Ground Penetrating Radar Method Research Articles

Shedding light on the Sudanese Dark Ages: Geophysical research at Old Dongola, a city-state of the Funj period (16th-19th centuries).

The article presents the results of magnetic and ground‐penetrating radar (GPR) research carried out in Old Dongola in northern Sudan in 2018 and 2020, within the framework of a project designed to investigate the transition from Christianity to Islam taking place in the capital of the Nubian kingdom of Makuria. The integrated datasets from the application of two geophysical methods, of which one is the standard magnetic method used on sites in the Nile Valley and the other ground‐penetrating radar, enhanced the archaeological interpretation, focused in this case on a reconstruction of the urban layout of the 16th–18th‐century Funj settlement within the walls of the Dongola Citadel. The magnetic method, the effectiveness of which has gone unquestioned with regard to the study of silt architecture in the Nile valley, was successful in mapping the general outline of the settlement on the Citadel hill and in the quarter north of the walls. The GPR survey (450‐MHz antenna) provided a much more detailed image of the street grid and was much more effective than the magnetic method in tracing the course of mud‐brick walls in a sandy matrix containing baked brick rubble. Verification of the geophysical results through the excavation of selected parts of the Citadel not only satisfied the objectives of the archaeological project, which was to establish the overall street and building layout in the research area, but also confirmed the effectiveness of the two prospection methods applied in combination and the potential of integrated research with the use of the GPR and magnetic methods for the study of mud‐brick and baked brick architecture on settlement sites in Sudan.

An Improved GPR Method Based on BP and RPCA for Tunnel Lining Defects Detection and Its Application in Qiyue Mountain Tunnel, China

Tunnel lining defects are one of the most common problems that tunnels experience during operation, and they can pose severe safety risks. The most popular nondestructive testing method for detecting tunnel lining defects is ground penetrating radar (GPR), one of the basic geophysical applications. However, detection responses might differ significantly from the real shape of tunnel lining defects, making it challenging to identify and interpret. When data quality is poor, interpretation and identification become more challenging, resulting in a high cost of tunnel repairs. The improved back projection (BP) imaging and robust principal component analysis (RPCA) are used in this work to offer a GPR data processing method. Even in the event of poor data quality, our method could recover GPR responses, allowing the shapes and locations of tunnel lining flaws to be clearly depicted. With BP imaging, this approach recovers the tunnel defects’ responses to better forms and positions, and with RPCA, it further isolates the target imaging from clutters. Several synthetic data demonstrate that the approach presented in this work may successfully repair and extract the positions and forms of lining defects, making them easier to identify and comprehend. Furthermore, our technique was used to GPR data gathered from the Qiyue Mountain Tunnel in China, yielding more accurate findings than the traditional method, which was validated by the actual scenario to illustrate the efficiency of our method on real data.

Application of Combined Geophysical Methods for the Examination of a Water Dam Subsoil

The paper presents the results of geophysical measurements that were carried out in the vicinity of the water dam/water reservoir supplying the city of Bielsko-Biala with drinking water. The measurements were performed in order to non-invasively detect faults, fractured zones and areas filled with breccia, which may be, at the same time, a preferential path of groundwater flow. The aforementioned factors influence the stability of the dam. The general identification of the examined media was realized by the electrical resistivity tomography method. The ERT surveys were supplemented by capacitively-coupled resistivity. The electrical methods allowed them to recognize geological settings, indicate possible fault locations, and point out the fault plane as a path of water flow. The ground penetrating radar method detected fractured and filled water areas and underground water paths in the dam’s forefield as a result of the method’s very high resolution. The high resolution seismic reflection method provided a clear and high resolution image of the relatively deep geological structure and verified a location and the run of the faults. In general, the complex geophysical-geological interpretation enabled classification of the unconsolidated/fractured zones associated with faults as a place where the erosion process is the most intense and can bring danger on the dam. Finally, it was confirmed that the area should be the subject of geophysical monitoring.

Research on application of ground penetrating radar array method based on plane beam signal in different geological models

The traditional common-offset ground penetrating radar method measures point by point along the survey line with a single transmitter and a single receiver. Due to the influence of the antenna radiation power and the low-pass filtering function of the earth medium, an intense amplitude gain cannot be obtained when the signal is intercepted. This article addresses a plane beam signal ground penetrating radar array observation method based on high radiation power gain. The transmitting antenna array simultaneously excites the pulse signal with the same centre frequency. All the transmitted signals interfere with each other at the near surface to form a plane beam signal, and the electromagnetic energy is superimposed mutually to increase the radiation power. We applied the plane beam signal ground penetrating radar array method to different geological models constructed by the finite difference time-domain (FDTD) algorithm for numerical simulation in this research. Since there are various offsets in the array ground penetrating radar observation method, we introduce a composite frequency shift-perfect matching layer (CFS-PML) based on the recursive convolution method as the absorbing boundary condition. It eliminates the problem of secondary reflection caused by the angle variation of the incident wave. The research result shows that the plane beam signal illuminates the target uniformly in space, can eliminate the discontinuity in profile data caused by the directivity of the antenna, improve the stability and quality of the echo signal, and enrich the target response parameters.

Integrating Ground Penetrating Radar, Induced Polarization and Aerial Photograph to Analyze Land Subsidence in Borehole Mining Operation Area: A Case Study from South Bangka Island

The remaining alluvial tin reserves around large ex-mining area can be an opportunity to optimize the potential reserves using a small-scale mining system. One of the latest breakthroughs in the mining system for the remaining alluvial tin reserves on land is the borehole mining (BHM) method. However, mining operations using BHM have several environmental impacts especially related to its former holes. This study aims to identify the changes in geometry of the former holes both on the surface and below the surface through direct field observations and measurements using geophysical methods. The study site is in the large ex-mining area of Air Nudur Block in South Bangka Regency, Bangka Belitung Islands Province. The geophysical methods used to identify the changes in the geometry of the BHM holes are GPR (ground penetrating radar) and IP (induced polarization). The GPR method has high resolution subsurface visual capabilities at shallow depths and this method can distinguish between stable and unstable layers. The IP method is used to determine the overburden layer and the condition of the alluvial layer where some of it has become a hole. These two methods will mutually reinforce in interpreting the change in the geometry of the BHM holes. Changes in hole diameter and depth were measured directly in the field within 2 (two) months from the completion of mining operations using the BHM method followed by the periodic topographic measurements using UAV (unmanned aerial vehicle). The results of observations on changes in the elevation of the ground surface around the former BHM hole indicated that the land level subsided by about 1 m. Meanwhile, the results of GPR data processing showed changes in the hole geometry with the hummocky radargram pattern into chaotic. Interpretation of IP data processing shows resistivity values of 250 - 1700 ohm.m and chargeability of 15 - 25 ms in the disturbed alluvial layer around the former BHM holes.

Multi frequency Ground-Penetrating Radar method for mapping underground pipes and man-made objects

Mapping of subsurface infrastructure such as pipelines, pipe ducts as well as man-made objects located below the earth surface is a difficult task in geotechnical engineering due to the need to direct contact to the object. Ground-Penetrating Radar (GPR) method as one of geophysical methods is an appropriate technique to solve such problems due to its capability to effectively provide the existence, the location and the depth of buried shallow objects. Despite many advantages, the application of GPR method is limited by achieved depth and resolution range that is frequency dependent. To overcome such problems, the so-called multi-frequency compositing method with Optimal Spectral Whitening (OSW) technique is studied and applied on real data acquired in the Muarakarang Combined Cycle Power Plant area located in the Northern part of Jakarta, the Capitol of Indonesia. Datasets from GPR measurement with 100 MHz and 250 MHz was used. Each radargram from the same path was processed individually and then joined to become multiple composite radargram. The resulted composite radargram from a GPR line we studied has shown clearer image for interpretation rather than individual interpretation. The applicability of this multi-frequency compositing recommend further study to solve some facing problems in geotechnical engineering.

A NEW BRANCH OF THE ANIO NOVUS AQUEDUCT (ROME, ITALY) REVEALED BY ARCHAEOLOGY AND GEOPHYSICS

Abstract. The area south-east of Rome is characterised by the presence of several roman aqueducts which brought water to the eternal city from the Apennine and Alban Hills springs. In the last 40 years, several pieces of evidence about these aqueducts were acquired during the realisation of archaeological test trenches before building activities. In 2019, a small branch of a subterranean aqueduct unknown to the Latin sources was unearthed in Via dei Sette Metri. Here we show that this aqueduct is a lateral branch of the Anio Novus, a major imperial aqueduct built between 38 and 52 CE. To achieve this result, we employed detailed photogrammetric restitution of the new aqueduct and an integrated geophysical survey focused in the area where the Anio Novus was supposed to pass. Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) methods were used to reconstruct aqueduct paths and their relative heights. Different light conditions were tested during the picture acquisition step to determine the best practice in the photogrammetric restitution. The results obtained in this study confirmed the great effectiveness of the integration between geophysical investigation methods and the modern archaeology approach in detecting buried ancient structures.

Using Ground Penetrating Radar for Permafrost Monitoring from 2015–2017 at CALM Sites in the Pechora River Delta

This paper describes the results of ground penetrating radar (GPR) research combined with geocryological data collected from the Circumpolar Active Layer Monitoring (CALM) testing sites in Kashin and Kumzha in August 2015, 2016, and 2017. The study area was located on the Pechora River delta. Both sites were composed of sandy ground and the permafrost depth at the different sites ranged from 20 cm to 8–9 m. The combination of optimum offset and multifold GPR methods showed promising results in these investigations of sandy permafrost geological profiles. According to direct and indirect observations after the abnormally warm conditions in 2016, the thickness and water content of the active layer in 2017 almost returned to the values in 2015 in the Kashin area. In contrast, the lowering of the permafrost table continued at Kumzha, and lenses of thin frozen rocks that were observed in the thawed layer in August of 2015 and 2017 were absent in 2016. According to recent geocryological and geophysical observations, increasing permafrost degradation might be occurring in the Pechora River delta due to the instability of the thermal state of the permafrost.

Contributions of ground‐penetrating radar in research of some predynastic and dynastic archaeological sites at the eastern and western banks of the River Nile, Assiut, Egypt

AbstractThe ground‐penetrating radar (GPR) prospection method has rarely been used previously in Egyptian archaeology and never for a necropolis. Archaeologists have looked at GPR as a powerful method for exploring subsurface spatial patterns in the archaeological record without excavation. The results of the GPR survey were compared with the archaeological excavation outcomes on two archeological sites in Assiut. The first site is the temple located on a rocky bench on the northern slopes of El‐Hamamia, the Eastern bank of the Nile (a part of El Badari civilization period, belongs to Predynastic cemeteries). The second is the rocky tomb at the Western bank of the Nile at Gahdem (belongs to the period from the IXth to the XXXth dynasty). The main purpose of this study is to correlate the types of reflections recorded from GPR profiles and high‐amplitude features visible in amplitude maps with unearthed archaeological features. The applied software was able to process and analyse different digital data set with the given parameters. In each investigated archaeological area, the details of the GPR model are correlated level‐by‐level to the data of archeological excavations of ancient ages and data of the historical documents. Three‐dimensional time‐slices of the GPR data allow the identification of the enhanced targets of potential archaeological interest before planning excavation. Therefore, this research paper can be used as a benchmark to evaluate the efficiency of GPR method for identifying buried archaeological artifacts/vestiges for future archaeological prospection in Egypt.

Using Ground Penetrating Radar and Resistivity Methods to Locate Unmarked Graves: A Review

The location of unmarked graves in forensic and archaeological investigations is legally and culturally important. In a forensic context, locating covert burials of missing persons can provide closure to the family, as well as facilitating the successful prosecution of the individual(s) responsible. Archaeologically, burials provide an important source of information about health, diet, physical anthropology, and culture. Despite the importance of these features, the location of unmarked graves with conventional archaeological and forensic techniques, such as excavation, is difficult and expensive. As a result, geophysical techniques have been widely applied to the location of unmarked graves as they are non-invasive, cost and time effective, and avoid the unnecessary disturbance of human remains. This article brings together the literature on ground penetrating radar (GPR), and two resistivity methods, electrical resistivity tomography (ERT) and fixed probe resistivity (FPR), on their ability to locate burials and reviews their use in forensic and archaeological investigations. This paper aims to provide law enforcement personnel, archaeologists, geophysicists, and interested academics with an overview of how these techniques work, how they have been previously applied to grave detection, and the strengths and weakness of these methods.

ANALISIS POTENSI LIKUIFAKSI DI DAERAH SERANGAN BALI SELATAN MENGGUNAKAN METODE PROBABILISTIK DAN METODE GROUND PENETRATING RADAR (GPR)

Liquefaction causes physical damage on land and has potential to cause more fatalities. In addition, southern part of Bali Island is one of the tourist destination areas with quite high liquefaction potential due to soil condition and large number of potential earthquakes. Research on liquefaction potential analysis at Serangan, Southern Bali was conducted by using probabilistic and ground penetrating radar (GPR) methods. This research aims to obtain information on shallow layers, land subsidence dueto earthquakes theoretically, and probability of liquefaction occurrences in the area of Serangan, Southern Bali by considering several parameters, such as Bali earthquake (2020) and Lombok earthquake (2018). The GPR data was processed by ReflexW 7.0 software, and probabilistic by Microsoft Excel 2010. The probabilistic and GPR results indicated ground water level was at 2 m depth and the liquefaction occurrence was 92.22% with ground acceleration of 0.5749 gal at 3.5 m in depth, which was 10 km away from epicenter due to an earthquake with a magnitude of 7.7.
 Keywords: Ground Water Level; Land Subsidence; Probability; ReflexW 7.0 Software

GPR-inferred fracture aperture widening in response to a high-pressure tracer injection test at the Äspö Hard Rock Laboratory, Sweden

We assess the performance of the Ground Penetrating Radar (GPR) method in fractured rock formations of very low transmissivity (e.g. T ≈ 10−9–10−10 m2/s for sub-mm apertures) and, more specifically, to image fracture widening induced by high-pressure injections. A field-scale experiment was conducted at the Äspö Hard Rock Laboratory (Sweden) in a tunnel situated at 410 m depth. The tracer test was performed within the most transmissive sections of two boreholes separated by 4.2 m. The electrically resistive tracer solution composed of deionized water and Uranine was expected to lead to decreasing GPR reflections with respect to the saline in situ formation water. The injection pressure was 5000 kPa leading to an injection rate of 8.6 mL/min (at steady state) that was maintained during 25 h, which resulted in a total injected volume of 13 L. To evaluate the fracture pathways between the boreholes, we conducted 3-D surface-based GPR surveys before and at the end of the tracer tests, using 160 MHz and 450 MHz antennas. Difference GPR data between the two acquisitions highlight an increasing fracture reflectivity in-between the boreholes at depths corresponding to the injection interval. GPR-based modeling suggests that the observed increasing reflectivity is not due to the tracer solution, but rather to a 50% widening of the fracture. Considering prevailing uncertainties in material properties, a hydromechanical analysis suggests that such a degree of widening is feasible. This research demonstrates that field-scale in situ GPR experiments may provide constraints on fracture widening by high-pressure injection and could help to constrain field-scale elastic parameters in fractured rock.

Archaeological Investigation and Hazard Assessment Using Magnetic, Ground-Penetrating Radar, and GPS Tools at Dahshour Area, Giza, Egypt

An archeological study using magnetic and ground-penetrating radar methods has been performed at the Dahshour region (Giza, Egypt), where various covered structures have not been found because of the long coercion of the zone under the military specialists. Dahshour is the southern extension of the Saqqara and Giza Pyramids plateau, around 25 km south of Cairo. The area is known for its colored pyramids—the white, red, and black pyramids, and the famous Bent Pyramid. Four investigation sites were chosen around the Bent Pyramid complex. The geophysical investigation has revealed the presence of some buried structures made up of mud bricks such as tombs, mud-brick walls, causeway, and remains of an ancient temple. Numerous limestone blocks were also detected. The study indicates the possible existence of an older valley temple made up of mud bricks and confirms the existence of another causeway that led to the Nile Valley. To protect the Egyptian heritage around this vital area, a detailed computation of the current crustal stress/strain state has been performed by taking into account all the available GPS observations. Achieved results indicated that the southern and the southeastern sectors of the investigated area are currently accumulating strain, and this means that there is a possibility for future earthquakes to occur around this vital archaeological area. Buried structures are preserved by confinement in the burial materials like a large mold. However, external load or stress can still cause damage. Therefore, during excavation, the stress should be reduced to avoid wall collapsing and structure damage. Therefore, it is recommended to start excavation from the stress direction from the southern side.

Nondestructive methods complemented by FEM calculations in diagnostics of cracks in bridge approach pavement

Nondestructive methods of road pavement diagnostics are an alternative to traditional approach to pavement failure investigation. The article presents a detailed multidisciplinary inspection carried out using ground-penetrating radar (GPR), laser scanning technology and finite element method (FEM) calculations. It was done in order to assess the factors that contributed to occurrence of premature cracks of a bridge approach pavement. Assessments of permittivity values in the GPR method are dependent on two factors: thickness of successive layers and electromagnetic wave reflection in time. Electromagnetic field propagation in the pavement structure was also simulated using two numerical models: the first one reflected the undamaged pavement, while the second one included the defects next to the bridge joint. The comparison of the radargrams for both models enables identification of reflections and anomalies caused by the assumed defects. Nonhomogeneous compaction zones in the bridge approach pavement structure were detected by analysis of layer permittivity and anomalies observed in the in situ GPR maps. The GPR measurements were positively verified afterwards by values of air void content in the pavement layers, determined in standard invasive tests. Laser scanning technology was also used in the distressed area in order to assess its geometric changes. Results are presented in the form of contour plots depicting differences between the measured and the designed surfaces. The three-dimensional finite element (FE) model of the approach pavement was created to determine pavement deformation under moving load and stress state next to the bridge joint. The influence of insufficient support of the top asphalt layers on pavement response was investigated. The analysis of the cracks shows that some errors were made both during the design process and construction of the bridge approach pavement.

Practical data acquisition strategy for time-lapse experiments using crosshole GPR and full-waveform inversion

Crosshole ground penetrating radar (GPR) methods are increasingly used in time-lapse studies of flow in the uppermost near subsurface with important implications for our understanding of e.g., water infiltration in the unsaturated zone, and fluid flow in the saturated zone. A particular challenge in such time-lapse crosshole studies is the trade-off between collecting sufficient data to be able to resolve how a tracer moves, and, minimizing the data acquisition time such that the data approximates a static state. We test how dense recording geometries are needed for resolving a gas bubble injected in a highly heterogeneous chalk reservoir analogue using a full-waveform inversion (FWI) approach for modelling the crosshole GPR data. We show that even relatively sparse geometries provide sufficient resolution of the permittivity contrast caused by the gas bubble, provided that the detailed background permittivity structure is known from prior (before gas injection) FWI analysis of densely recorded high-resolution data. The conductivity contrast caused by the gas is more challenging to recover and the resolution suffers to a higher degree when reducing the survey geometry or at higher noise levels. As long as the permittivity change during the time-lapse experiment is the main target, a significant reduction in acquisition time is therefore possible as compared to the time needed to record the background permittivity structure. This reduced acquisition time has important practical implications for time-lapse experiments under realistic conditions. Our results are based on synthetic analysis based on a realistic subsurface scenario closely linked to characterization of heterogeneous chalk reservoirs. However, our findings also have important implications for planning of future time-lapse studies in other settings.

Determination of historical graves by ground penetrating radar method: Sakarya Field Battle (August 23 – September 13, 1921, Turkey)

ABSTRACT The Sakarya Field Battle was the last phase of the forward operation of the Greek Asia Minor Army, which started at the end of March 1921. Although there are contradictory numbers regarding the losses of the parties in the Sakarya Field Battle in the literature, it is generally accepted that the Turkish Army lost 5,713 martyrs. The Ground Penetrating Radar (GPR) method was applied to determine the accuracy of findings observed on the surface and to determine burial sites. Geophysical anomalies were detected in 2D profiles from the obtained results. It was determined that the Turkish side buried the martyrs in east-west direction, depending on their religious traditions. The detected anomalies were evaluated in two and three dimensions and the boundaries of the burial areas and the approximate depths of the burials were obtained. The results obtained from data processing techniques showed that the GPR method is suitable for determining the locations of historical graves on battlefields. The new martyrs found as a result of the studies are thought to be soldiers whose fate was unknown, recorded as ‘missing’ in the records.

Localization of deep voids through geophysical signatures of secondary dewatering features

Discrete deep targets are a significant challenge for most surface-based geophysical techniques, even when considering high property contrasts. In general, surface-based geophysical methods lose lateral and vertical resolution with depth as a result of the limited acquisition geometry and increased signal attenuation. The former can be overcome through use of cross-borehole methods, but lateral localization is still needed for optimal borehole placement. As such, a relatively small, deep void located near the maximum depth of investigation (DOI) is very unlikely to be detected. Yet, secondary features associated with these voids can be exploited for enhanced detection performance. When voids are located below the groundwater table, a significant amount of dewatering and pumping is required to make them a functional passageway. This dewatering not only removes water from the void space but also the surrounding formation, resulting in a much larger, if more diffuse, secondary target: an induced groundwater table gradient. Many geophysical sensing methods are sensitive to subsurface moisture content. We have implemented a 2D joint-petrophysical mixing model (JPM), using inverted electrical resistivity tomography (ERT) and inverted seismic refraction models to sense changes in the groundwater table gradient. Our results are validated using the depth to bedrock, groundwater-surface water information, ground-penetrating radar, and time-domain reflectometry methods. Our initial proof of concept is applied to a shallow area with a significant soil moisture gradient, through different surface soil types and bedrock. The 2D JPM results are used to generate an estimate of air, moisture, and matrix percent fractions in the investigation area, providing a clear delineation of the groundwater surface and associated gradient. This refined hydraulic gradient estimate can then be used to laterally locate a void at or below the DOI of ERT and seismic refraction.

Ground-penetrating radar to investigate mud pumping distribution along a railway line

Mud pumping commonly occurs along railways in Taiwan and other countries. The current method for detecting mud pumping is to conduct visual inspections on nonoperational railroad tracks. When apparent mud pumping is identified on the ballast surface, it is reported to the authorities, and the mud pumping range is subsequently estimated. However, this method cannot soundly identify all occurrences of mud pumping, and implementing this method during the rainy season is challenging. In other countries, a nondestructive detection technology has been adopted to examine the structural completeness of the railroad bed, and preliminary results have been obtained. However, this technology has seldom been applied to identify mud pumping distributions. Therefore, this study proposed to use the ground-penetrating radar method to investigate mud pumping distributions. Unlike other conventional methods, the ground-penetrating radar method can identify parts of the mud pumping distribution that cannot be detected by naked eyes and can therefore prevent the occurrence of events caused by mud pumping in advance instead of relying on post remediation. The results of this study can serve as a reference for maintenance agencies to assess the range and volume of ballast replacement, thereby reducing labor and material costs.

Detection of buried human bodies using ground-penetrating radar method

Indonesia is a country that often experiences natural disasters as it is a meeting point of several tectonic plates. When a natural disaster occurs, most of the time the evacuation team having some trouble finding the buried victims underground. The Ground-Penetrating Radar (GPR) method is one of the solutions for this problem. GPR or also called georadar is a geophysical method that is used to investigate conditions under the earth’s surface using electromagnetic waves. This study aims to detect buried human bodies underground using the GPR method to increase the effectiveness and efficiency of natural disaster victims by doing a simulation measurement. It took place in one of the public cemeteries in Jakarta, Indonesia passing two graves with corpses buried around three years before the survey. GPR measurements were conducted using Geoscanners AKULA A9000+ Antenna GCB3070 to detect the buried human bodies underground. The GPR data then processed using MATLAB based program called matGPR. A series of adjustments and filters such as signal position adjustment, remove DC, mean filter, inverse amplitude decay, remove global background, and Karhunen-Loeve (KL) filter have been applied to the data. The result of data processing shows amplitude contrasts which are suspected to be the buried corpses. Further research can be conducted to investigate the buried victims from landslides, earthquakes, and other natural disasters.

Application of Technology of UAV-Mounted Ground Penetrating Radar in the Study of the Thickness of Soil Plow Layer

When the detection field is a large field, the traditional ground penetrating radar system has the problems of low detection efficiency and high labor cost. Aiming at this problem, an integrated system of UAV-mounted ground penetrating radar is designed, and a detection method based on UAV-mounted ground penetrating radar is proposed. Taking a small area of cultivated land in Taiyuan, Shanxi as an example, the detection method of UAV-mounted ground penetrating radar is applied to measure the thickness of soil cultivated layer. After the collected data is extracted and linearly interpolated, the thickness of the cultivated soil layer obtained by image analysis is similar to the measured thickness of the soil cultivated layer, which highlights the advantages of high efficiency and low cost based on the detection method of UAV-mounted ground penetrating radar , making the detection of concealed loose bodies in large sites becomes possible.