Artykuły w czasopismach na temat „Electromagnetic geophysics”
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Weiss, Chester J., G. Didem Beskardes, Kris MacLennan, Michael J. Wilt, Evan Schankee Um i Don C. Lawton. "Observing and modeling the effects of production infrastructure in electromagnetic surveys". Leading Edge 41, nr 2 (luty 2022): 100–106. http://dx.doi.org/10.1190/tle41020100.1.
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Electromagnetic (EM) methods are among the original techniques for subsurface characterization in exploration geophysics because of their particular sensitivity to the earth electrical conductivity, a physical property of rocks distinct yet complementary to density, magnetization, and strength. However, this unique ability also makes them sensitive to metallic artifacts — infrastructure such as pipes, cables, and other forms of cultural clutter — the EM footprint of which often far exceeds their diminutive stature when compared to that of bulk rock itself. In the hunt for buried treasure or unexploded ordnance, this is an advantage; in the long-term monitoring of mature oil fields after decades of production, it is quite troublesome indeed. Here we consider the latter through the lens of an evolving energy industry landscape in which the traditional methods of EM characterization for the exploration geophysicist are applied toward emergent problems in well-casing integrity, carbon capture and storage, and overall situational awareness in the oil field. We introduce case studies from these exemplars, showing how signals from metallic artifacts can dominate those from the target itself and impose significant burdens on the requisite simulation complexity. We also show how recent advances in numerical methods mitigate the computational explosivity of infrastructure modeling, providing feasible and real-time analysis tools for the desktop geophysicist. Lastly, we demonstrate through comparison of field data and simulation results that incorporation of infrastructure into the analysis of such geophysical data is, in a growing number of cases, a requisite but now manageable step.
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Høyer, Anne-Sophie, Ingelise Møller i Flemming Jørgensen. "Challenges in geophysical mapping of glaciotectonic structures". GEOPHYSICS 78, nr 5 (1.09.2013): B287—B303. http://dx.doi.org/10.1190/geo2012-0473.1.
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Glaciotectonic complexes have been recognized worldwide — traditionally described on the basis of outcrops or geomorphological observations. In the past few decades, geophysics has become an integral part of geologic mapping, which enables the mapping of buried glaciotectonic complexes. The geophysical methods provide different types of information and degrees of resolution and thus, a different ability to resolve the glaciotectonic structures. We evaluated these abilities on the basis of an integrated application of four commonly used geophysical methods: airborne transient electromagnetics, high-resolution reflection seismic, geoelectrical, and ground-penetrating radar (GPR). We covered an area of [Formula: see text] in a formerly glaciated region in the western part of Denmark. The geologic setting was highly heterogeneous with glaciotectonic deformation observed in the form of large-scale structures in the seismic and airborne transient electromagnetic data to small-scale structures seen in the GPR and geoelectrical data. The seismic and GPR data provided detailed structural information, whereas the geoelectrical and electromagnetic data provided indirect lithological information through resistivities. A combination of methods with a wide span in resolution capabilities can therefore be recommendable to characterize and understand the geologic setting. The sequence of application of the different methods is primarily determined by the gross expenditure required for acquisition and processing, e.g., per kilometer of the surveys. Our experience suggested that airborne electromagnetic data should be acquired initially to obtain a 3D impression of the geologic setting. Based on these data, areas can be selected for further investigation with the more detailed but also more expensive and time-consuming methods.
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Doyle, H. "Geophysics in Australia". Earth Sciences History 6, nr 2 (1.01.1987): 178–204. http://dx.doi.org/10.17704/eshi.6.2.386k258604262836.
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Geophysical observations began in Australia with the arrival of the first European explorers in the late 18th Century and there have been strong connections with European and North American geophysics ever since, both in academic and exploration geophysics. Government institutions, particularly the Bureau of Mineral Resources, have played a large part in the development of the subject in Australia, certainly more so than in North America. Academic research in geophysics has been dominated by that at the Australian National University. Palaeomagnetic research at the Australian National University has been particularly valuable, showing the large northerly drift of the continent in Cainozoic times as part of the Australia-India plate. Heat flow, electrical conductivity and upper mantle seismic velocities have been shown to be significantly different between Phanerozoic eastern Australia and the Western Shield. Geophysical exploration for metals and hydrocarbons began in the 1920s but did not develop strongly until the 1950s and 1960s. There are relatively few Australian geophysical companies and contracting companies, and instrumentation from North America and Europe have played an important role in exploration. Exploration for metals has been hampered by the deep weathered mantle over much of the continent, but the development of pulsed (transient) electromagnetic methods, including an Australian instrument (SIROTEM), has improved the situation. Geophysics has been important in several discoveries of ore-bodies. In hydrocarbon exploration the introduction of common depth point stacking and digital recording and processing in reflection surveys have played an important part in the discovery of offshore and onshore fields, as in other countries.
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Young, Charles T. "Tabletop Models for Electrical and Electromagnetic Geophysics". Journal of Geoscience Education 50, nr 5 (listopad 2002): 594–601. http://dx.doi.org/10.5408/1089-9995-50.5.594.
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Zhdanov, Michael S. "Electromagnetic geophysics: Notes from the past and the road ahead". GEOPHYSICS 75, nr 5 (wrzesień 2010): 75A49–75A66. http://dx.doi.org/10.1190/1.3483901.
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During the last century, electrical geophysics has been transformed from a simple resistivity method to a modern technology that uses complex data-acquisition systems and high-performance computers for enhanced data modeling and interpretation. Not only the methods and equipment have changed but also our ideas about the geoelectrical models used for interpretation have been modified tremendously. This paper describes the evolution of the conceptual and technical foundations of EM methods. It outlines a framework for further development, which should focus on multitransmitter and multireceiver surveys, analogous to seismic data-acquisition systems. Important potential topics of future research efforts are in the areas of multidimensional modeling and inversion, including a new approach to the formulation and understanding of EM fields based on flux and voltage representation, which corresponds well to geophysical experiments involving the measurement of voltage and flux of electric and magnetic fields.
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Greenhouse, John P., i David D. Slaine. "Geophysical modelling and mapping of contaminated groundwater around three waste disposal sites in southern Ontario". Canadian Geotechnical Journal 23, nr 3 (1.08.1986): 372–84. http://dx.doi.org/10.1139/t86-052.
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We present an approach to the use of electomagnetic geophysical methods for delineating groundwater contamination, and test the concepts at three waste disposal sites. The approach includes a technique for modelling a site's response to a variety of instruments, and a device-independent method of contouring the data. The modelling attempts to account for the noise inherent in the measurement process, particularly the effects of lateral variations in stratigraphy. These concepts are evaluated by comparing the geophysical response to groundwater conductivities measured in sampling wells. We conclude that geophysics offers a cost-effective supplement to drilling, and that it is best used in a reconnaissance mode to map the general distribution of contamination prior to a detailed sampling program. The correlation between the observed and predicted geophysical response as a function of groundwater conductivity is as good as can be expected given the uncertainties in the process. The methodology proposed is simple to use and practical. Key words: groundwater, contamination, geophysics, electromagnetic, mapping, modelling.
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Parshin, Alexander, Ayur Bashkeev, Yuriy Davidenko, Marina Persova, Sergey Iakovlev, Sergey Bukhalov, Nikolay Grebenkin i Marina Tokareva. "Lightweight Unmanned Aerial System for Time-Domain Electromagnetic Prospecting—The Next Stage in Applied UAV-Geophysics". Applied Sciences 11, nr 5 (26.02.2021): 2060. http://dx.doi.org/10.3390/app11052060.
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Nowadays in solving geological problems, the technologies of UAV-geophysics, primarily magnetic and gamma surveys, are being increasingly used. However, for the formation of the classical triad of airborne geophysics methods in the UAV version, there was not enough technology for UAV-electromagnetic sounding, which would allow studying the geological environment at depths of tens and hundreds of meters with high detail. This article describes apparently the first technology of UAV-electromagnetic sounding in the time domain (TDEM, TEM), implemented as an unmanned system based on a light multi-rotor UAV. A measuring system with an inductive sensor—an analogue of a 20 × 20 or 50 × 50 m receiving loop is towed by a UAV, and a galvanically grounded power transmitter is on the ground and connected to a pulse generator. The survey is carried out along a network of parallel lines at low altitude with a terrain draping at a speed of 7–8 m/s, the maximum distance of the UAV’s departure from the transmitter line can reach several kilometers, thus the created technology is optimal for performing detailed areal electromagnetic soundings in areas of several square kilometers. The results of the use of the unmanned system (UAS) in real conditions of the mountainous regions of Eastern Siberia are presented. Based on the obtained data, the sensitivity of the system was simulated and it was shown that the developed technology allows one to collect informative data and create geophysical sections and maps of electrical resistivity in various geological situations. According to the authors, the emergence of UAV-TEM systems in the near future will significantly affect the practice of geophysical work, as it was earlier with UAV-magnetic prospecting and gamma-ray survey.
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Chave, Alan D., i John R. Booker. "Electromagnetic induction studies". Reviews of Geophysics 25, nr 5 (1987): 989. http://dx.doi.org/10.1029/rg025i005p00989.
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WANNAMAKER, PHILIP E., i GERALD W. HOHMANN. "Electromagnetic Induction Studies". Reviews of Geophysics 29, S1 (styczeń 1991): 405–15. http://dx.doi.org/10.1002/rog.1991.29.s1.405.
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Everett, M. E., i A. D. Chave. "Energy flow in terrestrial controlled-source electromagnetic geophysics". European Journal of Physics 40, nr 6 (18.09.2019): 065202. http://dx.doi.org/10.1088/1361-6404/ab3de5.
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Tabarovsky, L. A., M. M. Goldman, M. B. Rabinovich i K. M. Strack. "2.5-D modeling in electromagnetic methods of geophysics". Journal of Applied Geophysics 35, nr 4 (październik 1996): 261–84. http://dx.doi.org/10.1016/0926-9851(96)00025-0.
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Reynolds, J. M. "The role of surface geophysics in the assessment of regional groundwater potential in Northern Nigeria". Geological Society, London, Engineering Geology Special Publications 4, nr 1 (1987): 185–90. http://dx.doi.org/10.1144/gsl.eng.1987.004.01.22.
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AbstractAn analysis has been made of the usefulness of surface geophysical site investigations as part of a rural water supply programme carried out in southern Kano State, northern Nigeria. Field work was undertaken under the auspices of the Kano State Agricultural Rural Development Project in conjunction with Groundwater Development Consultants (International) Ltd, Cambridge. The database for this study consists of the results of surface geophysical site investigations at over 200 rural villages and comprised electrical resistivity and/or electromagnetic ground conductivity methods together with hydrogeological data from boreholes drilled as tubewells. The groundwater potential of southern Kano State was determined as a result of field studies of hand-dug wells, water table levels, geological and geomorphological mapping, the use of aerial photographs and, in particular, surface geophysics. Areas with poor groundwater potential were successfully highlighted. A drilling programme was planned on the basis of these field studies which allowed the drilling rigs to be used to maximum effectiveness providing successful tubewells whilst the more problematical sites were investigated further. Wildcat wells sited without the aid of geophysics and drilled in the Basement Complex of the Younger Granite terrain in Kano State resulted in unacceptably high failure rates (c. 70%). Once geophysical methods were introduced, the failure rate fell to less than 32% and, following further development of geophysical field and interpretation techniques, the final failure rate was around 17%. For a project whose target was 1000 successful tubewells, each costing of the order of £15,000, the saving to the client as a result of reduced number of failures was of the order of £5 million. The use of resistivity surveys, especially in conjunction with electromagnetic induction methods, has proved invaluable in the evaluation of groundwater potential and the planning of extensive drilling programme in southern Kano State.
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Ahmad Alhassan, Auwal Aliyu, Abubakar Magaji, M.Nuruddeen Abdulkareem i Mohammed Abdullahi. "An Insight Into The Importance Of Application Of Geophysical Methods In Agriculture For National Economic Development". Global Sustainability Research 1, nr 1 (12.08.2022): 1–4. http://dx.doi.org/10.56556/gssr.v1i1.301.
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One of the keys to national development in developing countries like Nigeria is the diversification of economy. Nigeria’s economy depends majorly on crude oil. The oil sector continue to face challenges like price drop in international market, corruption, reduced quantity of production as forecasted (although new oils are been drilled). These among others makes it necessary for the country to diversify its economy. Agriculture is one of the areas Nigeria have started investing into. New methods are necessary for fast improvement in the sector among which is geophysics. The need for Agricultural Geophysics to be considered for national economic development is discussed. Geophysics as a branch of science that deal with physical processes and phenomena occurring in the earth and its vicinity is applicable to many fields that contribute to the development of the economy of any nation. Such fields include oil, Agriculture, natural resources among others. Geophysical methods applicable in Agriculture like resistivity, electromagnetic induction, and Ground penetrating radar are discussed with their applications in agriculture. The various geophysical methods that are useful in agriculture are reviewed and necessity of their application is also emphasized.
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Christensen, Nikolaj Kruse, Steen Christensen i Ty Paul A. Ferre. "Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models". Hydrology and Earth System Sciences 20, nr 5 (13.05.2016): 1925–46. http://dx.doi.org/10.5194/hess-20-1925-2016.
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Abstract. In spite of geophysics being used increasingly, it is often unclear how and when the integration of geophysical data and models can best improve the construction and predictive capability of groundwater models. This paper uses a newly developed HYdrogeophysical TEst-Bench (HYTEB) that is a collection of geological, groundwater and geophysical modeling and inversion software to demonstrate alternative uses of electromagnetic (EM) data for groundwater modeling in a hydrogeological environment consisting of various types of glacial deposits with typical hydraulic conductivities and electrical resistivities covering impermeable bedrock with low resistivity (clay). The synthetic 3-D reference system is designed so that there is a perfect relationship between hydraulic conductivity and electrical resistivity. For this system it is investigated to what extent groundwater model calibration and, often more importantly, model predictions can be improved by including in the calibration process electrical resistivity estimates obtained from TEM data. In all calibration cases, the hydraulic conductivity field is highly parameterized and the estimation is stabilized by (in most cases) geophysics-based regularization. For the studied system and inversion approaches it is found that resistivities estimated by sequential hydrogeophysical inversion (SHI) or joint hydrogeophysical inversion (JHI) should be used with caution as estimators of hydraulic conductivity or as regularization means for subsequent hydrological inversion. The limited groundwater model improvement obtained by using the geophysical data probably mainly arises from the way these data are used here: the alternative inversion approaches propagate geophysical estimation errors into the hydrologic model parameters. It was expected that JHI would compensate for this, but the hydrologic data were apparently insufficient to secure such compensation. With respect to reducing model prediction error, it depends on the type of prediction whether it has value to include geophysics in a joint or sequential hydrogeophysical model calibration. It is found that all calibrated models are good predictors of hydraulic head. When the stress situation is changed from that of the hydrologic calibration data, then all models make biased predictions of head change. All calibrated models turn out to be very poor predictors of the pumping well's recharge area and groundwater age. The reason for this is that distributed recharge is parameterized as depending on estimated hydraulic conductivity of the upper model layer, which tends to be underestimated. Another important insight from our analysis is thus that either recharge should be parameterized and estimated in a different way, or other types of data should be added to better constrain the recharge estimates.
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Hunziker, Jürg, Jan Thorbecke i Evert Slob. "The electromagnetic response in a layered vertical transverse isotropic medium: A new look at an old problem". GEOPHYSICS 80, nr 1 (1.01.2015): F1—F18. http://dx.doi.org/10.1190/geo2013-0411.1.
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We determined that the electromagnetic vertical transverse isotropic response in a layered earth can be obtained by solving two equivalent scalar equations, which were for the vertical electric field and for the vertical magnetic field, involving only a scalar global reflection coefficient. Besides the complete derivation of the full electromagnetic response, we also developed the corresponding computer code called EMmod, which models the full electromagnetic fields including internal multiples in the frequency-wavenumber domain and obtains the frequency-space domain solutions through a Hankel transformation by computing the Hankel integral using a 61-point Gauss-Kronrod integration routine. The code is able to model the 3D electromagnetic field in a 1D earth for diffusive methods such as controlled source electromagnetics as well as for wave methods such as ground penetrating radar. The user has complete freedom to place the source and the receivers in any layer. The modeling is illustrated with three examples, which aim to present the different capabilities of EMmod, while assessing its correctness.
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Christensen, Niels B. "Sensitivity functions of transient electromagnetic methods". GEOPHYSICS 79, nr 4 (1.07.2014): E167—E182. http://dx.doi.org/10.1190/geo2013-0364.1.
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Any geophysical measurement is a filter through which the distribution of a certain physical parameter in the subsurface is seen, and the sensitivity function is a characteristic of the method that reveals the nature of this filter. Insight into the structural pattern of the sensitivity function pertaining to a certain transmitter-receiver configuration provides the geophysicist with an image that allows an immediate qualitative understanding of the characteristics of the method. The assets and shortcomings of different measuring configurations can be discussed and understood, and the sensitivity function permits qualified predictions about resolution characteristics of new configurations and measuring strategies. I evaluated a rapid and accurate method for calculating 3D sensitivity functions of a homogeneous half-space model for a wide variety of transient electromagnetic configurations using the central loop and an airborne offset loop configuration as examples. Computations of 3D sensitivity functions were performed as convolutions in the time domain between the electric fields from the transmitter and the receiver, had it been used as a transmitter. The 2D and 1D sensitivity functions are found through numerical integration of the 3D functions. Beside offering insight into the resolution capability of the measuring configuration, the sensitivity functions lend themselves to rapid calculations of approximate responses and derivatives in various modeling and inversion strategies.
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Steeples, Don W. "Engineering and environmental geophysics at the millennium". GEOPHYSICS 66, nr 1 (styczeń 2001): 31–35. http://dx.doi.org/10.1190/1.1444910.
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Near‐surface geophysics is being applied to a broader spectrum of problems than ever before, and new application areas are arising continually. Currently, the tools used to examine the near‐surface environment include a variety of noninvasive methods employing electrical, electromagnetic, or mechanical energy sources, along with passive techniques that measure the physical parameters of the earth. Some of the advances of recent years have emerged from breakthroughs in instrumentation and computer‐processing techniques, and some have been driven by societal needs, such as the increasing demand for the accurate geophysical characterization of polluted sites. Other compelling factors, such as the ever‐expanding need for groundwater, the enactment of laws that have spurred geophysical surveying for archaeological purposes, and the necessity for better soil‐physics information in geotechnical engineering and agriculture, are present worldwide. For historical context, the reader is referred to an excellent review concerning the status of shallow exploration techniques in the mid-1980s (Dobecki and Romig, 1985).
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Garg, Nek R., i George V. Keller. "Spatial and temporal analysis of electromagnetic survey data". GEOPHYSICS 51, nr 1 (styczeń 1986): 85–89. http://dx.doi.org/10.1190/1.1442042.
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Development of a relatively straightforward approach to interpretation of electromagnetic survey data when the earth in the vicinity of the survey has a complex geoelectric structure will be necessary before such methods can assume their full role in geophysical exploration. One‐dimensional interpretation methods have been well developed to extract the resistivity‐depth profile from a transient electromagnetic (TEM) sounding when the earth is assumed to be simply layered. Extension of the same methods to more complicated earth structures is difficult because of the tedious calculations involved when three‐dimensional earth structures are examined. An alternate approach could be use of the information contained in the spatial spectra of a set of sounding measurements. In such an approach, it should be possible to obtain a clearer concept of the geoelectric structure by analytic continuation of the electromagnetic field in space, or by heuristic filtering of the field, as is done in various potential field methods in geophysics. To try this concept, a filtering technique developed for treating magnetic data was applied to a set of TEM data acquired in the Snake River plain of Idaho. The results are reasonable, but insufficient control information is available to prove their significance. The effort has demonstrated that such a filtering approach can be done quickly, but it places demands on how the field data are sampled in the space domain.
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Wang, Bochen, Jianxin Liu, Xiangping Hu, Jiawei Liu, Zhenwei Guo i Jianping Xiao. "Geophysical electromagnetic modeling and evaluation: A review". Journal of Applied Geophysics 194 (listopad 2021): 104438. http://dx.doi.org/10.1016/j.jappgeo.2021.104438.
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Spichak, Viacheslav, i Adele Manzella. "Electromagnetic sounding of geothermal zones". Journal of Applied Geophysics 68, nr 4 (sierpień 2009): 459–78. http://dx.doi.org/10.1016/j.jappgeo.2008.05.007.
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Djanni, Axel Tcheheumeni, Anton Ziolkowski i David Wright. "Electromagnetic induction noise in a towed electromagnetic streamer". GEOPHYSICS 81, nr 3 (maj 2016): E187—E199. http://dx.doi.org/10.1190/geo2014-0597.1.
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We have examined the idea that a towed neutrally buoyant electromagnetic (EM) streamer suffers from noise induced according to Faraday’s law of induction. A simple analysis of a horizontal streamer in a constant uniform magnetic field determined that there was no induction noise. We have developed an experiment to measure the induced noise in a prototype EM streamer suspended in the Edinburgh FloWave tank, and we subjected it to water flow along its length and to waves propagating in the same direction, at 45° and 90° to the streamer direction. The noise level was found to increase with increasing flow velocity. The motion of the prototype EM streamer in response to parallel constant current flow and wave motion was found to generate significant noise. The main finding is that wave motion was the major source of noise and was much larger than the noise of a static cable. The noise level can probably be reduced by towing the cable deeper and increasing the cable tension.
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Pang, Xiao Fen. "Equivalent Electromagnetic Properties of Composite Media". Applied Mechanics and Materials 596 (lipiec 2014): 822–25. http://dx.doi.org/10.4028/www.scientific.net/amm.596.822.
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This paper selects the dielectric properties of materials science, soil science, geophysics and other areas of computing model, comparative analysis of the applicability of various computational models. Mainly in the particle dispersion mixing model based validated multi-group model were compared and analyzed to establish the feasibility of centralized computing model. And the model is modified, and the results show modified model of the original model has greatly improved results.
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Alte-da-Veiga, Nuno M. S., Luis Fernando Sánchez-Sastre, Jesús Martín-Gil, Salvador Hernández-Navarro i Pablo Martín-Ramos. "Using EM Induction and ERI Geophysical Methods in Undergraduate Teaching: A Case-Centered, Discussion-Based Approach". Geosciences 12, nr 12 (2.12.2022): 444. http://dx.doi.org/10.3390/geosciences12120444.
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In the last decades, the application fields of exploration geophysics have considerably broadened, reinforcing the relevance of exploration geophysics courses both within geosciences and non-geosciences degrees. Among these courses, those with a hands-on, place-based pedagogical approach and aligned with problem-based and case-based learning methodologies have proven to be particularly successful in regard to addressing the recognized difficulty that students experience in transferring their classroom knowledge to the field environment. In this article, we report a theoretical–practical module for the teaching of exploration geophysics methods to undergraduate non-geoscience major students, and in particular, to forestry engineering students. The in-field activity, based on a combination of Electrical Resistivity Imaging (ERI) and electromagnetic induction (EM) methods, was complemented with in-class sessions covering the fundamentals of these methods and Archie’s equation, software usage, data analysis and interpretation, and critical in-group discussions. This situated, context-rich teaching and learning example may be reproduced in other teaching institutions to provide technology-driven educational experiences in their curricula, helping students recognize the relevance of the abovementioned geophysical methods to address research questions beyond geology.
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Løseth, Lars O., Hans M. Pedersen, Bjørn Ursin, Lasse Amundsen i Svein Ellingsrud. "Low-frequency electromagnetic fields in applied geophysics: Waves or diffusion?" GEOPHYSICS 71, nr 4 (lipiec 2006): W29—W40. http://dx.doi.org/10.1190/1.2208275.
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Low-frequency electromagnetic (EM) signal propagation in geophysical applications is sometimes referred to as diffusion and sometimes as waves. In the following we discuss the mathematical and physical approaches behind the use of the different terms. The basic theory of EM wave propagation is reviewed. From a frequency-domain description we show that all of the well-known mathematical tools of wave theory, including an asymptotic ray-series description, can be applied for both nondispersive waves in nonconductive materials and low-frequency waves in conductive materials. We consider the EM field from an electric dipole source and show that a common frequency-domain description yields both the undistorted pulses in nonconductive materials and the strongly distorted pulses in conductive materials. We also show that the diffusion-equation approximation of low-frequency EM fields in conductive materials gives the correct mathematical description, and this equation has wave solutions. Having considered both a wave-picture approach and a diffusion approach to the problem, we discuss the possible confusion that the use of these terms might lead to.
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Smith, Richard. "Electromagnetic Induction Methods in Mining Geophysics from 2008 to 2012". Surveys in Geophysics 35, nr 1 (9.04.2013): 123–56. http://dx.doi.org/10.1007/s10712-013-9227-1.
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Adams, Ryan F., Benjamin V. Miller, Wade H. Kress, Scott J. Ikard, Jason D. Payne i Walter H. Killion. "Evaluation of Electrical and Electromagnetic Geophysical Techniques to Inspect Earthen Dam and Levee Structures in Arkansas". Journal of Environmental and Engineering Geophysics 26, nr 4 (grudzień 2021): 287–303. http://dx.doi.org/10.32389/jeeg20-063.
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Within the State of Arkansas, there is an increasing number of aging dams and levees that have little to no documentation concerning their construction or composition. Surface geophysical surveys offer a non-intrusive method for investigating these structures to describe their lithologic makeup, evaluate the materials constructed upon, and identify potential flow paths through them. Techniques such as electrical resistivity tomography, seismic refraction, and electromagnetic induction have been used to image dams and levees. They require additional information from geologic outcrops, geotechnical borings, or drill cores to make informed geologic interpretations of the geophysical models. These geologic models then allow the owners of these structures to make more informed decisions about their operation and maintenance. Between 2011 and 2018, the U.S. Geological Survey conducted geophysical and geotechnical investigations of three earthen structures in Arkansas. Electrical and electromagnetic geophysical data were used to develop lithologic models of these structures and characterize the underlying geology. Self-potential surveys were utilized to detect the movement of water through these structures and identify any possible seepage pathways. Geotechnical methods such as electric and hydraulic direct-push well logs and cores acted as a control on the geophysical interpretations and a confirmation of anomalies. This integrated approach detected the lack of an impermeable core within a levee, imaged a change in lithology of the bedrock forming the seal beneath a gravity dam, and identified a potential seepage feature within the core of an earthen dam. These results further support that this method of extending known lithologic features via surface and borehole geophysics is a useful approach for characterizing earthen water-control structures.
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Tzanis, Andreas. "A MATLAB PROGRAM FOR THE ANALYSIS AND INTERPRETATION OF TRANSIENT ELECTROMAGNETIC SOUNDING DATA". Bulletin of the Geological Society of Greece 43, nr 4 (25.01.2017): 1941. http://dx.doi.org/10.12681/bgsg.11385.
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Herein we present a software system, written in MATLAB, to interpret TEM sounding data. The program, dubbed maTEM, is designed to process, model and invert multiple soundings, either individually, or simultaneously along profiles. The latter capability allows for laterally constrained inversion, so as to generate pseudo-2D or 2D resistivity sections based on the program EM1DINV v2.13 by the Hydro-Geophysics Group of the University of Aarhus, Denmark. Using maTEM, the analyst may import and display data multiple data sets, denoise and smooth the data, perform approximate inversions, design 1-D model(s) graphically, perform forward modelling and inversion and generate/ update data base in which to store the results. Finally, the analyst may use the data base to create 2-D and 3-D displays of the geoelectric structure with built-in graphical functions. maTEM is highly modular so that additional functions can be added at any time, at minimal programming cost. Although the software presented herein is focused on the analysis of TEM data, the maTEM concept has been designed ready to incorporate additional electrical and EM geophysical sounding methods and to mutually constrained analysis of different geophysical data sets.
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Tripp, Alan C. "Acheron's rainbow: Free associations on 75 years of exploration geo-electromagnetics". GEOPHYSICS 70, nr 6 (listopad 2005): 25ND—31ND. http://dx.doi.org/10.1190/1.2127107.
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Geophysics has proved to be an effective means of prospecting for the raw materials necessary for modern life. Electromagnetic techniques are the methods of choice when buried treasure has an anomalous electrical conductivity or dielectric permittivity. In the past 75 years, SEG has provided a forum for the usually rational exchange of ideas in electromagnetic prospecting as well as a bazaar for goods and services.
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Minsley, Burke J., Nathan Leon Foks i Paul A. Bedrosian. "Quantifying model structural uncertainty using airborne electromagnetic data". Geophysical Journal International 224, nr 1 (25.08.2020): 590–607. http://dx.doi.org/10.1093/gji/ggaa393.
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SUMMARY The ability to quantify structural uncertainty in geological models that incorporate geophysical data is affected by two primary sources of uncertainty: geophysical parameter uncertainty and uncertainty in the relationship between geophysical parameters and geological properties of interest. Here, we introduce an open-source, trans-dimensional Bayesian Markov chain Monte Carlo (McMC) algorithm GeoBIPy—Geophysical Bayesian Inference in Python—for robust uncertainty analysis of time-domain or frequency-domain airborne electromagnetic (AEM) data. The McMC algorithm provides a robust assessment of geophysical parameter uncertainty using a trans-dimensional approach that lets the AEM data inform the level of model complexity necessary by allowing the number of model layers itself to be an unknown parameter. Additional components of the Bayesian algorithm allow the user to solve for parameters such as data errors or corrections to the measured instrument height above ground. Probability distributions for a user-specified number of lithologic classes are developed through posterior clustering of McMC-derived resistivity models. Estimates of geological model structural uncertainty are thus obtained through the joint probability of geophysical parameter uncertainty and the uncertainty in the definition of each class. Examples of the implementation of this algorithm are presented for both time-domain and frequency-domain AEM data acquired in Nebraska, USA.
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Ferguson, Ian J., Jeffrey B. Young, Becky J. Cook, Ashley B. C. Krakowka i Cassandra Tycholiz. "Near-surface geophysical surveys at the Duport gold deposit, Ontario, Canada: Relating airborne responses to small-scale geologic features". Interpretation 4, nr 3 (1.08.2016): SH39—SH60. http://dx.doi.org/10.1190/int-2015-0216.1.
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Near-surface geophysical measurements using magnetometer, magnetic susceptibility, terrain conductivity, and time-domain electromagnetic instruments were made at the shear-hosted Duport gold deposit on Cameron Island in Shoal Lake, western Ontario, Canada, to help relate airborne total magnetic intensity (TMI) and helicopter electromagnetic survey data to small-scale geologic features. The magnetic airborne response provides a weak indication of a narrow anomaly within the Duport deformation zone, and the airborne electromagnetic response provides an indication of enhanced conductivity in the northwest of Cameron Island. In contrast, surface magnetic responses are dominated by the narrow 10,000–15,000 nT magnetic anomaly of a talc-chlorite-dolomite schistose basalt unit, a feature barely visible in the airborne TMI data. This geologic unit hosts the veins containing gold mineralization, so the surface TMI data provide a valuable response for delineating the corresponding rocks. Modeling of the TMI data indicates that the unit has a susceptibility of up to 0.7 SI and a corresponding magnetite content of up to 20%. The TMI data also reveal along-strike variations in the magnetic anomaly providing information on the component of ultramafic rocks in the protolith of the unit. The surface geophysical data allow the enhanced conductivity in the northwest part of Cameron Island to be attributed to several narrow sulfidized zones containing up to 10% pyrrhotite. Additional conductive and positively magnetized zones are associated with concentrations of 5%–10% of magnetite. The near-surface geophysics at the Duport deposit provided a rapid and inexpensive method for defining the magnetic and electrical properties of the geologic units at the site and for defining the exact location, width, and internal structure of features observed in the airborne geophysical data. Availability of magnetic susceptibility measurements from a single drill core enhanced the accuracy of the interpretations and the ability to relate the near-surface geophysical responses to geologic features.
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Trainor-Guitton, Whitney, i G. Michael Hoversten. "Stochastic inversion for electromagnetic geophysics: Practical challenges and improving convergence efficiency". GEOPHYSICS 76, nr 6 (listopad 2011): F373—F386. http://dx.doi.org/10.1190/geo2010-0223.1.
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Traditional deterministic geophysical inversion algorithms are not designed to provide a robust evaluation of uncertainty that reflects the limitations of the geophysical technique. Stochastic inversions, which do provide a sampling-based measure of uncertainty, are computationally expensive and not straightforward to implement for nonexperts (nonstatisticians). Our results include stochastic inversion for magnetotelluric and controlled source electromagnetic data. Two Markov Chain sampling algorithms (Metropolis-Hastings and Slice Sampler) can significantly decrease the computational expense compared to using either sampler alone. The statistics of the stochastic inversion allow for (1) variances that better reveal the measurement sensitivities of the two different electromagnetic techniques than traditional techniques and (2) models defined by the median and modes of parameter probability density functions, which produce amplitude and phase data that are consistent with the observed data. In general, parameter error estimates from the covariance matrix significantly underestimate the true parameter error, whereas the parameter variance derived from Markov chains accurately encompass the error.
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Chahine, Khaled. "Model-based parameter estimation applied to electromagnetic characterization of dispersive civil engineering media". GEOPHYSICS 76, nr 5 (wrzesień 2011): Z101. http://dx.doi.org/10.1190/2011-0926-geodis.2.
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Geophysics publishes abstracts of dissertations and titles of master’s theses both in print and online. Recent graduates are invited to submit their abstracts or titles by completing and submitting the appropriate form found at http://seg.org/dissertationabstracts. Abstracts and titles will be reviewed and accepted or rejected based on their relevance to the readers of Geophysics. Abstracts must be written in English and defended in 2009 or later.
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Peacock, J., i A. King. "Central loop transient electromagnetic soundings". Exploration Geophysics 16, nr 2-3 (czerwiec 1985): 261–65. http://dx.doi.org/10.1071/eg985261.
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Kneebone, R., R. Parums, A. Smelic i L. Thomas. "Drillhole Time-domain Electromagnetic Results". Exploration Geophysics 18, nr 1-2 (1.03.1987): 122–24. http://dx.doi.org/10.1071/eg987122.
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Ellis, Robert G. "Inversion of airborne electromagnetic data". Exploration Geophysics 29, nr 1-2 (marzec 1998): 121–27. http://dx.doi.org/10.1071/eg998121.
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Zollinger, R., H. F. Morrison, P. G. Lazenby i A. Becker. "Airborne electromagnetic bathymetry". GEOPHYSICS 52, nr 8 (sierpień 1987): 1127–37. http://dx.doi.org/10.1190/1.1442377.
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Airborne electromagnetic techniques provide an efficient means for determining the bathymetry of shallow seas and coastal regions. Offshore time‐domain data collected with the INPUT® system may be interpreted quickly and inexpensively using the simple table look‐up algorithm described here. This interpretation algorithm is based on two dimensionless parameters which depend on the six channel amplitudes of the recorded INPUT data. These amplitudes are computed and tabulated for a suite of simple two‐layer models in which seawater depth is the only variable quantity. The experimental data can then be interpreted by comparison with the tables of theoretical values to obtain the bathymetry beneath the flight path. The inversion algorithm has proven accurate and stable. In the range of 0–40 m of seawater, the representative difference between the interpreted depths and the charted depths is about 2 m. Bottom gradients lower than 5 percent were resolved accurately beneath 0–25 m of water. Independent interpretations of data sets collected at different altitudes and in different directions show excellent repeatability. The algorithm exhibits low sensitivity to changes in the transmitter‐receiver configuration and to variations in the underlying half‐space conductivities when conductivity values are in the range [Formula: see text]. The fractional error produced in the calculated depths by variations in the conductivity of the seawater is approximately equal to the fractional difference between the actual conductivity of the sea and the value of 4 S/m assumed in the model. ® Trademark of Barringer Research Ltd.
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Roberts, R. G. "Global electromagnetic induction". Surveys in Geophysics 8, nr 3 (wrzesień 1986): 339–74. http://dx.doi.org/10.1007/bf01904064.
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Hattula, Aimo, i Timo Rekola. "Exploration geophysics at the Pyhäsalmi mine and grade control work of the Outokumpu Group". GEOPHYSICS 65, nr 6 (listopad 2000): 1961–69. http://dx.doi.org/10.1190/1.1444879.
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The power of geophysics is often realized while surveying barren exploration holes. Integrated interpretation of borehole electromagnetic (EM) and lithogeochemical data led to the discovery of a new volcanogenic massive sulfide (VMS) ore deposit at 500 m depth in the Pyhäsalmi area, which belongs to the Main Sulfide ore belt in Finland. In the deep exploration program, wide‐band multifrequency EM ground surveys were successfully used to detect both new ore lenses and geological structures. Mise‐a‐la‐masse (MAM) borehole and ground surveys as well as borehole EM surveys were effectively used to correlate intersections between drill holes and to locate new orebodies. The latest modeling of MAM data resulted in an exploration target at 700 m depth. The use of geophysics for exploration has been extended to mine production at Outokumpu. Geophysical logging detects ore‐waste boundaries, reduces expensive core drilling, and obtains physical property information quickly on ore intersections. Depending on ore type, geophysical borehole logging can also be applied to classify mineralization, interpret lithology, and sometimes to transform physical responses to metal grades in ore. At the Pyhäsalmi zinc‐copper‐sulfur mine, density logging in percussion boreholes is used to locate mineable ore boundaries and to classify drillhole intersections as massive or semimassive sulfide ore types. Pyrrhotite‐bearing zones are separated from other sulfides by inductive conductivity logs. The use of geophysical logging for grade estimation and control has been most effective in the nickel mines at Enonkoski, Finland, and Namew Lake, Canada (using conductivity logs), and in the Kemi chromium mine, Finland (using gamma‐gamma density logs).
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Ji, Yanju, Tingzhe Huang, Wanyu Huang i Liangliang Rong. "Meshfree Method in Geophysical Electromagnetic Prospecting: The 2D Magnetotelluric Example". International Journal of Computational Methods 15, nr 02 (28.09.2017): 1750084. http://dx.doi.org/10.1142/s0219876217500840.
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As an important supplement and development of traditional methods, the meshfree method has received a great deal of attention in the field of engineering calculation, and has been successfully used to solve many problems which traditional methods have difficulty in solving. However, the application of meshfree method is relatively less in the area of geophysics. In this paper, we apply the meshfree method to the numerical simulation of geophysical electromagnetic prospecting, taking the 2D magnetotelluric as an example and deduce the corresponding meshfree radial point interpolation method (RPIM) equivalent linear equations in detail. The high-efficiency and accurate solutions of large-scale sparse linear equations are solved by the quasi-minimal residual method based on Krylov subspace. The optimal values of the shape parameters are given by numerical experiments. The correctness of the meshfree method is verified by a layered model. The root mean square error of the calculation results is no more than 0.35%, its accuracy is superior to the finite element method. We also compare the meshfree solution with FEM solution by calculating an inclined vein body model, and the calculation results are in good agreement. A continuously changing fault model and undulating terrain model which traditional methods have difficulty in simulating are respectively calculated, the sectional profiles of the apparent resistivity accurately reflect the trend of the anomalies. The meshfree method does not require the complicated mesh generation, and the physical parameters are loaded at a series of points, thus it is especially suitable for the calculation of the complex geological models. With the rapid development of computational science, the meshfree techniques will certainly become a new robust numerical simulation method in geophysical electromagnetic prospecting.
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Cosentino, P. L., P. Capizzi, R. Martorana, P. Messina i S. Schiavone. "From Geophysics to Microgeophysics for Engineering and Cultural Heritage". International Journal of Geophysics 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/428412.
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The methodologies of microgeophysics have been derived from the geophysical ones, for the sake of solving specific diagnostic and/or monitoring problems regarding civil engineering and cultural heritage studies. Generally, the investigations are carried out using different 2D and 3D tomographic approaches as well as different energy sources: sonic and ultrasonic waves, electromagnetic (inductive and impulsive) sources, electric potential fields, and infrared emission. Many efforts have been made to modify instruments and procedures in order to improve the resolution of the surveys as well as to significantly reduce the time of the measurements without any loss of information. This last point has been achieved by using multichannel systems. Finally, some applications are presented, and the results seem to be very promising and promote this new branch of geophysics. Therefore, these methodologies can be used even more to diagnose, monitor, and safeguard not only engineering buildings and/or large structures, but also ancient monuments and cultural artifacts, such as pottery, statues, and so forth.
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El-Qady, Gad, Andreas Junge i Toivo Korja. "Electromagnetic studies for mining, geothermal and hydrocarbons". Journal of Applied Geophysics 68, nr 4 (sierpień 2009): 449. http://dx.doi.org/10.1016/j.jappgeo.2008.05.004.
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Kamenetsky, Felix M., i George M. Trigubovich. "Transient electromagnetic field in magneto-viscous medium". Journal of Applied Geophysics 75, nr 2 (październik 2011): 373–78. http://dx.doi.org/10.1016/j.jappgeo.2011.07.016.
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Zhdanov, Michael. "On: “3-D localization of buried objects by nearfield electromagnetic holography” (Y. Guo, H. W. Ko, and D. M. White, GEOPHYSICS, 63, 3, 880–889)." GEOPHYSICS 64, nr 4 (lipiec 1999): 1335. http://dx.doi.org/10.1190/1.1444637.
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The authors present a method of localizing underground objects with low‐frequency electromagnetic field based on ideas of electromagnetic holography. Though I do strongly support this method and practical results presented in the paper, I should note that the authors neglected in their paper to reference the previous publications on this subject, where the basic principles, ideas, methods, and term “electromagnetic holography” have been already introduced and developed as applied to low‐frequency electromagnetic field underground imaging.
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Bekesi, G., A. Telfer, J. Woods, P. Forward, R. Burnell i M. Hatch. "Quantitative measure of salt interception using in-river transient electromagnetic geophysics". Australasian Journal of Water Resources 18, nr 1 (styczeń 2014): 55–69. http://dx.doi.org/10.7158/w12-030.2014.18.1.
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Chaumont-Frelet, Théophile, Serge Nicaise i David Pardo. "Finite Element Approximation of Electromagnetic Fields Using Nonfitting Meshes for Geophysics". SIAM Journal on Numerical Analysis 56, nr 4 (styczeń 2018): 2288–321. http://dx.doi.org/10.1137/16m1105566.
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Dobecki, T. L., i P. R. Romig. "Geotechnical and groundwater geophysics". GEOPHYSICS 50, nr 12 (grudzień 1985): 2621–36. http://dx.doi.org/10.1190/1.1441887.
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Because of a change in emphasis from power plant siting to projects principally involving process and facility monitoring and certification of existing structures (dams, pipelines, etc.), geotechnical and groundwater geophysics is in quite a healthy state after some lean years following the demise of nuclear energy construction projects. The orders‐of‐magnitude jump in the computational capability of geophysicists working in these fields has overshadowed advances in instrumentation (e.g., digital enhancement seismographs), field methods (e.g., cross‐borehole EM), and interpretive procedures. The advent of powerful, affordable microcomputers has enabled expansion into applications demanding finer resolution and quicker turnaround of results. As a result, shallow seismic reflection, seismic and electromagnetic geotomography, and the complementary use of surface and borehole electrical resistivity and seismic data will soon be common if not dominant methods in geotechnical and groundwater investigations. Future trends point to increased emphasis on environmental and economic issues (e.g., toxic wastes or the stability of underground petroleum storage facilities), cross‐fertilization with petroleum reservoir engineering (process monitoring and detailed reservoir description), and greater involvement of computers in the planning, data acquisition, and interpretive phases of our projects. As computers take over more of the data collection‐processing‐interpretation sequence, one of the greatest challenges facing us will be to define the proper role of humans and to use the new technology wisely.
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Kohnke, Colton, Lifei Liu, Rita Streich i Andrei Swidinsky. "A method of moments approach to model the electromagnetic response of multiple steel casings in a layered earth". GEOPHYSICS 83, nr 2 (1.03.2018): WB81—WB96. http://dx.doi.org/10.1190/geo2017-0303.1.
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In oil and gas production environments, controlled-source electromagnetics can be used to aid brownfield exploration, development, and reservoir monitoring efforts. However, such environments typically have many highly conductive steel-cased wells in the area of interest. We have developed a modeling algorithm using a method of moments (MoM) approach to calculate the electromagnetic response of multiple 3D steel-cased wells of arbitrary geometry in a layered earth conductivity model. This approach involves dividing each casing into a collection of segments, each carrying a uniform current density. A matrix is computed that describes how the casing segments interact with each other electromagnetically. Then, we solve a linear system for the current within each casing segment, given a transmitter of arbitrary frequency and location. From these currents we are able to solve for the secondary electromagnetic fields produced solely by the casings at any point in our layered model, and we add these to the primary fields produced by the transmitter. To validate the algorithm, we compared results with a pseudoanalytic MoM algorithm for a single vertical casing in a half-space. We also compare results with a finite-element solution using Comsol Multiphysics for vertical and single tilted wells buried in various layered earth models. Our results indicate a good match between these different approaches, with tilted casings in a layered model requiring further study. Finally, we applied our algorithm to a realistic synthetic model with three casings (one vertical and two deviated) extending into a layered earth model containing the classic thin resistive layer. This example illustrates how the algorithm can be used to compute the electromagnetic response of multiple steel casings. The example also illustrates how the electromagnetic field changes due to the presence of the casings and how the casings may be used to inject the signal at depth.
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Wen, Laifu, Jiulong Cheng, Shaohua Huang, Jin Zhou, Yangchun Han, Fei Li i Jiahong Zhao. "Review of Geophysical Exploration on Mined-out Areas and Water Abundance". Journal of Environmental and Engineering Geophysics 24, nr 1 (marzec 2019): 129–43. http://dx.doi.org/10.2113/jeeg24.1.129.
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With the increase in mining depth, the presence of goafs has become increasingly severe in mine safety. The accurate and effective detection of underground goafs and their water abundance is the key to ensure the safety of mine production. On the basis of the relevant research, this paper defines different goaf types from the perspective of geophysical exploration and discusses the geophysical prerequisites for goaf detection. DC methods, electromagnetic methods, seismic methods, and other geophysical methods on the ground and in the subsurface are reviewed and summarized using the method's principle, research status, and technical features. Research progress on the geophysical methods in goafs and their water abundance detection are introduced, including the electrical source short-offset transient electromagnetic method (SOTEM), the wave-field transformation and synthetic aperture of the transient electromagnetic method, and comprehensive detection. At the end of the paper, a direction for the development of coal mined-out areas and their water abundance detection is put forward, including information fusion technology, ground-airborne electromagnetic methods, magnetic resonance sounding (MRS), surface-borehole transient electromagnetic method, surface-borehole seismic methods, and seismic while tunneling technology. The application prospects of these methods are discussed, and the results of this study are expected to considerably improve the location precision and resolution of the goaf detection on the basis of the implications of these techniques.
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Strack, K. ‐M, E. Lüschen i A. W. Kötz. "Long‐offset transient electromagnetic (LOTEM) depth soundings applied to crustal studies in the Black Forest and Swabian Alb, Federal Republic of Germany". GEOPHYSICS 55, nr 7 (lipiec 1990): 834–42. http://dx.doi.org/10.1190/1.1442897.
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The long‐offset transient electromagnetics (LOTEM) sounding method is a valuable complementary technique for deep seismic exploration as applied to earth crustal investigations. During 1986, two LOTEM surveys were conducted to augment completed seismic investigations for crustal studies in southern West Germany, east of the Rhine graben. Our studies were motivated by the geoscientific activities within the framework of the German Continental Deep Drilling (KTB) project. The survey objectives were (1) to determine the applicability of the LOTEM method to crustal geophysics, (2) to investigate the correlation of resistivity anomalies with velocity anomalies, and (3) to confirm the method and interpretation in an area of known geology with existing geophysical data. The Black Forest and the Urach geothermal area survey results exhibit conductive features in the upper 10 km of the crust which were not previously defined by other geophysical data. Importantly, the results demonstrate a very strong correlation of a low‐velocity zone with low electrical resistivity at 5 to 7 km depth within the crystalline basement at both locations.
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Vrbancich, Julian, Michael Hallett i Greg Hodges. "Airborne electromagnetic bathymetry of Sydney Harbour". Exploration Geophysics 31, nr 1-2 (marzec 2000): 179–86. http://dx.doi.org/10.1071/eg00179.
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