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Electrical Resistivity Tomography
Electrical resistivity tomography (ERT) or electrical resistivity imaging (ERI) is a geophysical technique for imaging sub-surface structures from electrical resistivity measurements made at the surface, or by electrodes in one or more boreholes. If the electrodes are suspended in the boreholes, deeper sections can be investigated. It is closely related to the medical imaging technique electrical impedance tomography (EIT), and mathematically is the same inverse problem. In contrast to medical EIT, however, ERT is essentially a direct current method. A related geophysical method, induced polarization (or spectral induced polarization), measures the transient response and aims to determine the subsurface chargeability properties. Electrical resistivity measurements can be used for identification and quantification of depth of groundwater, detection of clays, and measurement of groundwater conductivity. History The technique evolved from techniques of electrical prospecting th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2D Inversion Of Electrical Resistivity Data
D, or d, is the fourth Letter (alphabet), letter in the Latin alphabet, used in the English alphabet, modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is English alphabet#Letter names, ''dee'' (pronounced ), plural ''dees''. History The Semitic languages, Semitic letter Daleth, Dāleth may have developed from the logogram for a fish or a door. There are many different Egyptian hieroglyphs that might have inspired this. In Semitic, Ancient Greek and Latin, the letter represented ; in the Etruscan alphabet the letter was archaic, but still retained (see letter B). The equivalent Greek letter is Delta, Delta (letter), Δ. Architecture The Lower case, minuscule (lower-case) form of 'd' consists of a lower-story left Typeface anatomy#Strokes, bowl and a Typeface anatomy#Strokes, stem ascender. It most likely developed by gradual variations on the upper case, majuscule (capital) form 'D', and today now composed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Resistance Tomography
Electrical impedance tomography (EIT) is a noninvasive type of medical imaging in which the electrical conductivity, permittivity, and impedance of a part of the body is inferred from surface electrode measurements and used to form a tomographic image of that part. Electrical conductivity varies considerably among various biological tissues (absolute EIT) or the movement of fluids and gases within tissues (difference EIT). The majority of EIT systems apply small alternating currents at a single frequency, however, some EIT systems use multiple frequencies to better differentiate between normal and suspected abnormal tissue within the same organ (multifrequency-EIT or electrical impedance spectroscopy). Typically, conducting surface electrodes are attached to the skin around the body part being examined. Small alternating currents will be applied to some or all of the electrodes, the resulting equi-potentials being recorded from the other electrodes (figures 1 and 2). This process ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inverse Problems
An inverse problem in science is the process of calculating from a set of observations the causal factors that produced them: for example, calculating an image in X-ray computed tomography, source reconstruction in acoustics, or calculating the density of the Earth from measurements of its gravity field. It is called an inverse problem because it starts with the effects and then calculates the causes. It is the inverse of a forward problem, which starts with the causes and then calculates the effects. Inverse problems are some of the most important mathematical problems in science and mathematics because they tell us about parameters that we cannot directly observe. They have wide application in system identification, optics, radar, acoustics, communication theory, signal processing, medical imaging, computer vision, geophysics, oceanography, astronomy, remote sensing, natural language processing, machine learning, nondestructive testing, slope stability analysis and many other ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Doklady Akademii Nauk SSSR
The ''Proceedings of the USSR Academy of Sciences'' (russian: Доклады Академии Наук СССР, ''Doklady Akademii Nauk SSSR'' (''DAN SSSR''), french: Comptes Rendus de l'Académie des Sciences de l'URSS) was a Soviet journal that was dedicated to publishing original, academic research papers in physics, mathematics, chemistry, geology, and biology. It was first published in 1933 and ended in 1992 with volume 322, issue 3. Today, it is continued by ''Doklady Akademii Nauk'' (russian: Доклады Академии Наук), which began publication in 1992. The journal is also known as the ''Proceedings of the Russian Academy of Sciences (RAS)''. ''Doklady'' has had a complicated publication and translation history. A number of translation journals exist which publish selected articles from the original by subject section; these are listed below. History The Russian Academy of Sciences dates from 1724, with a continuous series of variously named publications dat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertical Electrical Sounding
Vertical electrical sounding (VES) is a geophysical method for investigation of a geological medium. The method is based on the estimation of the electrical conductivity or resistivity of the medium. The estimation is performed based on the measurement of voltage of electrical field induced by the distant grounded electrodes (current electrodes). Measurements Figures 1–4 show the possible configuration of the measurement setup. The electrodes ''A'' and ''B'' are current electrodes which are connected to a current source; ''N'' and ''M'' are potential electrodes which are used for the voltage measurements. As source, the direct current or low frequency alternating current is used. The interpretation of the measurements can be performed based on the apparent resistivity values. The depth of investigation depends on the distance between the current electrodes. In order to obtain the apparent resistivity as the function of depth, the measurements for each position are performed w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telluric Current
A telluric current (from Latin ''tellūs'', "earth"), or Earth current, This has a detailed history of observations as understood at the time. is an electric current which moves underground or through the sea. Telluric currents result from both natural causes and human activity, and the discrete currents interact in a complex pattern. The currents are extremely low frequency and travel over large areas at or near the surface of the Earth. Description Telluric currents are phenomena observed in the Earth's crust and mantle. In September 1862, an experiment to specifically address Earth currents was carried out in the Munich Alps (Lamont, 1862). Including minor processes, there are at least 32 different mechanisms which cause telluric currents. The strongest are primarily geomagnetically induced currents, which are induced by changes in the outer part of the Earth's magnetic field, which are usually caused by interactions between the solar wind and the magnetosphere or solar radiat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seismo-electromagnetics
Seismo-electromagnetics are various electro-magnetic phenomena believed to be generated by tectonic forces acting on the earth's crust, and possibly associated with seismic activity such as earthquakes and volcanoes. Study of these has been prompted by the prospect they might be generated by the increased stress leading up to an earthquake, and might thereby provide a basis for short-term earthquake prediction. However, despite many studies, no form of seismo-electromagnetics has been shown to be effective for earthquake prediction. A key problem is that earthquakes themselves produce relatively weak electromagnetic phenomena, and the effects from any precursory phenomena are likely to be too weak to measure. Close monitoring of the Parkfield earthquake revealed no significant pre-seismic electromagnetic effects. However, some researchers remain optimistic, and searches for seismo-electromagnetic earthquake precursors continue. VAN method The VAN method – named after P. Varot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetotellurics
Magnetotellurics (MT) is an electromagnetic geophysical method for inferring the earth's subsurface electrical conductivity from measurements of natural geomagnetic and geoelectric field variation at the Earth's surface. Investigation depth ranges from 300 m below ground by recording higher frequencies down to 10,000 m or deeper with long-period soundings. Proposed in Japan in the 1940s, and France and the USSR during the early 1950s, MT is now an international academic discipline and is used in exploration surveys around the world. Commercial uses include hydrocarbon (oil and gas) exploration, geothermal exploration, carbon sequestration, mining exploration, as well as hydrocarbon and groundwater monitoring. Research applications include experimentation to further develop the MT technique, long-period deep crustal exploration, deep mantle probing, sub-glacial water flow mapping, and earthquake precursor research. History The magnetotelluric technique was introduc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Impedance Tomography
Electrical impedance tomography (EIT) is a noninvasive type of medical imaging in which the electrical conductivity, permittivity, and impedance of a part of the body is inferred from surface electrode measurements and used to form a tomographic image of that part. Electrical conductivity varies considerably among various biological tissues (absolute EIT) or the movement of fluids and gases within tissues (difference EIT). The majority of EIT systems apply small alternating currents at a single frequency, however, some EIT systems use multiple frequencies to better differentiate between normal and suspected abnormal tissue within the same organ (multifrequency-EIT or electrical impedance spectroscopy). Typically, conducting surface electrodes are attached to the skin around the body part being examined. Small alternating currents will be applied to some or all of the electrodes, the resulting equi-potentials being recorded from the other electrodes (figures 1 and 2). This process ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Capacitance Tomography
Electrical capacitance tomography (ECT) is a method for determination of the dielectric permittivity distribution in the interior of an object from external capacitance measurements. It is a close relative of electrical impedance tomography and is proposed as a method for industrial process monitoring. Although capacitance sensing methods were in widespread use the idea of using capacitance measurement to form images is attributed to Maurice Beck and co-workers at UMIST in the 1980s. Although usually called tomography, the technique differs from conventional tomographic methods, in which high resolution images are formed of slices of a material. The measurement electrodes, which are metallic plates, must be sufficiently large to give a measureable change in capacitance. This means that very few electrodes are used, typically eight to sixteen electrodes. An N-electrode system can only provide N(N−1)/2 independent measurements. This means that the technique is limited to p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil Resistivity
Soil resistivity is a measure of how much the soil resists or conducts electric current. It is a critical factor in design of systems that rely on passing current through the Earth's surface. It is a very important parameter for finding the best location of a transmitter working on low frequiencies (VLF, LF, MF and lower shortwave) as such radio stations usually use ground as counterpole. An understanding of the soil resistivity and how it varies with depth in the soil is necessary to design the grounding system in an electrical substation, or for lightning conductors. It is needed for design of grounding (earthing) electrodes for substations and High-voltage direct current transmission systems. It was formerly important in earth-return telegraphy. It can also be a useful measure in agriculture as a proxy measurement for moisture content. In most substations the earth is used to conduct fault current when there are ground faults on the system. In single wire earth return power tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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