bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fresnel reflection coefficients for GPR‐AVA analysis and detection of seawater and NAPL contaminants
Authors: Carcione José M. , Gei Davide , Botelho Marco A.B. , Osella Ana , de la Vega Matias 
Published: August 2009

ABSTRACTWe obtain the transverse electric (TE) and transverse magnetic (TM) Fresnel reflection coefficients for different interfaces in the subsoil: air/fresh‐water, air/seawater, fresh‐water/seawater, air/NAPL (non‐aqueous phase liquid), NAPL/water and water/NAPL. We consider a range of NAPL saturations, where the complementary fluid is water with 0.65 ppt (parts per thousand) of NaCl. The common feature is that the TM mode (parallel polarization) has a negative anomaly and the TE mode (perpendicular polarization) has a positive anomaly. For the cases studied in this work, pseudo‐Brewster angles appear beyond 40° for the air/NAPL and NAPL/water interfaces and at near offsets (below 40°) for the water/NAPL interface. Pseudo‐critical angles are present for the water/NAPL interface. Besides the reflection strength, the phase angle can be used to discriminate between low‐ and high‐conductivity NAPL, when the properties of the upper medium are known. A wavenumber–frequency domain method is used to compute the reflection coefficient and phase angle from synthetic radargrams. This method and the curves can be used to interpret the amplitude variations with angle (AVA) of reflection events in radargrams obtained with ground‐penetrating radar (GPR).
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

ABSTRACTAirborne 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

ABSTRACTIn 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

ABSTRACTSince 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

ABSTRACTWe 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.
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.
High‐resolution seismic investigation of Lake Tana, northern Ethiopia
Authors: Richard Bates C. , Lamb Henry F. , Umer Mohammed 
Published: August 2009

ABSTRACTHigh‐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

ABSTRACTWe 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

ABSTRACTIn 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

ABSTRACTIn 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTIn 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

ABSTRACTWe 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.