bluuebunny/crossref_metadata_2025 huggingface dataset:
Using seismic traveltime tomography in geoarchaeological exploration: an application at the site of Chatby cemeteries in Alexandria, Egypt
Authors: Polymenakos L. , Papamarinopoulos St. P.
Published: August 2009

We apply seismic traveltime tomography in an investigation of the subsurface of a geoarchaeological site at Chatby cemeteries (Alexandria, Egypt). We are interested in obtaining information about the geological structure and the remains of man‐made structures. Energy sources are placed at the surface and recorders are distributed vertically in an underground location. Traveltime data are inverted with a three‐dimensional tomographic algorithm. Inversion results are evaluated and interpreted with the aid of independent geophysical and archaeological information, and various tests are carried out with different initial velocity models and synthetic traveltimes.

The inversion results show good correlation with the estimated geological structure, in particular at deeper levels, as suggested by independent geophysical and archaeological information and later confirmed by excavation. The depth and variations of the bedrock surface are satisfactorily imaged. Indications of possible man‐made structures are presented and discussed. Shallow velocity features are evaluated and interpreted using tests with synthetic traveltimes. The main goal of imaging the deeper structure was successful.

As inversion tests with different initial velocity models indicate, the subsurface structure and the complexity of data information in this particular case are better handled when using a single‐layer model than when using an average two‐layer model. The single‐layer model allows for a more versatile velocity variation and raypath distribution, while the two‐layer model leads to an inversion result that is considerably influenced by the initial velocity distribution. Enhancement of particular aspects of the single‐layer inversion result can be derived with the use of an initial velocity model, that permits a gradual increase of velocity with depth. The gradient model improves the raypath distribution and limits velocity artefacts.

The resulting images can assist in the assessment of the archaeological potential of a site, particularly in excavation design, in a non‐destructive manner. They can be also of great value in other applications, for example in engineering works, when detailed information on the subsurface is sought in areas of restricted access.
Three‐dimensional probability tomography of self‐potential anomalies of graphite and sulphide mineralization in Orissa and Rajasthan, India
Authors: Bhattacharya Bimalendu B. , Shalivahan  , Jardani A. , Bera Aparna
Published: August 2009

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

The results of a geophysical survey carried out in the historical area of “Sassi of Matera” (Basilicata region, southern Italy) are presented and discussed. Matera is one of the most fascinating and ancient towns of the Mediterranean area and is listed in the UNESCO World Heritage List. It represents an example of a town where the communities developed a cave‐life culture in the cavities excavated through the substratum of the hill of Matera. The urban area of Matera, therefore, is characterized by a complex system of interconnected and overlapping ancient shallow cavities: residences, galleries, cisterns, crypts, graves, etc. Consequently, local surface deformation phenomena are often observed.

We describe the results from a ground‐penetrating radar (GPR) survey carried out in St. Rocco Square, one of the most interesting areas of the historical centre of Matera, that was affected by both spread out and local subsidence phenomena. Great attention was paid to GPR data processing and inversion. In particular, a novel microwave tomography approach was applied to obtain high‐resolution images of shallow ancient cavities that caused the local surface deformations. Moreover, the GPR survey was integrated with an electrical resistivity tomography survey in order to prospect those subsurface zones with a high electrical conductivity, where GPR investigation was not possible. The geophysical investigation enabled us to identify the cause of the subsidence phenomena and to reconstruct the geometry of the complex system of shallow cavities partially filled with unconsolidated material.
GPR investigations for the study and the restoration of the rose window of Troia Cathedral (southern Italy)
Authors: Masini Nicola , Nuzzo Luigia , Rizzo Enzo
Published: August 2009

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

Ground‐penetrating radar (GPR) surveys are frequently used to delineate the distribution of subsurface water. This paper demonstrates that GPR is suitable for detecting water leakage from underground construction areas because it produces detailed images of changes in water‐level that are related to water leaks. For this experiment, we used a test pit filled with river sand and a buried mortar wall that divides the pit into two sections. To simulate water leaks, we drilled holes through the mortar wall at a depth of 1.15 m and maintained constant water levels of 1.4 m and 0.4 m below the surface on each side of the wall. Water‐levels were controlled by pump‐extraction and injection using water‐control wells. Variations in water‐level under dynamic hydraulic conditions caused by water leakage through the holes were delineated by dense GPR single‐fold profiling measurements. Wide‐angle reflection and refraction (WARR) measurements were also performed to obtain velocity information and to support the interpretation of profiling data. To image minor changes in waterlevel accurately, we took minor topographic changes into account and applied finite‐difference method migration and time‐variant depth conversion to the GPR single‐fold profiling data. We were able to construct a three‐dimensional water‐level map using the water‐table depths extracted from migrated depth sections. Our results clearly demonstrate a rising trend in water‐level approaching the mortar wall, indicating water leakage from the drilled holes. In addition, the WARR data confirmed that the upward trend in water‐level continues to the mortar wall; it was not possible to image this trend on the single‐fold profiling section within 0.5–1 m of the mortar wall because of interference from measuring equipment buried close to the wall.
Geophysical surveying an active well catchment in the presence of significant topography and anthropogenic disturbances
Authors: Paasche Hendrik , Tronicke Jens , Maurer Hansruedi , Green Alan G. , Auken Esben , Stauffer Fritz
Published: August 2009

Traditional approaches to surveying well catchments usually involve investigations at two quite different spatial scales: very high resolution borehole‐based studies and low resolution tracer and pump tests. In recent years, various researchers have attempted to fill the wide gap between the two scales of acquired data by using a variety of geophysical tools that have high‐to‐medium resolution capabilities. Although geophysical surveying may be relatively straightforward at many locations, there are numerous regions where topography, the presence of ubiquitous metal objects and/or a lack of suitably placed boreholes cause the acquisition, processing, inversion and interpretation of certain types of geophysical data to be extremely challenging. It was necessary for us to address such problems in an investigation of an active well catchment near Zurich, Switzerland. The principal goals of our project were to determine the geometries and physical properties of the shallow sedimentary layers, with emphasis on a key water‐bearing gravel unit. To achieve these goals, four different geophysical methods were employed. In a first step, frequency‐domain electromagnetic measurements allowed the locations of buried metal pipes to be established. A 2D tomographic seismic refraction survey then provided information on the interface between the low‐velocity surface loamy topsoil and underlying high‐velocity morainal material. The high electrical resistivity of the important gravel unit allowed its upper boundary to be outlined in 2D models derived from geoelectric data and its lower boundary to be delineated in models based on 1D linked inversions of geoelectric and transient electromagnetic data.
Plus�minus method to solve large�amplitude near�surface static corrections
Authors: Bridle Ralph
Published: August 2009

The surface conditions in Saudi Arabia demonstrate significant variability ranging from flat gravel plains to sand�dunes,sabkhas(salt flats) and desertwadis(washouts). Saudi Aramco has used a single�layer velocity model from surface to datum for most of the prospective areas for both 2D and 3D seismic data. Source gathers have been interpreted by picking the first arrivals to obtain a linear fit for the direct and refractor arrivals using the intercept�time method. This creates depth and velocity control input for a multiple‐layer model of the near‐surface, from which static corrections to datum are calculated. On 2D lines with very large amplitude near‐surface anomalies, the plusminus technique has been applied to solve local areas. The implementation of the plus‐minus technique utilizes a variable near‐surface velocity derived from either upholes or the direct‐arrival velocity determined from source gathers. With this method, multiple source‐pairs build up effective spreads. Then by compiling high fold of delay‐times at a location, a statistical average is taken where the high fold reduces the significance of picking errors. The model is built utilizing multiple refraction layers and is referenced to the datum, thus tying it to the regional model.

The example 2D seismic line has a static model calculated from the single‐layer velocity model. The intercept‐time method was applied locally over a near‐surface anomaly caused by unconsoli‐dated material at the foot of a cliff. Further analysis of the near‐surface involved the plus‐minus method to solve the high amplitude time shifts.
Near‐surface characterization of a geotechnical site in north‐east Missouri using shear‐wave velocity measurements
Authors: Ismail Ahmed , Anderson Neil
Published: August 2009

Shear‐wave velocity (Vs) as a function of soil stiffness is an essential parameter in geotechnical characterization of the subsurface. In this study, multichannel analysis of surface wave (MASW) and downhole methods were used to map the shear‐wave velocity‐structure and depth to the bedrock surface at a 125m × 125m geotechnical site in Missouri. The main objective was to assess the suitability of the site for constructing a large, heavy building. The acquired multichannel surface wave data were inverted to provide 1D shear‐wave velocity profile corresponding to each shot gather. These 1D velocity profiles were interpolated and contoured to generate a suite of 2D shear‐wave velocity sections. Integrating the shear‐wave velocity data from the MASW method with the downhole velocity data and the available borehole lithologic information enabled us to map shear‐wave velocity‐structure to a depth on the order of 20m. The bedrock surface, which is dissected by a significant cut‐and‐fill valley, was imaged. The results suggest that the study site will require special consideration prior to construction. The results also demonstrate the successful use of MASW methods, when integrated with downhole velocity measurements and borehole lithologic information, in the characterization of the near surface at the geotechnical sites.
Efficient ERT measuring and inversion strategies for 3D imaging of buried antiquities
Authors: Papadopoulos N.G. , Tsourlos P. , Tsokas G.N. , Sarris A.
Published: August 2009

The optimum processing technique (2D vs. 3D inversion) to interpret and visualize parallel and/or orthogonal two‐dimensional surface Electrical Resistivity Tomography data collected from archaeological sites is examined in this work. A simple modification of a standard resistance‐meter geophysical instrument was implemented in order to collect parallel two‐dimensional sections along the X‐, Y‐ or XY‐direction in a relatively short time, employing a pole–pole array.

The sensitivity analysis showed that the distance between the parallel 2D lines must be smaller or, at the most, equal to the basic inter‐electrode spacing in order to produce reliable 3D resistivity images of the subsurface. This was confirmed by modelling and inversion of both synthetic and real data.

Direct comparisons of the quasi‐3D images, resulting from a posteriori combination of the inverted 2D sections, with the full 3D inverted resistivity models indicated the superiority of the 3D inversion algorithm in the reconstruction of buried archaeological structures, even in complex archaeological sites. Due to the inherent three‐dimensionality of many archaeological targets, quasi‐3D images suffer from artefacts. The combination of a single survey‐direction with a full 3D processing and interpretation scheme is adequate to image the 3D subsurface resistivity variation in detail. Furthermore, the implementation of a quasi‐Newton Jacobian matrix update technique reduced the processing time by one‐half without any significant loss of accuracy and resolution.
GPR surveying over burial mounds: correcting for topography and the tilt of the GPR antenna
Authors: Goodman Dean , Hongo Hiromichi , Higashi Noriaki , Inaoka Hiromichi , Nishimura Yasushi
Published: August 2009

A new method for static corrections of radargrams, which accounts for the tilt that the GPR antenna encounters on sites with topography, has been developed. The method uses the average electromagnetic wave velocity and assumed antenna tilt according to the first derivative of the topography profile, in order to adjust the normal ray projecting from the GPR antenna into its correct subsurface location. Static tilt corrections for radargrams with under sampled scan locations can be effectively adjusted using scan sweeping across small angles. Radargrams that are corrected for topography and antenna tilt show that changes in the imaged locations of subsurface structures can be significant, resulting in improved focusing and more accurate positioning of reflections.
Extended comparison of different GPR systems and antenna configurations at the Roman site of Carnuntum
Authors: Seren Sirri , Eder‐Hinterleitner Alois , Neubauer Wolfgang , Löcker Klaus , Melichar Peter
Published: August 2009

To evaluate the suitability of ground‐penetrating radar (GPR) systems for archaeological prospecting, three different GPR systems with several antenna configurations were tested on one test area at the Roman site of Carnuntum, under identical environmental conditions, in 2004. Due to developments in hardware and software within the last year, these measurements where repeated and compared with the previous results. The data processing considers the needs of the different systems and antennas and aims to produce depth slices for best interpretation from an archaeological point of view. The results show advantages and disadvantages of the different systems and antennas, the need to process the data differently and the necessity to increase the power of the antennas.
Verification and topographic correction of GPR data in three dimensions
Authors: Leckebusch Jürg , Rychener Jürg
Published: August 2009

Two sites in a Roman town allowed a direct comparison between GPR interpretation and excavation results in three dimensions. All the reflection features mapped by the geophysical survey were identified in the subsequent archaeological excavation. Some of these anomalies were shown to be walls preserved as a single layer of stone or completely robbed out. However, a number of walls that were later excavated were either not detected at all by the GPR or not imaged to their full depth. The reason for this is the limited penetration depth of the radar energy due to attenuation, which can be visually estimated from the data. In addition, the presentation of the GPR results was enhanced when the depth information was coded into the map of the interpretation. Finally a new processing step called topographic correction was developed to compensate for the antenna tilt and elevation in three dimensions. The differences and advantages of this method compared to 2D tilt corrections are discussed. Apart from migration, this topographic correction significantly improves the geometrical 3D accuracy and interpretation of the GPR data.
Estimating subsurface porosity and salt loads using airborne geophysical data
Authors: Ley‐Cooper Yusen , Macnae James , Tweed Sarah
Published: August 2009

We aim to map dissolved salts in aquifers which, with rising water tables, are a threat to fresh water resources and ecosystem health. Interpolated groundwater electrical conductivity (EC) maps from borehole measurements are combined with spatially detailed bulk electrical conductivities estimated from airborne electromagnetics to provide, through Archie’s law, a detailed prediction of subsurface porosity and total dissolved salt load of any near‐surface aquifer. This technique quantitatively integrates airborne electromagnetic and groundwater measurements of EC to provide the subsurface detail necessary for hydraulic properties. The process has been applied in Australia’s Murray River Basin, where the presence of salt is a threat to agriculture and fresh water supplies. Porosity predictions range between 1% and 50% and are spatially consistent with known geology, dissolved salt loads are estimated to be between 100 and 4000 tonnes per hectare. The predictions are yet to be compared to in‐situ measurements but if proven, will be a useful tool when in‐situ porosity is under‐sampled or is not available.
Application of tensorial electrical resistivity mapping to archaeological prospection
Authors: Varga Mihály , Novák Attila , Szarka László
Published: August 2009

At an archaeological site (Pilisszentkereszt Cistercian Monastery, Hungary) we carried out 3D tensorial geoelectric mapping measurements. We applied the well‐known tensorial form of Ohm’s differential law, where a 2 × 2 resistivity tensor relates to the horizontal current density vector and the corresponding electric field vector. In the DC apparent resistivity tensor there are three independent rotational invariants, and we defined two alternative sets. In the field, the current electrode distance was fixed to 15 m; two perpendicular AB directions were used, and 16×15=240 potential electrodes (with an equidistant space of ) were put in the central (nearly square, 7.5 m × 7 m) area between the current electrodes. Due to a four‐channel measuring system, it was possible to determine both components of a horizontal electric vector at the same time. The time needed to measure all potential differences between the neighbouring potential electrodes (thus to obtain 15×14=210 resistivity tensors), was about 40 minutes. So far, about 239 such maps have been completed, thus we have more than fifty thousand resistivity tensors around the monastery. The tensorial results are shown together with the results of traditional measurements. In field conditions, any resistivity estimation provides reliable information about the subsurface (both the tensor invariants and the traditional mean values). At the same time, the multidimensional (2D and 3D) indicators proved to be informative only in case of significant subsurface inhomogeneities.
Electrical strike imaging and anisotropy diagnosis from surface resistivity measurements
Authors: Senos Matias M.J.
Published: August 2009

Field resistivity measurements are often affected by the inhomogeneity and anisotropy of subsurface formations. The crossed square array is an electrode array particularly suited to investigating these problems. Herein, its use to obtain concealed formations electrical strike pseudosections will be shown. Field and 2D data modelling will be discussed and images of computed strike in depth and space will be presented and interpreted. Data modelling was carried out by using theoretical solutions based on the application of image theory to simple 2D outcropping models. More complex 2D concealed model solutions were obtained by physical analogue modelling. Furthermore, it has also been difficult to distinguish ground inhomogeneity and lateral resistivity variations from anisotropy in field data. Hence, it will also be shown that with crossed square array data anisotropy analysis it is possible to distinguish fracture anisotropy and structural anisotropy from media that conform closely to real anisotropy situations.
GPR multi‐component data analysis
Authors: Capizzi P. , Cosentino P.L.
Published: August 2009

In order to test the capabilities of ground‐penetrating radar (GPR) detection, models were reproduced in a laboratory using both plastic and metal cylinders as well as sheets to represent anomalies buried in a plastic tank containing sand. These models, which represent pipes and dipping layers in a homogeneous medium (i.e., sand), were used to detect the object’s position and study its polarization properties based on the different dielectric contrasts between the object and the surrounding medium. We paid particular attention to the choice of medium through which the wavefield propagated, to be sure of its isotropy and homogeneity, in order for the velocity to be the same for every path travelled.

Experimental tests were carried out by changing the dielectric contrasts from the target to the surrounding medium. In particular, the dielectric cylinders (which have a lower permittivity than that of the surrounding sand) were filled with different substances to represent targets such as PVC pipes, either empty or filled with hydrocarbons or water. The resulting scattered field depended on the electrical properties of both the cylinder and the surrounding material, the distance from the cylinder and the scattering angle.

Further experimental tests were carried out by using multi‐component GPR data to study the possibility of calculating the angle between the direction of the profile and that of the anomalies. The experimental data obtained as responses to the physical models proved that this method can be successfully applied to detect the orientation of dipping layers, cylinders and vertical fractures.
Two‐dimensional inverse filtering for the rectification of the magnetic gradiometry signal
Authors: Tassis G.A. , Hansen R.O. , Tsokas G.N. , Papazachos C.B. , Tsourlos P.I.
Published: August 2009

The magnetic difference, the quantity measured by magnetic gradiometers, is considered to be the convolution between a function that controls the anomaly pattern and another that controls the strength signal. These are called shape and amplitude functions, respectively. They are distinct and analytically determined; thus, after the assessment of a suitable model, its shape function can be inverted to serve as a filter. If this filter is next convolved with the measured field, a series of amplitude functions is recovered, provided that the subsurface structures can be simulated by a combination of a number of models similar to the one whose anomaly was inverted. The recovered series is essentially the subsurface distribution of the amplitude function.

Alternatively, the scheme can be viewed as a transformation of the original field of magnetic differences. The signals, transformed in this context, comprise rectified monopolar versions of the originals, positioned directly above the centre of the targets. Furthermore, their amplitude is a measure of the magnetization of the targets. Thus, the new anomalies can be viewed as a kind of magnetization or susceptibility mapping. Inversion filters are computed in the Wiener mode by inverting the shape function of the anomalies caused by vertical sided finite prisms. This particular model is appropriate for a wide variety of targets that are commonly met in archaeological prospecting. Converting the magnetic signal from the dual lobe pattern to single monopolar anomalies cause them to resemble the usual outcome of resistivity exploration. In this context, this work aims to form a scheme that makes the magnetic gradiometry outcome directly comparable to the outcome of resistivity mapping. Furthermore, it can be applied without contradicting or excluding any other processing operation.

The method is implemented in a FORTRAN program that is reasonably user‐ friendly. The efficiency of the scheme is tested both on synthetic and real data sets.
Inversion stability analysis of multimode Rayleigh‐wave dispersion curves using low‐velocity‐layer models
Authors: Liang Qing , Chen Chao , Zeng Chong , Luo Yinhe , Xu Yixian
Published: August 2009

Surface wave inversion is increasingly applied to estimate near‐surface shear (S)‐wave velocities for geological structures. Our study addresses the sensitivity and stability of the Rayleigh‐wave multimode dispersion‐curve inversion for earth models containing a low‐velocity layer. Due to the dependence of Rayleigh‐waves on the S‐wave velocity over a range of depth, the inverted generally have uncertainties that vary with depth and structure. An evolutionary algorithm was used to provide a population of final models from inversion of multimode Rayleigh‐wave dispersion curves. We analysed the uncertainties of inversion results for three irregular structures, i.e., three models with a low S‐wave velocity layer.

The results show that 1) because the low‐velocity layer traps the energy of Rayleigh‐waves and makes the wave travel within it, Rayleigh‐wave phase velocities are insensitive to variations in layers beneath a low‐velocity layer. This characteristic can influence the inversion stability for these layers’ parameters. 2) The high degrees of uncertainties of inverted for these layers still remain although the higher mode Rayleigh‐wave data are included in the inversion procedure. It can be concluded that estimates for layers beneath a low‐velocity layer are with a low degree of confidence and need to be treated with extra caution.
The very low‐frequency step‐frequency GPR system and its application to active fault detection
Authors: Zeng Zhaofa , Huang Ling , Liu Sixin , Liu Fengshan , Sun Jiguang
Published: August 2009

Ground‐penetrating radar (GPR) in the high‐frequency range is subject to attenuation, which limits its application in many fields, such as underground water detection and other near‐surface geological studies. We built a very low‐frequency GPR system based on a vector network analyser (VNA) and developed the system controlling software using visual basic for application (VBA). We also built a wire‐line antenna with a central frequency of 10 MHz on the ground. Results from an experiment on a water reservoir dam showed that the system works well.

Active fault evaluation is important for city planning and construction. The soil layer in Changchun City, Northeast China, has low‐resistivity and a depth of 10–20 metres. It is difficult for conventional GPR systems to detect bedrock in Changchun City. In this paper, we investigate the active fault in Changchun City using the very low‐frequency step‐frequency GPR system. The results from the step‐frequency GPR shows clearly the undulation of the bedrock. From this and the resistivity soundings we are able to interpret the location and the depth of the fault.
Vertical radar profiling for the assessment of landfill capping effectiveness
Authors: Cassiani Giorgio , Fusi Nicoletta , Susanni Daniele , Deiana Rita
Published: August 2009

In this paper we present the results of the characterization of a large landfill cap by means of ground‐penetrating radar (GPR) measurements. The GPR data were collected in boreholes, using a vertical radar profile (VRP) configuration, where one antenna was kept at the ground surface while the other was progressively lowered into the borehole. This yields a vertical profile of GPR velocity from which a moisture content profile can be obtained. VRPs were conducted in 15 boreholes available on‐site, all having been drilled through the protective cap and the waste mass into the underlying native soil. The separation between the boreholes (many tens of metres) makes it infeasible to characterize the site via other forms of hole‐to‐hole GPR measurements, with the exception of a few pairs of holes drilled at the periphery of the waste mass and therefore of limited usefulness. The VRP data allowed for the characterization of the moisture content profile across the waste body down to the water table, very close to the natural land surface, providing evidence that the waste is generally fairly dry (moisture content less than 10% on average). In order to assess the effectiveness of the cap, two surveys where conducted in March and April 2005 using all the boreholes with the aim of identifying moisture content changes due to natural rainfall and especially artificial irrigation over a limited area surrounding one of the boreholes. The time‐lapse VRP results show that in the irrigated area a measurable amount of water seeps through the cap and changes the waste moisture content. Elsewhere, we basically observed no changes in moisture content due to natural infiltration during the same period: this fact does not confirm or exclude that some degree of leakage can occur. Direct in‐situ permeability measurements, albeit more localized than VRP data, confirm that the landfill cap is not totally impermeable, thus corroborating the results derived from geophysical measurements.
Geophysical characterization of derelict coalmine workings and mineshaft detection: a case study from Shrewsbury, United Kingdom
Authors: Pringle J.K. , Stimpson I.G. , Toon S.M. , Caunt S. , Lane V.S. , Husband C.R. , Jones G.M. , Cassidy N.J. , Styles P.
Published: August 2009

A study site of derelict coalmine workings near Shrewsbury, United Kingdom was the focus for multi‐phase, near‐surface geophysical investigations. Investigation objectives were: 1) site characterization for remaining relict infrastructure foundations, 2) locate an abandoned coalmine shaft, 3) determine if the shaft was open, filled or partially filled and 4) determine if the shaft was capped (and if possible characterize the capping material).

Phase one included a desktop study and 3D microgravity modelling of the relict coalmine shaft thought to be on site. In phase two, electrical and electromagnetic surveys to determine site resistivity and conductivity were acquired together with fluxgate gradiometry and an initial microgravity survey. Phase three targeted the phase two geophysical anomalies and acquired high‐resolution self potential and ground penetrating radar datasets. The phased‐survey approach minimised site activity and survey costs.

Geophysical results were compared and interpreted to characterize the site, the microgravity models were used to validate interpretations. Relict buildings, railway track remains with associated gravel and a partially filled coalmine shaft were located. Microgravity proved optimal to locate the mineshaft with radar profiles showing ‘side‐swipe’ effects from the mineshaft that did not directly underlie survey lines.

Geophysical interpretations were then verified with subsequent geotechnical intrusive investigations. Comparisons of historical map records with intrusive geotechnical site investigations show care must be taken using map data alone, as the latter mineshaft locations was found to be inaccurate.
Potential and pitfalls of GPR traveltime tomography for ancient buildings investigation: experiments on a small‐scalem real and synthetic calcarenitic block
Authors: Nuzzo L. , Quarta T. , Galati M.B. , Fedi M. , Garofalo B.
Published: August 2009

Even if its use is not widespread in the archaeological community, GPR tomography is a viable tool in the maintenance of Cultural Heritage and for the diagnosis of internal defects in masonry, originating either at the building stage or later because of normal decay or natural disasters. Two‐dimensional GPR traveltime tomography aims to obtain information on the distribution of the dielectric constant on a section of the investigated medium from the picked direct arrival traveltimes between sources and receivers. This paper shows the results of a GPR tomographic experiment on a calcarenitic stone block with an empty central hole, using 1000 MHz as transmitter and 1800 MHz as receiver antennas. The original aims of this work were firstly, to assess the usefulness and limits of very basic tomographic tools, accessible also to the non academic community, in the limited case of locating voids in small‐scale structures (pillars or columns) and secondly, to identify possible pitfalls due to acquisition/ processing procedures or to inadequacy of the inversion algorithm. We examine some problems encountered in data acquisition and we propose a method to estimate the effective bandwidth of antenna pairs of different nominal frequencies and to estimate the zero time correction. The experiment shows that picking the first arrivals is a very delicate operation when the airwaves interfere with the transmitted ones and that using the wrong picked traveltimes in the inversion could lead to inconsistencies or to strong reconstruction artefacts. Finite‐difference numerical modelling is helpful both for identifying the correct arrivals to be picked and for exploring the dependence of the tomographic inversion on cell size, geometry of transmitters and receivers and initial model. The inversion results show a strong dependence on the angular ray coverage. The general improvement observed by increasing the illumination directions confirms the opportunity of using, whenever all sides are accessible, as in the case of columns or pillars, both parallel and orthogonal antenna positioning. In the presence of strong velocity gradients, as in this case, even using the best acquisition configuration for transmitters and receivers, the straight‐ray tomography based on the SIRT algorithm can only detect the anomaly but is unable to resolve adequately its geometry and dielectric constant. Although more time‐demanding, curved‐ray tomography or more sophisticated algorithms are therefore necessary for a better characterization of internal defects in most problems of structural assessment.
Localization of small PEC spheres by multiview/single‐frequency data
Authors: Solimene Raffaele , Buonanno Aniello , Pierri Rocco
Published: August 2009

The problem of determining the number and the locations of perfect electric conducting small spheres from the knowledge of their scattered far‐field is addressed. A multistatic/multiview/single‐frequency configuration is considered. The multiple scattering between the spheres is neglected in the problem formulation and the scatterers’ locations are represented as the support of (δ‐functions. This allows us to cast the problem as the inversion of a linear integral operator with the (δ‐functions being the actual unknowns of the problem. The inversion of such a linear integral operator is achieved by means of the truncated‐singular value decomposition. The performances achievable by the inversion algorithm are checked by synthetic exact data against model error and an additive white Gaussian noise.
The reconstruction of inhomogeneous targets from single view transient data
Authors: Belkebir K. , Catapano I. , Geffrin J.‐M.
Published: August 2009

This paper addresses the problem of characterizing scattering systems from the knowledge of transient scattered fields measured when only one source is used to illuminate an investigating region. The inverse problem is formulated in the frequency domain rather than in the time domain and the modified2 conjugate gradient method, which is a hybrid strategy belonging to the class of the modified conjugate gradient approaches, is exploited to retrieve the unknown permittivity and/or conductivity profiles. The aim of the paper is to investigate how the reconstruction capabilities of the adopted inversion procedure may be improved by acting on the characteristic parameters of the incident pulse that is its central frequency and bandwidth. In order to provide a preliminary analysis, experimental data corresponding to inhomogeneous two‐dimensional objects embedded into a homogenous medium are processed.
Practical representations of electromagnetic interferometry for GPR applications: a tutorial
Authors: Slob Evert , Slob Evert
Published: August 2009

Starting from the reciprocity theorems of the time‐convolution and time‐correlation types, several exact interferometric representations for electric and magnetic field Green’s functions due to electric dipole and quadrupole sources are derived. The abundance of ambient noise, over a wide electromagnetic spectrum from sources in the atmosphere or in space, is used to define three different practical acquisition geometries that can be used to create new data from cross‐correlations of the noise recordings. Similar setups are given for band limited transient sources to create new data from cross‐correlations or cross‐convolutions of the recordings from these transient sources. In all these applications the Earth can be arbitrarily anisotropic and dissipative as long as one receiver is located at the Earth’s surface or in the air above. In applications where both receivers are located in the Earth we show that cross‐correlations of such recordings lead to accurate new GPR data when the Earth is almost lossless.
A time frequency domain feature extraction algorithm for landmine identification from GPR data
Authors: Lopera Olga , Milisavljević Nada , Daniels David , Gauthier Alain , Macq Benoît
Published: August 2009

Ground‐penetrating radar (GPR) is a promising technique for demining procedures since it is able to detect both plastic and metal cased antipersonnel landmines. Yet, landmine identification using GPR is a challenging task since other buried reflectors such as stones or metallic debris can be detected. In this paper, a target discrimination approach is analysed and tested experimentally. It is based on relevant features extracted from 1D, GPR signals in the time frequency domain using the Wigner‐Ville distribution. Firstly, a filtering algorithm is applied to remove unwanted reflections from the background (e.g., soil surface reflection). Secondly, the preprocessed signal is transformed into a time frequency image using the Wigner‐Ville distribution. Finally, relevant features are extracted based on the singular value decomposition of the time frequency distribution. The algorithm is tested on radar data collected using two different hand‐held systems: (i) an impulse GPR‐based dual‐sensor system and (ii) a stepped‐frequency continuous‐wave GPR. Data were acquired over different types of soil and for different landmines and objects. Results are compared to features extracted using the wavelet transform and the Wilk’s lambda value is used as a criterion for optimal discrimination. Promising results are obtained, which show that time frequency features from Wigner‐Ville distribution could be used for differentiating between landmines and false alarms and could contain more valuable information than the features extracted using wavelet transform.
Biorheology
Authors: Dietrich Bauer Rudolf , Volk Tilmann
Published: August 2009

The article contains sections titled:

Introduction

Rheological Concepts

Basic Constitutive Equations

Viscoelastic Models

Transient Tests

Oscillatory Tests

Pressure–Volume Relationships

Pressure–Flow Relationships

Laminar Flow

Turbulent Flow

Oscillatory Flow

Rheology of Body Fluids

Viscosity of Non‐Newtonian Fluids

Instrumentation

Rheology of Blood

Macrorheology

Microrheology

Rheology of Viscoelastic Body Fluids

Hemodynamics

Heart Mechanics

Events of the Cardiac Cycle

Rheological Properties of the Heart

Rheological Approaches to Arteries

Quasistatic Mechanical Properties of Arteries

Dynamic Mechanical Properties of Arteries

Pressure and Flow in the Vascular System

Systemic Arteries

Pulmonary System

Arterial Dynamics

Pressure and Flow in Veins

Pneumodynamics

Functional Anatomy of the Lungs

Airways

Lung Volumes

Ventilation

Mechanics of Breathing

Mechanics of Inspiration

Mechanics of Expiration

Rheology of the Respiratory Tract

Rheology of the Lung

Rheology of the Chest

Rheology of the Lung–Chest System

Air Flow in the Respiratory Tract

Intrapulmonary Pressure

Distribution of Airway Resistances

Pressure–Air Flow Relationship

Acronyms
Excited State Dynamics in Biomolecules
Authors: Groenhof Gerrit , Schäfer Lars V. , Boggio‐Pasqua Martial , Robb Michael A.
Published: August 2009

Organisms have evolved a wide variety of mechanisms to utilize and respond to light. In many cases, the biological response is mediated by structural changes that follow photon absorption. These reactions typically occur at femto‐ to picosecond timescales. As the relevant time and spatial resolutions are notoriously hard to access experimentally, molecular dynamics (MD) simulations are the method of choice to study such ultrafast processes.

In the simulations, a multiconfigurational quantum mechanical (QM) description (CASSCF, CASPT2) is required to model the electronic rearrangement of those parts of the system that are involved in the absorption. For the remainder, typically consisting of the apoprotein and the solvent, a simple forcefield model (MM) suffices. QM/MM gradients have to be computed on‐the‐fly, and surface hopping procedures are needed to model the excited state decay. In this chapter, the computational framework underlying the atomistic simulation of photochemical events is reviewed and a few representative applications are discussed that demonstrate the validity of hybrid QM/MM approaches for photobiological reactions.
Protein–Lipid Interactions in Biological Membranes
Authors: Nielsen Claus Helix
Published: August 2009

The canonical Singer–Nicolson model of lipid bilayers with embedded proteins emphasize the passive barrier properties of the bilayer component. It is, however, becoming increasingly clear that the notion of bilayers as essentially inert two‐dimensional sheets of liquid hydrocarbon is problematic. There is increasing evidence for regulation of integral membrane protein function by the molecular composition of the bilayer matrix. In many cases, the regulation is nonspecific in the sense that the regulation is coupled to a physical property of the bilayer such as equilibrium thickness and spontaneous monolayer curvature. This regulation can be rationalized by considering the hydrophobic matching between proteins and the lipid bilayer. Thus, whenever an integral membane protein undergoes a conformational change involving its hydrophobic transmembrane moiety, part of the free energy associated with the conformational change is determined by the physical properties of the lipid bilayer. This chapter first reviews the basic structural properties of lipid bilayers and the two main structural classes of integral membrane proteins: alpha‐helical bundles and beta‐barrels. Then, examples of recent advances in electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopy revealing structural and orientational information about integral membrane protein in fluid lipid bilayers are presented. Finally, a continuum elastic description of protein–lipid interactions is presented with emphasis on how to quantify the energetics of protein–lipid interactions.
Single Molecule Biophysics with Fluorescence
Authors: Prummer Michael , Huebner Christian
Published: August 2009

We give an overview of the physical basics, experimental techniques, and selected applications of single molecule fluorescence in biophysical research. The photophysical principles underlying single molecule fluorescence resonance energy transfer (smFRET) experiments are treated. Its application in protein biophysics, in particular protein folding and conformational dynamics associated with enzymatic activity, is outlined with selected model systems.