bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging subsurface objects by seismic P‐wave tomography: numerical and experimental validations
Authors: Grandjean Gilles
Published: August 2009

We tackle the problem of characterizing the subsurface, more specifically detecting shallow buried objects, using seismic techniques. This problem is commonly encountered in civil engineering when cavities or pipes have to be identified from the surface in urban areas. Our strategy consists of processing not only first arrivals, but also later ones, and using them both in tomography and migration processes, sequentially. These two steps, which form the basis of seismic imaging, can be carried out separately provided that the incident and diffracted wavefields are separated in the data space. Tomography is implemented here as an iterative technique for reconstructing the background velocity field from the first‐arrival traveltimes. The later signals are then migrated by a Kirchhoff method implemented in the space domain. To study the reliability of this methodology, it is first applied to synthetic cases in the acoustic and elastic approximation. Both the background velocity field and the local impedance contrasts are reconstructed as defined in the predicted model. An experimental case, specifically designed for the purpose, is then considered in order to test the algorithms under real conditions. The resulting image coincides well with the predicted model when only P‐waves are generated. In the elastic mode, surface waves make P‐wave extraction difficult, so that the reconstruction remains incomplete. This is confirmed by the real data example. Finally, we demonstrate the appropriateness of the proposed method under such circumstances, provided that suitable preprocessing of data is carried out, in particular, the removal of surface waves.
Site characterization and assessment using the microgravity technique: a case history
Authors: Branston M.W. , Styles P.
Published: August 2009

A microgravity survey was undertaken to investigate the area surrounding the collapse of a riverbank retaining wall. Initial site investigation identified the presence of a void in the immediate area of the collapse. The objective of the geophysical survey was to assess the extent of the identified void and identify any similar features in the surrounding area. Several geophysical techniques were considered but due to the urban environment, the microgravity technique was chosen. Forward modelling using the data from the initial site investigation was undertaken to optimize the survey parameters. The gravity data was processed to the Bouguer anomaly and the terrain effects of the river‐channel morphology accounted for. Anomalies identified within the data set have been analysed using the Euler deconvolution method, which has provided estimates of the depth to the top of the anomalous areas. Inversion of the gravity data using the Cordell and Henderson method has provided an image of the 3D extent of the anomalous areas identified. Guided by this information, a secondary invasive site investigation was conducted which confirmed the interpretation of the geophysical results. The combination of a non‐invasive geophysical investigation together with selective invasive control has enabled the full subsurface characterization of this site.
EMI data from an archaeological resistive target revisited
Authors: Lascano E. , Martinelli P. , Osella A.
Published: August 2009

In a previous work, we presented the analysis and interpretation of geophysical data acquired at the Floridablanca archaeological site in Patagonia, Argentina. The electromagnetic induction method (EMI) was used to detect and localize the anomalous zone of interest quickly. Afterwards, a quantitative characterization of the structure responsible for this anomaly was achieved by inverting geoelectrical data.

In this work, we re‐analyse the EMI data to discover whether it could also provide us with quantitative information about our target, which exhibits a resistive signature with respect to the host medium. First, an alternative visualization of the data is carried out; this allows us to detect some features of the anomaly that could not be distinguished before. It also makes clear which of the configurations used in the data acquisition exhibits the best sensitivity and resolution. The EMI data corresponding to the anomalous zone are then adjusted with a trial‐and‐error procedure, using a 2D forward modelling method based on a Raleigh–Fourier approach. The response of two adobe walls with a tile deposit in between them is calculated and the resulting model shows good agreement with the model obtained from the inversion of the geoelectrical data. Also, the synthetic response of two adobe walls without the tile deposit is calculated; we find that this response is different and the data cannot be adjusted with this model. We conclude that the EMI method is appropriate for discriminating different types of resistive structure and that it can be used to obtain quantitative information when 2D modelling is performed.
A discrete conductor transformation of airborne electromagnetic data
Authors: Smith Richard S. , Salem Ahmed S.
Published: August 2009

Airborne electromagnetic moment data are transformed to two depth sections that display the properties of a spherical conductor. In addition to the spherical conductor being small or distant, we made other simplifying assumptions: the conductor is always below the traverse line and the strike of the plane containing the current flow is always perpendicular to the flying line.

The transformation algorithm compares measured moment data with synthetic moment data in a look‐up table. An index of fit is calculated to measure how closely the data in the look‐up table match the measured data. When the fit is good, we use bright colours on the depth section to indicate the properties of the discrete conductor; when the fit is poor, we make the section grey. The estimated properties displayed on the two sections are the product of conductivity and the square of the radius (CRS) on one section and the dip of the current flow on the other section. The position and depth can also be inferred from the location where the fit is best.

The data displayed on the depth sections are also summarized in plan view, with colour being used to indicate the estimated properties of the sphere (CRS, dip and depth). This colour map can be displayed in combination with a greyscale image of the electromagnetic data as this illustrates the context of the colour features.

Application of the method to two field data sets shows that the method works well for isolated bedrock conductors. However, no features were resolved when there was interference from nearby conductors. Also, we found that wide bodies were not necessarily well resolved. In some cases the features on the sections were confusing, but this can reflect data that is complex or difficult to interpret. Where coherent features are displayed, the estimated values of the depth, CRS and dip seemed reasonable.
Polarisation and slowness of seismoelectric signals: a case study
Authors: Strahser Matthias H.P. , Wolfgang Rabbel , Schildknecht Friedrich
Published: August 2009

In saturated porous media, seismic compressional waves can generate electric and electromagnetic signals of observable amplitudes. These signals can be recorded with dipoles consisting of two electrodes each. As the generation of seismoelectric signals is connected with properties, such as hydraulic permeability, porosity, and fluid salinity, it is possible that the seismoelectric method could be used in hydrogeophysics for determining these parameters. However, the seismoelectric method still remains in the experimental stage. This is mainly due to the difficulties involved in seismoelectric measurements.

We present repeatable seismoelectric field data with exceptionally high signal‐to‐noise ratios and prove that the assumed seismoelectric signals are not artefacts but the desired signal converted from seismic compressional waves at subsurface boundaries. Their amplitude distribution, arrival times and slownesses, as well as their polarisations, are checked against theoretical predictions and comparisons with other methods, such as refraction seismics, borehole logging data and downhole seismics and seismoelectrics. Conventional velocity filters in the frequency_wavenumber domain accentuate the seismoelectric signals converted at subsurface boundaries from incident seismic compressional waves, differentiating them from the usually less informative seismoelectric waves travelling inside compressional waves and being confined to these waves.

The recording of three‐component seismoelectric data enabled us to perform a polarisation study showing that the polarisations of the seismoelectric signals encountered are mainly found on the radial and the vertical components and thus follow the predictions. The three‐component data suggest the existence of a composite signal from a thin layer which would have remained undetected with one‐component measurements. Repeatable signals were also encountered on the transverse component which we interpret as 3D effects of a layer dipping in the transverse direction.
Effects of the fracture water of bedrock on superconducting gravimeter data
Authors: Hokkanen Tero , Korhonen Kimmo , Virtanen Heikki , Laine Eeva Liisa
Published: August 2009

Since 1994, the Finnish Geodetic Institute has operated a superconducting gravimeter (SG) at the Metsähovi research station in southern Finland. Superconducting gravimeter measurements are very sensitive to different environmental effects due to their high precision and low drift (3 gal/year). In order to gain more complete knowledge of the measured data, we have worked extensively to discover and isolate different factors influencing SG data.

In this study, we introduce one independent factor influencing SG data, i.e. the water flowing in the fractures of bedrock above the groundwater table. In order to estimate its effect on SG data, we conducted a ground‐penetrating radar survey to locate fractures below the gravity station. In addition, structural geology investigations were carried out to determine the type of fractures. On the basis of our studies, we constructed a 3D fracture model and calculated the effect that water‐filled fractures have on the gravity field at Metsähovi. The results of our calculations indicate that water flowing in the fractures at the Metsähovi site may cause an effect of several hundreds of nanogals.
Assessing foundation stability and soil‐structure interaction through integrated geophysical techniques: a case history in Rome (Italy)
Authors: Cardarelli Ettore , Cercato Michele , Di Filippo Gerardina
Published: August 2009

We present a case history in which several geophysical methods were used to investigate a five‐floor residential building, constructed from reinforced concrete, which has been seriously damaged by differential settlement. The results from various geophysical methods (electrical resistivity tomography, seismic refraction, multichannel analysis of surface waves, cross‐hole seismic surveys) were integrated and correlated to give an overall picture of the subsoil geometry and characteristics in the area under investigation, with particular regard to the stiffness properties and the degree of saturation. The ability of geophysics to investigate non‐invasively has proven successful for dealing with buildings affected by foundation instability. The resolution of the results obtained from experimental data provides additional insight into the geological scenario and the causes of the settlement. Moreover, geophysical data may be used as a guide to optimize borehole locations for coring and soil specimen collection, which are necessary steps in designing the restoration intervention.
The effect of a dipping layer on the first‐arrival traveltime from zero‐offset and fixed‐offset borehole radar
Authors: Rucker Dale , Ferré Ty P.A.
Published: August 2009

The effect of a dipping layer on the first‐arrival traveltime from single‐offset profiling with borehole radar is investigated, including both zero‐offset and fixed‐offset profiling. In our study, offset refers to the vertical distance between bistatic radar antennae. Using forward modelling of electromagnetic wave travel, the traveltime of zero‐offset and fixed‐offset profiles through a dipping layer is compared to those of flat‐lying layers. The model considers three distinct raypaths: direct, critically refracted and cross‐dip refracted. Whereas critical refraction only occurs in a layer of low propagation velocity relative to an adjacent high‐velocity layer, cross‐dip refraction can occur in any velocity structure. The forward model demonstrated that the slope of the traveltime through the cross‐dip portion of the profile is approximately half of that in the critically refracted portion. To obtain the electromagnetic wave propagation velocities above and below the dip, only one profile is necessary. However, to invert for the dip angle and position, two profiles with different offsets must be considered together.
Retrieving self‐potential anomalies in a complex volcanic environment: an SP/elevation gradient approach
Authors: Lénat Jean‐François
Published: August 2009

The problem of differentiating self‐potential (SP) anomalies from different origins on volcanoes is addressed using the SP/elevation gradient. Surveys on volcanoes classically show the presence of a purely hydrogeological zone on the flanks and a hydrothermal zone in the central area. The hydrogeological zone is characterized by negative SP/elevation gradients, ranging typically between 0 and −2 mV/m, whilst gradients vary in a broader range in the hydrothermal zone. Simple models show how these gradients will be perturbed in the presence of perched water tables, lateral variations of physical properties (e.g. resistivity) or by positive anomalies associated with upward hydrothermal circulations of fluids. The SP/elevation gradient is much more sensitive to the perturbations than the SP and, therefore, it is proposed that the gradient is used to enhance the anomalies. Using digital SP and topographic grids, the gradient can be computed in 2D and a regional SP map of the Piton de la Fournaise volcano (La Réunion, Indian Ocean) is used to illustrate the method. Anomalies are easily identified in the active central area, but are difficult to discern in other areas. Conversely, the anomaly zones are clearly shown on the gradient map as well as the different types of terrain (i.e. with different SP/elevation gradient values) in the hydrogeological zone. In the summit area, where the data coverage is dense, a comparison of the gradient information as a function of the SP map resolution is carried out to illustrate the sensitivity of the method to detect small‐scale structures. As a technique, the gradient approach appears to be very promising for the qualitative interpretation of SP surveys in volcanic areas as well as in other environments.
Improving the processing of vibroseis data for very shallow high‐resolution measurements
Authors: Buness Hermann
Published: August 2009

Very shallow seismic surveys, i.e. 20–100 m target depth, require a large bandwidth of high frequencies to ensure detailed resolution. A survey with a small hydraulic vibrator across young glacial structures in northern Germany that gave unsatisfactory results was repeated with monitored vibrator motions. This enabled us to use the groundforce signal as correlation operator and to apply sweep deconvolution.

The application of the groundforce signal resulted in a distinct improvement compared to correlation using the reference sweep, whatever the data compression technique used. This is due to harmonics that show high amplitudes at high frequencies and contribute considerably to signal energy. Sweep deconvolution works at least as well as correlation. Due to the minimum‐phase nature of sweep deconvolved data, this technique, if combined with a minimum‐phase deconvolution, gave the best results. The geological target, consisting of thin interstadials embedded in a sequence of sands deposited during the last glaciation, could be imaged much more clearly than before.
3D resistivity imaging from an archaeological site in south‐western Anatolia, Turkey: a case study
Authors: Drahor M.G. , Göktürkler G. , Berge M.A. , Kurtulmuş T.Ö. , Tuna N.
Published: August 2009

A large‐scale resistivity imaging survey was performed in the acropolis area of Archaic Cnidos, south‐western Turkey. This survey was a part of the geophysical studies conducted between 1999 and 2004. Two‐dimensional resistivity data were acquired along a number of parallel lines using a pole–pole array. The data was processed using a 3D inversion algorithm based on a robust technique. We also applied shaded‐relief processing to enhance the representation of the images of apparent‐resistivity data and inversion results. In addition, the inverted resistivity data were visualized by a volumetric representation technique to display both the horizontal and the vertical extents of the archaeological structures. The inversion results revealed that a rectangular gridding pattern and a dense structuring existed in the depth range 0.35–1.5 m in the acropolis. Moreover, the bedrock was the base of the archaeological structures in the area. Based on the resistivity survey, four test excavations were carried out in various localities in the acropolis in 2004. These excavations yielded results supporting those obtained by the resistivity inversion. This indicated that large‐scale 3D resistivity imaging can be a useful tool in archaeological prospection.
Array GPR investigation of the cathedral of Uppsala
Authors: Gustafsson J. , Alkarp M.
Published: August 2009

We present an example of a so‐called array GPR investigation outside the Cathedral of Uppsala, Sweden. The aim of the investigation was to reveal historically interesting features in surroundings where excavations are not allowed. In the investigation, 17 different GPR antennae of the same frequency were used to obtain measurements in 16 parallel profiles simultaneously. When several separate transmitter and receiver antennae are combined into one single antenna array unit, exactly positioned parallel profiles are obtained, resulting in a seamless high‐resolution 3D picture of the subsurface. Processing the radar data into the resulting images involves several steps, such as aligning traces, removing static shifts and matching the mean response. Radar data are merged with geometry data from a total station (used to track the position of the antenna array) and then gridded and migrated. In the Uppsala case presented here, the resulting pictures in the form of time slices gave archaeologists very valuable help in understanding the subsurface and mapping historical anomalies. The findings indicate former paths and early medieval streets, among other features.
High‐resolution seismic investigation of Lake Tana, northern Ethiopia
Authors: Richard Bates C. , Lamb Henry F. , Umer Mohammed
Published: August 2009

High‐resolution single‐channel seismic reflection data and sediment core samples from Lake Tana, Ethiopia, reveal a dynamic Holocene and late Pleistocene history of the lake. The seismic data show a sequence of sediments in excess of 45 m thick with four strong reflection horizons. The horizons are interpreted to be a consequence of climate conditions resulting in complete lake desiccation. The youngest of these surfaces, at a depth of 8–12 m beneath the present lake floor, is dated at about 17 k cal BP and is correlated with desiccation of Lake Victoria during Heinrich event 1. Similar surfaces were mapped at depths of approximately 25, 30 and 45 m below the lake floor, suggesting numerous late‐Pleistocene lowstands. No features within the seismic sections suggest deep‐water depositional environments. Deeply incised channel sequences cut through the near‐surface sediments above the strong lake‐wide reflection horizons and represent periods of significant erosion during the early Holocene. These events are tied to core intervals dated to 8.4 and 12.1 k cal BP, which also correspond to climate change during regional arid periods. On the northern lake margin, the geometry of sediment accumulation suggests recent faulting with associated continuing basin subsidence in this active tectonic region. The seismic and core data from Lake Tana can be summarized as showing a sedimentation history through the Holocene and late‐Pleistocene that reflects the interplay between rapid climate change and long‐term basin subsidence.
Beyond image analysis in processing archaeomagnetic geophysical data: case studies of chamber tombs with dromos
Authors: Piro S. , Sambuelli L. , Godio A. , Taormina R.
Published: August 2009

We analysed the effectiveness of three methods for interpreting magnetic maps in the third dimension, i.e. the depth. The possible synergies among the information obtained by each method have also been examined. The approach is based on a preliminary evaluation of the depth of the causative body according to the solution of Euler’s equation; the application of a two‐dimensional cross‐correlation technique enables the estimation of the spatial orientation, the shape and the susceptibility contrast of the causative bodies. The preliminary interpretation allows the input parameters and the necessary constraints (e.g. susceptibility contrast, maximum depth of the magnetic targets) to be tuned for the subsequent 3D modelling and inversion. We adopt the strategies for the quantitative interpretation, i.e. depths and shape, of the archaeological remains in the Sabine Necropolis of Colle del Forno, Montelibretti, Rome. The approach is shown to be effective for imaging the dromos and cavities of the tombs of this necropolis.
Geophysical investigations at the Himera archaeological site, northern Sicily
Authors: Capizzi P. , Cosentino P.L. , Fiandaca G. , Martorana R. , Messina P. , Vassallo S.
Published: August 2009

In this paper we present a geophysical survey that was carried out as a research activity during field trips to the Himera archaeological site, where relics of a large Greek settlement are still buried, effected by a joint group of archaeologists and geophysicists during an educational project. Two‐dimensional (2D) resistivity and ground‐penetrating radar (GPR) surveys were performed to locate buried archaeological structures at this archaeological site. The results of the GPR surveys show some anomalies characterized by semi‐hyperbolic shapes. In some restricted areas of the town, two grids of parallel GPR profiles were acquired while time‐ and depth‐slices were calculated to identify the extension of the buried structures. In fact, the shapes of many anomalies recognized in the slices seem to describe the distribution of the relics (i.e. walls, roads, etc.).

A 2D electrical resistivity profile showed clear anomalies, which were connected with wall‐like relics. This was also obtained by using on‐site calibration on partially uncovered structures, while the low background resistivity values were interpreted as representing river deposits having different moisture characteristics. Recommendations were also given to the archaeological site‐excavators, following which some of the results were confirmed by subsequent archaeological excavations.
Integrated geophysical survey to detect buried structures for archaeological prospecting. A case‐history at Sabine Necropolis (Rome, Italy)
Authors: Cardarelli E. , Fischanger F. , Piro S.
Published: August 2009

In the last few years, the location and characterization of buried historical objects is a task that generally lends itself to geophysics, thanks to the improvement of automatically measuring geophysical systems and the development of specific software for inversion problems. Furthermore, the integration of different methods permits an interpretation in which potential misunderstandings and the uncertainty of results can be reduced. The aim of the present work was to detect buried structures in an unexplored area of a Sabine Necropolis (700‐300 B.C.) located in the area of the National Research Council (at Montelibretti, Rome). During the survey, three different geophysical techniques have been employed; fluxgate gradiometry, Electrical Resistivity Tomography and Ground‐Penetrating Radar. The results are compared, integrated and interpreted indicating location of unknown buried tombs.

An additional objective of this study consisted of testing new finite element modelling routines that have been integrated into the inversion algorithm developed by the authors in the past years, and, to compare the 2D inversion results with the ones achieved with the 3D Finite element inversion software ERTLab.

Finally, the interpreted geophysical results have been verified through archaeological direct excavation in 2005, which have confirmed the location, dimensions and shape of the buried structure (tomb).
A 3D seismic land‐streamer system
Authors: Dolena Trevor M. , Speece Marvin A. , Link Curtis A. , Duaime Terence E.
Published: August 2009

The 3D seismic reflection method has not been extensively utilized for shallow subsurface investigations because of the relatively high cost of performing 3D surveys. We have designed and constructed a system that could make 3D seismic reflection an affordable option for shallow subsurface exploration by significantly reducing time and labour. In a fashion similar to marine work, a vehicle tows an array of four parallel seismic cables, or land streamers. Each streamer consists of 24 gimballed geophones. The vehicle drags the array from station to station and shots are taken while the array is stationary. We tested our system near Belt, Montana, in an attempt to image an abandoned subsurface coal seam and associated mine workings at a depth of approximately 88 m. For this survey, receiver, receiver line, source and source line spacings were all 1 m. In total, we surveyed a surface area of 100 m × 34 m, achieving a nominal fold of 24. Typical combined advance and occupation times for each station were less than 30 s, using a crew of three people. We were able to image the layered geology in the area and the coal seam; although we were not able to view the individual mine workings because of limited resolution. This testing shows that our system has the potential to expand the application of 3D seismic reflection to shallow subsurface exploration by greatly increasing efficiency.
A new sensor for the automatic detection of the state of ground
Authors: Stacheder M. , Koeniger F. , Schuhmann R. , Brandelik A. , Schmitt G. , Sommer W. , Fiel R.
Published: August 2009

The following paper reports on the development and field test of a new sensor for the determination of the state of ground according to the codes established by the Deutscher Wetterdienst (German Weather Service, DWD). Based on the requirements of the DWD and the results of a feasibility study, an electromagnetic technique was used to design a measurement system which allows for the detection of different soil surface states, such as dry, moist, wet, frozen or snow‐covered by evaluating the dielectric properties of the soil and its cover.

The system consists of an impedance analyser and a 1 m2 large permeable sensor mat with interlaced electrode cables. The sensor and the device were tested in the field on both naturally undisturbed soil and an artificial concrete surface.

The new system proved to be reliable and field‐capable. With the help of suitable reference measurements of temperature and precipitation as well as visual observations, a decision matrix with several criteria, such as the measured soil capacitance, temperature and state‐of‐ground history, could be established. It allows for the interpretation of the measurements and, hence, an automatic determination of the state of ground.

The measurement system presented could be a promising new tool for the automatic characterization of the state of ground, for example for weather forecast and traffic control services as well as for agricultural and forestry applications.
Resistivity imaging in steep and weathered terrains
Authors: Mendoza J.A. , Dahlin T.
Published: August 2009

In areas where tectonics and weathering have hydrogeological significance, electrical methods can assist in mapping the subsurface. In this work, resistivity imaging was used to map fractures, faults and quartz veins emplaced in strongly weathered volcanic rocks. The aim was to map geological units related to the formation of groundwater systems in the Río Artiguas basin, Nicaragua. Eight 2D resistivity surveys selected from two sites with characteristic geological features are discussed in this article. The resistivity lines were carried out with a multi‐electrode system together with different electrode geometries. The data inversion was done by applying the robust (L1‐norm) method and a finite element grid to accommodate the steep topography. The data interpretation included numerical modelling to assess the suitability of all used electrode arrays in relation to the expected geological settings. The results indicated a top high resistive layer consisting of colluviums with laterite (>50 Ω m), underlain by conductive clay weathered layers (10–50 Ω m). Below the conductive layer less weathered or fresh rock can be found with higher values (50–600 Ω m). The quartz veins and dykes stand out as the highest resistive bodies (100–4000 Ω m). The results indicated an overall weathering thickness of 10–30 m or more. In conclusion, the extensive resistivity imaging surveys allowed delineation of geological structures and weathering layers throughout the study area. Furthermore, the vertical extension of weathering was examined at all locations. A finite element grid in the inversion prevented distortions arising from topography regardless of the steep slope observed at the survey locations. The numerical modelling results revealed the strengths of different arrays for the particular cases of a fault and a quartz vein in irregular terrains.
Soil water content monitoring on a dike model using electrical resistivity tomography
Authors: Rings Joerg , Scheuermann Alexander , Preko Kwasi , Hauck Christian
Published: August 2009

We explore the viability of electrical resistivity tomography (ERT) to quantify soil water content in a full‐scale dike model. While ERT is an established method to detect changes in soil water content, the retrieval of two‐dimensional water content distributions from surface‐based surveys is a much more challenging application. We conducted a series of experiments on a full‐scale dike model comprising rainfall and flooding events. The dike was surveyed with an ERT line down the land‐side slope and monitored with permanently installed spatial time‐domain reflectometry (TDR) cables for comparison. Water content changes were calculated by applying Archie’s equation and agreed well with comparison measurements from spatial TDR measurements. The saturation exponent in Archie’s equation was estimated by combining spatial TDR and ERT measurements and agreed well with literature data of comparable sands. The choice of the inversion type, e.g., time‐lapse inversion or least‐squares versus robust constraint, as well as the influence of inversion parameters, such as regularization and the choice of convergence criterion, is discussed in the context of an apparent inversion artefact for the rainfall experiment, using forward modelling of synthetic data sets. The results indicate that ERT may be a feasible method to quantify water content changes under certain conditions, provided an initial water content estimate is available.
A new broadband radiomagnetotelluric instrument: applications to near surface investigations
Authors: Tezkan B. , Saraev A.
Published: August 2009

A new radiomagnetotelluric (RMT) instrument has been developed that can record time series of electric and magnetic fields in the frequency range from 10 kHz to 1 MHz. Military and civilian radio stations broadcasting in this frequency range are used as transmitters. Transfer functions (e.g., apparent resistivities and phases as a function of frequency) are determined by spectral analysis using a newly developed processing software. The transfer functions presented here are the first ones ever at frequencies above 300 kHz and they can lead to a better resolution of the shallow structure. The new RMT instrument enables quick and efficient mapping of shallow structures and supports tensor measurements thereby allowing a 2D or 3D interpretation of field data. The new RMT system was tested in the laboratory and then applied successfully in the field to several environmental and engineering problems. Case studies from applications in St. Petersburg, Russia and in Uzin, Ukraine will be presented. The observed apparent resistivities and phases are reliable and they show smooth frequency dependence. The data were inverted for 2D conductivity models under the assumption that the strike direction was known beforehand.
Seismic characterization of an Alpine site
Authors: Valentina Socco Laura , Boiero Daniele , Comina Cesare , Foti Sebastiano , Wisén Roger
Published: August 2009

Site amplification of earthquake ground motion can arise from local stratigraphic and morphological conditions. In this respect, a detailed geo‐mechanical 2D model is needed, in particular for peculiar situations such as the ones in Alpine valleys. This paper reports a site characterization case history for seismic response analysis, where a combination of both body and surface wave seismic techniques has been used. In particular, it is shown that synergies and mutual cross‐checking of information lead to a reliable 2D model for site amplification studies.

The evaluation of the deep structure and the location of the seismic bedrock have been obtained through seismic reflection and combined active‐passive surface wave analysis, while the shear‐wave velocity profile of the sediments has been obtained by downhole measurements and surface wave tests. Furthermore, a detailed compressional wave velocity model has been retrieved by tomographic inversion of the first arrivals picked on seismic reflection records. This model is useful for geological interpretation as well as for quality control of the other methods. Surface wave analysis has also been performed on the ground roll of the seismic reflection records. The large amount of profile oriented data has made it possible to reconstruct lateral variations of the shear‐wave velocity in the soil deposit. The final pseudo‐2D shear‐wave velocity model is the product of an innovative inversion approach, based on the integration of the Monte Carlo and laterally constrained least‐squares techniques. In the laterally constrained inversion the shear‐wave velocity profiles obtained from downhole tests and data from passive surface wave measurements have been used to constrain the inversion. This has greatly improved the final solution.

This case history underlines the necessity of combining different seismic techniques to derive an accurate and reliable 2D model for site amplification studies. Through several different and independent analyses of the same seismic records, the cost effectiveness of the whole survey is optimized and a full exploitation of the information contained in the reflection seismic data set is achieved.
A multicomponent GPR survey in Marambaia Isthmus
Authors: Travassos J. M. , André S. , Musa J. E.
Published: August 2009

This work deals with a multicomponent ground‐penetrating radar data set obtained on Quaternary unconsolidated deposits of eolian, alluvial, lacustrine and marine sands with a choice of two cross‐dipole and two co‐polar antenna configurations. The geophysical response is characterized by strong reflectors observed in both co‐ and cross‐polarized 100 MHz data sets down to a two‐way time (TWT) of 400 ns. With this data set we delineate a given horizon using its overall polarization direction, which is different from that defined by the position of the antennas and of profile direction. That horizon, whose existence was not previously known, represents a more complex situation than an isolated body, e.g., a buried metallic pipe, a situation well studied elsewhere.

The polarizing horizon is characterized by linear polarization and a reasonable uniformity of an Alford rotation angle that maximizes the co‐polar responses. With the modal Alford angle we produce improved images corresponding to the two co‐polar components and a conspicuous improvement in the continuity of the reflectors across the polarizing horizon. All goes as if the antennas were oriented parallel and perpendicular to the main polarizing direction of the structure. In addition, the two co‐polar components display a good degree of independence from each other as revealed by their eigenvalues. Our results illustrate how a data set collected with less than optimal field geometry can still satisfactorily reveal the subsurface.
Frequency‐dependent attenuation and velocity characteristics of nano‐to‐micro scale, lossy, magnetite‐rich materials
Authors: Cassidy Nigel. J.
Published: August 2009

In many situations, the magnetic properties of sub‐surface materials are often considered unimportant when compared to their ‘dielectric’ characteristics (i.e., the permittivity and conductivity). However, if significant amounts of magnetic minerals exist, such as magnetite, hematite, maghemite, etc., then the relaxation phenomena of these magnetically lossy minerals can have a significant effect on the complex apparent permittivity of the materials. In this paper, the apparent complex permittivity, attenuation and propagation characteristics of a range of nano‐to‐micro scale quartz/magnetite mixtures are investigated with the aim of determining how the lossy magnetic minerals affect the propagation of ground‐penetrating radar waves in the near‐surface environment. In addition, the investigated results are compared to popular ‘dielectric‐based’ mixing models (such as the complex refractive index model – CRIM) where the performance of the model is evaluated in terms of its appropriateness for practical situations. The results indicate that even with relatively low amounts of magnetite, the magnetic materials can have a considerable effect on the attenuation, wave propagation velocity and interface reflectivity and that the current non‐linear complex mixing models (such as CRIM) are inadequate for the description of nano‐to‐micro scale, magnetically lossy mixtures.
Numerical modelling of ground‐penetrating radar response from rough subsurface interfaces
Authors: Giannopoulos Antonios , Diamanti Nectaria
Published: August 2009

Ground‐penetrating radar (GPR) modelling is employed to study the electromagnetic wave scattering that emanates from a rough subsurface interface. The numerical analysis is achieved by using a finite‐difference time‐domain numerical modelling algorithm. For the 2D GPR models, the rough interfaces are generated using both Gaussian and fractal statistics. For a given root mean square interface roughness height, we study the effect that the change in correlation length has on the incident wavefield for a randomly generated surface with a Gaussian roughness spectrum. Similarly, for an interface generated using fractal statistics, we examine the effect of fractal dimension for two different values of maximum wavenumber. For the Gaussian case, the correlation length is the most important parameter in defining the target signature. But, when fractals are used, an increase in clutter is observed as the fractal dimension increases. In addition, the clutter is more pronounced when the highest value of maximum wavenumber is used. Detection performance is evaluated by utilising 3D ground‐penetrating radar models. Comparing the 3D models with and without the presence of a rough subsurface interface, increased wavefield attenuation and strong depolarization effects were observed from a fractal subsurface terrain.
Measuring soil surface water content in irrigated areas of southern Tunisia using full‐waveform inversion of proximal GPR data
Authors: Lambot Sébastien , Slob Evert , Chavarro Diana , Lubczynski Maciek , Vereecken Harry
Published: August 2009

Full‐waveform inverse modelling of proximal ground‐penetrating radar was used to measure soil surface water content in irrigated areas of southern Tunisia. The ground‐penetrating radar system consisted of a hand held vector network analyser combined with an off‐ground monostatic horn antenna, thereby setting up an ultra wideband stepped‐frequency continuous‐wave radar. Inversion of the radar Green’s function was performed in the time‐domain, on a time window focused on the surface reflection only. Results were compared with volumetric and time‐domain reflectometry measurements, as well as with an improved version of the standard reflection coefficient method. Except for water contents close to saturation, good agreements were obtained between ground‐penetrating radar, time‐domain reflectometry and volumetric samples. Significant differences were observed when the soil electric conductivity was high and could not be neglected anymore in the inversion process. Accounting for electric conductivity provided better results. Remaining errors were attributed to the different scales of characterization dealt with in relation to the vertical variability of water content in the top few centimetres of the soil. The proposed method appears to be more practical and accurate than the standard reflection coefficient method and shows great promise for real‐time mapping of surface soil moisture at the field scale.
Pastoraat en jeugtrauma, die ‘sondebokmodel’, en Jesus as rolmodel
Authors: Endres Annelize , Dreyer Yolanda
Published: August 2009

Pastoral care with traumatised youth, the ‘scapegoat’ model, and Jesus as role modelExisting research shows that adolescents are victimised and traumatised more often than adults. Many a time it is left to pastoral counsellors to assist such traumatised youth to overcome such experiences. This article therefore aims to empower pastors in this task with reference to the insights of René Girard. As violence is inherent to traumatic experiences, two aspects of Girard’s insights are pertinent. Girard’s notions of imitation with regard to violence, as well as the scapegoat ritual can be useful to pastors who want to guide adolescents through their trauma. Girard’s contribution has been widely acknowledged and used by theologians in their hermeneutical and theological endeavours. This article now applies these insights to the field of Practical Theology. In theology, Jesus has become both the ‘role model’ and the ‘scapegoat’. This article applies both these aspects of Jesus’ life to pastoral care with traumatised youth.
The development of a hassle-based diagnostic scale for predicting burnout in call centres
Authors: Visser Willie A. , Rothmann Sebastiaan
Published: August 2009

The aim of this study was to develop a brief daily hassle diagnostic questionnaire that could be used to identify daily hassles for customer service representatives within a call centre environment, and to investigate the relationship between daily hassles and burnout. A crosssectional survey was used with an accidental sample (N = 394) taken from a service and sales call centre. An exploratory factor analysis of the data resulted in a six-factor model of daily hassles consisting of daily demands, continuous change, co-worker hassles, demotivating work environment, transportation hassles and personal concerns. The internal consistency of one factor, namely personal concerns, was low. Exhaustion was best predicted by four categories of daily hassles, namely daily demands, continuous change, a demotivating work environment, and transportation hassles.
Towards a workplace conducive to the career advancement of women
Authors: Lewis-Enright Karen , Crafford Anne , Crous Freddie
Published: August 2009

The aim of this study was to start designing a workplace conducive to women’s career advancement. Appreciative inquiry was selected as an appropriate methodology, given the slow progress that has been made in addressing gender equality at work. Seventeen men and women working in the finance division of a large organisation were invited to participate in an appreciative inquiry workshop. This was followed by interviews with four leadership team members. While no original ideas or solutions emerged from the interventions, participants of the appreciative inquiry process demonstrated a shift in thinking, more positive emotional responses, a shared vision for the future and improved willingness to assume accountability for change.
Association studies of −3081(A/T) polymorphism of norepinephrine transporter gene with attention deficit/hyperactivity disorder in Korean population
Authors: Joung Yoosook , Kim Chun‐Hyung , Moon Jisook , Jang Won‐Seok , Yang Jaewon , Shin Dongwon , Lee Soonyoung , Kim Kwang‐Soo
Published: August 2009

Recent studies showing the improvement of ADHD symptoms obtained with the highly selective noradrenergic reuptake inhibitor, atomoxetine, demonstrate that the noradrenergic system plays the role of pathophysiology in this disorder. It is revealed that the norepinephrine transporter gene (SLC6A2) is a possible candidate gene directly related to ADHD. To determine possible roles of the SLC6A2 as a susceptibility gene for ADHD, we performed the genetic association study for a functional −3081(A/T) polymorphism, located in the promoter region of SLC6A2. For the present study of association between ADHD and the SLC6A2, 103 male patients with ADHD and 103 normal male controls were randomly gathered. Significant differences were found in the allele frequencies (χ2 = 5.60, P = 0.02) and the odds ratio for the allele T between the ADHD and normal subjects was 1.59 (95% CI: 1.08–2.34) suggesting that T allele is critical to make the group difference. Significant group difference was also found in AA, AT, TT genotypes (χ2 = 7.1, P = 0.02). The odds ratio for TT and AT genotypes was 4.57 (95% CI: 2.56–8.15) and 1.96 (95% CI: 0.96–3.78), respectively. Findings in the present study provided further evidence of association between ADHD and −3081(A/T) polymorphism of SLC6A2. © 2009 Wiley‐Liss, Inc.
Multifunctionality of layered fabric systems based on electrospun polyurethane/zinc oxide nanocomposite fibers
Authors: Lee Seungsin
Published: August 2009

To examine the feasibility of developing multifunctional textiles, layered fabric systems with electrospun polyurethane/zinc oxide nanocomposite fiber webs layered on cotton substrates were developed to impart UV‐protection and antibacterial functions. The morphology of polyurethane/zinc oxide nanocomposite fibers was examined using a field‐emission scanning electron microscope and a transmission electron microscope. UV transmission properties were assessed for layered fabric systems with various levels of electrospun web area density. Antimicrobial properties of zinc oxide nanocomposite fibers and layered fabric systems were evaluated qualitatively using the Parallel Streak method, and quantitatively by measuring the bacterial reductions of a Gram‐positive bacterium (Staphylococcus aureus) and a Gram‐negative bacterium (Klebsiella pneumoniae). A thin layer of electrospun zinc oxide nanocomposite fiber web significantly reduced the transmission of UV radiation and exhibited an ultraviolet protection factor of greater than 50, indicating excellent UV protection. Layered fabric systems with zinc oxide nanocomposite fiber webs containing 5 wt % zinc oxide exhibited over 98% reduction in both Staphylococcus aureus and Klebsiella pneumoniae. The results show that the successful imparting of multifunctionalities such as UV‐protection and antibacterial functions to cotton fabrics is achievable through simultaneous electrospinning of the polymer material with zinc oxide nanoparticles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009