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Geophysical Methods (geophysical + methods)
Selected AbstractsGeophysical identification of unmarked historic gravesGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2010Rinita A. Dalan Down-hole magnetic susceptibility techniques were explored as a means of improving near-surface geophysical surveys in historic grave detection. These techniques were used to document distinctive magnetic characteristics of grave shafts at three historic cemeteries first surveyed using various near-surface geophysical methods. Tests revealed a low magnetic susceptibility signature that soil magnetic studies indicated was largely related to differential soil compaction associated with the excavation and refilling of grave shafts. Most apparent at depths beyond those reached by soil penetrometers, this magnetic signature offers a way to assess anomalies identified by near-surface techniques that potentially represent graves. At one cemetery, magnetic studies of the interments themselves suggested spatially patterned, magnetically enhanced zones that might also aid in burial identification in certain contexts. While down-hole techniques will not be foolproof, they do provide another geophysical tool that can be used to improve grave detection. © 2010 Wiley Periodicals, Inc. [source] Geophysical exploration of Guajará, a prehistoric earth mound in BrazilGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 3 2003Bruce W. Bevan An interdisciplinary team studied Guajará, a prehistoric artificial mound in the Brazilian Amazon. The geophysical surveys and excavations were interactive;this interaction furnished more information than either geophysics or excavation alone could have provided. While seven different geophysical methods were applied, the magnetic survey reported here was particularly valuable. A detailed interpretation of this survey quantified the magnetic material in the mound, and this furnished an initial estimate of the number of cooking hearths in the mound. Ten test excavations were concentrated at magnetic anomalies. These excavations located cooking hearths and burial urns. A reevaluation of the magnetic survey was then done in order to refine the estimate of the number of hearths in the mound; this yielded an estimate of 2200 hearths. This allowed the population of the site to be approximated at 78,156 people. The geophysical survey and excavations also identified possible locations for subsequent broad-area excavations. © 2003 Wiley Periodicals, Inc. [source] An electromagnetic modelling tool for the detection of hydrocarbons in the subsoilGEOPHYSICAL PROSPECTING, Issue 2 2000Carcione Electromagnetic geophysical methods, such as ground-penetrating radar (GPR), have proved to be optimal tools for detecting and mapping near-surface contaminants. GPR has the capability of mapping the location of hydrocarbon pools on the basis of contrasts in the effective permittivity and conductivity of the subsoil. At radar frequencies (50 MHz to 1 GHz), hydrocarbons have a relative permittivity ranging from 2 to 30, compared with a permittivity for water of 80. Moreover, their conductivity ranges from zero to 10 mS/m, against values of 200 mS/m and more for salt water. These differences indicate that water/hydrocarbon interfaces in a porous medium are electromagnetically ,visible'. In order to quantify the hydrocarbon saturation we developed a model for the electromagnetic properties of a subsoil composed of sand and clay/silt, and partially saturated with air, water and hydrocarbon. A self-similar theory is used for the sandy component and a transversely isotropic constitutive equation for the shaly component, which is assumed to possess a laminated structure. The model is first verified with experimental data and then used to obtain the properties of soils partially saturated with methanol and aviation gasoline. Finally, a GPR forward-modelling method computes the radargrams of a typical hydrocarbon spill, illustrating the sensitivity of the technique to the type of pore-fluid. The model and the simulation algorithm provide an interpretation methodology to distinguish different pore-fluids and to quantify their degree of saturation. [source] Magnetic Resonance Sounding: New Method for Ground Water AssessmentGROUND WATER, Issue 2 2004M. Lubczynski The advantage of magnetic resonance sounding (MRS) as compared to other classical geophysical methods is in its water selective approach and reduced ambiguity in determination of subsurface free water content and hydraulic properties of the media due to the nuclear magnetic resonance (NMR) principle applied. Two case examples are used to explain how hydrogeological parameters are obtained from an MRS survey. The first case example in Delft (the Netherlands) is a multiaquifer system characterized by large signal to noise ratio (S/N = 73), with a 24 m thick, shallow sand aquifer, confined by a 15 m thick clay layer. For the shallow aquifer, a very good match between MRS and borehole data was obtained with regard to effective porosity nc,28% and specific drainage Sd,20%. The MRS interpretation at the level deeper than 39 m was disturbed by signal attenuation in the low resistivity (,10 ,m) media. The second case of Serowe (Botswana) shows a fractured sandstone aquifer where hydrogeological parameters are well defined at depth >74 m below ground surface despite quite a low S/N = 0.9 ratio, thanks to the negligible signal attenuation in the resistive environment. Finally, capabilities and limitations of the MRS technology are reviewed and discussed. MRS can contribute to subsurface hydrostratigraphy description, hydrogeological system parameterization, and improvement of well siting. The main limitations are survey dependence upon the value of the S/N ratio, signal attenuation in electrically conductive environments, nonuniformity of magnetic field, and some instrumental limitations. At locations sufficiently resistive to disregard the signal attenuation problems, the MRS S/N ratio determines how successfully MRS data can be acquired. Both signal and noise vary spatially; therefore, world scale maps providing guidelines on spatial variability of signal and noise are presented and their importance with respect to the MRS survey results is discussed. The noise varies also temporally; therefore, its diurnal and seasonal variability impact upon the MRS survey is covered as well. [source] The apparent electrical conductivity as a surrogate variable for predicting earthworm abundances in tilled soilsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2010Monika Joschko Abstract Noninvasive geophysical methods have a great potential for improving soil-biological studies at field or regional scales: they enable the rapid acquisition of soil information which may help to identify potential habitats for soil biota. A precondition for this application is the existence of close relationships between geophysical measurements and the soil organism of interest. This study was conducted to determine whether field measurements of apparent electrical conductivity (ECa) are related to abundances of earthworms in tilled soils. Relationships between ECa and earthworm populations were investigated along transects at 42 plots under reduced and conventional tillage at a 74 ha field on sandy-loam soil in NE Germany. Relations were analyzed with linear-regression and spatial analysis. The apparent electrical conductivity (ECa) was quantitatively related to earthworm abundances sampled 5 months after the geophysical measurements. No relationship was found, however, in plots under conventional tillage when analyzed separately. If earthworm abundances were known at every other location along the transects and if the state-space approach was used for analysis, the analysis of ECa measurements and earthworm abundances indicated that 50% of the earthworm samples could have been substituted by ECa measurements. Further research is needed to fully evaluate the potential of ECa measurements for predicting earthworm habitats in tilled soil. [source] Geophysical surveys designed to delineate the altitudinal limit of mountain permafrost: an example from Jotunheimen, NorwayPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2004Christian Hauck Abstract Three geophysical methods have been applied to delineate the altitudinal limit of permafrost at Juvvasshøe/Jotunheimen in southern Norway. By using each method in a complementary way according to its applicability, the permafrost distribution could be analysed on both large and small scales. In addition, temperature-based methods such as the BTS method (bottom temperature of snow cover) were used to validate the results. On a large scale, electromagnetic induction profiling with the EM-31 was used to detect the location of the transition area between frozen and unfrozen ground. Within this area direct-current (DC) resistivity and refraction seismic tomography were also applied to further characterize and visualize the permafrost transition. The large scale surveys revealed a sharp increase in conductivity, indicating an increase in unfrozen water content, near 1400,m a.s.l., with a possible transition zone between 1500,m a.s.l. and 1380,m a.s.l. The small scale investigation delineated the altitudinal limit of permafrost between 1470,m a.s.l. and 1410,m a.s.l., with sporadic ground ice occurrences and temperatures near the freezing point. Copyright © 2004 John Wiley & Sons, Ltd. [source] Karstic morphologies identified with geophysics around Saulges caves (Mayenne, France)ARCHAEOLOGICAL PROSPECTION, Issue 3 2010Rémi Valois Abstract Geophysical measurements were carried out around Saulges caves that sought to highlight the local karstic morphologies and the impact on preservation of archaeological material within the caves. Electrical resistivity tomographies (ERTs) and apparent conductivity mapping detected a soil cover on the plateaus that ends abruptly over fractured limestone or over a bowl-shaped structure filled with clay soil. Moreover, there is at least one zone of soil accumulation with a basin form with almost no soil cover around this structure. The ERT and seismic refraction tomography (SRT) detected an important anomaly in the valley. Many clues indicate that this anomaly is a karstic conduit filled with water or clay. Therefore, some karstic dissolution zones have been found and only geophysical methods are able to detect such features. Detection of preferential pathways could help to protect prehistoric art within the caves and new karstic morphologies help to better understand this karstic system. Copyright © 2010 John Wiley & Sons, Ltd. [source] Geophysical Archaeology Research Agendas for the Future: Some Ground-penetrating Radar ExamplesARCHAEOLOGICAL PROSPECTION, Issue 2 2010Lawrence B. Conyers Abstract Archaeological geophysics research and its applications to archaeology are today positioned to move in a number of directions, building on successes in the past few decades. The basics of data acquisition, processing and interpretation are now commonplace, and along with a variety of new geophysical tools and software, readily available to most dedicated practitioners. It is now time to move beyond the basics to develop new areas of research for the coming decades. Here, we propose some future avenues that can be followed, using ground-penetrating radar (GPR) as an example. One avenue is the application of these techniques to test ideas about culture and history in ways not possible using traditional archaeological methods. Another is the application of sophisticated new equipment and three-dimensional processing methods that can produce greater precision in the products produced, while simplifying data acquisition and revealing more information about buried archaeological features. While we discuss below our ideas with regard to the future of GPR, these basic concepts and future pathways are potentially applicable to the other commonly used near-surface geophysical methods. Copyright © 2010 John Wiley & Sons, Ltd. [source] Multimethodological approach to investigate chamber tombs in the Sabine Necropolis at Colle del Forno (CNR, Rome, Italy)ARCHAEOLOGICAL PROSPECTION, Issue 2 2009Salvatore Piro Abstract Non-destructive geophysical prospecting methods are increasingly used for the investigation of archaeological sites, especially where a detailed physical and geometrical reconstruction of structures is required prior to any excavation work. Often, due to the limited size and depth of an archaeological structure, it may be rather difficult to single out its position and extent because of the generally low signal-to noise (S/N) ratio. This can be overcome by improving data acquisition and processing techniques and integrating different geophysical methods. In this work the results of a multimethodological surveys, used with the aim of detecting sharp discontinuities (boundary of cavities and fractures in the host medium) at the Archaeological Test Site of Sabine Necropolis at Research Area of National Research Council of Rome (Montelibretti, Italy) are shown. For the survey a combination of passive and active methods (magnetic, ground-penetrating radar (GPR), and dipole,dipole geoelectric (DDG)), topographical and three-dimensional laser scanner surveys and archaeological excavations were used to study the state of conservation of underground tombs. With all geophysical methods a high-resolution data acquisition was adopted with the aim of reconstructing a global vision of the study area. Signal processing and amplitude time-slice representation techniques were used for the analysis of GPR data. The bi-dimensional cross-correlation technique was applied to enhance the S/N ratio of the magnetic data. An example of the integration (both qualitative and quantitative) of these results is presented for a portion of the investigated area in the Sabine Necropolis at Colle del Forno (Rome, Italy). Archaeological excavations were then conducted systematically after completing the geophysical surveys and interpretations (from 2000 to 2006), which confirmed the location and shape of the individual chamber tombs with associated corridors. Copyright © 2009 John Wiley & Sons, Ltd. [source] A geophysical investigation of subsurface structures and Quaternary geology at San Marcos Pueblo, New MexicoARCHAEOLOGICAL PROSPECTION, Issue 4 2008Emily A. Hinz Abstract San Marcos Pueblo site (LA 98), located in the Galisteo Basin south of Santa Fe, New Mexico, encompasses the remains of 43 identified room blocks, a Spanish mission and 20 middens. As part of ongoing field investigations at San Marcos, students and faculty from the Summer of Applied Geophysical Experience (SAGE) field programme are using multiple geophysical techniques to non-invasively investigate the site. Modelling of the underlying Quaternary stream terrace geology and the detection of subsurface Pueblo-era features were accomplished through the integrated interpretation of data from seismic refraction and reflection, electromagnetic, magnetic and ground-penetrating radar methods. Although to date only a targeted spatially small extent of the site has been explored using these methods, the SAGE field programme has been able detect a variety of anthropogenic structures and debris. The SAGE field programme validated the presence of excavations in the natural stream terrace sequence over areas believed to contain kivas, mapped the geometry of walls over a closed room block, and detected an area of magnetized debris associated with smelting operations. Collectively, the data from the SAGE field programme demonstrate the value of using multiple, complementary, geophysical methods for archaeological prospection. Copyright © 2008 John Wiley & Sons, Ltd. [source] Characterization of buried inundated peat on seismic (Chirp) data, inferred from core informationARCHAEOLOGICAL PROSPECTION, Issue 4 2007Ruth Plets Abstract Peat horizons provide a wide range of critical environmental and direct archaeological information for both archaeologists and Quaternary geologists. At present, such data are typically obtained from terrestrial exposures or cores, and occasional offshore cores. These data can provide invaluable and detailed site-specific environmental information but require a relatively high spatial sampling strategy to provide more regional-scale information. Through a comparison of laboratory, in situ acoustic and sedimentary analyses, this paper presents evidence to suggest that peat buried in fine to medium grained, marine, siliciclastic sediments has an easily identifiable acoustic signature. The very low densities recorded by buried peats result in a distinct negative peak in the reflectivity series. Comparison of synthetic seismograms with in situ seismic data confirms that this negative peak can be easily identified from seismic profiles. Reanalysis of a decade of Chirp (sub-bottom) data, acquired from the Solent Estuary, indicates that possible extensive peat deposits, dating from the Late-glacial to early Holocene, can be traced at depth in this estuary using geophysical methods. The results of this study could be significant for future research into submerged landscape reconstructions. Copyright © 2007 John Wiley & Sons, Ltd. [source] New approach to the study of city planning and domestic dwellings in the ancient Near EastARCHAEOLOGICAL PROSPECTION, Issue 2 2007Christophe BenechArticle first published online: 8 MAY 200 Abstract This paper presents the results of a magnetic survey on the Hellenistic and Roman site of Doura- Europos in Syria. The interpretation of the magnetic data is based on an original approach by considering the use of space in a domestic unit. This type of study has been developed for sociological research but is adapted to the information carried within geophysical data. After a brief presentation of the role of geophysical methods for the study of city planning, the most important components of the ,space syntax' will be presented and applied to two blocks of Doura-Europos, one that has been excavated in the twentieth century by the Yale University and another surveyed using the magnetic method. Copyright © 2007 John Wiley & Sons, Ltd. [source] Application of the self-potential method to archaeological prospection: some case historiesARCHAEOLOGICAL PROSPECTION, Issue 2 2004M. G. DrahorArticle first published online: 12 MAY 200 Abstract The self-potential (SP) method is very rarely used in archaeological prospection because related phenomena are not very well known. The aim of this study is to discuss the different SP phenomena that might be observed at archaeological sites, and therefore the SP method was applied at different archaeological sites in Anatolia (Turkey), such as Acemhöyük, Amorium, Burgaz and Ulucakhöyük archaeological areas and the Sinop amphorae workshop site. These studies indicated that SP anomalies existed over both burned or unburned materials at archaeological sites, such as walls, pits, kilns, etc. Furthermore, SP anomalies were also found over areas of complex soil distribution and visible physical changes on the surface. Other kinds of SP anomalies were also observed in those archaeological structures located very close to the coastline. These results were confirmed by archaeological excavations, which were carried out after geophysical surveys in the areas studied. All the studies supported that electrokinetic and electrochemical potentials might be the main cause of SP anomalies in the buried archaeological structures. The SP data collected with the gradient and total measurement techniques were processed by forward and inversion methods, and the main SP parameters (h, Q and x0) were determined. In addition, the SP results were compared with other applied geophysical methods such as resistivity and magnetic. Copyright © 2004 John Wiley & Sons, Ltd. [source] Geophysical surveys of Bury Walls hill fort, ShropshireARCHAEOLOGICAL PROSPECTION, Issue 4 2003Ruth E. Murdie Abstract The hill fort of Bury Walls in Shropshire has been surveyed extensively by topographical and geophysical methods with the aims of recovering evidence for occupation, characterising the use of the hill fort and clarifying the chronological development of the site. Topographic surveys delineated the current extent of the fort and its massive fortifications. Resistance surveys showed several interesting features inside the fort, including extensive use of the geology to make flattened ledges in an otherwise quite uneven fort interior, a possible cross dyke, interior roads and traces of possible dwellings. Magnetic gradient surveys again showed clearly the possible cross dyke. Additional geophysical surveys attempted to define the depths of these features found in the resistance and magnetic gradient maps. This study, although not fully answering the original aims, provides a useful basis for future excavation. Copyright © 2003 John Wiley & Sons, Ltd. [source] Archaeogeophysical investigations around the Bilge Qagan monument in Khosho Tsaidam, MongoliaARCHAEOLOGICAL PROSPECTION, Issue 1 2002Abdullah Ates Abstract Ancient Turkish monuments in Mongolia are historically important owing to the earliest Turkish and Chinese inscriptions written on them. In this paper, magnetic and conductivity meter surveys conducted in the vicinity of the Bilge Qagan monument are presented. Magnetic and conductivity maps show rectangular shaped anomalies, which could be caused by a buried wall-like structure or floor tiles to protect the Bilge Qagan monument. The Altar Stone, which is also described as a base for a pagoda, gives a strong magnetic anomaly. This anomaly is processed by advanced geophysical methods and it is demonstrated that the actual rock body has some form of remanent magnetization, which causes the magnetic anomaly. By means of conductivity surveying, it also can be suggested that the near-surface formations have significant water content. Copyright © 2002 John Wiley & Sons, Ltd. [source] Application of magnetic and spectrometry methods in the detection of human activity in soils: a case study at the archaeological site of Kitros (Northern Greece)ARCHAEOLOGICAL PROSPECTION, Issue 3 2001E. V. Aidona Abstract In the present study the archaeological site of (Louloudies,Kitros) (northern Greece) is investigated by the use of magnetic and spectrometry geophysical methods. Soil samples were collected from several trenches within the archaeological site, as well as from radial traverses around kilns, which were used for glass production. Moreover, samples were collected from a long traverse, starting from the middle of the archaeological site and extending outside the site, in order to identify the limits of the settlement. Measurements were successful in identifying the different occupation levels and the boundaries of the archaeological site. High values of magnetic susceptibility and iron oxide content correlated well with the periods of intense human activity. Around the kilns, the mean values of the magnetic susceptibility indicated the effect of the fire mechanism in the surrounding area and gave some first evidence concerning the use of the kilns. Comparison of the magnetic and chemical properties of the anthropogenic soils suggests that their enhancement may be used as an index for locating areas and features of archaeological interest. Additionally, archaeomagnetic data have been obtained from a pottery and a glass kiln of the site. The magnetic directions (D = 355°, I = 62°, a95 = 3.6 and D = 356°, I = 51°, a95 = 2.3) were correlated to the reference curves compiled for Bulgaria and showed a satisfactory consistency for the declination, but the inclination values of the recorded magnetic field were divergent by about 10°. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||