Статті в журналах: "Electromagnetic induction geophysic"

1

Ahmad Alhassan, Auwal Aliyu, Abubakar Magaji, M.Nuruddeen Abdulkareem, and Mohammed Abdullahi. "An Insight Into The Importance Of Application Of Geophysical Methods In Agriculture For National Economic Development." Global Sustainability Research 1, no. 1 (August 12, 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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2

Chave, Alan D., and John R. Booker. "Electromagnetic induction studies." Reviews of Geophysics 25, no. 5 (1987): 989. http://dx.doi.org/10.1029/rg025i005p00989.

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3

WANNAMAKER, PHILIP E., and GERALD W. HOHMANN. "Electromagnetic Induction Studies." Reviews of Geophysics 29, S1 (January 1991): 405–15. http://dx.doi.org/10.1002/rog.1991.29.s1.405.

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4

Alte-da-Veiga, Nuno M. S., Luis Fernando Sánchez-Sastre, Jesús Martín-Gil, Salvador Hernández-Navarro, and Pablo Martín-Ramos. "Using EM Induction and ERI Geophysical Methods in Undergraduate Teaching: A Case-Centered, Discussion-Based Approach." Geosciences 12, no. 12 (December 2, 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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5

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, no. 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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6

Everett, Mark E., and Alan D. Chave. "On the physical principles underlying electromagnetic induction." GEOPHYSICS 84, no. 5 (September 1, 2019): W21—W32. http://dx.doi.org/10.1190/geo2018-0232.1.

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This paper provides a theoretical overview of some of the fundamental concepts underlying electromagnetic (EM) induction exploration methods using marine controlled-source EMs as an exemplar. In particular, it will be shown, from different vantage points, that EM induction operates in the magnetoquasistatic regime in which inductive effects dominate, capacitive effects are ignored, and the displacement current is negligible; hence, charge polarization and dielectric phenomena play no role. We determine some of the major physical consequences of this approximation, and we make a distinction between wave physics and diffusive behavior, which is of particular interest in the special case of time-periodic excitation. We distinguish the fundamentally different roles of mobile charge carriers and bound charges in EM induction. It is emphasized that EM induction cannot be fully understood by comparing and contrasting Maxwell’s equations with governing equations from other disciplines that possess a similar mathematical structure. It is suggested that visualizations of energy flow using the Poynting vector and the Joule heating parameters provide a powerful tool to understand how the geologic medium shapes EM induction responses.

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7

Roberts, R. G. "Global electromagnetic induction." Surveys in Geophysics 8, no. 3 (September 1986): 339–74. http://dx.doi.org/10.1007/bf01904064.

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8

Adams, Ryan F., Benjamin V. Miller, Wade H. Kress, Scott J. Ikard, Jason D. Payne, and 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, no. 4 (December 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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9

Wilson, Gavin, Jacob Conrad, John Anderson, Andrei Swidinsky, and Jeffrey Shragge. "Developing a low-cost frequency-domain electromagnetic induction instrument." Geoscientific Instrumentation, Methods and Data Systems 11, no. 2 (August 5, 2022): 279–91. http://dx.doi.org/10.5194/gi-11-279-2022.

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Abstract. Recent advancements and the widespread availability of low-cost microcontrollers and electronic components have created new opportunities for developing and using low-cost, open-source instrumentation for near-surface geophysical investigations. Geophysical methods that do not require ground contact, such as frequency-domain electromagnetics, allow one or two users to quickly acquire significant amounts of ground resistivity data in a cost-effective manner. The Colorado School of Mines electromagnetic system (CSM-EM) is a proof-of-concept instrument capable of sensing conductive objects in near-surface environments, and is similar in concept to commercial-grade equipment while costing under USD 400 to build. We tested the functionality of the CSM-EM system in a controlled laboratory setting during the design phase and validated it over a conductive target in an outdoor environment. The transmitter antenna can generate a current of over 2.5 A, and emit signals that are detectable by a receiver antenna at offsets of up to 25 m. The system requires minor refitting to change the functioning frequency, and has been operationally validated at 0.4 and 1.6 kHz. The receiver signal can be measured by off-the-shelf digital multimeters. Future directions will focus on improving the electronic and mechanical stability of the CSM-EM with the goal of using acquired data to make quantitative measurements of subsurface resistivity.

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10

Parshin, Alexander, Ayur Bashkeev, Yuriy Davidenko, Marina Persova, Sergey Iakovlev, Sergey Bukhalov, Nikolay Grebenkin, and Marina Tokareva. "Lightweight Unmanned Aerial System for Time-Domain Electromagnetic Prospecting—The Next Stage in Applied UAV-Geophysics." Applied Sciences 11, no. 5 (February 26, 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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11

Constable, S. C. "Marine electromagnetic induction studies." Surveys in Geophysics 11, no. 2-3 (September 1990): 303–27. http://dx.doi.org/10.1007/bf01901663.

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12

Smith, Richard. "Electromagnetic Induction Methods in Mining Geophysics from 2008 to 2012." Surveys in Geophysics 35, no. 1 (April 9, 2013): 123–56. http://dx.doi.org/10.1007/s10712-013-9227-1.

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13

Won, I. J., Dean Keiswetter, and Elena Novikova. "Electromagnetic Induction Spectroscopy." Journal of Environmental and Engineering Geophysics 3, no. 1 (March 1998): 27–40. http://dx.doi.org/10.4133/jeeg3.1.27.

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14

Reid, James E., Andreas Pfaffling, and Julian Vrbancich. "Airborne electromagnetic footprints in 1D earths." GEOPHYSICS 71, no. 2 (March 2006): G63—G72. http://dx.doi.org/10.1190/1.2187756.

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Existing estimates of footprint size for airborne electromagnetic (AEM) systems have been based largely on the inductive limit of the response. We present calculations of frequency-domain, AEM-footprint sizes in infinite-horizontal, thin-sheet, and half-space models for the case of finite frequency and conductivity. In a half-space the original definition of the footprint is extended to be the side length of the cube with its top centered below the transmitter that contains the induced currents responsible for 90% of the secondary field measured at the receiver. For a horizontal, coplanar helicopter frequency-domain system, the in-phase footprint for induction numbers less than 0.4 (thin sheet) or less than 0.6 (half-space) increases from around 3.7 times the flight height at the inductive limit to more than 10 times the flight height. For a vertical-coaxial system the half-space footprint exceeds nine times the flight height for induction numbers less than 0.09. For all models, geometries, and frequencies, the quadrature footprint is approximately half to two-thirds that of the in-phase footprint. These footprint estimates are supported by 3D model calculations that suggest resistive targets must be separated by the footprint dimension for their individual anomalies to be resolved completely. Analysis of frequency-domain AEM field data acquired for antarctic sea-ice thickness measurements supports the existence of a smaller footprint for the quadrature component in comparison with the in-phase, but the effect is relatively weak. In-phase and quadrature footprints estimated by comparing AEM to drillhole data are considerably smaller than footprints from 1D and 3D calculations. However, we consider the footprints estimated directly from field data unreliable since they are based on a drillhole data set that did not adequately define the true, 3D, sea-ice thickness distribution around the AEM flight line.

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15

Djanni, Axel Tcheheumeni, Anton Ziolkowski, and David Wright. "Electromagnetic induction noise in a towed electromagnetic streamer." GEOPHYSICS 81, no. 3 (May 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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Hattula, Aimo, and Timo Rekola. "Exploration geophysics at the Pyhäsalmi mine and grade control work of the Outokumpu Group." GEOPHYSICS 65, no. 6 (November 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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Everett, Mark, and Colin Farquharson. "Near-surface electromagnetic induction — Introduction." GEOPHYSICS 77, no. 4 (July 1, 2012): WB1—WB2. http://dx.doi.org/10.1190/geo-2012-0601-spsein.1.

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Kozhevnikov, N. O., and E. Yu Antonov. "Aftereffects in the Transient Electromagnetic Method: Inductively Induced Polarization." Russian Geology and Geophysics 62, no. 12 (December 1, 2021): 1440–48. http://dx.doi.org/10.2113/rgg20204258.

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Abstract —Inductively induced electric polarization (IIP) is one of the aftereffects inherent in the geologic materials and affecting results of the transient electromagnetic method. Its effect on the inductive transient response manifests itself as a nonmonotonic EMF decay, including the polarity reversal. The dependence of IIP on many conditions makes it difficult to study the basic regularities in its manifestation. One of the ways to address this problem is to present the simulation results as a normalized transient response. From the most general point of view, the intensity and time range of the IIP manifestation are controlled by the competition between induction and induced polarization phenomena. Induced polarization manifests itself differently, depending on the transmitter used for the excitation of the ground response. Therefore, when studying polarizable ground, the results of the conventional IP method and those of the TEM method do not always correlate.

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Vonder Mühll, Daniel, Christian Hauck, and Hansueli Gubler. "Mapping of mountain permafrost using geophysical methods." Progress in Physical Geography: Earth and Environment 26, no. 4 (December 2002): 643–60. http://dx.doi.org/10.1191/0309133302pp356ra.

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Permafrost distribution in nonpolar mountain areas is strongly influenced by topo-graphical effects. Conditions therefore change within short distances and consequently the permafrost pattern is often very complex. Warm permafrost with temperatures between -2°C and 0°C is sensitive in terms of slope failures. It is also crucial to determine the lower permafrost boundary by geophysical means in order to calibrate models. Various geophysical methods have been applied to the mapping of mountain permafrost, including bottom temperature of the snow cover (BTS), refraction seismics, DC resistivity, ground penetrating radar (GPR), electromagnetic induction and radiometry. This paper gives an overview of investigations to map mountain permafrost distribution showing the potential of the modern use of geophysical methods. The two-dimensional DC resistivity tomography makes it possible to get an impression of internal structures. Electromagnetic induction methods showed good results, in particular the EM-31 for determining the permafrost distribution and the PROTEM to assess the overall permafrost thickness. Using passive microwave (11.4 GHz), the BTS, which is used as an indicator for the presence of permafrost, was measured. After ground surveys, an airborne test measurement from a helicopter was made. Traditional BTS measurements agreed very well with the BTS determined by radiometry.

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20

Rastogi, R. G. "Electromagnetic induction by the equatorial electrojet." Geophysical Journal International 158, no. 1 (July 2004): 16–31. http://dx.doi.org/10.1111/j.1365-246x.2004.02128.x.

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21

Correia, António. "Mathematical methods for geo-electromagnetic induction." Tectonophysics 244, no. 4 (April 1995): 286–87. http://dx.doi.org/10.1016/0040-1951(95)90040-3.

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22

Cosentino, P. L., P. Capizzi, R. Martorana, P. Messina, and 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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Gomez-Ortiz, David, Isabel Blanco-Montenegro, Jose Arnoso, Tomas Martin-Crespo, Mercedes Solla, Fuensanta Montesinos, Emilio Vélez, and Nieves Sánchez. "Imaging Thermal Anomalies in Hot Dry Rock Geothermal Systems from Near-Surface Geophysical Modelling." Remote Sensing 11, no. 6 (March 21, 2019): 675. http://dx.doi.org/10.3390/rs11060675.

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Convective hydrothermal systems have been extensively studied using electrical and electromagnetic methods given the strong correlation between low conductivity anomalies associated with hydrothermal brines and high temperature areas. However, studies addressing the application of similar geophysical methods to hot dry rock geothermal systems are very limited in the literature. The Timanfaya volcanic area, located on Lanzarote Island (Canary Islands), comprises one of these hot dry rock systems, where ground temperatures ranging from 250 to 605 °C have been recorded in pyroclastic deposits at shallow (<70 m) depths. With the aim of characterizing the geophysical signature of the high ground temperature areas, three different geophysical techniques (ground penetrating radar, electromagnetic induction and magnetic prospecting) were applied in a well-known geothermal area located inside Timanfaya National Park. The area with the highest ground temperatures was correlated with the location that exhibited strong ground penetrating radar reflections, high resistivity values and low magnetic anomalies. Moreover, the high ground temperature imaging results depicted a shallow, bowl-shaped body that narrowed and deepened vertically to a depth greater than 45 m. The ground penetrating radar survey was repeated three years later and exhibited subtle variations of the signal reflection patterns, or signatures, suggesting a certain temporal variation of the ground temperature. By identifying similar areas with the same geophysical signature, up to four additional geothermal areas were revealed. We conclude that the combined use of ground penetrating radar, electromagnetic induction and magnetic methods constitutes a valuable tool to locate and study both the geometry at depth and seasonal variability of geothermal areas associated with hot dry rock systems.

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Jin, Song, Paul Fallgren, Jeffrey Cooper, Jeffrey Morris, and Michael Urynowicz. "Assessment of diesel contamination in groundwater using electromagnetic induction geophysical techniques." Journal of Environmental Science and Health, Part A 43, no. 6 (April 10, 2008): 584–88. http://dx.doi.org/10.1080/10934520801893550.

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Trichtchenko, Larisa. "Modelling natural electromagnetic interference in man-made conductors for space weather applications." Annales Geophysicae 34, no. 4 (April 14, 2016): 427–36. http://dx.doi.org/10.5194/angeo-34-427-2016.

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Abstract. Power transmission lines above the ground, cables and pipelines in the ground and under the sea, and in general all man-made long grounded conductors are exposed to the variations of the natural electromagnetic field. The resulting currents in the networks (commonly named geomagnetically induced currents, GIC), are produced by the conductive and/or inductive coupling and can compromise or even disrupt system operations and, in extreme cases, cause power blackouts, railway signalling mis-operation, or interfere with pipeline corrosion protection systems. To properly model the GIC in order to mitigate their impacts it is necessary to know the frequency dependence of the response of these systems to the geomagnetic variations which naturally span a wide frequency range. For that, the general equations of the electromagnetic induction in a multi-layered infinitely long cylinder (representing cable, power line wire, rail or pipeline) embedded in uniform media have been solved utilising methods widely used in geophysics. The derived electromagnetic fields and currents include the effects of the electromagnetic properties of each layer and of the different types of the surrounding media. This exact solution then has been used to examine the electromagnetic response of particular samples of long conducting structures to the external electromagnetic wave for a wide range of frequencies. Because the exact solution has a rather complicated structure, simple approximate analytical formulas have been proposed, analysed and compared with the results from the exact model. These approximate formulas show good coincidence in the frequency range spanning from geomagnetic storms (less than mHz) to pulsations (mHz to Hz) to atmospherics (kHz) and above, and can be recommended for use in space weather applications.

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Swidinsky, Andrei, and Chester J. Weiss. "On coincident loop transient electromagnetic induction logging." GEOPHYSICS 82, no. 4 (July 1, 2017): E211—E220. http://dx.doi.org/10.1190/geo2017-0134.1.

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Coincident loop transient induction wireline logging is examined as the borehole analog of the well-known land and airborne time-domain electromagnetic (EM) method. The concept of whole-space late-time apparent resistivity is modified from the half-space version commonly used in land and airborne geophysics and applied to the coincident loop voltages produced from various formation, borehole, and invasion models. Given typical tool diameters, off-time measurements with such an instrument must be made on the order of nanoseconds to microseconds — much more rapidly than for surface methods. Departure curves of the apparent resistivity for thin beds, calculated using an algorithm developed to model the transient response of a loop in a multilayered earth, indicate that the depth of investigation scales with the bed thickness. Modeled resistivity logs are comparable in accuracy and resolution with standard frequency-domain focused induction logs. However, if measurement times are longer than a few microseconds, the thicknesses of conductors can be overestimated, whereas resistors are underestimated. Thin-bed resolution characteristics are explained by visualizing snapshots of the EM fields in the formation, where a conductor traps the electric field while two current maxima are produced in the shoulder beds surrounding a resistor. Radial profiling is studied using a concentric cylinder earth model. Results found that true formation resistivity can be determined in the presence of either oil- or water-based mud, although in the latter case, measurements must be taken several orders of magnitude later in time. The ability to determine true formation resistivity is governed by the degree that the EM field heals after being distorted by borehole fluid and invasion, a process visualized and particularly evident in the case of conductive water-based mud.

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Reid, James E., and James C. Macnae. "Resistive limit modeling of airborne electromagnetic data." GEOPHYSICS 67, no. 2 (March 2002): 492–500. http://dx.doi.org/10.1190/1.1468609.

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When a confined conductive target embedded in a conductive host is energized by an electromagnetic (EM) source, current flow in the target comes from both direct induction of vortex currents and current channeling. At the resistive limit, a modified magnetometric resistivity integral equation method can be used to rapidly model the current channeling component of the response of a thin-plate target energized by an airborne EM transmitter. For towed-bird transmitter–receiver geometries, the airborne EM anomalies of near-surface, weakly conductive features of large strike extent may be almost entirely attributable to current channeling. However, many targets in contact with a conductive host respond both inductively and galvanically to an airborne EM system. In such cases, the total resistive-limit response of the target is complicated and is not the superposition of the purely inductive and purely galvanic resistive-limit profiles. Numerical model experiments demonstrate that while current channeling increases the width of the resistive-limit airborne EM anomaly of a wide horizontal plate target, it does not necessarily increase the peak anomaly amplitude.

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28

De Carlo, Lorenzo, Gaetano Alessandro Vivaldi, and Maria Clementina Caputo. "Electromagnetic Induction Measurements for Investigating Soil Salinization Caused by Saline Reclaimed Water." Atmosphere 13, no. 1 (December 31, 2021): 73. http://dx.doi.org/10.3390/atmos13010073.

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This paper focused on the use of electromagnetic induction measurements in order to investigate soil salinization caused by irrigation with saline reclaimed water. An experimental activity was carried out during the growing season of tomato crop in order to evaluate expected soil salinization effects caused by different saline agro-industrial wastewaters used as irrigation sources. Soil electrical conductivity, strictly related to the soil salinity, has been monitored for three months by means of Electromagnetic Induction (EMI) measurements, and evident differences in the soil response have been observed. The study highlighted two aspects that can improve soil investigation due to the utilization of geophysical tools. First, EMI data can map large areas in a short period of time with an unprecedented level of detail by overcoming practical difficulties in order to massively sample soil. At the same time, repeated measurements over time allow updating real-time soil salinity maps by using accurate correlations with soil electrical conductivity. This application points out how integrated agro-geophysical research approaches can play a strategic role in agricultural saline water management in order to prevent soil salinization risks in medium to long-term periods.

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29

Benson, Alvin K., Kelly L. Payne, and Melissa A. Stubben. "Mapping groundwater contamination using dc resistivity and VLF geophysical methods–A case study." GEOPHYSICS 62, no. 1 (January 1997): 80–86. http://dx.doi.org/10.1190/1.1444148.

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Geophysical methods can be helpful in mapping areas of contaminated soil and groundwater. Electrical resistivity and very low‐frequency electromagnetic induction (VLF) surveys were carried out at a site of shallow hydrocarbon contamination in Utah County, Utah. Previously installed monitoring wells facilitated analysis of water chemistry to enhance interpretation of the geophysical data. The electrical resistivity and VLF data correlate well, and vertical cross‐sections and contour maps generated from these data helped map the contaminant plume, which was delineated as an area of high interpreted resistivities.

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30

Glaser, Dan R., Fridon Shubitidze, and Benjamin E. Barrowes. "Standoff High-Frequency Electromagnetic Induction Response of Unsaturated Sands: A Tank-Scale Feasibility Study." Journal of Environmental and Engineering Geophysics 27, no. 1 (March 2022): 45–51. http://dx.doi.org/10.32389/jeeg21-030.

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Standoff electromagnetic induction (EMI) measurements of complex conductivity and complex permittivity for engineering soil properties have the potential to revolutionize the way the US Army handles route planning and infrastructure assessment. An unmanned aerial system (UAS) based EM platform for soil interrogation would have wide reaching impact in a variety of applications including: civil infrastructure inspection, in-theater ingress and egress routing, reduction of false positives in IED detection, and permafrost mapping, among many others. Traditional frequency domain EMI instruments assess conductivity at low-frequencies, generally in the range of 1–20 kHz; however, recent advancements have resulted in instrumentation targeting a broadband range of frequencies, from 10 kHz through 20 MHz. This advancement, known as high-frequency electromagnetic induction (HFEMI) allows the potential to evaluate frequency domain relaxation effects in soils by acquiring both the in phase and quadrature response of the secondary field from the soil. Relaxation phenomena such as induced polarization and dielectric permittivity are related to important soil properties that can potentially be exploited using this HFEMI system. While conductivity measurements using the quadrature component of the EMI response are well established in EMI instrumentation, understanding of the relationship between direct electrical measurements and standoff HFEMI measurements is lacking. In an effort to illuminate this relationship between various electrical and electromagnetic methods at a scale suitable for soil property estimation, we perform side-by-side measurements using galvanic geoelectrical methods (ERT, IP), electromagnetics, time-domain reflectometry (TDR) and ground penetrating radar (GPR). We compare HFEMI obtained quadrature and in-phase responses to ERT, IP, TDR and GPR measurements. A tank-scale test cell was developed for comparison of the above methods and allowed assessment of sand at varying saturation levels. Further, the HFEMI response at varying heights above the sand surface was also assessed. Qualitative observations are reported in an initial attempt to relate the HFEMI response to important soil parameters.

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31

Caminha-Maciel, George, and Irineu Figueiredo. "Error Analysis in Measured Conductivity under Low Induction Number Approximation for Electromagnetic Methods." ISRN Geophysics 2013 (December 5, 2013): 1–4. http://dx.doi.org/10.1155/2013/720839.

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We present an analysis of the error involved in the so-called low induction number approximation in the electromagnetic methods. In particular, we focus on the EM34 equipment settings and field configurations, widely used for geophysical prospecting of laterally electrical conductivity anomalies and shallow targets. We show the theoretical error for the conductivity in both vertical and horizontal dipole coil configurations within the low induction number regime and up to the maximum measuring limit of the equipment. A linear relationship may be adjusted until slightly beyond the point where the conductivity limit for low induction number (B=1) is reached. The equations for the linear fit of the relative error in the low induction number regime are also given.

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32

Mochizuki, E. "Electromagnetic induction in an aspherically conducting mantle." Geophysical Journal International 113, no. 2 (May 1993): 518–23. http://dx.doi.org/10.1111/j.1365-246x.1993.tb00904.x.

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33

Everett, Mark E. "Theoretical Developments in Electromagnetic Induction Geophysics with Selected Applications in the Near Surface." Surveys in Geophysics 33, no. 1 (July 5, 2011): 29–63. http://dx.doi.org/10.1007/s10712-011-9138-y.

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34

Badea, Eugene A., Mark E. Everett, Gregory A. Newman, and Oszkar Biro. "Finite‐element analysis of controlled‐source electromagnetic induction using Coulomb‐gauged potentials." GEOPHYSICS 66, no. 3 (May 2001): 786–99. http://dx.doi.org/10.1190/1.1444968.

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A 3-D finite‐element solution has been used to solve controlled‐source electromagnetic (EM) induction problems in heterogeneous electrically conducting media. The solution is based on a weak formulation of the governing Maxwell equations using Coulomb‐gauged EM potentials. The resulting sparse system of linear algebraic equations is solved efficiently using the quasi‐minimal residual method with simple Jacobi scaling as a preconditioner. The main aspects of this work include the implementation of a 3-D cylindrical mesh generator with high‐quality local mesh refinement and a formulation in terms of secondary EM potentials that eliminates singularities introduced by the source. These new aspects provide quantitative induction‐log interpretation for petroleum exploration applications. Examples are given for 1-D, 2-D, and 3-D problems, and favorable comparisons are presented against other, previously published multidimensional EM induction codes. The method is general and can also be adapted for controlled‐source EM modeling in mining, groundwater, and environmental geophysics in addition to fundamental studies of EM induction in heterogeneous media.

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35

Van De Vijver, Ellen, Marc Van Meirvenne, Laura Vandenhaute, Samuël Delefortrie, Philippe De Smedt, Timothy Saey, and Piet Seuntjens. "Urban soil exploration through multi-receiver electromagnetic induction and stepped-frequency ground penetrating radar." Environmental Science: Processes & Impacts 17, no. 7 (2015): 1271–81. http://dx.doi.org/10.1039/c5em00023h.

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36

Manstein, A. K., G. L. Panin, and S. Yu Tikunov. "A device for shallow frequency-domain electromagnetic induction sounding." Russian Geology and Geophysics 49, no. 6 (June 2008): 430–36. http://dx.doi.org/10.1016/j.rgg.2007.10.013.

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37

Unsworth, Martyn J., Bryan J. Travis, and Alan D. Chave. "Electromagnetic induction by a finite electric dipole source over a 2-D earth." GEOPHYSICS 58, no. 2 (February 1993): 198–214. http://dx.doi.org/10.1190/1.1443406.

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A numerical solution for the frequency domain electromagnetic response of a two‐dimensional (2-D) conductivity structure to excitation by a three‐dimensional (3-D) current source has been developed. The fields are Fourier transformed in the invariant conductivity direction and then expressed in a variational form. At each of a set of discrete spatial wavenumbers a finite‐element method is used to obtain a solution for the secondary electromagnetic fields. The finite element uses exponential elements to efficiently model the fields in the far‐field. In combination with an iterative solution for the along‐strike electromagnetic fields, this produces a considerable reduction in computation costs. The numerical solutions for a horizontal electric dipole are computed and shown to agree with closed form expressions and to converge with respect to the parameterization. Finally some simple examples of the electromagnetic fields produced by horizontal electric dipole sources at both the seafloor and air‐earth interface are presented to illustrate the usefulness of the code.

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38

Smith, Richard S., and G. F. West. "Electromagnetic induction in an inhomogeneous conductive thin sheet." GEOPHYSICS 52, no. 12 (December 1987): 1677–88. http://dx.doi.org/10.1190/1.1442284.

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Distinguishing between the electromagnetic (EM) response of a subsurface conductor and the EM response of an overburden whose conductivity and/or thickness varies laterally requires a capability to calculate the EM response of both types of conductor. While methods for calculating the response of some simple subsurface conductors such as dipping rectangular sheets are already available, methods for computing the response of an irregular overburden are not common. Using Price’s analysis, we have formulated two numerical techniques for calculating the response of a laterally varying overburden which is thin and flat, and which lies on a perfectly resistive subspace. The first technique is a frequency‐domain method in which a large matrix equation is solved to find the horizontal‐wavenumber components of the secondary vertical magnetic field. The method is best suited to calculating the response of the overburden when the EM source and receiver are located above the sheet, such as in airborne EM systems. Helicopter EM profiles calculated using this technique have been checked against a simple scale model. The second method calculates the time‐domain step response of the overburden by time‐stepping the vertical component of the magnetic field. The method is suitable for calculating the response of the overburden when the EM source is a large transmitter loop close to the overburden. Using the time‐domain method to investigate the response of simple conductance structures illustrates that the zero crossing of the vertical magnetic field moves more slowly across conductive regions than across resistive regions. This is because the rate of decay of the vertical field in a region varies in proportion to the resistance of the region. A response profile from a UTEM survey shows a response that could be interpreted as due to a dipping subsurface conductor. This response has been modeled using the time‐domain method, and a geologically acceptable pattern of lateral variations in the overburden conductance yields a response close to the measured EM response. Thus, a subsurface conductor need not lie below the profile line to explain the response.

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39

Jiracek, George R. "Near-surface and topographic distortions in electromagnetic induction." Surveys in Geophysics 11, no. 2-3 (September 1990): 163–203. http://dx.doi.org/10.1007/bf01901659.

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40

Martinez-Garcia, Mario. "Electromagnetic induction in geothermal fields and volcanic belts." Surveys in Geophysics 13, no. 4-5 (September 1992): 409–34. http://dx.doi.org/10.1007/bf01903485.

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41

Duba, A. G., and T. J. Shankland. "Analyzing electromagnetic induction data: Suggestions from laboratory measurements." Pure and Applied Geophysics PAGEOPH 125, no. 2-3 (1987): 285–90. http://dx.doi.org/10.1007/bf00874498.

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42

Bensdorp, Silvian, Steen A. Petersen, Per-Atle Olsen, Frank Antonsen, Peter M. van den Berg, and Jacob T. Fokkema. "An approximate 3D inversion method for inversion of single-well induction-logging responses." GEOPHYSICS 81, no. 1 (January 1, 2016): E43—E56. http://dx.doi.org/10.1190/geo2014-0540.1.

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Electromagnetic logging is a technique used to probe differences in electric conductivity around a measurement device. Electromagnetic logging while drilling can contribute to proactive geosteering to improve well placement in reservoirs because such measurements can serve as an indication for the structure of the surrounding geology. We have developed a novel way of predicting the 3D conductivity distribution around a drilling tool, based on the contrast-source inversion method, in which we have replaced the full integral-equation approach by the single spherical scatterer (SSS) approximation. The approximation took into account the dominant features of the diffusive electromagnetic field. This allowed for a substantial gain in computational speed and storage of the inversion method for reconstruction of the conductivity distribution. In view of the limited range of the electromagnetic probing, the overall reconstruction can be segmented in several local windows. This reduced the computational speed requirements and the storage requirements dramatically, while safeguarding the overall 3D character of reconstruction. We have synthesized 3D electromagnetic logging data using synthetic models and conductivity maps from a hydrocarbon North Sea reservoir model. Reconstructions were made for multiple source frequencies, and the results were compared with the results obtained from the Born approximation. We have observed that reconstruction based on the SSS approximation was superior to the one based on the Born approximation. Our algorithm helped us determine the feasibility of producing reconstructions of reservoir sections in a short time frame, which allows for real-time decision making during drilling operations.

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43

De Smedt, Philippe, Samuël Delefortrie, and Francis Wyffels. "Identifying and removing micro-drift in ground-based electromagnetic induction data." Journal of Applied Geophysics 131 (August 2016): 14–22. http://dx.doi.org/10.1016/j.jappgeo.2016.05.004.

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44

Petersons, H. F. "Electromagnetic Induction in the Earth Using Long Period Geomagnetic Variations." Exploration Geophysics 24, no. 2 (June 1993): 157–59. http://dx.doi.org/10.1071/eg993157.

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45

Giesecke, A., C. Nore, F. Stefani, G. Gerbeth, J. Léorat, F. Luddens, and J. L. Guermond. "Electromagnetic induction in non-uniform domains." Geophysical & Astrophysical Fluid Dynamics 104, no. 5-6 (October 2010): 505–29. http://dx.doi.org/10.1080/03091929.2010.507202.

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46

Walker, Peter W., and Gordon F. West. "Parametric estimators for current excitation on a thin plate." GEOPHYSICS 57, no. 6 (June 1992): 766–73. http://dx.doi.org/10.1190/1.1443290.

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Parametric analysis is used to predict whether induction or current channeling dominates the current excitation in a conductive body in the earth. Knowing that one mode dominates the current response permits the use of relatively simple models that account for only a single mode of excitation in place of more complicated general ones that account for both modes of the current response. This is useful both in forward modeling and in inversion. In interpretation, predicting the current excitation is useful for verifying that the assumed mode of excitation is consistent with the interpreted body. Prediction is done with a set of “current excitation ratios” that we demonstrate for a thin conductive plate in a conductive half‐space. To derive the excitation ratios, parametric theory is used to estimate the strength of the inductive and galvanic modes of the current response of the plate. The ratios then follow by dividing the inductive estimate into the galvanic one. When this ratio is less than one, induction will dominate the current response. When it is greater than one, current channeling will dominate. Current excitation ratios are simple to calculate, and consist of two components. One component is a product of model parameters such as conductivity, dimension, and permeability, and can be calculated by hand. The second component consists of what we term the “local impedance” of the source field at the conductor. This component can be calculated with a simple half‐space or layered earth electromagnetic modeling algorithm and then contoured for later reference. The predictive capability of the current excitation ratios is tested by calculating the current response on a vertical plate in a half‐space with a full electromagnetic scattering solution. We find the correspondence between the two to be very good, and that it is possible to successfully predict the dominant mode of the current response through parametric theory where assumptions used in the parametric analysis are valid.

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47

Noh, Kyubo, Ki Ha Lee, Seokmin Oh, Soon Jee Seol, and Joongmoo Byun. "Numerical evaluation of active source magnetics as a method for imaging high-resolution near-surface magnetic heterogeneity." GEOPHYSICS 82, no. 5 (September 1, 2017): J27—J38. http://dx.doi.org/10.1190/geo2016-0435.1.

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We have evaluated a geophysical method that uses a low-frequency magnetic source to image subsurface magnetic heterogeneity. This active source approach can be used to image magnetic features at higher resolutions than the conventional passive geomagnetic method. Importantly, this frequency-domain active source approach is independent of the effects of remanent magnetization, which complicates the interpretation of geomagnetic data. We carried out forward modeling of frequency-domain electromagnetic (EM) data and we found that, at frequencies of a few hertz, the magnetostatic response due to the induced magnetization dominates the EM induction response. The result suggests that it is possible to make magnetic interpretation of low-frequency EM data without having to consider the conductivity structure and the corresponding EM induction effect. We compare the anomalous magnetic responses with magnetic noise components and find that the proposed active source magnetic (ASM) method has a depth of investigation of approximately 300 m. Free-space field and inductive noise are considered as the most important issues affecting the depth of investigation. We also determine the potential for linear interpretation of magnetic heterogeneity under 0.1 SI by showing that the low-frequency magnetic response can be approximated by a linear magnetic response. In our synthetic experiments, inversion of the ASM data shows a marked enhancement in resolution, with no effect of the remanent magnetization, in contrast to geomagnetic inversion. These results show that the ASM method is a useful geophysical tool, especially when high-resolution imaging of magnetic susceptibility is required or where strong remanent magnetization complicates the magnetic interpretation.

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48

Witten, Alan, I. J. Won, and Stephen Norton. "Imaging Underground Structures Using Broadband Electromagnetic Induction." Journal of Environmental and Engineering Geophysics 2, no. 2 (September 1997): 105–14. http://dx.doi.org/10.4133/jeeg2.2.105.

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49

Livelybrooks, D. "Mathematical methods for geo-electromagnetic induction." Journal of Atmospheric and Terrestrial Physics 57, no. 10 (August 1995): 1186–87. http://dx.doi.org/10.1016/0021-9169(95)90101-9.

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50

Lee, Seunghee, George McMechan, and Carlos Aiken. "On: “Phase‐field imaging: The electromagnetic equivalent of seismic migration” by S. Lee, G. A. McMechan, and C. L. V. Aiken (GEOPHYSICS, 52, 678–693, May 1987)." GEOPHYSICS 53, no. 6 (June 1988): 863. http://dx.doi.org/10.1190/1.1442521.

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We were very happy to see the paper by Lee et al. which contains many interesting applications of electromagnetic migration to the solution of geoelectric problems. However, we were very suprised the authors were unaware of our previous papers published in both Eastern and Western international journals concerning the same subject (cf., bibliography). We proposed the generalization of seismic migration for electromagnetic data for the first time in 1982 during the Sixth Workship on EM-induction in the Earth and Moon (Zhdanov and Frenkel, 1982). Dr. John Booker from The University of Washington was the first to suggest calling our method “electromagnetic migration”; a detailed description of our method was given in Zhdanov and Frenkel (1983a and b). Work on electromagnetic migration was published by Zhdanov and Frenkel (1983c) in a special issue of the Proceedings of Oulu University. In 1985 we presented an invited paper (Velikhov et al., 1987) on this topic at the Prague General Assembly of IAGA.

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