts. The main parts of both fine and large clasts appear to be locally derived. Seaward-dipping reflections form downlap points, which are clearly identified in all beach-ridge GPR profiles. Most of them are located at the boundary between a unit with reflection characteristics representing palaeo-foreshore deposits and a deeper and more complex radar unit characterised by diffractions; the deeper unit is not penetrated to large depths by the GPR signals. Based on observations of the active shoreface regime, large clasts are interpreted to give rise to scattering observed near the top of the deeper radar unit. We regard the downlap points located at this radar boundary as markers of palaeo-low-tide levels. In some places, scattering hyperbolas are more pronounced and frequent than in others, suggesting differences in the occurrence of large boulders.

Microgravimetric and GPR surveys for detection of unconsolidated zones in a levee

Selected results of complex geophysical surveys carried out on the Vistula river flood levee in Cracow are herein presented. Two complementary geophysical methods were applied for detection of potential unconsolidated zones in the body of the levee, i.e. microgravimetry and ground-penetrating radar (GPR). The surveys were carried out in 2D mode, along a profile at the crown of the flood levee. Microgravimetric data reveal anomalies showing zones of decreased bulk density. These zones provide information about poor quality of the levee. The main anomaly was interpreted in a quantitative manner using gravity modelling. Non-standard GPR processing and visualization of radargrams were employed to better extract information concerning the distribution of unconsolidated zones. High resolution GPR surveys allow to outline such zones which was the basis for construction of the 2D model used in the gravimetric modelling. Integration of these two geophysical methods provided important information about the spatial variations of mass density in several unconsolidated zones within the body of the flood levee.

Coastal erosion and recovery from a Cascadia subduction zone earthquake and tsunami

Tsunamis generated by great earthquakes threaten coastal infrastructure, development, and human life. Earlier work has documented the inland extent and frequency of past tsunamis, but little is known about the magnitude of material eroded during prehistoric tsunamis and how erosion and coastal recovery are recorded in coastal stratigraphy. In this study we use high-resolution ground-penetrating radar (GPR) to image and quantify coastal erosion experienced during a late Holocene (~900calBP) Cascadia subduction zone earthquake and tsunami along the northern California coast. The GPR profiles illustrate three stratigraphic signatures created during co-seismic subsidence and tsunami erosion and coastal recovery. The first is erosional truncation of the underlying seaward-dipping reflections created by pre-tsunami normal beach progradation. The second is a series of landward-dipping, flat-lying, and channelized reflections marking the filling of erosional topography and coastal reworking of the irregular shoreline following inundation and erosion. The third is an abrupt landward termination of the stratigraphic unit marking coastal straightening and post-tsunami rejuvenation of normal coastal progradation. Erosion from the ~900calBP earthquake and tsunami extended >110m inland of the contemporary shoreline and removed/reworked 225,000±28,000m3 of sand from a 1.7-km stretch of the coast, far exceeding anything experienced during historical El Niños along the Pacific Coast of North America. This study provides the first quantitative estimate of the amount of coastal erosion from a pre-historic earthquake and tsunami and outlines a strategy for estimating erosion during similar events elsewhere.

Integration of Complementary Archaeological Prospection Data from a Late Iron Age Settlement at Vesterager—Denmark

The complementary use of various archaeological prospection data sets offers a series of new possibilities for the investigation of prehistoric settlements. In addition to the separate interpretations of the single methods, the implementation of image fusion provides an additional tool to obtain an even higher degree of data integration during the interpretation process. To investigate some possibilities and risks of image fusion, a procedure frequently used in the medical field but rarely applied in archaeology, various algorithms inside a dedicated MATLAB toolbox TAIFU (Toolbox for Archaeological Image FUsion) were tested on the geophysical prospection data from an Iron Age settlement near Vesterager in West Jutland, Denmark. The Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology had conducted large-scale, high-resolution ground-penetrating radar (GPR) and magnetometry surveys at the site in 2014, based on its discovery by the Ringkobing Museum through aerial photos and the results of a follow-up excavation in 2009. The aim was to determine if, and to what extent, geophysical prospection together with a novel integrative interpretational approach was able to add more detailed information to an already known prehistoric settlement. Results yielded a variety of deeper insights into the separate farms (dated to around AD 400), including the discovery of several new structures and more information about the construction of the longhouses, as well as a first suggestion on how to implement image fusion into the process of analysis and archaeological interpretation of geophysical data sets.

Palaeoenvironmental analysis of large-scale, high-resolution GPR and magnetometry data sets: the Viking Age site of Gokstad in Norway

Large-scale, high-resolution geophysical data sets offer new possibilities for the comprehensive study of archaeological landscapes. In addition to the mere archaeological component, these data sets carry palaeoenvironmental information about the study area. Such information was known but rarely used in conventional geophysical surveys, which is mainly due to methodological issues. The Viking Age site of Gokstad in the Norwegian Province of Vestfold was chosen as a pilot study in order to perform a palaeoenvironmental analysis of large-scale, high-resolution ground-penetrating radar (GPR) and magnetometry data sets. The aim was to investigate how much palaeoenvironmental information is contained in such data sets, how this information can be extracted and analysed and whether it is relevant for the archaeological interpretation. Results yielded a variety of different palaeoenvironmental aspects including characteristics of the Viking Age shoreline, traces of former topography as well as insights into the palaeohydrology of the study area.

High-resolution ground-penetrating radar profiles of perennial lake ice in the McMurdo Dry Valleys, Antarctica: Horizon attributes, unconformities, and subbottom penetration

Ground-penetrating radar (GPR) is not commonly used to study lake ice, and in general, the ground-based use of radar frequencies greater than 500 MHz in cryosphere geophysics is rare, due to a general interest in deeper stratigraphy and the difficulty of extensive profiling over rough snow surfaces. Our goal was to find further information on the origin of the deposition and formation of intra-ice layers, bottom topography, and subbottom deposits using GPR with pulses centered near 850 MHz on two permanently ice-covered lakes in the McMurdo Dry Valleys, Antarctica. The profiles were obtained using a one-person sled operation over Lake Bonney, which is typical of lakes in the region, having an ice thickness that ranges between 3 and 5 m, and Lake Vida, where the maximum ice depth is at least 27 m. Lake Bonney exhibits a semicontinuous sediment horizon at approximately a 2-m depth and several minor horizons. In contrast, Lake Vida contains unconformably eroded and folded continuous reflection horizons, packages of minor horizons between major horizons, evidence of incised fluvial deposition along the bottom, and subbottom penetration of at least 4.5 m in some areas. Where the ice thickness is less than 20 m, the lake is frozen to the bottom. Most horizon waveform phase attributes indicate relatively lower permittivity than in the surrounding matrix. Consequently, we interpreted these strata to be caused by layers of pure ice embedded within a salty and dirty ice matrix, which were formed during minor flooding. These findings supported previous conclusions that Lake Vida ice formed from surface runoff in combination with periods of ablation.

Application of resistivity and GPR techniques for the characterization of the coastal litho-stratigraphy and aquifer vulnerability due to seawater intrusion

The objective of this study is to identify geological properties and structural settings, allowing salt-water intrusion to the aquifers in oceanic originated rock formations of the South Andaman Island. To evaluate the impact of seawater in groundwater aquifer, several geophysical surveys using ground penetrating radar (GPR) and resistivity sounding were performed through the most significant sites, located near coastal areas, tidal channels and agriculture land. High-resolution GPR images were obtained and combined with resistivity sounding, which allows to identify the mixing/transition zone of fresh and saline groundwater and also successfully delineated the structural geometry and litho-stratigraphic details of aquifers. We show that the sedimentary formations are highly susceptible to seawater intrusion than the mantle originated ophiolites. Further, potential impacts from seawater intrusion are higher along the west coast than the east coast because of macro-pore tendency of soils allows seawater filtration.

Automated high-resolution GPR data collection for monitoring dynamic hydrologic processes in two and three dimensions

An automated GPR data-collection system was constructed to monitor dynamic hydrologic processes with high spatiotemporal resolution. The design of the system allows for fast acquisition of constant-offset profiles (COP) and common-midpoint surveys (CMP) to monitor unsaturated flow at multiple locations. A fast and accurate motion-control system enables the high-resolution monitoring of spatial patterns of reflectors through time while preserving important information about the normal moveout of reflectors for velocity analysis. In two experiments, infiltration was monitored using time-lapse ground-penetrating radar (GPR) measurements in two and three dimensions. The data from both experiments provide substantial qualitative insight about the dynamics of hydrologic events and a path forward for quantitative analysis of surface-based GPR monitoring data. Analysis shows (1) the advantages of collecting high-resolution time-lapse data, (2) the complexities of patterns associated with the wetting of the soil, and (3) evidence of nonuniform propagation of a wetting front through the soil column.

Improved high-resolution GPR imaging and characterization of prehistoric archaeological features by means of attribute analysis

We propose a novel procedure for the analysis and interpretation of Ground-Penetrating Radar (GPR) data from archaeological data and we test the method in challenging conditions at a prehistoric settlement on the Stromboli Island (Italy). The main objective of the proposed procedure is to enhance the GPR capability of identifying and characterizing small-size and geometrically irregular archaeological remains buried beneath rough topographic surface conditions. After the basic GPR processing sequence, including topographic correction using a high-resolution Digital Elevation Model acquired from 3-D Laser Scanner, the procedure encompasses a multi-attribute analysis and iso-attribute surfaces calculation with different volume extraction solutions to emphasize vertical and lateral variations within GPR data cubes. The test was performed in cooperation with the archaeological team to calibrate the results and to provide detailed information about buried targets of potential archaeological interests to plan further excavations. The results gave evidence of localized buried remains and allowed detailed pre-excavation planning. The archaeological excavations validated the results obtained from the GPR survey. The research demonstrates that the proposed GPR procedure enhances the ability to identify and characterize archaeological remains with high accuracy even in complex surface and subsurface conditions. Such logistical situation is very common, particularly in prehistoric sites, which are often characterized by discontinuous, small and irregular targets that cannot be identified by standard processing and analysis strategies.

High resolution GPR mapping of Late Bronze Age architecture at Kalavasos-Ayios Dhimitrios, Cyprus

At the Late Bronze Age site of Kalavasos-Ayios Dhimitrios in southern Cyprus, the subterranean remains of previously unknown buildings were recently discovered and mapped with ground-penetrating radar (GPR). Though the fine-grained calcareous substrate at the site was not necessarily ideal for GPR—exhibiting a high clay fraction, significant volumetric water content, and scattering rubble—the buildings were mapped in excellent resolution with sufficient detail to indicate walls, entry-ways, and other architectural details. This was achieved with a somewhat lower frequency antenna (250 MHz center frequency) than is commonly recommended in archeological geophysics. The 250 MHz system was employed in order to mitigate the potentially negative effects of the lossy substrate, which had proved problematic for past research using higher frequency antennas. Our work showed that excellent GPR results were possible in this substrate by simply lowering the antenna frequency, and that electromagnetic attenuation likely improved spatial resolution allowing for the detection of greater detail than might be expected. The resulting GPR findings offer a fresh perspective on this important archeological site, while indicating that conservative antenna selection is not only sometimes warranted, but may be crucial in some archeological GPR investigations.

Integrating EMI and GPR data to enhance the three-dimensional reconstruction of a circular ditch system

Abstract Ground Penetrating Radar (GPR) reflections occur at sharp interfaces between contrasting soil layers. Generally, the depth of the interface is expressed as the two-way travel time from the transmitting to the receiving antenna. Converting these travel times to depths requires knowledge of the propagation speed of the GPR wave in the soil. This velocity is influenced by the electric properties of the soil water content, mainly by the dielectric permittivity (e). The soil electrical conductivity (σ), which also depends on the soil water content, can be accounted for by electromagnetic (EMI) induction prospecting. A procedure was proposed to thoroughly characterize a circular ditch system by inverting the apparent electrical conductivity (σ a ) measurements from a multi-receiver EMI instrument based on GPR profile data. A fitting procedure allowed to calibrate both the propagation speed of the GPR waves up to the interface between the ditch infilling and the underlying sand and the conductivities of both layers. Integrating the simultaneous EMI measurements and high-resolution GPR depth profiles and – slices improved the non-invasive dimensioning of the circular ditch system.

Sedimentological and Geophysical Signatures of A Relict Tidal Inlet Complex Along A Wave-Dominated Barrier: Assateague Island, Maryland, U.S.A

Abstract Assateague Island is a classic example of a wave-dominated, retrograding barrier island, with its recent geological history punctuated by episodes of overwash and breaching (comparable to the Outer Banks, North Carolina; northern New Jersey coast; Long Island, New York, etc.). This study aims to provide high-resolution data of a paleo-inlet which may lead to a more precise evolutionary model of other wave-dominated barrier islands. The study focuses on a historically stable segment fronting the Green Run Bay. The site lies north of the historical Green Run Inlet (active until 1880); however, there is no morphological or historical evidence of this inlet occupying the more northerly position, thus suggesting that the study site may represent a relict part of the barrier. High-resolution ground-penetrating radar (GPR) images, complemented with sediment cores and multi-dating techniques, were used to reconstruct the geological legacy of the Green Run Bay segment. The findings indicate that a shallow backbarrier channel, still visible within the Green Run Bay, can be traced to a large (> 380 m wide, 3.0–3.5 m thick) channel cut-and-fill structure beneath the barrier. The channel fill consists of tangential- to sigmoidal-oblique, southward-dipping reflections downlapping onto channel lag facies, which overlie subhorizontal bay-fill strata. Mollusks from the bay fill yield calibrated ages of 4419–2018 yr BP. The paleo-channel facies overlying the bay deposits exhibit a fining-upward sequence, with a mean grain size decreasing from 0.44 to 2.43 φ (0.74 to 0.19 mm). Optically stimulated luminescence dating places the middle part of the inlet fill at 730–590 yr BP. The paleo-channel fill does not extend to the south and therefore is a separate relict feature that predates the historical Green Run Inlet. The paleo-tidal prism of the relict channel was at least 17 × 106 m3, which is comparable to many wave-dominated historical and active inlets along the Atlantic Seaboard. Findings in this study provide the geological background for coastal hazard assessments and offer a mesoscale example of inlet-facies architecture in wave-dominated barrier sequences identified in the rock record.

GPR investigation of tephra fallout, Cerro Negro volcano, Nicaragua: a method for constraining parameters used in tephra sedimentation models

Most tephra fallout models rely on the advection–diffusion equation to forecast sedimentation and hence volcanic hazards. Here, we test the application of the advection–diffusion equation to tephra sedimentation using data collected on the proximal (350 to ~1,200 m from the vent) to medial (greater than ~1,200 m from the vent) tephra blanket of a basaltic cinder cone, Cerro Negro volcano, located in Nicaragua. Our understanding of tephra depositional processes at this volcano is significantly improved by combination of sample pit data in the medial zone and high-resolution ground-penetrating radar (GPR) data collected in the near vent and proximal zones. If the advection–diffusion equation applies, then the thickness of individual tephra deposits should have Gaussian crosswind profiles and exponential decay with distance away from the vent. At Cerro Negro, steady trade winds coupled with brief eruptions of relatively low energy (VEI 2–3) create relatively simple deposits. GPR data were collected along three crosswind profiles at distances of 700–1,600 m from the vent; sample pits were used to estimate thickness of the 1992 tephra deposit up to 13 km from the vent. Horizons identified in proximal GPR profiles exhibit Gaussian distributions with a high degree of statistical confidence, with diffusion coefficients of ~500 m2 s−1 estimated for the deposits, confirming that the advection–diffusion equation is capable of modeling sedimentation in the proximal zone. The thinning trend downwind of the vent decreases exponentially from the cone base (350 m) to ~1,200 m from the vent. Beyond this distance, deposit overthickening occurs, identified in both GPR and sample pit datasets. The combined data reveal three depositional regimes: (1) a near-vent region on the cone itself, where fallout remobilizes in granular flows upon deposition; (2) a proximal zone in which particles fall from a height of less than ~2 km; and (3) a medial zone, in which particles fall from ~4 to 7 km and the deposit is thicker than expected based on thinning trends observed in the proximal zone of the deposit. This overthickening of the tephra blanket, defining the transition from proximal to medial depositional facies, is indicative of transition from sedimentation dominated by fallout from plume margins to that dominated by fallout from the buoyant eruption cloud—a feature of deposits previously identified in larger-volume eruptions. We interpret this change to represent a change in diffusion law, occurring at total particle fall times (the fall time threshold of numerical models) of ~400 s. Thus, the detailed GPR profiles and pit data collected at Cerro Negro help to validate current numerical models of tephra sedimentation.

Ground Penetrating Radar: Water Table Detection Sensitivity to Soil Water Retention Properties

We are interested in Ground Penetrating Radar (GPR) as a geophysical tool useful for determining the depth of the ground water table (GWT) and for monitoring shallow water infiltration in sandy soils. At hydrostatic equilibrium, the water content distribution in a homogeneous unsaturated soil down to the water saturated zone depends on the soil water retention function. A classical way to fit retention curve data is to use the van Genuchten continuous model. Using Finite Difference Time Domain simulations, we study the sensitivity of the GPR signal reflected by a van Genuchten type transition to the hydraulic parameters. We show a power type relationship between the reflected signal amplitude and the slope of the soil retention curve. Furthermore, for simulating GPR reflection data acquired above a transition from unsaturated to saturated soil, geophysicists often approximate the soil water retention curve by a piecewise linear model. We test the validity of such an approximation depending on the frequency of the radar signal and the abruptness of the retention curve. We illustrate our results with high resolution GPR data (1600 MHz) acquired above a fluctuating water table in a sand column at the laboratory scale.

Inversion of multiple intersecting high-resolution crosshole GPR profiles for hydrological characterization at the Boise Hydrogeophysical Research Site

Abstract The integration of geophysical data into the subsurface characterization problem has been shown in many cases to significantly improve hydrological knowledge by providing information at spatial scales and locations that is unattainable using conventional hydrological measurement techniques. In particular, crosshole ground-penetrating radar (GPR) tomography has shown much promise in hydrology because of its ability to provide highly detailed images of subsurface radar wave velocity, which is strongly linked to soil water content. Here, we develop and demonstrate a procedure for inverting together multiple crosshole GPR data sets in order to characterize the spatial distribution of radar wave velocity below the water table at the Boise Hydrogeophysical Research Site (BHRS) near Boise, Idaho, USA. Specifically, we jointly invert 31 intersecting crosshole GPR profiles to obtain a highly resolved and consistent radar velocity model along the various profile directions. The model is found to be strongly correlated with complementary neutron porosity-log data and is further corroborated by larger-scale structural information at the BHRS. This work is an important prerequisite to using crosshole GPR data together with existing hydrological measurements for improved groundwater flow and contaminant transport modeling.

Geological characteristics and spatial distribution of paleo-inlet channels beneath the outer banks barrier islands, North Carolina, USA

Nearly 200 km of high-resolution ground penetrating radar (GPR) data were acquired along the Outer Banks barrier island system of North Carolina, USA. GPR data combined with lithofacies and biofacies data reveal multiple depositional facies including inlet channel, flood-tide delta, overwash, peat and inner shelf. Previously undocumented paleo-inlet channels constitute a significant portion of the shallow geologic framework between Oregon Inlet and Cape Hatteras. GPR data reveal the complex stratigraphy associated with multiple sequences of cut-and-fill within inlet channels. Two types of paleochannels (non-migrating and migrating) were classified based on geometry and fill-patterns. Sediments and foraminifera collected from vibracores were correlated to GPR data to define the regional shallow stratigraphic framework. Channel-fill facies are characterized by clinoform packages, sometimes bounded by erosional surfaces, indicating variable sediment transport directions from the ocean and sound sides. Channels are incised into older flood-tide delta deposits corresponding to older inlet activity when barriers existed further seaward. Flood-tide delta deposits are capped with marsh peat and overwash units. Migrating inlet facies occur under the widest portions of the island, whereas narrow portions of the island are underlain by the non-migrating inlet facies or flood-tide delta/overwash facies. This geologic/geomorphic relationship is attributed to the successional stage of island evolution during transgression, and sediment transport processes associated with the different inlet types. The radar facies, lithofacies, and biofacies provide a comprehensive dataset that will permit more precise identification of barrier island facies in the geologic record.

Processing strategies for high-resolution GPR concrete inspections

A high-resolution multi-sensor and multi-polarization Ground Penetrating Radar (GPR) dataset was acquired on a concrete retaining wall. This dataset was characterised as a low pass filter with the help of a moving window spectral analysis. In order to examine the benefits and limits of innovative processing strategies, the dataset was processed with three different methods: classical 2-D processing, full 3-D processing followed by data fusion and inverse scattering followed by data fusion. A comparison of the results for two layers of rebar present in the wall shows that the innovative approaches improve the results for near surface structures when compared to classical 2-D processing. For deeper structures, the benefits of the innovative approaches are limited because of the low pass properties of the concrete.

IMPROVED 3-D GPR DETECTION BY NUFFT COMBINED WITH MPD METHOD

A combined method of the non-uniform fast fourier transform (NUFFT) migration and the least-square based matching pursuit decomposition (MPD) algorithms is proposed to obtain better discrimination and interpretation for subsurface from ground penetrating radar (GPR) signals. By using the modifled NUFFT migration algorithm, a fast and high resolution GPR reconstruction can be obtained with an additional reduction in storage and computation requirements. By incorporating the MPD algorithm into a migration method, denoised reconstructions are obtained to enhance objects detection, including the identiflcation of objects' geometries and the estimation of their sizes and locations. Several examples from synthetic data and fleld data are demonstrated to establish the efiectiveness of the synergic efiect by comparing it with the conventional migration methods.

Dune advance into a coastal forest, equatorial Brazil: A subsurface perspective

Abstract A large active parabolic dune along the coast of Para State, northern Brazil, was analyzed using aerial photography and imaged with high-resolution ground-penetrating radar (GPR) to map the subsurface facies architecture and point-source anomalies. Most high-amplitude (8–10 dB) subsurface anomalies are correlated with partially buried mangrove trees along the leading edge (slipface) of the advancing dune. Profiles along a 200-m long basal stoss side of the dune reveal 66 targets, most of which lie below the water table and are thus inaccessible by other methods. Signal amplitudes of point-source anomalies are substantially higher than those associated with the reflections from continuous subsurface features (water table, sedimentary layers). When complemented with exposures and excavations, GPR provides the best means of rapid continuous imaging of the geological record of complex interactions between vegetation and aeolian deposition.