bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integrated study of the sinkhole development site on the Western shores of the Dead Sea using geophysical methods
Authors: Ezersky Michael , Bruner Ilan , Keydar Shemer , Trachtman Pini , Rybakov Michael 
Published: August 2009

This paper presents a combination of high‐resolution seismic diffraction, reflection, refraction, continuous vertical electric sounding (CVES), ground‐penetrating radar (GPR) and microgravity methods to study the structure and properties of the shallow subsurface at the sinkhole development site in the Nahal Hever southern area (on the shore of the Dead Sea) in Israel. These methods have different resolutions and penetration depths. The methods are complementary to each other and reveal useful information about the subsurface. Each one investigates certain characteristics, but when combined they provide us with new information about the subsurface. The seismic refraction method is utilized to map salt layers and to detect dissolved zones. The analysis of all of the seismic refraction data obtained at the Dead Sea area, verified by the information gained from a borehole, has shown that the P‐wave velocity of the salt layer varies from 2900 to 4250 m/s. The velocity of 2900 m/s was used as the minimum velocity criterion for salt‐layer identification at this site.A low‐velocity zone (VP < 2800 m/s) revealed within a high‐velocity area ( m/s) is interpreted as a dissolved salt or non‐saline unit. The site is characterized by two significant geological features. The first feature is a water‐filled cave, detected recently by a borehole in the depth interval 23–28.5 m, and the second feature is a depression at the surface. Geophysical results show that the depression site is presently characterized as a heavily perturbed zone in both lateral and vertical directions. Soil decompaction in the subsurface is clearly identified by the CVES method as a high‐resistivity anomaly. This decompaction is assumed to be associated with the voids and fractures occurring down to a depth of 100–120 m (by diffraction data) and in the uppermost subsurface (by GPR data). The zone containing the cave is characterized by a lateral (funnel) and vertical (faults) distortion of the subsurface structure (by seismic reflection data) and has a faint diffraction anomaly in the shallow subsurface. A slightly increased resistivity anomaly appears in the depth interval 6–12 m (from CVES data). Drilling data reveal this interval as a decompaction zone. No GPR anomalies were detected at the buried cave site. The microgravity survey at the buried void site in 1999 detected an anomaly that is very similar to the funnel‐shaped one.
A study of the groundwater seepage at Hibis Temple using geoelectrical data, Kharga Oasis, Egypt
Authors: Sultan S.A. , Santos F.A.M. , Helal A. 
Published: August 2009

Geoelectric techniques have been used to detect and define the subsurface stratigraphy and structures around Hibis Temple in Kharga Oasis, Egypt. We used 2D and 3D inversion approaches to interpret the data set obtained from 20 dipole‐dipole resistivity profiles with electrode spacings of 3 and 5 m and lengths between 39 and 85 m.Five vertical electrical soundings, with a maximum array length of 200 m, along a profile crossing the study area were also carried out. A preliminary quantitative interpretation of the vertical electrical sounding curves was achieved using two‐layer standard curves and generalized Cagniard graphs. The final models were obtained by 1D inversion using the results of the manual interpretation as initial models. Model results were used to construct a geoelectric cross‐section that correlated very well with the stratigraphic units.Five geoelectric units were identified: the first (the uppermost) is a high‐resistivity layer consisting of fill deposits (rubble); the second is a muddy clay with moderate resistivity values; the third is also a muddy clay but with decreased resistivity due to the increase in salt content originated by the evaporation of the groundwater seepage; the fourth unit, at a depth of 7–13 m, is a muddy clay saturated with water seepage from the agricultural areas surrounding the temple; the final unit is a more resistive layer corresponding to dry muddy clay. The differences in the groundwater level, and its salt content, correlated with the irrigation activities around the temple. We concluded that the high corrosion potential of the seepage water might be connected with its salt content.
A review of practical numerical modelling methods for the advanced interpretation of ground‐penetrating radar in near‐surface environments
Authors: Cassidy Nigel J. 
Published: August 2009

ABSTRACTAs ground‐penetrating radar (GPR) technology improves, there is an increasing demand for more sophisticated and detailed interpretational tools. Numerical modelling has become one of the most popular advanced analysis methods and there is a wide range of electromagnetic modelling approaches available to the GPR user. The finite‐difference time‐domain (FDTD) technique is one of the most common, as it provides modellers with a robust, flexible, yet accurate, modelling scheme that is capable of simulating GPR wave propagation in complex, three‐dimensional, heterogeneous, lossy, subsurface environments. Through the use of a well‐constrained example, the realistic modelling of near‐surface GPR is evaluated including the practical limitations, computational procedures and application constraints of the FDTD method. The results show that, despite some obvious deficiencies, even a relatively basic FDTD model can provide important additional information for the advanced interpretation of observed GPR data.
Thin‐wire antenna design for GPR applications using a multi‐objective GA
Authors: Moreno de Jong van Coevorden C. , Rubio Bretones A. , Fernández Pantoja M. , García Ruiz F. , Garcia Salvador G. , Monorchio A. , Gómez Martín R. 
Published: August 2009

ABSTRACTA Pareto multi‐objective genetic algorithm (MOGA) has been applied to the design of non‐dispersive, ultra‐wideband (UWB), resistively loaded, thin‐wire antennas for ground‐penetrating radar (GPR) applications. The radiation characteristics of the antennas are optimized, seeking to maximize the bandwidth and the front‐to‐back ratio. The variables in the design are the value and position of the resistive loads located along the antenna wires, the number of wires and the angular distances between those wires. The radiation characteristics of the optimized antennas are explored and an example of an application to detect cracks in marble blocks is presented.
A linear inverse scattering algorithm for realistic GPR applications
Authors: Soldovieri Francesco , Hugenschmidt Johannes , Persico Raffaele , Leone Giovanni 
Published: August 2009

ABSTRACTThe paper deals with a microwave‐tomography‐based solution algorithm tailored for use with GPR data‐processing applications. The algorithm tackles an inverse scattering problem in the frequency domain through the use of a linear model of the electromagnetic scattering, based on the Born approximation. In particular, we evaluate the reconstruction capabilities of the linear inversion algorithm in terms of the retrievable spatial variations of the unknown contrast function, whilst considering the problem of choosing an optimal frequency measurement step, theoretically, using diffraction tomography arguments. A numerical analysis of the technique is performed by means of the singular‐value decomposition tool, which allows us to extend the theoretical results to more realistic cases involving lossy soils. Finally, we present a series of reconstructions, obtained using synthetic and experimental data, which show the performance of the method under realistic conditions.
Clutter reduction in GPR measurements for detecting shallow buried landmines: a Colombian case study
Authors: Lopera Olga , Milisavljević Nada , Lambot Sébastien 
Published: August 2009

ABSTRACTDetection of land‐mines from ground‐penetrating radar data is a challenging task demanding accurate and useful filtering techniques to reduce soil‐surface and antenna reflections, which obscure the landmine response. In this paper, we apply and adapt a recently proposed filtering approach to enhance the detection of shallow buried anti‐personnel land‐mines from data acquired in typical mine‐affected soils in Colombia. The methodology combines a radar‐antenna‐subsurface model with phase‐shift migration to filter out antenna and soil‐surface effects from off‐ground monostatic radar two‐dimensional data. Firstly, antenna multiple reflections are removed using linear transfer functions. Secondly, simulated Green's functions accounting for the surface reflection are subtracted. These functions are derived using the relative dielectric permittivity of the surface, which is estimated by full‐wave inversion of the radar signal for measurements taken in local land‐mine‐free areas. Finally, the antenna radiation pattern effect is filtered out by performing phase‐shift migration, and information about size and shape is extracted. Data are acquired using a hand‐held vector network analyser connected to an off‐ground monostatic horn antenna. Typical Colombian targets such as low‐metallic anti‐personnel land‐mines and low‐ and non‐metallic improvised explosive devices are used. Results prove that the proposed technique effectively reduces clutter under non‐controlled conditions and yields target features that are useful for detection of these land‐mines.
GPR, VES and refraction seismic surveys in the karstic area “Spedicaturo” near Nociglia (Lecce, Italy)
Authors: Nuzzo Luigia , Leucci Giovanni , Negri Sergio 
Published: August 2009

ABSTRACTThe present work shows some results of an early ground‐penetrating radar (GPR) study performed in a hazardous karstic area near the village of Nociglia in the central part of the Salento peninsula (Apulia, southern Italy), after a sudden subsidence event occurred on March 13th, 1996. The geophysical study, also involving vertical electric sounding (VES) and refraction seismics, is part of a multidisciplinary research project, aimed at determining the climatic, geological, morphological and hydrogeological conditions of the area in order to assess geological hazards and to prevent groundwater pollution due to agricultural activities. GPR transects led to the identification of some shallow subsurface structures including a known cave and probable karstified bedding joints, weakened shallow layers, fractures, fault zones, and burrows. The VES and seismic surveys resulted in a better understanding of the geology of the area and supported the interpretation of the GPR data.
Effective frequency and attenuation measurements of glass beads/magnetite mixtures by time‐domain reflectometry
Authors: Mattei E. , De Santis A. , Pettinelli E. , Vannaroni G. 
Published: August 2009

ABSTRACTSamples with different percentages (5–30%) of magnetite and different ranges of grain size are analysed by time‐domain reflectometry (TDR). The passband, the attenuation factor and the effective frequency are derived from the TDR measurements. The passband was obtained from the second edge of the sample by eliminating the DC component and applying a Fourier transform to the residual signal. The bandwidth of the resulting spectral shape decreases as the magnetite percentage increases. The second edge was also used to evaluate the effective attenuation factor , using multiple‐reflection theory, terminated at the second reflection. The attenuation values can be estimated independently by means of the electromagnetic parameters obtained using an LCR meter. To compare and , an effective TDR frequency is introduced. The agreement between the values obtained from TDR and LCR‐meter techniques supports the reliability of the attenuation derived from the second TDR reflection, and that computed from the effective frequency. The shapes of the passbands and the and values for magnetite/glass‐beads mixtures, which simulate dry soils with increasing iron oxides content, are reported and discussed.
On hydrogeological noise in superconducting gravimeter data
Authors: Hokkanen Tero , Virtanen Heikki , Pirttivaara Mika 
Published: August 2009

ABSTRACTThe purpose of this research was to gain a better knowledge of the signals contained in superconducting gravimeter data at the Metsähovi station in southern Finland. Because superconducting gravimeter data are very sensitive to various environmental effects, we must first identify and understand the characteristics of these effects and only after that are we able to correct for them if necessary. In this study we used the continuous wavelet transform to analyse correlations between the gravity residuals, precipitation, and groundwater level. As a result, we determined and isolated the source of a long‐term effect, i.e. the varying flow rate of groundwater in an inhomogeneous ground. The causes of this flow‐rate variability are changes in the porosity of the ground due to changes in the type of medium, and the amount of fracturing in the bedrock. Topography is also a cause of the flow‐rate variation. Therefore, a single observation well to determine the groundwater level at the study site is not sufficient to provide coefficients that are precise enough to reduce the gravity effect due to variations in the groundwater level, and several access tubes will be needed to assess the correction coefficients accurately.
Using seismic traveltime tomography in geoarchaeological exploration: an application at the site of Chatby cemeteries in Alexandria, Egypt
Authors: Polymenakos L. , Papamarinopoulos St. P. 
Published: August 2009

We apply seismic traveltime tomography in an investigation of the subsurface of a geoarchaeological site at Chatby cemeteries (Alexandria, Egypt). We are interested in obtaining information about the geological structure and the remains of man‐made structures. Energy sources are placed at the surface and recorders are distributed vertically in an underground location. Traveltime data are inverted with a three‐dimensional tomographic algorithm. Inversion results are evaluated and interpreted with the aid of independent geophysical and archaeological information, and various tests are carried out with different initial velocity models and synthetic traveltimes.The inversion results show good correlation with the estimated geological structure, in particular at deeper levels, as suggested by independent geophysical and archaeological information and later confirmed by excavation. The depth and variations of the bedrock surface are satisfactorily imaged. Indications of possible man‐made structures are presented and discussed. Shallow velocity features are evaluated and interpreted using tests with synthetic traveltimes. The main goal of imaging the deeper structure was successful.As inversion tests with different initial velocity models indicate, the subsurface structure and the complexity of data information in this particular case are better handled when using a single‐layer model than when using an average two‐layer model. The single‐layer model allows for a more versatile velocity variation and raypath distribution, while the two‐layer model leads to an inversion result that is considerably influenced by the initial velocity distribution. Enhancement of particular aspects of the single‐layer inversion result can be derived with the use of an initial velocity model, that permits a gradual increase of velocity with depth. The gradient model improves the raypath distribution and limits velocity artefacts.The resulting images can assist in the assessment of the archaeological potential of a site, particularly in excavation design, in a non‐destructive manner. They can be also of great value in other applications, for example in engineering works, when detailed information on the subsurface is sought in areas of restricted access.
Three‐dimensional probability tomography of self‐potential anomalies of graphite and sulphide mineralization in Orissa and Rajasthan, India
Authors: Bhattacharya Bimalendu B. , Shalivahan  , Jardani A. , Bera Aparna 
Published: August 2009

ABSTRACTCharge occurrence probability (COP) and dipole occurrence probability (DOP) tomographic imaging of graphite and sulphide orebodies, which were earlier detected by a self‐potential (SP) survey, were carried out. Three typical examples, two shallower graphite lenses in Bender and Berni, Orissa State, and one relatively deeper sulphide deposit in Kayar, Rajasthan State, are presented. An exploratory test hole, drilled on the basis of the SP results in Bender and Berni, struck graphite. A mise‐à‐la‐masse survey was also carried out on these two deposits to delineate the orebody. The graphite deposits have subsequently been mined. The shapes of the graphite bodies, especially the upper parts, are now known. The Bender deposit is a single graphite lens, whereas the graphite occurrences in Berni are complex multilens‐type deposits. Both the COP and DOP techniques clearly imaged the single lens at Bender, as well as the multilens deposits at Berni. The Kayar sulphide deposit, unlike the graphite deposits, has not yet been mined, and therefore it is not delineated as precisely as the graphite orebodies. However, its outline is known from the drilling data. The imaging results of COP and DOP show good agreement with the drilling results of the sulphide deposits.
GPR and microwave tomography for detecting shallow cavities in the historical area of “Sassi of Matera” (southern Italy)
Authors: Piscitelli Sabatino , Rizzo Enzo , Cristallo Filippo , Lapenna Vincenzo , Crocco Lorenzo , Persico Raffaele , Soldovieri Francesco 
Published: August 2009

ABSTRACTThe results of a geophysical survey carried out in the historical area of “Sassi of Matera” (Basilicata region, southern Italy) are presented and discussed. Matera is one of the most fascinating and ancient towns of the Mediterranean area and is listed in the UNESCO World Heritage List. It represents an example of a town where the communities developed a cave‐life culture in the cavities excavated through the substratum of the hill of Matera. The urban area of Matera, therefore, is characterized by a complex system of interconnected and overlapping ancient shallow cavities: residences, galleries, cisterns, crypts, graves, etc. Consequently, local surface deformation phenomena are often observed.We describe the results from a ground‐penetrating radar (GPR) survey carried out in St. Rocco Square, one of the most interesting areas of the historical centre of Matera, that was affected by both spread out and local subsidence phenomena. Great attention was paid to GPR data processing and inversion. In particular, a novel microwave tomography approach was applied to obtain high‐resolution images of shallow ancient cavities that caused the local surface deformations. Moreover, the GPR survey was integrated with an electrical resistivity tomography survey in order to prospect those subsurface zones with a high electrical conductivity, where GPR investigation was not possible. The geophysical investigation enabled us to identify the cause of the subsidence phenomena and to reconstruct the geometry of the complex system of shallow cavities partially filled with unconsolidated material.
GPR investigations for the study and the restoration of the rose window of Troia Cathedral (southern Italy)
Authors: Masini Nicola , Nuzzo Luigia , Rizzo Enzo 
Published: August 2009

ABSTRACTThe development of cracks and distortions caused by past seismic events compromised the integrity of the rose window of Troia Cathedral, one of the most precious Romanesque monuments in southern Italy. Ground‐penetrating radar (GPR) using high‐frequency antennae (mainly 1500 MHz) was selected from among various non‐destructive testing methods for its high‐resolution imaging to scan the internal structure of the various architectural elements of the wheel window: the decimetre‐diameter columns constituting the rays, the ring decorated with intersecting arched ribwork and the surrounding circular ashlar curb. GPR was employed in the classical continuous reflection mode, moving the antennae manually along the architectural elements and paying exceptional care in the acquisition and processing stages to avoid positioning errors. Indeed, the challenging aspects of this case study were the geometrical complexity and small dimensions of the structural elements, causing many logistic/coupling problems. In spite of this, through proper interpretation techniques, based on signal analysis (presence of reflections and diffractions, velocity and attenuation variations) and correlation with features detected by visual inspection of the external surfaces, the GPR survey provided useful information on the internal structure of the rose window, detecting fractures and the boundaries of previously restored parts and locating hidden metallic components connecting the architectural elements. Information on the internal structure and spatial distribution of metallic junctions was essential for gaining insight into building techniques in order to discriminate between restoration strategies which may require either total or partial dismantling of the rose window. GPR results provided crucial evidence in favour of one of the (conflicting) hypotheses about the original building techniques, leading to the selection of partial dismantling as the most suitable restoration strategy. Analysis of measurements revealed the potential of GPR in the field of cultural heritage restoration, even in those cases characterized by complex geometry, structural brittleness and logistic difficulties, such as that discussed in this paper.
Application of ground‐penetrating radar in detecting water leakage from artificial sandy ground
Authors: Jee Seol Soon , Yokota Toshiyuki , Mitsuhata Yuji , Kwon Hyoung‐Seok , Uchida Toshihiro 
Published: August 2009

ABSTRACTGround‐penetrating radar (GPR) surveys are frequently used to delineate the distribution of subsurface water. This paper demonstrates that GPR is suitable for detecting water leakage from underground construction areas because it produces detailed images of changes in water‐level that are related to water leaks. For this experiment, we used a test pit filled with river sand and a buried mortar wall that divides the pit into two sections. To simulate water leaks, we drilled holes through the mortar wall at a depth of 1.15 m and maintained constant water levels of 1.4 m and 0.4 m below the surface on each side of the wall. Water‐levels were controlled by pump‐extraction and injection using water‐control wells. Variations in water‐level under dynamic hydraulic conditions caused by water leakage through the holes were delineated by dense GPR single‐fold profiling measurements. Wide‐angle reflection and refraction (WARR) measurements were also performed to obtain velocity information and to support the interpretation of profiling data. To image minor changes in waterlevel accurately, we took minor topographic changes into account and applied finite‐difference method migration and time‐variant depth conversion to the GPR single‐fold profiling data. We were able to construct a three‐dimensional water‐level map using the water‐table depths extracted from migrated depth sections. Our results clearly demonstrate a rising trend in water‐level approaching the mortar wall, indicating water leakage from the drilled holes. In addition, the WARR data confirmed that the upward trend in water‐level continues to the mortar wall; it was not possible to image this trend on the single‐fold profiling section within 0.5–1 m of the mortar wall because of interference from measuring equipment buried close to the wall.