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Bavusi, M., A. Loperte, V. Lapenna, U. Moscatelli i S. Minguzzi. "Magnetic and ground penetrating radar for the research of Medieval buried structures in Marche Region". Advances in Geosciences 24 (29.04.2010): 89–95. http://dx.doi.org/10.5194/adgeo-24-89-2010.
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Abstract. A magnetic and Ground Penetrating Radar joint survey was carried out in the framework of the R.I.M.E.M. project that has the aim of supporting the archaeological prospections and drive the selection of the excavation areas related to the Late Roman Period and Early Middle Ages in the Central and Southern Italy. In particular, this papers deals with the magnetic surveys acquired near "Madonna della Valle" and GPR and magnetic joint surveys carried out in "Monastero"site. Most of magnetic maps carried out in "Madonna della Valle" site shown the absence of structured magnetic anomalies, despite of the presence of archaeological signs. Several hypothesis were given to explain this evidence. Joint interpretation performed in "Monastero" site shown more intense magnetic anomalies related with shallower reflections due to probably to buried pipes. Other reflections are related with magnetic anomalies compatible with archaeological targets, but some significant reflections do not correspond to any magnetic anomaly, indicating magnetic method could be "blind" respect the archaeological target. New field surveys including the electrical resistivity tomography could be carried out in order to overcome these acquisition and interpretation difficulties.
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Wagner, Steffen, i H. Lindner. "Interpretation of geomagnetic anomalies in Dronning Maud Land, East Antarctica". Antarctic Science 3, nr 3 (wrzesień 1991): 317–21. http://dx.doi.org/10.1017/s0954102091000378.
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The geomagnetic field pattern in the vicinity of Georg Forster station, Antarctica, is discussed. Induced magnetization is assumed to model the regional minimum in the total field intensity (MAGSAT) located here, and an associated anomalous body at a depth of 50 km is calculated and interpreted. This model is, however, discounted in favour of a cross section derived from a meridional ground magnetic profile recorded over a distance of about 200 km. The most striking features of the profile are positive anomalies over the ice shelf which are explained by dykes of basic rocks emanating from the lower crust and from the mantle. The derived crustal structure reflects a transition from continental crust to transitional type crust.
3
Pro, Carmen, Bento Caldeira, Maria Teresa de Tena, Cristina Charro, Rui Jorge Oliveira, José Fernando Borges i Victorino Mayoral. "Exploring the Consistency of Data Collected in Archaeological Geophysics: A Case Study from the Iron Age Hillfort of Villasviejas del Tamuja (Extremadura, Spain)". Remote Sensing 12, nr 12 (20.06.2020): 1989. http://dx.doi.org/10.3390/rs12121989.
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Different geophysical methods applied at the settlement of Villasviejas del Tamuja (Botija, Spain) have identified robust anomalies located at the same position, but some anomalies are reflected by only one method. Furthermore, analysing the spatial correlation of these anomalies is of fundamental importance for obtaining a correct archaeological interpretation. In this work, we analysed the main results of electrical resistivity tomography (ERT), ground-penetrating radar (GPR) and magnetic gradiometry methods in a particular area of the archaeological site. In this analysis, we performed graphical and numerical spatial correlation analyses of the anomalies and observed strong agreement among the results provided by each method. Certain anomalies were reflected only in the magnetic and ERT studies. The results highlight the importance of applying several geophysical methods and performing spatial correlational analyses. Furthermore, the methodology that we have applied to evaluate the spatial correlation offers interesting results.
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Ndlovu., Thabisani, Mashingaidze R. T. i Mpofu P. "Analytic Signal and Euler Depth Interpretation of Magnetic Anomalies: Applicability to the Beatrice Greenstone Belt". Journal of Geography and Geology 7, nr 4 (2.12.2015): 108. http://dx.doi.org/10.5539/jgg.v7n4p108.
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We apply the Analytic Signal and Euler depth filtering techniques on magnetic data to identify a magnetic causative body location-depth relationship, two parameters of importance in both geophysical exploration and ore body modelling. We identify a dipping magnetic contact from the interpreted Euler depth anomalies, showing a good agreement with both the Total Field Magnetic (TFM) map and the Analytic Signal (AS) map. The Euler depth anomalies correlate well with the locations and edges of shallow causative bodies. The deeper Euler interpreted sources explain the magnetic high on the regional aeromagnetic map which is coincident with neither geological contacts nor the more recent dolerite intrusions. This suggests that the magnetic highs on the regional aeromagnetic map are due to deep seated sources, otherwise invisible on the regional geological map. The results show the usefulness and relevancy of these two filters not only in interpreting routine TFM data from the study area, but up to a regional scale. While the aeromagnetic data shows that the magnetisation pattern is predominantly divorced from the geological map, the ground magnetic data interpretation points to a more recent magnetisation of the belt, enabling conclusions to be drawn about the geological history and structural geology otherwise not evident on the geological map.
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Yang, Tao, Jintian Gao, Zuowen Gu, Baatarkhuu Dagva i Batsaikhan Tserenpil. "Petrophysical Properties (Density and Magnetization) of Rocks from the Suhbaatar-Ulaanbaatar-Dalandzadgad Geophysical Profile in Mongolia and Their Implications". Scientific World Journal 2013 (2013): 1–12. http://dx.doi.org/10.1155/2013/791918.
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Petrophysical properties of 585 rock samples from the Suhbaatar-Ulaanbaatar-Dalandzadgad geophysical profile in Mongolia are presented. Based on the rock classifications and tectonic units, petrophysical parameters (bulk density, magnetic susceptibility, intensity of natural remanent magnetization, and Köenigsberger ratio) of these rocks are summarized. Results indicate that (1) significant density contrast of different rocks would result in variable gravity anomalies along the profile; (2) magnetic susceptibility and natural remanent magnetization of all rocks are variable, covering 5-6 orders of magnitude, which would make a variable induced magnetization and further links to complex magnetic anomalies in ground surface; (3) the distribution of rocks with different lithologies controls the pattern of lithospheric magnetic anomaly along the profile. The petrophysical database thus provides not only one of the keys to understand the geological history and structure of the profile, but also essential information for analysis and interpretation of the geophysical (e.g., magnetic and gravity) survey data.
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Cholifah, Latifatul, Nurul Mufidah, Eden Lazuardi, Bagus Jaya Santosa, Sungkono Sungkono i Arif Haryono. "Identification of the Grindulu Fault in Pacitan, East Java using Magnetic Method". Jurnal Penelitian Fisika dan Aplikasinya (JPFA) 10, nr 1 (13.07.2020): 22. http://dx.doi.org/10.26740/jpfa.v10n1.p22-33.
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Magnetic method in geophysical surveys is common for its non-destructive use of sub-surface structure delineation. In this study, ground-based measurements of magnetic intensity were performed using a set of instruments in some regions of Pacitan, a city in the southern area of East Java province. Based on these measurements, data acquisition was used to identify the Grindulu faulting zone in the region of interest, potentially vulnerable to geohazards. The data were first corrected using the IGRF and diurnal corrections. A filtering technique of upward continuation at a height of 900 m was then applied to separate local anomalies from regional ones as the targeted sources in the present case. These separate anomalies and their corresponding reductions to the poles as further filtering processes were analyzed for predicting the location and direction of the fault. The results, extracted from data analysis and interpretation, show that the main path of the Grindulu is directed along the NE-SW fault line or N60oE. The resulting anomalies also reflect that the Grindulu is a normal fault with surrounding minor faults lying across the Grindulu, calling for increased awareness of vulnerability in the city to seismic threats.
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Batbaatar, Erdene, Munkhjargal Todbileg, Otgonbayar Sansar i Baatar Bataa. "The geophysical signature of Oyut deposits, Oyu Tolgoi, Mongolia". Mongolian Geoscientist 26, nr 52 (23.06.2021): 80–96. http://dx.doi.org/10.5564/mgs.v26i52.1323.
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The well-known Oyu Tolgoi Cu-Au group deposits can be divided into three main deposits: Hugo Dummett deposit (Hugo North and Hugo South), Oyut deposits (South Oyu, Southwest Oyu and Central Oyu), and Heruga deposit in the south. These deposits sit along 26 km long, north-northeast trending belt termed as the Oyu Tolgoi trend. This paper reviews investigations on geophysical signatures of the South Oyu, Southwest Oyu and Central Oyu deposits and compares geophysical models of the mineral deposits with their lithology, alteration, mineralization, and structures. A variety of datasets including induced polarization, ground magnetic, gravity survey are used in the study and generated inversion products of ground magnetic and gravity data with integrated interpretation. Typical responses from the Oyut deposits are: up to 0.1 mGal positive gravity anomaly above background, 100–200 nT low or high magnetic anomaly compared to background depending on the geological situations, and from 12 mV/V to 30 mV/V chargeability anomalies and low resistivity signatures from 100 ohm.m to 400 ohm.m. The interpreted geological-geophysical models of porphyry Cu-Au deposits presents in this study have emphasis on integrated interpretation of geophysical techniques, and inversions of gravity and magnetic data in gold rich porphyry copper system.
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Ezeh, C. C., O. S. Okanya, A. O. Usman i O. P. Odoh. "Evaluation of Aeromagnetic Data Over Some Parts of Lower Benue Trough, Nigeria Using Spectral Analysis". Journal La Multiapp 3, nr 1 (7.03.2022): 8–17. http://dx.doi.org/10.37899/journallamultiapp.v3i1.555.
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We obtained, processed, and interpreted spectral analyses of aeromagnetic data across a portion of the Lower Benue Trough with the goal of estimating the depth to magnetic basement, modeling a conspicuous magnetic anomaly, identifying the basement topography, and evaluating basin configurations. Qualitative interpretation based on visual examination of the total magnetic intensive anomalies map, residual contour map, and first vertical derivative map reveals major faults trending east-west (E-W) and minor faults trending northeast-southwest (NE-SW), which is consistent with the structure of the lower Benue Trough. The western portion of the research region indicates structural change near the towns of Afikpo and Ishiagu, indicating areas of documented intrusive igneous body activity. According to the quantitative interpretation of the aeromagmatic data, the average sedimentary thickness is between (2.3 and 3.2 kilometers) and Quantitative interpretation utilizing spectral analysis identifies two distinct depth sources in the region: shallower sources ranging from 1.09 to 1.6 kilometers in the southern portion of the research area, and deeper sources ranging from 1.61 to 4.90 kilometers in the northern section. Additionally, the research reveals that the depths to the centroid and magnetic bodies (sedimentary thicknesses) vary between 5.02 and 10.65 kilometers and 0.23 and 3.5 kilometers, respectively. It was recommended that a ground magnetic survey be used in conjunction with this work to provide a more conclusive result.
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Liang, Shengjun, Siyuan Sun i Hongfei Lu. "Application of Airborne Electromagnetics and Magnetics for Mineral Exploration in the Baishiquan–Hongliujing Area, Northwest China". Remote Sensing 13, nr 5 (27.02.2021): 903. http://dx.doi.org/10.3390/rs13050903.
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Airborne electromagnetics is an effective and efficient exploration tool in shallow mineral exploration for its high efficiency and low cost. In 2016, airborne electromagnetic and airborne magnetic surveys have been carried out at the border of Xinjiang Uygur Autonomous Region and Gansu Province, the Northwest China. With an integrated system, the airborne electromagnetics and airborne magnetic data were collected simultaneously by AreoTEM-IV system from Aeroquest International Limited in Vancouver, BC, Canada, and the CS3 Cesium Vapor magnetometer from Scintrex in Concord, ON, Canada. About 3149 line-km of both data with 250 m line space were acquired. After data processing, the comprehensive analysis and interpretation of resistivity and magnetic anomalies has been carried out to infer lithological structure and outline the potential ore deposits. Verified by the ground surveys, seven outlined anomalies are consistent with the known ore sites, and one new gold deposit and several mineralization clues were found. The prospective reserves of gold are expected to exceed 10 tons. Besides, some prospecting target areas were outlined as the possible locations of copper–nickel deposits. The successful case shows the airborne magnetic data accords with geological structures, and the airborne electromagnetic method is effective in finding metal mineral resources, which can help to quickly identify potential ore targets with no surface outcrop.
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Lee, Madeline, Yuleika Madriz, Richard Gloaguen i Suzanne McEnroe. "UAV magnetics over the Bjerkreim-Sokndal Intrusion, Rogaland, Norway: A first look". Leading Edge 42, nr 2 (luty 2023): 90–97. http://dx.doi.org/10.1190/tle42020090.1.
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The Bjerkreim-Sokndal layered intrusion in Rogaland Anorthosite Province in southwestern Norway has been the focus of decades of research due to its complex geology, the presence of prominent remanent magnetic anomalies, and current economic interest in critical minerals. In 2021, collaborative geophysical fieldwork was conducted by the Norwegian University of Science and Technology and Helmholtz Institute Freiberg for Resource Technology. Despite challenging environmental conditions, more than 100 line-km of magnetic data were collected by a custom multirotor unmanned aerial vehicle (UAV) along the eastern margin of the Bjerkreim lobe of the Bjerkreim-Sokndal Intrusion. Data collection was focused over two areas. The first is an area in the south near the prominent Heskestad magnetic anomaly that is associated with large reversed magnetic remanence in a magnetite-ilmenite-gabbronorite unit. The second is an area in the north near Lake Teksevatnet that hosts mineralized zones and the Lauvneset magnetic anomaly. Initial analysis of the UAV-acquired magnetic data shows additional details on the geologic contacts of key units, especially where in-situ measurements are difficult to collect. UAV surveys help in the construction of an anomaly's geometry through incremental source-sensor separations at various flight altitudes above ground. The UAV data set is an intermediate step between ground and airborne surveys for multiscale interpretation and potentially extreme magnetic scales (from microscopic to planetary).
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Martin, William A., James E. Bruseth i Robert J. Huggins. "Assessing Feature Function and Spatial Patterning of Artifacts with Geophysical Remote-Sensing Data". American Antiquity 56, nr 4 (październik 1991): 701–20. http://dx.doi.org/10.2307/281547.
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Magnetic surveys and electromagnetic conductivity surveys were conducted at several sites during the course of field work at the Richland/Chambers Reservoir in north-central Texas between 1982 and 1985. Much of this work was conducted at the Bird Point Island site (41FT201), which was used as a proving ground to test the effectiveness of various remote-sensing techniques. Two devices, a Geometrics proton precession magnetometer and a Geonics Limited EM-38 electromagnetic conductivity sensor were tested. The data produced by the EM-38, although initially successful for locating large archaeological features, were less useful for site interpretation than those yielded by the magnetometer.Replicative experiments were conducted to test hypotheses related to feature function and to identify the sources of magnetism present in features. After an experimental hearth and a pit were created on an off-site area, a magnetic survey was conducted and the results were compared with the magnetic responses obtained from archaeological features. Remarkably similar magnetic responses were observed between the experimental features and certain classes of prehistoric archaeological features. Five-cracked rock, consisting of small fragments of iron-enriched sandstone and ironstone, was identified as the primary source of magnetism.In addition to identifying locations of features, the magnetic data also provided information regarding whether or not features had been subjected to multiple episodes of disturbance and reuse. Episodes of recurrent use were indicated by irregular symmetry and unusual magnetic polarity. Several large pit features, which archaeological evidence indicated had been reused, exhibited anomalies with multiple peaks of strong magnetic highs surrounded in several directions by peaks of weak to moderate magnetic lows. In contrast, hearths and pits lacking archaeological evidence of major disturbance or reuse were associated with anomalies that exhibited the normal dipolar signature associated with cultural features—a strong magnetic high with a strong magnetic low immediately to the north. The results of this study demonstrate that the magnetometer has a great potential for aiding in the interpretation of archaeological features in addition to its traditional use as a tool for identifying feature locations.
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Poikonen, Ari, i Ilkka Suppala. "On modeling airborne very low‐frequency measurements". GEOPHYSICS 54, nr 12 (grudzień 1989): 1596–606. http://dx.doi.org/10.1190/1.1442627.
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Numerical models employed in ground VLF modeling use a normally incident (homogeneous) plane wave as a primary field. We show that these models are not directly applicable to modeling the impedance and wavetilt in the air, quantities needed in the interpretation of airborne VLF resistivity measurements. Instead, the primary field must be replaced by an inhomogeneous plane wave incident on the ground at an angle close to 90 degrees in order to provide the correct behavior of the apparent resistivities in the air. VLF magnetic polarization parameters, however, can be modeled in the air using the normally incident plane wave as a primary field. We also show that the plane‐wave analysis provides the same attenuation characteristics for the wavetilt in the air that is predicted by the Norton’s surface wave obtained by using the vertical electric dipole as a source. Use of the inhomogeneous plane wave introduces the vertical component of the electric field in the model. A 2‐D modeling technique based on the network solution is used to demonstrate the effects of the vertical electric field in the H‐polarization case. The vertical electric field generates charge distributions on the horizontal boundaries of conductors. In the case of a vertical sheet‐like conductor, these charges cause a slight asymmetry in apparent‐resistivity anomalies. Attenuation characteristics of various VLF anomalies with altitude are also presented. The H‐polarization anomalies attenuate much more rapidly in the air than those for E‐polarization due to the difference in the dominating source of EM fields in each polarization.
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Pozdnyakova, O. A., E. V. Balkov, P. G. Dyadkov, Z. V. Marchenko, A. E. Grishin i N. D. Evmenov. "Integrative Geophysical Studies at the Novaya Kurya-1 Cemetery in the Kulunda Steppe". Archaeology, Ethnology & Anthropology of Eurasia 49, nr 4 (4.01.2022): 69–79. http://dx.doi.org/10.17746/1563-0110.2021.49.4.069-079.
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We outline the results of prospection studies at the Novaya Kurya-1 cemetery in the south of Western Siberia, using remote sensing methods such as aerial photography, ground-based magnetometry, high-precision aeromagnetic survey, electromagnetic profi ling, and electrotomography. Original techniques were used to construct relative relief maps, and an inversion of data from ground-based magnetic survey at various altitudes was carried out. The fi rst technique reduces the effect of natural relief, and highlights anthropogenic altitudinal anomalies, making the analysis of digital elevation models more effi cient. The second technique is helpful for assessing the thickness and depth of anomalous magnetic bodies or horizons, not only providing planigraphic information but enabling us to evaluate two- and threedimensional geometric properties of the detected objects. As a result of the analyses, at least 14 kurgans were identifi ed at the cemetery, six of which lack salient outward features. Structural details suggest that most of them date to the Early Scythian time (800–400 BC). On the basis of the interpretation of the results of highly effi cient prospection analyses using the UAV platform, offering the possibility of surveying a large area (about 25 ha), the boundaries of the site were determined. Several features were detected. To identify these, further studies are needed.
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de Miranda, Fernando Pellon, Anne E. McCafferty i James V. Taranik. "Reconnaissance geologic mapping of a portion of the rain‐forest‐covered Guiana Shield, Northwestern Brazil, using SIR-B and digital aeromagnetic data". GEOPHYSICS 59, nr 5 (maj 1994): 733–43. http://dx.doi.org/10.1190/1.1443631.
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This paper documents the result of an integrated analysis of spaceborne radar (SIR-B) and digital aeromagnetic data carried out in the heavily forested Guiana Shield. The objective of the research is to interpret the geophysical data base to its limit to produce a reconnaissance geologic map as an aid to ground work planning in a worst‐case setting. Linear geomorphic features were identified based on the interpretation of the SIR-B image. Digital manipulation of aeromagnetic data allowed the development of a color‐shaded relief map of reduced‐to‐pole magnetic anomalies, a terrace‐magnetization map, and a map showing the location of maximum values of the horizontal component of the pseudogravity gradient (magnetization boundary lines). The resultant end product was a reconnaissance geologic map where broad terrane categories were delineated and geologic faults with both topographic and magnetic expression were defined. The availability of global spaceborne radar coverage in the 1990s and the large number of existing digital aeromagnetic surveys in northwestern Brazil indicate that this approach can be potentially useful for reconnaissance geologic mapping elsewhere in the Guiana Shield.
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Jackisch, Madriz, Zimmermann, Pirttijärvi, Saartenoja, Heincke, Salmirinne, Kujasalo, Andreani i Gloaguen. "DroneBorne Hyperspectral and Magnetic Data Integration: Otanmäki FeTiV Deposit in Finland". Remote Sensing 11, nr 18 (5.09.2019): 2084. http://dx.doi.org/10.3390/rs11182084.
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The technical evolution of unmanned aerial systems (UAS) for mineral exploration advances rapidly. Recent sensor developments and improved UAS performance open new fields for research and applications in geological and geophysical exploration among others. In this study, we introduce an integrated acquisition and processing strategy for droneborne multisensor surveys combining optical remote sensing and magnetic data. We deploy both fixedwing and multicopter UAS to characterize an outcrop of the Otanmäki FeTiV deposit in central Finland. The lithology consists mainly of gabbro intrusions hosting ore bodies of magnetiteilmenite. Large areas of the outcrop are covered by lichen and low vegetation. We use two droneborne multi and hyperspectral cameras operating in the visible to nearinfrared parts of the electromagnetic spectrum to identify dominant geological features and the extents of ore bodies via ironindicating proxy minerals. We apply band ratios and unsupervised and supervised image classifications on the spectral data, from which we can map surficial ironbearing zones. We use two setups with threeaxis fluxgate magnetometers deployed both by a fixedwing and a multicopter UAS to measure the magnetic field at various flight altitudes (15 m, 40 m, 65 m). The total magnetic intensity (TMI) computed from the individual components is used for further interpretation of ore distribution. We compare to traditional magnetic groundbased survey data to evaluate the UASbased results. The measured anomalies and spectral data are validated and assigned to the outcropping geology and ore mineralization by performing surface spectroscopy, portable Xray fluorescence (pXRF), magnetic susceptibility, and traditional geologic mapping. Locations of mineral zones and magnetic anomalies correlate with the established geologic map. The integrated survey strategy allowed a straightforward mapping of ore occurrences. We highlight the efficiency, spatial resolution, and reliability of UAS surveys. Acquisition time of magnetic UAS surveying surpassed ground surveying by a factor of 20 with a comparable resolution. The proposed workflow possibly facilitates surveying, particularly in areas with complicated terrain and of limited accessibility, but highlights the remaining challenges in UAS mapping.
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Spector, Allan, i Thomas L. Lawler. "Application of aeromagnetic data to mineral potential evaluation in Minnesota". GEOPHYSICS 60, nr 6 (listopad 1995): 1704–14. http://dx.doi.org/10.1190/1.1443903.
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Aeromagnetic, ground magnetic, and gravity data, together with all available drillhole data and physical property measurements, were used to map the Precambrian geology of an area in Minnesota that is virtually devoid of outcrop. The work was done for purposes of land use planning and to encourage minerals exploration and mostly consisted of the analysis of profiles of aeromagnetic data to map magnetic/lithologic contacts, to infer structure, and to determine thickness of overburden cover. Two greenstone belts were resolved. They comprise higher density rocks separated by nonmagnetic metasedimentary intervals. The belts are deformed into synclinal structures that, according to modeling, range from 1 km to as much as 5 km in depth. Lithologic predictions were confirmed in five out of six holes drilled on completion of the magnetic interpretation. In over 40% of the area, Precambrian rocks are apparently mantled by less than 50 m of overburden, and in 50% of the area there is between 50 and 100 m of overburden cover. In the remaining 10%, the magnetic basement is overlain by a thick blanket of nonmagnetic Precambrian sedimentary rocks, over 200 m thick. Basement depth determinations were subsequently tested at six holes. Depth determinations at all drill sites were found to lie within the 20% error expectation of the method of depth determination. Thirty‐seven sites were resolved from the aeromagnetic data as targets for basemetal sulfide (copper, zinc) as well as precious metal (gold) mineralization. Thirteen magnetic anomalies were identified as possible kimberlite pipes.
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Misiewicz, Krzysztof, Jamel Hajji i Tomasz Waliszewski. "Prospections non invasives sur le site de Mustis/Musti (El Krib) en Tunisie". Światowit 57 (17.12.2019): 207–22. http://dx.doi.org/10.5604/01.3001.0013.6817.
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The objective of the first step of the non-invasive survey carried out on the Mustis site described herein was to verify the possibility of locating archaeological remains and to detect the location of the supposed remains by geophysical measurements (magnetic and electric methods). Magnetic measurements were made with Geometrics G-858 Cesium magnetometer with two probes located on the same horizontal level at 0.5 m distance or on the same vertical level at 0.5 m and 0.75 m above the ground level. The instrument recorded the values of the total vector of the magnetic field strength and made it possible to calculate the pseudo-gradient of its components (horizontal or vertical). Electric measurements were made by means of axial dipole-dipole electrode configurations (parallel) with AB current electrodes with spacing of one metre and electrodes of potential MN (identical spacing) at equal distance D at 4 and 6 metres, which made it possible to record values of apparent resistivity of the subsoil, with the penetration depth of the current of c. 2.0 and 3.5 m, respectively, below the current ground level. At the time of the data interpretation, the suspected locations of the remains causing the anomalies were indicated by means of dashes of different colours and thicknesses (depending on the assumed depth of the structures). These indications, transferred on maps, can serve as a starting point for extensive analyses of the entire site and its surrounding area. The first non-invasive surveys carried out in Mustis have demonstrated the usefulness of magnetic and electric methods in mapping the preserved remains both inside and around the city. The obtained results enabled elaborating a strategy for the work to come. It is quite probable that the magnetic method will prove capable of indicating places where vestiges of constructions are preserved, while the electric method will determine the depth and conditions of deposition of localised structures.
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Shragge, Jeffrey, David Lumley, Nader Issa, Tom Hoskin, Alistair Paterson i Jeremy Green. "Surveying Batavia’s Graveyard: Geophysical controlled experiments and subsurface imaging of archaeological sites on an Indian Ocean coral island". GEOPHYSICS 82, nr 4 (1.07.2017): B147—B163. http://dx.doi.org/10.1190/geo2016-0531.1.
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We conducted geophysical surveys on Beacon Island in the Houtman Abrolhos archipelago offshore Western Australia, to investigate areas of archaeological interest related to the 1629 Batavia shipwreck, mutiny, and massacre. We used three complementary near-surface geophysical survey techniques (total magnetic intensity, electromagnetic induction mapping, and ground-penetrating radar) to identify anomalous target zones for archaeological excavation. Interpreting near-surface geophysical anomalies is often complex and nonunique, although it can be significantly improved by achieving a better understanding of site-specific factors including background conditions, natural variability, detectability limits, and the geophysical response to, and spatial resolution of, buried targets. These factors were not well-understood for Beacon Island nor indeed for the Australian coastal environment. We have evaluated the results of controlled experiments in which we bury known targets at representative depths and analyze the geophysical responses in terms of an ability to detect and resolve targets from natural background variability. The maximum depth of detectability of calibration targets on Beacon Island is limited to approximately 0.5 m due to significant variations in background physical properties between a thin ([Formula: see text]) and highly unconsolidated dry sand, shell, and coral layer of variable thickness overlying a sea-water-saturated sandy half-space. Our controlled measurements have implications for calibrating and quantifying the interpretation of geophysical anomalies in areas of archaeological interest, particularly in coastal and sandy-coral island environments. Our geophysical analyzes contributed to the discovery of archaeological materials and five historical burials associated with the 1629 Batavia shipwreck.
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Mohammad, Ashmeer, Anup K. Prasad, Kehe-u. Wetsah, Mohammad Azad, Vivek Aryan i Hesham El-Askary. "Titaniferous-Vanadiferous, Magnetite-Ilmenite Mineralization in a Mafic Suite within the Chhotanagpur Gneissic Complex, Bihar, India". Minerals 12, nr 7 (5.07.2022): 860. http://dx.doi.org/10.3390/min12070860.
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Titanium or vanadium metals or their alloys are important industrial metals/alloys. Because these resources are in short supply, the investigation of potential titaniferous-vanadiferous deposits needs special attention to bridge the supply-demand gap. The study integrates geological, geochemical, remote sensing, and geophysical data for assessing the potentiality of titaniferous-vanadiferous, magnetite-ilmenite mineralization in and around the Sudamakund and Paharpur areas, Gaya and Jehanabad districts, Bihar, India, and delineation of specific targets for detailed exploration. Field visits for large scale mapping on (1:12,500 scale) were used to conduct a reconnaissance survey for magnetite-ilmenite mineralization in parts of toposheet number 72G/04 in the Gaya and Jehanabad districts of Bihar, as well as the collection of bedrock samples (BRS), pit/trench samples (PTS), petrographic samples (PS), and petrochemical samples (PCS), followed by petrographic and ore microscopic study, and interpretation of chemical results. Signatures of oxidized iron-bearing sulphides (iron-oxides ratio) and other ferrous-iron-bearing minerals surrounded by altered rocks (clay bearing minerals) are visible in remote sensing images. The geological work was followed by ground geophysical gravity and magnetic surveys in selected blocks by the Geophysics Division, eastern region (ER) on a 1:12,500 scale. The magnetite ore is hard, compact, crystalline, and at some places, granular in nature. The analytical value of these magnetite ore bodies indicates average Fe content at 49.53% (range 25.85–60.78%), with a considerable amount of TiO2 (average 15.85%, range 1.47–26.77%), and V (average 144.79 ppm, range 30.00–256.00 ppm, from PTS). The trends of these magnetite ore deposits correspond to the major lineaments (NE-SW and NW-SE). The superimposition of gravity and magnetic contour maps with the geological map (1:12,500 scale) helps explain the observed geophysical anomalies, and the possible subsurface (horizontal and vertical) expansion of magnetite ore deposits in alluvium cover regions warrants further investigation.
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Arzate, Jorge, Pierre Lacan, Fernando Corbo-Camargo, Claudia Arango-Galván, Rafael Felix-Maldonado, Jesús Pacheco i Rodrigo León-Loya. "Crustal structure of the eastern Acambay Graben, central Mexico, from integrated geophysical data". Revista Mexicana de Ciencias Geológicas 35, nr 3 (22.11.2018): 228–39. http://dx.doi.org/10.22201/cgeo.20072902e.2018.3.864.
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The Acambay graben is a ∼70 km long E–W seismically active structure located within the Trans-Mexican Volcanic Belt (TMVB). Quaternary volcanism has contributed to shaping the graben morphology and reported hydrothermal activity suggests the existence of potential geothermal reservoirs. Our work aims at providing information about the unstudied subsurface structure of the graben using magnetotelluric (MT) soundings, as well as gravity and aeromagnetic data as preliminary work for near-future integrated 3D approach. We analyzed the distribution of magnetic anomalies and its relation to faulting using total field (TFM) aeromagnetic digital charts E14 and F14 (https://www.gob.mx/sgm) and through the analysis of the tilt derivative of TFM. The gravity and magnetic horizontal derivatives provided complementary results to constrain the location of the main fault and to contrast the response of the Pastores and Acambay-Tixmadejé faults. For the subsurface interpretation, we present the results of a 25 km magnetotelluric (MT) profile across the eastern tip of the Acambay graben, oriented approximately perpendicular to the azimuth of the main ∼E–W fault systems. The resulting resistivity model incorporates gravity and aeromagnetic coincident model profiles. Density and magnetic susceptibility models were constrained with field sample data, surface geology and with the resistivity structure obtained from the 2D inversion of the measured MT soundings. The dimensionality and electric strike of the 13 MT stations that compose the profile were analyzed for a period band of 0.01 to 100 s. The average electric azimuth obtained was 88.5°±10°, which was used to invert the rotated to the electric strike MT profile. The integrated geophysical model reveals important lithological contrasts at the northern and southern bounding faults of the graben. While the northern Acambay-Tixmadejé fault affects a resistive ground and is associated to a >20 mGal gravity anomaly, the southern Pastores fault corresponds to a contrasting conductive zone with relatively low gravity anomaly (∼5 mGal). In contrast, the magnetic anomaly shows the opposite behavior; at the Pastores fault the observed amplitude is of 400 nT while the amplitude across the Acambay-Tixmadejé fault is insignificant. The geophysical model shows that both the Acambay-Tixmadejé and Pastores faults have constant and opposite dipping angles of about 70°, defining a nearly symmetric graben structure. According to our results, the Acambay-Tixmadejé fault as well as the central graben fault system converge at a depth of ∼18 km that is consistent with the depth of the seismogenic crustal layer.
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Hernandez Pardo, Orlando. "Vichada meteorite impact effects from simulation of regional environmental consequences of a meteoroid impact on Earth". Earth Sciences Research Journal 22, nr 1 (1.01.2018): 7–12. http://dx.doi.org/10.15446/esrj.v22n1.65459.
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This study estimates the regional environmental consequences of the impactor extraterrestrial body that could produce the probable Vichada impact crater structure on the Vichada Plain, in Colombia, South America. This paper details the parameter assumptions upon which the estimation is made. It describes an approach to quantifying the principal impact processes that could have affected the landscape in the vicinity of the probable Vichada impact event in the past. The key parameters are impactor diameter, impactor density, impact velocity before atmospheric entry, impact angle, and the distance from the impact at which the environmental effects are to be calculated, and the target type of sedimentary rock or crystalline rock. These parameters were chosen with support from The Vichada Structure dimensions obtained from remote sensing data interpretation, regional geologic mapping and interpreted satellite data and ground-based gravity and magnetic anomalies. The calculations are based on compiled novel algorithms for estimating the thermal radiation emitted by the impact-generated vapor plume or fireball, and the intensity of seismic shaking. Model validation is performed by obtaining the approximates various dimensions of the Vichada impact crater and ejecta deposit, as well as estimating the severity of the air blasting both crater-forming and air burst impacts. We illustrate the utility of the calculations by examining the predicted environmental consequences in seven localities of the Colombian territory, through hypothetical impact scenarios occurring in Cumaribo and Puerto Carreño (Vichada), Puerto Inirida (Guainía), Puerto Gaitán and Villavicencio (Meta), Mitú (Vaupes) and Bogotá, D.C. It is concluded that the most wide-reaching environmental consequence is seismic shaking. Both ejecta deposit thickness and air-blast pressure decay much more rapidly with distance than with seismic ground motion. Close to the impact site, the most devastating effect is from thermal radiation; however, the curvature of the Earth implies that distant localities are shielded from direct thermal radiation because the fireball is below the horizon. These results would guide further detailed fieldwork hunting for direct impact crater evidence and interpret high-resolution geophysical studies and borehole that could be carried out in the probable Vichada impact crater area shortly.
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Sparlin, Mark A., i Richard D. Lewis. "Interpretation of the magnetic anomaly over the Omaha Oil Field, Gallatin County, Illinois". GEOPHYSICS 59, nr 7 (lipiec 1994): 1092–99. http://dx.doi.org/10.1190/1.1443665.
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A 40 nanoTesla (nT) magnetic anomaly identified in an aeromagnetic survey over southern Illinois contours as a localized magnetic high on the west flank of a regional magnetic low. This magnetic anomaly is generally coincident with the Omaha Oil Field in northwest Gallatin County, Illinois. It was initially assumed that cultural sources of steel associated with this oil field were the primary source of the magnetic feature; however, similar oil fields overflown by the survey do not exhibit magnetic anomalies in the data set. The Luther Rister et ux ♯1 well, drilled near the apex of the Omaha structural dome, encountered two zones of ultramafic intrusive rock containing 9.0 percent by volume magnetite. These intrusives were identified to be alnöites which are a class of mantle‐derived ultramafic rock that can be associated with the incipient stages of crustal rifting. A ground magnetic survey verified the presence of the anomaly, and provided detailed data for 3-D modeling of the source. Petrophysical evaluations, magnetic susceptibility measurements and thin section modal analysis were made on drill cuttings from the ultramafic intrusives encountered in the Luther Rister ♯1 well. These measurements were made to constrain the 3-D magnetic modeling by the petrophysical characteristics of the source. After removal of the regional magnetic field, the resulting 140 nT residual magnetic anomaly was successfully modeled using two ultramafic sills with an igneous feeder plug. The two igneous sills adequately account for the structural closure exhibited in the Omaha Oil Field and raise the interesting possibility of other hydrocarbon trapping structures generated by intrusives emplaced into the sedimentary section.
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Juusola, Liisa, Heikki Vanhamäki, Ari Viljanen i Maxim Smirnov. "Induced currents due to 3D ground conductivity play a major role in the interpretation of geomagnetic variations". Annales Geophysicae 38, nr 5 (15.09.2020): 983–98. http://dx.doi.org/10.5194/angeo-38-983-2020.
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Abstract. Geomagnetically induced currents (GICs) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents and the three-dimensional (3D) distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH∕dt) is closely related to the electric field via Faraday's law and provides a convenient proxy for the GIC risk. However, forecasting dH∕dt still remains a challenge. We use 25 years of 10 s data from the northern European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that, instead of the primary ionospheric currents, the measured dH∕dt is dominated by the signature from the secondary induced telluric currents at nearly all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to high-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the stations involved. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible (i.e., a dense observation network is available).
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Oliveira, Saulo Pomponet, Jeferson De Souza, Luis Gustavo De Castro i Francisco José Fonseca Ferreira. "Interpretation of magnetic anomaly profiles using a decomposition in Hilbert transform pairs". Brazilian Journal of Geophysics 40, nr 4 (23.12.2022). http://dx.doi.org/10.22564/brjg.v40i4.2185.
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ABSTRACT. We propose a simple transformation to aid the interpretation of magnetic anomalies generated by linear structures. The profile of such anomalies perpendicular to the strike can be decomposed into two signals, one symmetric and the other antisymmetric concerning the center of the source. The symmetric component serves as input data to various depth estimation techniques that often assume the anomaly is reduced to the pole. We use the fact that these components form a Hilbert transform pair to transform a skewed anomaly profile into a symmetric one. Unlike in previous works that rely on the decomposition into even and odd functions, the profile does not need to be shifted to the source's center of symmetry or limited to one isolated anomaly. Multiple effective magnetization directions presented by different dikes are modeled by a function representing the different local effective dip angles. We validate the method with synthetic data and ground magnetic survey data from a dike swarm at Ponta Grossa Arch, southern Brazil. We also illustrate the usefulness of reconstructed anomalies for depth estimation methods. The results also show that the method can handle interfering sources with distinct effective magnetization directions.
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Nielsen, Bo M., i Thorkild M. Rasmussen. "Geological correlation of magnetic susceptibility and profiles from Nordre Strømfjord, southern West Greenland". GEUS Bulletin, 3.12.2002, 48–56. http://dx.doi.org/10.34194/ggub.v191.5128.
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NOTE: This article/monograph was published in a former series of GEUS Bulletin. Please use the original series name when citing this article/monograph.
Nielsen, B. M., & Rasmussen, T. M. (1). Geological correlation of magnetic susceptibility and profiles from Nordre Strømfjord, southern West Greenland. Geology of Greenland Survey Bulletin, 191, 48-56. https://doi.org/10.34194/ggub.v191.5128
The Palaeoproterozoic Nagssugtoqidian orogen is dominated by reworked Archaean gneisses with minor Palaeoproterozoic intrusive and supracrustal rocks. The Nagssugtoqidian orogen (Fig. 1) was the focus of regional geological investigations by the Geological Survey of Denmark and Greenland (GEUS) in 2001 (van Gool et al. 2002, this volume). In conjunction with this project, geophysical studies in the inner part of Nordre Strømfjord, Kuup Akua and Ussuit were undertaken as part of the Survey’s mineral resource assessment programme in central West Greenland. The studies include geophysical modelling of airborne magnetic data, follow-up studies of aeromagnetic anomalies by magnetic ground surveying, and geostatistical treatment and integration of different geological, geophysical and geochemical data. The aim is to obtain an interpretation of the region in terms of both regional geological features and modelling of local features of relevance for the mineral resource assessment. This paper presents an account of the field work and some of the new data.
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Iqbal, Ibrar, Bin Xiong, Gang Tian, Amjad Ali, Sanxi Peng, Gao Wen, Xingfu Huang, Aqsa Anees, Umar Ashraf i Amr Abd El-Raouf. "Analysis of 2D and 3D GPR data interpretation using continuous wavelet transforms: Case study from an archaeological test site". Frontiers in Earth Science 10 (30.09.2022). http://dx.doi.org/10.3389/feart.2022.1008757.
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Ground-penetrating radar (GPR) is one of the most important techniques for obtaining high-resolution data in archaeological research, and it is becoming increasingly important. The continuous wavelet transform (CWT), which is non-numerical technique, gives an overcomplete representation of a signal by continuously varying the wavelet’s translation and scale parameters in the time series dataset. This paper focuses on the novel technique of integrating CWT and the wavelet transform maxima (WTM) to extract information from an archaeological test site in south-eastern China. For the characterization of archaeological features, we assessed the importance of dense and accurate data collection as well as GPR signal processing. The mathematical formulation and applicability of GPR attributes, particularly amplitude-based attributes, to identify and characterize archaeological buried targets are also discussed. GPR data is acquired using co-polarized and cross-polarized configurations with transverse-electric (TE) and transverse-magnetic (TM) broadside frequency plates at 100 and 200 MHz. Next, CWT was applied using six different wavelet levels, followed by amplitude comparison. The archaeological targets were successfully interpreted using peak amplitude and CWT. The proposed methodology has significantly improved data visualization and interpretation of GPR data, and it also gave us good results in identifying archaeological anomalies.
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Cao, Xiaoyue, Xin Huang, Liangjun Yan, Fang Ben i Jianhua Li. "3D joint inversion of airborne ZTEM and ground MT data using the finite element method with unstructured tetrahedral grids". Frontiers in Earth Science 10 (11.01.2023). http://dx.doi.org/10.3389/feart.2022.998005.
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As an airborne electromagnetic method induced by natural sources, the Z-axis tipper electromagnetic (ZTEM) system can primarily recover near-surface shallow structures, due to band-limited frequencies (usually 30–720 Hz) of the airborne survey and high sample rate acquisition along the terrain. In contrast, traditional ground magnetotellurics (MT) allows better recovery of deep structures as the data acquired are typical of large site intervals (usually higher than 1 km) and lower frequencies (usually lower than 400 Hz). High-resolution MT surveys allow for shallow small and deep large anomalies to be adequately interpreted but need large site intervals and broadband frequency range, which are seldom used as they are quite costly and laborious. ZTEM data are tippers that relate local vertical to orthogonal horizontal fields, measured at a reference station on the ground. As the 1D structures produce zero vertical magnetic fields, ZTEM is not sensitive to background resistivity. Thus, in general, ZTEM can only reveal relative resistivities and not real resistivities. A combination of the ZTEM and MT methods can be an effective technique, alleviating the shortcomings of the individual methods. At present, complex underground structures and topography introduce difficulties for data inversion and interpretation, as conventional ZTEM and MT forward modeling are generally used on structured grids with limited accuracy. To effectively recover complex underground structures with topography, we developed a 3D framework for joint MT and ZTEM inversion with unstructured tetrahedral grids. The finite element method is used for the forward problem because of its flexibility with unstructured tetrahedral meshes. The limited-memory quasi-Newton algorithm (L-BFGS) for optimization is used to solve the joint inverse problem, which saves memory and computational time by avoiding the explicit calculation of the Hessian matrix. To validate our joint inversion algorithm, we run numerical experiments on two synthetic models. The first synthetic model uses two conductive anomalous bodies of different sizes and depths. At the same time, a simple quadrangular is used for comparing the inversions with and without topography. In contrast, the second synthetic model represents a realistic topography with two different conductivities and the same depth. Both single-domain and joint inversions of the ZTEM and MT data are carried out for the two synthetic models to demonstrate the complementary advantages of joint inversion, while the second model is also used to test the adaptability of the joint inversion to complex topography. The results demonstrate the effectiveness of the finite element method with unstructured tetrahedral grids and the L-BFGS method for joint MT and ZTEM inversion. In addition, the inversion results prove that joint MT and ZTEM inversion can recover deep structures from the MT data and small near-surface structures from the ZTEM data by alleviating the weaknesses of the individual methods.
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Ben, Ubong C., Stephen E. Ekwok, Ogiji-Idaga M. Achadu, Anthony E. Akpan, Ahmed M. Eldosouky, Kamal Abdelrahman i David Gómez-Ortiz. "A Novel Method for Estimating Model Parameters From Geophysical Anomalies of Structural Faults Using the Manta-Ray Foraging Optimization". Frontiers in Earth Science 10 (23.03.2022). http://dx.doi.org/10.3389/feart.2022.870299.
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The Manta-Ray Foraging Optimization has been adapted and implemented in computing model parameters from potential field anomalies originating from two-dimensional dipping faults. The inversion technique was originally demonstrated on magnetic anomalies from uncorrupted–then, corrupted synthetic datasets. Thereafter, it was experimented on profiles taken from mining fields in the United States, and Australia. The results obtained showed that the design procedure is admirably stable and flexible, especially when dealing with noisy data. It is also notably efficient in the quantitative resolution of geophysical inverse problems. The consistency in results obtained from analysis of deep-seated and shallow field examples, even when compared against background results, is also impressive. The new technique has also exhibited notable superiorities over other well-known and conventional techniques, especially on the grounds of convergence rate, cost, and quality of resolved anomaly parameters. Consequently, it is recommended for interpretation of other structures and modeling of other geophysical data like self-potential and resistivity data.