bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multiple‐gradient array measurements for multichannel 2D resistivity imaging
Authors: Dahlin Torleif , Zhou Bing 
Published: August 2009

ABSTRACTTwo‐dimensional resistivity imaging using multiple gradient, Wenner and dipole‐dipole electrode arrays was carried out at two field sites in Sweden and one in Nicaragua, with the objective of confirming the practical applicability of results obtained with numerical modelling. The results support earlier numerical modelling studies that concluded that the gradient array, using multiple current electrode combinations, has resolution as good as or better than the commonly used Wenner array. The array behaved well in terms of sensitivity to noise at the test sites, and the results obtained generally agree with dipole‐dipole array results, although the latter at two of the sites gave resistivities that differed significantly from the other arrays in the deeper parts of the inverted models. A formula proposed for pseudosection plotting works well for data quality assessment, where it can be an advantage to make separate plots for each m‐factor (the distance between the midpoints of the current and potential electrode pairs) or for each a‐spacing. The gradient array is well suited for multichannel data acquisition, and can significantly increase the speed of data acquisition in the field and at the same time give higher data density, but it is also an attractive option for single‐channel data acquisition. The Wenner array, on the other hand, is not suitable for measuring in more than one channel. Compared to the dipole‐dipole array, it offers lower sensitivity to noise which may be a major advantage in real data acquisition, and the remote electrode needed for the pole‐dipole array is avoided, which is often a significant advantage for field logistics.
Identification of buried valleys using the BGR helicopter‐borne geophysical system
Authors: Eberle D.G. , Siemon B. 
Published: August 2009

ABSTRACTA study of four airborne electromagnetic data sets collected during the past decade by the BGR helicopter‐borne geophysical system over various geological settings shows that such data sets indicate not only layered horizontal geological features but also vertically and laterally confined structures, such as buried valleys. Indicative geological markers comprise conductive cover layers, conductive fills in resistive bedrock, and incisions in a conductive host filled with resistive materials. In cases where the valleys are incised into a magnetic basement and refilled with non‐magnetic material, the magnetic data records can also be used for identification and thickness estimates of the infill.From a hydrogeological point of view, buried valleys are becoming increasingly important as they host groundwater reserves, which are in many cases big enough to satisfy the future demand for fresh water. This paper describes two examples from the North‐West German lowlands and another two from the Namib coastal plains, where the Kuiseb and the Omaruru ephemeral rivers reach the shore of the South Atlantic Ocean.
Subsurface water‐content identification in a crypt using GPR and comparison with microclimatic conditions
Authors: Leucci Giovanni , Cataldo Rosella , De Nunzio Giorgio 
Published: August 2009

ABSTRACTThe effects of climate, pollution and human negligence cause severe and sometimes irreversible damage to buildings and monuments of cultural interest. It is well known that the presence of water and/or moisture content in a porous material is the initial cause of deterioration. In a previous paper, the authors reported an integrated study on a building of cultural importance, namely the crypt of the Cattedrale di Otranto in Apulia, Italy, based on non‐destructive integrated biological and physical surveys. The method described was able to identify the ‘internal’ factors responsible for deterioration. It was discovered that the distribution of moisture in the stone depended mainly on adverse environmental conditions, and the presence of wet buried structures in the ground.The first aim of the present study was to identify subsurface water‐content in this same crypt using a ground‐penetrating radar (GPR) technique, and to compare these results with those of the previous microclimatic survey. In particular, the existence of underground discontinuities was verified; we located them and analysed their influence. Moreover, by means of velocity analysis, we obtained a quantitative estimate of the volumetric water‐content under the pavement of the crypt. This finding completes the results of the previous research, as it indicates the causes of the deterioration in the crypt and provides significant information, on the basis of which, effective decisions can be made for safeguarding the historic building.
Detecting brine zones in salt deposits with the ground penetrating radar (GPR) for safety assessments of underground waste disposals
Authors: Igel Jan , Kurz Gerhard , Schulz Rüdiger 
Published: August 2009

ABSTRACTThe presence of brine is one of the principal hazards of underground waste disposal. A clear reflection at a brine reservoir would be expected when carrying out ground‐penetrating radar (GPR) measurements because of the high contrast in the electrical conductivity between dry rock‐salt and brine. However, this is not the case as many previous measurements have shown, and as is also demonstrated by some of our GPR measurements.The lack of a distinct reflection at higher frequencies can be explained by the presence of a gradient zone leading to a frequency‐dependent reflection coefficient. Therefore, measurements at two frequencies (25 and 100 MHz) were carried out in a potash salt‐mine with a massive brine reservoir. When comparing the energy distributions of these measurements, the area of the brine reservoir shows a frequency‐dependent reflection coefficient as opposed to areas without brine. Several finite‐difference forward calculations using different frequencies and models deduced from drill‐cores from the area of the brine reservoir are presented. They demonstrate that brine zones are detectable by comparing different frequencies if they are not enclosed by a sharp interface but by a gradual increase in the brine content.
Electrical resistivity tomography to detect buried cavities in Rome: a case study
Authors: Cardarelli E. , Di Filippo G. , Tuccinardi E. 
Published: August 2009

Cavities located in shallow layers of the subsoil represent a major hazard especially in sites located in town centres. For this reason, it is necessary to determine their location and size in order to evaluate the risk of subsidence and to draw up plans for restoration and safety.In this study, electrical resistivity tomography was carried out, both to detect cavities and to test a new inversion algorithm that we developed. The cavities are located in a volcanic formation in a public recreation park where there are municipal buildings. The survey was performed using two different arrays: dipole‐dipole and Wenner. A new approach to adopting an initial model and inequality constraints was used and the results from different algorithms were compared. The effective range of the dimensions of cavities was determined in order to make an approximate evaluation of ground stability and any potential subsidence hazard.
Mine action: status of sensor technology for close‐in and remote detection of anti‐personnel mines
Authors: Acheroy Marc 
Published: August 2009

ABSTRACTAfter a broad introductory discussion on the mine action problem, this paper presents the status of close‐in mine detection technologies, including operational characteristics, without aiming at being exhaustive. Signal processing aspects and important lessons on data fusion are also discussed briefly. The detection is considered as a global process in which the outputs of the sensors, considered as skilled specialists, are integrated in a fusion operation. Next, the paper briefly addresses the problem of area reduction using remote sensing. In this case, information, collected with appropriate sensors and associated with context information from the field, is integrated in a geographical information system. This part of the paper is intentionally limited to a very short description of the SMART project funded by the European Commission, which uses multispectral and full polarimetric radar data in order to assist image analysts in their interpretation of mined scenes during an area reduction process.
Mutually and laterally constrained inversion of CVES and TEM data: a case study
Authors: Christiansen Anders V. , Auken Esben , Foged Nikolai , Sørensen Kurt I. 
Published: August 2009

ABSTRACTMutually constrained inversion in combination with laterally constrained inversion (MCI‐LCI) between transient electromagnetic (TEM) and direct current (DC) resistivity methods was successfully used to characterize a buried valley structure. Although both methods measure, in some sense, the electrical resistivity, or conductivity, of the subsurface, they sample different volumes and have different sensitivities, which are exploited with mutually and laterally constrained inversion of combined, coincident profile data sets. The output models incorporate the information from both data sets to obtain optimum layered 1D models, fitting both data sets and constraints.The set‐up of constraints contains three parts. First, we constrain the individual data sets along their profile using lateral constraints producing a chain of TEM data and a chain of DC data. Next, we merge the information from these two chains by setting up mutual constraints between the TEM and the DC models. Finally, we adjust the mutual constraints to resemble the increasing sampling volumes with depth, i.e. wide constraints at large depths and short constraints at shallow depths. All data sets are inverted simultaneously; a common objective function is minimized, and the number of output models is equal to the number of 1D soundings. The lateral and mutual constraints are part of the inversion, and consequently the output models are balanced between the constraints and the data‐model fit. Information from one model will spread to the neighbouring models through the constraints, helping to resolve parameters that are poorly resolved by any of the individual data sets.A field example illustrates that MCI‐LCI allows the governing information from each method to dominate the inversion process. Thus, the model resolution in both the shallow and the deeper parts of the model is significantly enhanced. This could not be obtained by inverting the two data sets separately with a subsequent comparison of the output models. Our results are confirmed by drill‐hole data.
HELP ACEH – A post‐tsunami helicopter‐borne groundwater project along the coasts of Aceh, northern Sumatra
Authors: Siemon Bernhard , Steuer Annika , Meyer Uwe , Rehli Hans‐Joachim 
Published: August 2009

ABSTRACTAfter the earthquake and the tsunami event on December 26, 2004, the Indonesian and German governments set up a project dedicated to re‐installing the public life of the people in the coastal region of Aceh Province in northern Sumatra, Indonesia. As the tsunami waves caused large‐scale coastal salt‐water intrusions and destroyed thousands of shallow drinking‐waterwells, the focal point was water assessment along the shorelines of Aceh about nine months after the tsunami. The target areas were the city of Banda Aceh and the district of Aceh Besar on the north coast and the area on the west coast between the towns of Calang (district of Aceh Jaya) and Meulaboh (district of Aceh Barat). A helicopter‐borne survey including electromagnetics (HEM), magnetics and gamma‐ray spectrometry was conducted by the airborne group of the German Federal Institute for Geosciences and Natural Resources from August to October 2005. The HEM surveys revealed shallow coastal salt‐water occurrences caused by the tsunami, deep salt‐water occurrences up to several kilometres inland, and a number of potential freshwater resources. Numerous requests for information on the geological and hydrogeological situation at sites for planned water‐wells were successfully evaluated.
Characterization of small local noise sources with array seismology
Authors: Ritter Joachim R.R. , Sudhaus Henriette 
Published: August 2009

ABSTRACTSeismic noise is often regarded as a stochastic, incoherent and unwanted signal. However, at a closer look, noise also contains coherent signals which can be used to characterize its sources and/ or the subsurface. Here, we propose the use of array seismological methods for engineering purposes to locate and identify small, local noise sources. A detailed knowledge of noise sources enables appropriate measures to be taken to mitigate unwanted noise effects. As a case study, we report results from a temporary array of ten seismic broadband stations which were installed at the building site of a high‐precision physics laboratory. Standard analyses of power spectra and amplitude measurements indicate that the highest noise amplitudes are caused by heavy trucks passing by. Burst‐like coherent waves, excited by vehicles, appear to have a recurring pattern. Using array techniques, we were able to measure the slowness and backazimuth of the coherent arrivals. These could be identified as Rayleigh waves generated at small pot‐holes and bumps of a near‐by road and were found to propagate with a speed of 130–200 m/s.
Non‐destructive DC resistivity surveying using flat‐base electrodes
Authors: Athanasiou E.N. , Tsourlos P.I. , Vargemezis G.N. , Papazachos C.B. , Tsokas G.N. 
Published: August 2009

ABSTRACTThe application of flat‐base electrodes to geoelectrical measurements is examined. This study is motivated by the inability to apply geoelectrical techniques in environments where conventional spike electrodes cannot be inserted into the ground. The performance of flat‐base electrodes is examined in various environments, using different measuring modes. It is shown that flat‐base electrodes can be satisfactorily used in most cases, producing data that are almost identical to the measurements obtained using standard electrodes. Several case studies in various urban locations in Greece, where flat‐base electrodes have been successfully employed, are also presented. The results indicate that flat‐base electrodes provide the advantage of a fully non‐destructive application and, therefore, the extension of geoelectrical methods to environments that, otherwise, would not have been considered suitable.
Seismic tomography on the castle hill in Quedlinburg
Authors: Schicht Th. , Lindner U. , Heckner J. , Strobel G. , Rappsilber I. 
Published: August 2009

ABSTRACTThe collegiate church of Saint Servatius (part of the UNESCO world heritage list) and other buildings on the castle hill in Quedlinburg show evidence of frequent damage caused by foundation subsidence. The geological structure consists of sandstone of differing hardness from the Cretaceous period. Geotechnical investigations to date have provided information about the underground structure at various points, but no comprehensive 3D spatial model of the entire area was heretofore available. Therefore, the non‐destructive seismic tomography method was used. On different locations around and on top of the castle hill, elastic waves were generated with a weight drop. On the other hillside the arrivals of the seismic waves were recorded by geophones. The result was a tomographic model of the 3D distribution of P‐wave velocities. The results showed a zonally differentiated seismic velocity scheme. Considerable differences in the rock strength were shown. Areas with slower seismic velocities indicate lower rock quality and therefore geotechnically weak zones. The areas of our investigations, which were identified as deconsolidated rock, correspond to damage to the buildings above.
TDEM magnetic viscosity prospecting using a Slingram coil configuration
Authors: Thiesson Julien , Tabbagh Alain , Flageul Sébastien 
Published: August 2009

ABSTRACTSoil magnetic properties are significantly modified by pedogenesis and human activity; consequently their study is an important source of information about soil structure and history. In addition to measurements of magnetic susceptibility, now commonly practised, magnetic viscosity measurements can be undertaken as a routine survey method if well‐matched instruments that are easy to use in the field and that offer a sufficient depth of investigation, exist.A theoretical study, supported by field tests of a prototype, demonstrates that a Slingram perpendicular coil configuration with a one‐metre inter‐coil spacing allows the required one‐metre depth of investigation to be reached for both 1D and 3D models. The sensitivity of the instrument response to the viscosity is also very high over the whole measurement range (10μs to 1ms), while the sensitivity to electrical conductivity is reduced to a minimum.A first experiment at the Roman site of Vieil‐Évreux illustrates how viscosity measurements can complement magnetic field and susceptibility measurements for a more accurate identification of an archaeological feature.
Time‐lapse electrical resistivity tomography to delineate mud structures in archaeological prospections
Authors: Ranieri G. , Sharpe L. , Trogu A. , Piga C. 
Published: August 2009

ABSTRACTArchaeological sites in rural areas are often characterized by structural remains that are made of mud or raw brick, and that produce a very small contrast in physical characteristics, as the surrounding materials of both anthropogenic and natural origins have similar lithological and mineralogical properties. The main measurable differences are due to changes in compaction and porosity and, as a consequence, in permeability, which influence the hydrological behaviour of the subsurface materials.In this paper, we present some applications based on Electrical Resistivity Tomography (ERT) surveys that are routinely applied in archaeological prospection, carried out over two different weather conditions. Measurement of the changing resistivity, corresponding to different moisture conditions in the subsoil, allowed us to identify archaeological strata and structures surrounded by natural, undisturbed soil.A number of tests carried out on a physical model permitted a further definition of the acquisition parameters and methodologies to be used to secure the best results. The field surveys were carried out in the necropolis of “Pill’e Matta” (IV BC ‐ V AD), located in the suburbs of the metropolitan area of Cagliari, in the southern part of Sardinia, and in a Punic and Roman site near the village of Terralba, located in the Campidano plane, in the western part of Sardinia. The results show that time‐lapse prospecting can increase the resistivity contrast between archaeological structures and soil.
Aquifer characterization in the Ouarzazate Basin (Morocco): A contribution by TEM and RMT data
Authors: Steuer A. , Helwig S.L. , Tezkan B. 
Published: August 2009

ABSTRACTIn this case study we present the first application of the radio magnetotelluric (RMT) technique in Africa. We applied the RMT and transient electromagnetic (TEM) methods to study an aquifer of the Ouarzazate Basin between the High Atlas and the Anti Atlas in Morocco. The main objective of the survey was to constrain the geometry of the near surface sediment layer by mapping the aquitard, an underlying clay layer.We collected RMT data in the frequency range of 16 kHz to 207 kHz and TEM data in the time range of 4 μs to 1 ms along an 8 km long profile in a desert area crossing an oasis region. After 2D inversion of the RMT data and 1D inversion of the TEM data, we carried out 1D joint inversion to enhance the resolution of the subsurface resistivity structure.From the inversions we derived the resistivity distribution down to a depth of about 100 m and identified a relatively resistive layer as the aquifer sediments, overlying a more conductive clay layer. Inversion statistics indicate that the depth of the clay layer is well resolved. Compared with the lithological logs of drillings located at distances of 150 m to 3 km from the profile, the depth of the clay layer beneath the aquifer in the south of the geophysical section agrees to ± 3 m. Furthermore, we observed a lateral resistivity contrast close to the surface separating the desert area and the oasis, due to differences in humidity.
Semi‐automatic feature extraction from GPR data for archaeology
Authors: Leckebusch Jürg , Weibel Andreas , Bühler Flurin 
Published: August 2009

ABSTRACTA new method and working tool to interpret 3D ground‐penetrating radar data has been developed. Algorithms for feature extraction based on three‐dimensional regression techniques are developed to generate 3D models of the archaeological reflection features in the subsurface.After several attempts to reasonably visualize the information of a 3D ground‐penetrating radar (GPR) data cube by manual and automatic techniques, we propose a new approach: the visualization and interpretation steps are combined in an efficient and objective process in order to extract the geometrical information of the mapped archaeological features. Each object is modelled by six independent planes that form the structure that should be extracted. This is an appropriate approximation for walls, floors, stones as well as for pipes. To speed up calculation and because routines operating on the complete data set were not successful so far, the system utilizes a start line which is defined by the user. After 3D pre‐filtering with a sequence of median – dilation – erosion, followed by a 3D gradient filter, planes are matched to the borders of the anomaly by using a least‐median‐of‐squares algorithm. Finally, the found planes are refined by an analytical regression and the final box displayed in a 3D GIS software. The small computing time for a single object makes this method feasible for routine application of feature extraction from a 3D GPR data cube. The presented technique allows visualizing and extracting the imaged archaeological features rapidly and into an easy understandable representation.
High‐resolution magnetic survey in a quasi‐urban environment
Authors: Ciminale Marcello , Gallo Danilo 
Published: August 2009

ABSTRACTA high‐resolution magnetic survey was performed on a large cultivated field located inside a heavily built‐up town in Southern Italy. Measurements with a vertical gradiometer were even carried out relatively close (down to 35 m) to sources of strong magnetic noise. Despite these particularly unfavourable surroundings, the geophysical investigation made it possible to detect and recognize buried archaeological remains from the Neolithic age.