Geophysical Survey Systems Research Articles

Developing a realistic numerical equivalent of a GPR antenna transducer using global optimizers

AbstractNumerical modelling of a ground‐penetrating radar (GPR) has been widely used for predicting and assessing its performance. As the transmitter and the receiver are the most essential components of a GPR system, an accurate representation of them should be included in a model. Simulating a real system is particularly challenging, especially when it comes to commercial GPR systems. A three‐dimensional model based on a 2000 MHz ‘palm’ antenna from Geophysical Survey Systems, Inc. (GSSI) is presented in this paper. The geometric features of the transducers were modelled via visual inspection, whereas their unknown dielectric properties were estimated using global optimizers in order to minimize the differences between real and synthetic measurements. In particular, the antenna was calibrated in free space and on top of a metal plate. Subsequently, the resulting model was successfully tested in various case studies to assess its performance. Models of two units of the same transducer were developed, showing that units of the same system in general are not identical. The results support the premise that global optimizers can be used to provide information on key aspects of the dielectric structure of the transducer and allow us to accurately model its behaviour in various environments.

Development of Condition Assessment Index of Ballast Track Using Ground-Penetrating Radar (GPR).

The condition of the ballast is a critical factor affecting the riding quality and the performance of a track. Fouled ballast can accelerate track irregularities, which results in frequent ballast maintenance requirements. Severe fouling of the ballast can lead to track instability, an uncomfortable ride and, in the worst case, a derailment. In this regard, maintenance engineers perform routine track inspections to assess current and future ballast conditions. GPR has been used to assess the thickness and fouling levels of ballast. However, there are no potent procedures or specifications with which to determine the level of fouling. This research aims to develop a GPR analysis method capable of evaluating ballast fouling levels. Four ballast boxes were constructed with various levels of fouling. GPR testing was conducted using a GSSI (Geophysical Survey Systems, Inc.) device (400, 900, 1600 MHz), and a KRRI (Korea Railroad Research Institute) GPR device (500 MHz), which was developed for ballast tracks. The dielectric permittivity, scattering of the depth (thickness) values, signal strength at the ballast boundary, and area of the frequency spectrum were compared against the fouling level. The results show that as the fouling level increases, the former two variables increase while the latter two decrease. On the basis of these observations, a new integrated parameter, called a ballast condition scoring index (BCSI), is suggested. The BCSI was verified using field data. The results show that the BCSI has a strong correlation with the fouling level of the ballast and can be used as a fouling-level-indicating parameter.

Ground Penetrating Radar as a Functional Tool to Outline the Presence of Buried Waste: A Case Study in South Italy

The ability of the ground penetrating radar (GPR) method as a rapid preliminary survey to detect the presence of illegally buried waste is presented in this paper. The test site is located in the countryside of “Sannicandro di Bari” (Southern Italy) and has a surface area of 1500 m2. A total of five parallel profiles were acquired in 2014 using a geophysical survey system instrument (GSSI) equipped with 400 and 200 MHz antennae in the monostatic configuration. Two of the five profiles were registered in a control area to compare a natural condition to a suspected waste buried zone. As a result of a processing and elaboration workflow, GPR investigations allowed us to interpret the signal qualitatively within a maximum depth of about 3 m, identifying many signal anomalies, whose characteristics can be considered typical of buried waste. The GPR response of the three profiles acquired in the suspected area showed substantial differences not found in the control’s profiles. Anomalies related to the presence of intense scattering, of dome structures not attributable to cavities, but rather to a flattening and compacting of different layers, therefore, less electrically conductive, were identified in the suspected area. The interpretation of the results obtained by the GPR profiles was confirmed by excavations carried out with bulldozers. Large quantities of solid waste illegally buried (e.g., waste deriving from construction and demolition activities, bituminous mixtures, discarded tires, glass, plastic, municipal waste) were revealed in all the sites where anomalies and non-conformities appeared compared to the control natural soil.

Ground-penetrating radar inspection of subsurface historical structures at the baptism (El-Maghtas) site, Jordan

Abstract. The baptism (El-Maghtas) site is located to the north of the Dead Sea on the eastern bank of the Jordan River. Previous archeological excavations in the surrounding area have uncovered artifacts that include the location that was home to “John the Baptist”, who lived and preached in the early 1st Century AD and is known for baptizing Jesus. Archeological excavations have revealed walls, antiquities, and ancient water systems that include conduits, pools, and ancient pottery pipes. A ground-penetrating radar (GPR) survey was carried out at select locations along parallel profiles using a subsurface interface radar system (Geophysical Survey Systems Inc. SIRvoyer-20) with 400 MHz or 900 MHz mono-static shielded antennas in order to locate archeological materials at shallow depths. The GPR profiles revealed multiple subsurface anomalies across the study area. At the John the Baptist Church site a buried wall was detected along the profiles, and at the pool site the survey delineated several buried channels. GPR data also confirmed the extension of an ancient pottery pipe at the Elijah's Hill site through the production of a clear diffraction hyperbola anomaly related to the ancient pottery pipe that could be discriminated from the 2D profiles. The GPR data were displaced using 3D imaging to define the horizontal and vertical extent of the pipe.

Exploring ground-penetrating radar and sediment magnetic susceptibility analyses in a sandstone rockshelter in northern Australia

Ground-penetrating radar (GPR) surveys offer several advantages for non-invasively assessing stratigraphy in archaeological rockshelters, including providing information about subsurface stratigraphy and the location of features such as roof fall and bedrock. Challenges to understanding the record of human impact and site formation processes in Australian rockshelter deposits include where to position archaeological excavations, how best to determine the onset of human occupation within sequences beyond the presence of stone artefacts (which can be limited at depth owing to sampling issues) and how to resolve issues relating to stratigraphic associations. This paper demonstrates how GPR can be used to gain a better understanding of buried deposits in a Pleistocene-aged rockshelter. When compared with results from sediment magnetic susceptibility studies, GPR verified the major stratigraphic units identified at the site, the depth of bedrock and the presence of roof fall, but it also provided information on the sediment volume within the stratigraphic units. This is a unique outcome for exploring rockshelter deposits and geophysical signatures overall, aiding in the interpretation of complex site sediments and offering a useful tool for future site investigations. Abbreviations: GPR: ground-penetrating radar; GS1: Gledswood Shelter 1; SU: stratigraphic unit; LOI: loss on ignition; MHz: mega hertz; ns: nanosecond; GSSI: Geophysical Survey Systems Inc.; Hz: hertz; P: phosphorus; Xfd: frequency dependence; PSA: particle size analysis; Tc: Curie temperature; YR: yellow red

Measurement of Sounds Emitted by Certain High-Resolution Geophysical Survey Systems

Scientific questions regarding the impact of anthropomorphic noise in the marine environment have resulted in an increasing number of regulatory requirements and precautionary mitigation strategies to reduce the risks associated with high-resolution marine geophysical surveys performed in waters subjected to government jurisdiction. An example of regulatory frameworks includes the Marine Mammal Protection Act in the United States and the Marine Strategy Framework Directive 2008/56/EC in the European Union. Regulatory compliance often requires an assessment of the potential ecological risks before initiating a marine geophysical survey. However, the acoustic source data needed to estimate the risk associated with the operation of a given high-resolution survey system are frequently lacking. A comprehensive measurement program was performed to quantify the characteristics of sounds radiated by a variety of commercial marine geophysical survey systems, including boomers, sparkers, airguns, chirp sub-bottom profilers, sidescan sonars, and swath-bathymetric sonars [Crocker and Fratantonio, “Characteristics of high-frequency sounds emitted during high-resolution marine geophysical surveys,” Naval Undersea Warfare Center, Newport, RI, USA, NUWC-NPT Tech. Rep. 12, 203, 2016]. Calibrated acoustic source data, including source levels, source spectra, and beam patterns, were acquired for a total of 18 different marine geophysical survey systems. The data support modeling to estimate the potential ecological impacts resulting from the operation of certain high-resolution marine geophysical survey systems.

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

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

Peat stratigraphy mapping using ground penetration radar and geotechnical engineering implications

A Combined Land and Marine Ground Penetrating Radar (GPR) surveys was carried out in Southwestern part of Lagos, Badia, Nigeria with a view of delineating the subsurface peat stratigraphy that would aid geotechnical engineering design of the appropriate soil stability processes. The GPR study was conducted along eight parallel traverses trending East-West, using the Geophysical survey system incorporated (GSSI) SIR-3000 200MHZ Monostatic shielded antenna. Geographically, the study area is approximately between latitude 715000N and 716000N and longitude 538600E and 540300E of the universal traverse Mercator. The antenna was present with three gain points in order to improve the scans during data acquisition while 33 scans per meter were taken (representing 3cm station spacing) with a sampling window of 400ns with offset of +25ns.The topography is generally flat with localized undulations due to sand heaps from canals dredging and sand filling activities in the area. The peat depth was found to vary from 1.5m to 6m and the thicknesses from traverse one (1) to eight (8) on chainage 625m to 1100m. The area belongs to Dahomey Basin which is also known as Dahomey Embayment or Benin Benin or as West Nigeria Basin. The mineralogy, micro-fabrics and Morphology of the delineated stratigraphy was determined using the Scanning Electron Microscope (SEM) and X-Ray diffraction (XRD) methods. The results obtained revealed the presence of five subsurface (Topsoil/ sand filled Layer, Silty Clay, Peat, sandy Clay and Silty Sand) geological Layers, distinct geomorphological features, and high, moderate and low amplitudes, to continuous and discontinuous planer relax Facies structures. SEM and XRD analyses of the field samples obtained showed the dominance of Kaolinite, illite and quarts minerals in the clay/peat mapped. The derived engineering parameters suggest that the peat found in the study area are “fibrous peat” with low strength and medium to low bedding stress. It is observed that the peat generally depict high compressibility value, low internal frictional angle, they exhibit low elastic properties such as low shear modulus, low bulk modulus and young modulus values. The findings confirm the efficacy and relevance of GPR technique for pre-construction engineering investigation.

System stability and calibrations for hand-held electromagnetic frequency domain instruments

There are a few multiple-frequency domain electromagnetic induction (EMI) hand-held rigid boom systems available for shallow geophysical resistivity investigations. They basically measure secondary field real and imaginary components after the system calibrations. One multiple-frequency system, the EMP-400 Profiler from Geophysical Survey Systems Inc., was tested for system calibrations, stability and various effects present in normal measurements like height variation, tilting, signal stacking and time stability.Results indicated that in test conditions, repeatable high-accuracy imaginary component values can be recorded for near-surface frequency soundings. In test conditions, real components are also stable but vary strongly in normal surveying measurements. However, certain calibration issues related to the combination of user influence and measurement system height were recognised as an important factor in reducing for data errors and for further processing like static offset corrections.

Automated Target Detection for Geophysical Applications

In many geophysical surveys, there is a predefined goal—to detect and locate very specific anomalies, those that correspond to buried objects (targets). The types of targets range from various types of pipes (metallic or not), to rebars or wires in walls to land mines. This paper presents a novel unsupervised method for automatically detecting targets, and extracting information about them and the medium in which they reside. Most existing detection methods are supervised, which means that one has to provide a training set (which can be labor expensive) in order to train a classifier. By contrast, the method presented here is unsupervised and is model based, which alleviates the need to manually annotate a training set. Another drawback of many existing methods is the underlying assumption of a homogeneous medium. This assumption is greatly relaxed for this method, since it assumes no a priori knowledge of the medium. Instead, it learns the medium’s properties from the targets themselves. Furthermore, our method is designed to be computationally efficient and applicable in real-time applications. It was implemented on the StructureScan Mini XT system (Geophysical Survey Systems, Inc.), and the runtime on that system was measured to be $20~\mu \text{s}$ per scan of 512 samples. Experiments on 50 ground penetrating radar images with 278 targets show that our method is able to detect the targets with high positioning accuracy, with a 95.3% detection rate and near-zero false alarm rate.

Helicopter-borne ground-penetrating radar investigations on temperate alpine glaciers: A comparison of different systems and their abilities for bedrock mapping

On the basis of a large data set, comprising approximately 1200 km of profile lines acquired with different helicopter-borne ground-penetrating radar (GPR) systems over temperate glaciers in the western Swiss Alps, we have analyzed the possibilities and limitations of using helicopter-borne GPR surveying to map the ice-bedrock interface. We have considered data from three different acquisition systems including (1) a low-frequency pulsed system hanging below the helicopter (BGR), (2) a stepped frequency system hanging below the helicopter (Radar Systemtechnik GmbH [RST]), and (3) a commercial system mounted directly on the helicopter skids (Geophysical Survey Systems Incorporated [GSSI]). The systems showed considerable differences in their performance. The best results were achieved with the BGR system. On average, the RST and GSSI systems yielded comparable results, but we observed significant site-specific differences. A comparison with ground-based GPR data found that the quality of helicopter-borne data is inferior, but the compelling advantages of airborne surveying still make helicopter-borne data acquisition an attractive option. Statistical analyses concerning the bedrock detectability revealed not only large differences between the different acquisition systems but also between different regions within our investigation area. The percentage of bedrock reflections identified (with respect to the overall profile length within a particular region) varied from 11.7% to 68.9%. Obvious factors for missing the bedrock reflections included large bedrock depths and steeply dipping bedrock interfaces, but we also observed that internal features within the ice body may obscure bedrock reflections. In particular, we identified a conspicuous “internal reflection band” in many profiles acquired with the GSSI system. We attribute this feature to abrupt changes of the water content within the ice, but more research is required for a better understanding of the nature of this internal reflection band.

Investigation of snow-firn thickness and ground in the East Antarctica by means of geophysical radar

Results of field investigations of snow-and-firn thickness and ground structures performed with the use of geophysical radar GPR (Ground-Penetrating Radar) are discussed in the paper. Industrial radar GSSI SIR10B (Geophysical Survey Systems, Inc., USA) with «5106» antenna (pulses frequency of 200 MHz) was used. Its mean wavelength is 1.57±0.18 km. The main purpose of this work was to test this new technique for solution of glaciological and geological problems. The works were done during the austral summer season of 2012 – 2013 (58 th Russian Antarctic Expedition) in the Eastern Antarctica and mainly concentrated in the vicinity of the Lake Vostok, between the Russian stations Vostok and Progress (the Larsemann Hills). The GPR sounding was carried out together with precise geodetic measurements. The electromagnetic wave propagation in the snow-firn layer was analyzed using the data on density obtained from the 5G borehole at the Vostok Station. Investigations near the Vostok Station focused on a huge snow ridge or so-called “megadune” located eastward from the station at a distance of 30 km. About 80 km of the GPR cross-sections were collected there. Eight internal layers were traced. They demonstrated wavy forms with amplitudes of about 10 m high which corresponded to the megadunes. Main result of GPR investigations in the Larsemann Hills was our understanding of the snow-firn and ground structures in this region. The GPR data collected on structures of crevasses near Progress-1, shallow glacier near the Progress-3, and ground not far from Progress-2 are also discussed. Methodological recommendations on using the GPR under conditions of the Eastern Antarctica were developed.

Structure of an Ancient Egyptian Tomb Inferred from Ground‐Penetrating Radar Imaging of Deflected Overburden Horizons

AbstractGeophysical data acquisitions in most archaeological campaigns aim to image the target structure directly. The presence of a target, however, may be inferred from its interaction with surrounding layers, if its relationship with those layers can be characterized sufficiently. In this paper, we show the use of ground‐penetrating radar (GPR) to detect the subsurface continuation of the Ancient Egyptian tomb of the high‐official Karakhamun (Theban Tomb 223) at the South Asasif tomb complex (Luxor, Egypt). Data were acquired using a Sensors & Software pulseEKKO PRO system, equipped with antennas of 500 MHz centre‐frequency, on a silty–sandy sediment surface directly over the target structure. A test vertical radar profile (VRP) suggested that the tomb superstructure was buried too deeply beneath sedimentary overburden to be imaged directly: 500 MHz energy would propagate for only ~2 m before becoming undetectable. Attenuative layers within that overburden were strongly reflective, however, and could be used to provide indirect evidence of any underlying structure. When observed in the GPR grid, these layers showed a discrete zone of deflection, ~0.9 m in amplitude and ~4 m wide, aligned with the long‐axis of the tomb. This deflection was attributed either to a collapsed vestibule beneath the survey site, or sediment settling within an unroofed staircase descending from ground‐ to tomb‐floor‐level; supporting evidence of this was obtained towards the end of the excavation campaign and in the following year. We highlight the value of such indirect imaging methods as a potential means of improving the capabilities of a given geophysical survey system, in this case allowing the GPR to characterize a target at greater depth than would typically be considered practical. © 2014 The Authors. Archaeological Prospection published by John Wiley & Sons Ltd.

The use of ground penetrating radar for mapping rock stratigraphy and tectonics: Implications for geotechnical engineering

This paper presents results from ground penetrating radar surveys using the SIR-10B GPR instrument (manufactured by Geophysical Survey System Inc., USA), with 400 MHz monostatic antenna (model 5 103). Survey was made over 3 excavation levels along the highway section at the Ras en Naqab escarpment area, Southwest Jordan. A total of 217 m along 4 profiles were covered in the winter of 2012. The objectives of the study are (i) to evaluate the resolution of the GPR technique in the field for detecting and locating anomalies caused by subsurface structures like cavities, fractures and faults, and (ii) to describe stratigraphic nomenclature of the subsurface rocks of the area. 2D interpre- tation of the obtained data and the geological information demonstrate a strong correlation between the GPR anomalies and the subsurface geology. Based upon the lateral and vertical velocity changes with depth, the thickness and orientation of the subsurface layers are outlined. Analysis of the exposed sec- tion shows good agreement between the estimated thicknesses of lithostratigraphic units and the quan- titative assessment of the radar waves velocity inferred from GPR data.

Analytical Qualification of Heliborne TDEM Equipments Subjected to Static, Shock and Vibration Loadings

In geophysical survey system, a Time Domain Electro-Magnetic (TDEM) technique is used to detect the presence of uranium in the earth crust. For heliborne survey, certain equipments, such as power converter and data acquisition system are installed on a helicopter. The power converter is responsible for the generation of high current pulses to feed the transmitter for setting up the required electromagnetic field. The power converter consists of a free running inverter, which sits over a DC-DC converter. Data acquisition system acquires data from various sensors for further processing and interpretation. Data acquisition system consists of a highly vibration sensitive onboard computer (IDAN boxes) rigidly mounted over a plate inside the data acquisition system enclosure. Since the power converter and data acquisition system are installed on the floor inside the surveying helicopter, it is mandatory to qualify these equipments for vibration & shock as per MIL standard before onboard installation. To evaluate the structural integrity of power converter and data acquisition system under various loading conditions of vibration and shock, a preliminary estimation of stresses and deflections was made by hand calculations and then, finite element analysis has been performed to optimize the design. Modal analysis has been performed to estimate the natural frequencies of power converter. Since the natural frequencies of the power converter were within the disturbing frequency range (i.e., 10 to 84 Hz), thickness of converter base plate and inverter base plate has been increased to avoid resonance. Since the data acquisition system consists of a highly vibration sensitive onboard computer, it has been proposed to mount it on isolators to minimize the vibration. To evaluate the structural integrity of data acquisition system under various loading conditions, finite element analysis has been performed. This paper presents the methodology adopted for design and analysis of the equipments for the specified input of vibration and shock.

Ground penetrating radar (GPR) study to detect seepage pathways in the Ajanta Caves in India

The present study used the ground penetrating radar (GPR) tool to decipher the presence of fractures which may be possible pathways for seepage into the Ajanta Caves in India. GPR data were collected by 40- and 200-MHz antennas from Geophysical Survey Systems, Inc. (GSSI). The data were edited and processed using the RADAN 6.5 software. The processed data indicate the presence of fractures of varying orientation in the basaltic formations. The study shows high reflection zones indicative of fractures as well as strong absorbance zones which may be a homogeneous zone without any fractures.

Attenuation of Ground Penetrating Radar Signal Amplitude in Monitoring Reinforced Steel Corrosion

In this study, the reduction of ground penetrating radar (GPR) signal amplitude magnitudes were measured to monitor the reinforcing steel corrosion in concrete slab. Geophysical Survey System Incorporation (GSSI) BridgeScan system which includes a SIR-3000 Windows, based on portable GPR data collection with 1.6 GHz ground-couple antenna has been used to generate electromagnetic waves and analysis of the signal on a slab sample. Four 16 mm diameter reinforcing steel were embedded in a 255 mm x 455 mm x 60 mm grade 40 concrete slab in the transverse direction and three in the longitudinal. The slab was immersed in concentrated sodium chloride solution (8 g/l) for three months to simulate the corrosive environment on the reinforced slab. The average signal amplitude decreases from 1139.75 dB (at day 7) to -404.25 dB (at day 61) and finally drop to -782.75 dB (at day 93) as the corrosion process progressing. The presence of corrosion activity on the reinforcing steel was confirmed based on the potential difference reading by Half Cell (HC) which shows that the reinforcing steel experienced probability of corrosion level by more than 90 % after 61 and 93 days. GPR method is found to be a promising approach as it possesses high sensitivity towards changes in amplitude at par with high potential changes in HC method in corrosion detection.

Discrimination between landmine and mine-like targets using wavelets and spectral analysis

Landmine is an explosive apparatus hidden in or on the ground, which blows up when a person or vehicle passes over it. Egypt is one of the countries suffering due to the unexploded ordnance (UXO). Around 2 million UXO are present in the Egyptian soil especially at Al-Alameen province, north of the western desert. Detection of buried landmines is a problem of military and humanitarian importance.Ground penetrating radar (GPR) is a powerful and non-destructive geophysical approach with a wide range of advantages in the field of landmine inspection. In the present paper, we apply different simulation models with Vivaldi antenna and mine-like targets by using the CST Microwave studio program. The field work is carried out by using a GPR device of model SIR 2000 from GSSI (Geophysical Survey Systems Incorporation) connected to 900MHz antenna where the targets were buried in sand soil. Depending on the fact that the receiving powers (reflected, refracted and scattered) from the different materials are different, we study the spectral power densities for the received power from the different targets. The techniques used in this study are: direct fast Fourier transform, short time Fourier transform (spectrogram), wavelets transform and denoising techniques. Our results ought to be considered as finger prints for different scanned targets during this work. So we can discriminate between landmines and mine-like targets.

Demonstration of ground-penetrating radar as a useful tool for assessing pocket gopher burrows

Ground-penetrating radar (GPR) is an innovative and non-invasive method that uses radar to penetrate the ground and develop three-dimensional digital images of the top several meters of the earth. Ground-penetrating radar has been used extensively in the fields of engineering, military science, forensic science, archaeology, and environmental remediation, but has received little attention by wildlife professionals. We demonstrated a possible application of GPR for wildlife studies for mapping burrow systems using maritime pocket gophers (Geomys personatus maritimus), a subspecies of concern as listed by the U.S. Fish and Wildlife Service. Ground-penetrating radar surveys were conducted at Naval Air Station—Corpus Christi on five 15-m × 15-m areas with >200 above-ground gopher mounds/ha during July 2007. Survey areas were scanned with a Geophysical Survey Systems Inc. SIR-3000, GPR digital control unit and a 900-MHz ground-coupled antenna. Within the 5 areas, we located 8 gophers and mapped 267 m of tunnels that had an average depth of 0.6 m. We were able to differentiate deteriorating or abandoned tunnels from active tunnels, detect an underground pipeline, and distinguish changes in soil texture using GPR. Ground-penetrating radar is a non-destructive and non-invasive method to gain knowledge of fossorial animal movements and potential destabilization of soil integrity. © 2013 The Wildlife Society.

Applications of ground-penetrating radar to investigate the Quaternary evolution of the south part of the Paraiba do Sul river delta (Rio de Janeiro, Brazil)

Rocha, T.B.; Fernandez, G.B. and Peixoto, M.N.O.The coastline of the Rio de Janeiro is dominated by coastal sandy barriers which the main aspects of Quaternary evolution is determined by sea level oscillations in the Pleistocene and the Holocene. Such barriers have been studied in terms of geomorphological mapping, sediment transport and detailed morphology, mainly in the Holocene barrier. This work pretend by using geophysical techniques, describe the characteristics in subsurface of the coastal plain in part of Paraiba do Sul River Delta, one of worldwide example of wave dominated deltas. To achieve the objectives we use different frequencies with the antennas with 80, 200 and 400 MHz, with the equipment made by Geophysical Survey System Inc. The results showed that the GPR lines obtained in the Pleistocene Beach ridges describe a observation of sequences of reflectors of foredunes in the top, and beach and upper and lower shoreface in the base of the line, a typical sequence of regressive coastal barrier, formed under conditions of sea level falling. On the other hand the morphology of the Holocene barrier is characterized by transgressive barrier and lagoon spit, even of the regressive pattern of the sea level in the last 5.500 years B.P. In this case the radar facies showed a well preserved sedimentary structures by the continuous overwhash process and lagoon spits, along barrier lagoon system. We conclude that the radar facies showed important indicators about the genesis of these features and the relative sea level.