Dissertations / Theses on the topic 'Electromagnetic geophysics'
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Linde, Niklas. "Characterization of Hydrogeological Media Using Electromagnetic Geophysics." Doctoral thesis, Uppsala universitet, Geofysik, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5912.
Full textMallan, Robert Keays 1968. "Model studies of radio frequency electromagnetic geotomography." Thesis, The University of Arizona, 1996. http://hdl.handle.net/10150/278551.
Full textJohansson, Linnéa. "Modelling and interpretation of VTEM data from Soppero, Sweden." Thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-64879.
Full textShank, Jared Wyatt. "A geophysical investigation to locate missing graves utilizing ground penetrating radar, electromagnetic, and magnetic methods." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1389704983.
Full textTorikka, Niklas. "3D Modelling of TEM Data : from Rajapalot Gold-Cobalt prospect, northern Finland." Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75756.
Full textRajapalot guld-kobolt-projektet i norra Finland är en spännande, relativt ny upptäckt som fortfarande undersöks med hopp om att starta gruvbrytning i framtiden. Området upptäcktes via en IP/Resistivitets-undersökning under 2013. Omfattande geofysiska undersökningar har avgränsat flera elektromagnetiska anomalier, varav en, döpt Raja, är den anomali som den här masteruppsatsen är uppbyggd kring. En TEM-undersökning utfördes under slutet av augusti, början av september 2018. Insamlade data analyserades, bearbetades och modellerades senare i Maxwell med hjälp av Leroi, en insticksmodul från CSIRO. Tre separata modeller togs fram med respektive, en, två, och tre plattor. Resultatet jämfördes mot befintliga VTEM-, och resistivitetsmodeller.
Nassar, Elias M. "Numerical and experimental studies of electromagnetic scattering from sea ice/." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487948440826275.
Full textThunehed, Hans. "Two topics related to interpretation of transient electromagnetic measurements." Licentiate thesis, Luleå tekniska universitet, 1997. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26657.
Full textCassidy, Nigel John. "The application of mathematical modelling in the interpretation of near-surface archaeological ground-penetrating radar." Thesis, Keele University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.344057.
Full textDebroux, Patrick Serge 1957. "A numerical electromagnetic study of shallow geophysical targets." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/288769.
Full textBarongo, Justus Obiko. "Application of transient airborne electromagnetic and ground resistivity methods to geological mapping in tropical terrains." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75983.
Full textInversion of ground resistivity sounding data from the greenstone belt in western Kenya yields conductivities and thicknesses that are consistent with geology. A similar inversion of modelled time-domain airborne electromagnetic data shows that conductivity, thickness and depth to the top of the conductive weathered layer can be uniquely determined if its response does not suffer the thin sheet response problem. The results further show that this problem can be quite common in tropical regions since much of the weathered layer has low conductivity and thickness and, consequently, the response is weak. In this situation, conductivity and thickness are correlated and conductivity-thickness product is better determined than these two parameters independently.
By virtue of the weak time-domain AEM response of the weathered layer, much of the response remains buried in noise. This situation introduces further complications for an inverse problem that is highly non-linear. A method for reducing some of this noise before carrying out the inversion is presented.
Pearson, Patrick Ian 1964. "Application of electric and electromagnetic geophysical methods to detect fractures in unsaturated tuff." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278223.
Full textFortson, Samuel King. "Usability Engineering Applied to an Electromagnetic Modeling Tool." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/33665.
Full textMaster of Science
Bedrosian, Paul Andrew. "Electromagnetic imaging of active fault zones /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/9791.
Full textAnderson, Carl E., Moussa Bari, Robert W. Cook, Jennifer N. Hall, Daniel R. Hartley, Jonathon Jakucki, Jared W. Jordan, Jeffrey R. Kennedy, Ben K. Sternberg, and Timothy M. Wallace. "TRANSIENT ELECTROMAGNETIC (TEM) INVESTIGATIONS INTHE UPPER SAN PEDRO RIVER BASIN, BENSON, ARIZONA." LASI Laboratory for Advanced Surface Imaging, The University of Arizona (Tucson, AZ), 2007. http://hdl.handle.net/10150/624624.
Full textCallegary, James Briggs. "Spatial sensitivity of low-induction-number frequency-domain electromagnetic-induction instruments." Diss., The University of Arizona, 2005. http://hdl.handle.net/10150/282901.
Full textThomas, Scott James 1961. "Modeling and testing the LASI electromagnetic subsurface imaging systems." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/282186.
Full textGoedecke, Walter 1954. "Field studies and scale modeling using cross-borehole electromagnetic diffraction probing." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/278261.
Full textHarris, Jane C. "Pieces of a Puzzle: Fitting Electromagnetic Induction into Geophysical Strategies to Produce Enhanced Archaeological Characterisation." Thesis, University of Bradford, 2016. http://hdl.handle.net/10454/15743.
Full textCulbertson, Chris, William E. Lytle, Melissa M. McMillan, Ben K. Sternberg, and Kyle B. Withers. "TRANSIENT ELECTROMAGNETIC (TEM) INVESTIGATION OF MICROBASIN MORPHOLOGY ALONG THE SANTA CRUZ RIVER, NOGALES, ARIZONA." LASI Laboratory for Advanced Surface Imaging, The University of Arizona (Tucson, AZ), 2010. http://hdl.handle.net/10150/624627.
Full textBergman, Andrew William. "Searching for the Unmarked Henry Kinsey Family Graves at the VA Hospital Grounds in Dayton, Ohio, Using Magnetic, Electromagnetic, and Radar Methods." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1494956391476108.
Full textOskooi, Behrooz. "A Broad View on the Interpretation of Electromagnetic Data (VLF, RMT, MT, CSTMT)." Doctoral thesis, Uppsala University, Department of Earth Sciences, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4146.
Full textThe resolution power of single Very Low Frequency (VLF) data and multi-frequency Radiomagnetotelluric (RMT) data in delineating conductive structures typical for the sedimentary cover and crystalline basement in Scandinavia is studied with a view to future developments of the technique to increasing the frequency range into the LW radio band. Airborne and ground VLF data are interpreted and correlated with RMT measurements made on the ground to better understand the resolution power of VLF data. To aid in this understanding single and multifrequency VLF and RMT responses for some typical resistivity structures are analyzed. An analytic model is presented for obtaining unique transfer functions from measurements of the electromagnetic components on board an air-plane or on the ground. Examples of 2D inversion of ground and airborne VLF profiles in Sweden are shown to demonstrate the quantitative interpretation of VLF data in terms of both lateral and depth changes of the resistivity in the uppermost crust.
Geothermal resources are ideal targets for Electromagnetic (EM) methods since they produce strong variations in underground electrical resistivity. Modelling of Magnetotelluric (MT) data in SW Iceland indicates an alteration zone beneath the surface, where there are no obvious geothermal manifestations, in between Hengill and Brennisteinsfjoll geothermal systems. It suggests that a hydrothermal fluid circulation exists at depth. It also proves that the MT method, with its ability to map deep conductive features can play a valuable role in the reconnaissance of deep geothermal systems in active rift regimes such as in Iceland.
A damped nonlinear least-squares inversion approach is employed to invert Controlled Source Tensor MT (CSTMT) data for azimuthal anisotropy in a 1D layered earth. Impedance and tipper data are inverted jointly. The effects of near-surface inhomogeneities are parameterized in addition to each layer parameter(s). Application of the inversion algorithm to both synthetic and field data shows that the CSTMT method can be used to detect azimuthal anisotropy under realistic conditions with near surface lateral heterogeneities.
Parks, Eric M. "Analysis of Electromagnetic and Seismic Geophysical Methods for Investigating Shallow Sub-surface Hydrogeology." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2007.
Full textFernandes, Roland Anthony Savio. "The effects of cultural noise on controlled source electromagnetic resonses of subsurface fractures in resistive terrain." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2751.
Full textKoldan, Jelena. "Numerical solution of 3-D electromagnetic problems in exploration geophysics and its implementation on massively parallel computers." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/130833.
Full textBirken, Ralf Andreas. "Neural network interpretation of electromagnetic ellipticity data in a frequency range from 1 kHz to 32 MHz." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282407.
Full textCastillo, Reyes Octavio. "Edge-elements formulation of 3D CSEM in geophysics : a parallel approach." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461190.
Full textLos métodos electromagnéticos (EM) son una herramienta de investigación inestimable en geofísica, cuya relevancia ha aumentado rápidamente en los últimos años debido a su amplia adopción industrial. En particular, el modelado electromagnético de fuente controlada (3D CSEM FM) se ha convertido en una técnica importante para reducir las ambigüedades en la interpretación de datos geofísicos a través del mapeo de las variaciones de conductividad en el subsuelo. Como resultado, el 3D CSEM FM tiene aplicación en muchas áreas como la exploración de hidrocarburos/minerales, monitoreo de yacimientos, caracterización de almacenamiento de CO2, imágenes de yacimientos geotérmicos, entre otros, debido a que éstos muestran contrastes de conductividad con respecto a sus sedimentos circundantes. Sin embargo, el 3D CSEM FM a escala real implica un desafío numérico que requiere un esfuerzo computacional importante, a menudo demasiado exigente para arquitecturas multicore modestas, especialmente si éste forma parte de un proceso de inversión. Por otra parte, aunque el desarrollo aplicaciones HPC está dominado por lenguajes compilados, la popularidad de los lenguajes de alto nivel para cómputo científico ha aumentado considerablemente. Entre todos ellos, Python es probablemente el idioma que ha mostrado más interés, principalmente a su flexibilidad y sintaxis simple. Sin embargo, su uso para geocómputo con HPC sigue siendo limitado, lo que sugiere un camino para la investigación, el desarrollo y la mejora. Por lo tanto, esta tesis describe el diseño e implementación de una metodología que hasta ña fecha no se ha aplicado sistemáticamente para resolver el 3D CSEM FM con una aplicación HPC basada en Python. La contribución neta de este esfuerzo es el desarrollo y documentación de un nuevo código open-source para el modelado 3D CSEM FM en geofísica, es decir, Parallel Edge-based Tool for Geophysical Electromagnetic Modelling (PETGEM). La importancia del desarrollo de estas herramientas radica en el hecho de que proporcionan resultados sintéticos que pueden ser comparados con datos reales, lo cual tiene un uso práctico en la industria y el mundo académico. A pesar de ello, los códigos disponibles para 3D CSEM FM suelen estar escritos en lenguajes de bajo nivel, y en muchos casos sus métodos no son accesibles a la comunidad científica ya que son comerciales. PETGEM ha sido principalmente escrito en Python y se basa en paquetes mpi4py y petsc4py para cálculos paralelos. El código está diseñado para hacer frente a los principales desafíos que se encuentran en la simulación numérica del problema en cuestión: abordar problemas realistas con precisión, eficiencia y flexibilidad. Además, utiliza el Método de Elementos Finitos de Borde (EFEM) como técnica de discretización ya que sus bases son muy adecuadas para resolver las ecuaciones de Maxwell. Además, soporta mallas tetraédricas no estructuradas que permiten la representación de geometrías complejas y refinamiento local, impactando positivamente la precisión de la solución. A lo largo del documento se investiga la implementación paralela en arquitecturas de memoria compartida/distribuida. Además, la tesis revisa los desafíos numéricos y físicos del problema 3D CSEM FM. A través de este trabajo, las ecuaciones de Maxwell en el dominio de la frecuencia se han discretizado utilizando EFEM y validado contra soluciones analíticas y datos previamente publicados, lo que demuestra que los resultados del modelado son precisos. Por otra parte, este trabajo discute una estrategia de adaptación automática de malla y la tasa de convergencia de los solvers iterativos que se utilizan ampliamente en la literatura. En resumen, esta tesis muestra que es posible integrar Python y HPC para la solución de 3D CSEM FM a gran escala de una manera efectiva. La nueva herramienta de modelado es fácil de usar y los algoritmos adoptados no sólo son precisos y eficientes, sino también flexibles.
Dickins, David. "Controlled-source electromagnetic modeling of the masking effect of marine gas hydrate on a deeper hydrocarbon reservoir." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1932.
Full textTyler, Robert H. "Electromagnetic fields generated by ocean currents and the potential for using geomagnetic data in ocean and climate studies." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39884.
Full textFirst, general relativity theory is used to formally establish the proper set of electromagnetic equations to be used for observers in a rotating (accelerating) frame of reference observing a medium (the ocean, in this case) with relative velocity. Extra terms due to rotation are derived and described and a generalized Schiff's charge density is shown to be potentially significant for the application to ocean circulation.
We extend the theory of electromagnetic fields generated by ocean currents. Many analytical solutions are found for idealized ocean features including sheared flow, jets, and a Stommel gyre. Results indicate that the ocean-induced magnetic fields will typically have magnitudes of 10's-100's of nT within the ocean. Outside of the ocean, the magnitudes are smaller (typically 1-10 nT) but decay on scales set by the horizontal scale of the ocean feature.
We investigate the time-scales associated with the adjustment of electromagnetic fields generated by low-frequency ocean currents. We find that the time scales can be quite long, prohibiting a quasistatic assumption in the treatment of the electromagnetic fields generated by the important tidal, inertial, and diurnal-frequency ocean currents.
Three-dimensional explicit time-dependent and steady-state finite-difference numerical models are constructed to study the electromagnetic fields generated by more realistic ocean current and conductivity features.
The ocean currents generate electromagnetic forces on the fluid at the surface of the earth's core. If these forces lead to significant core motion, the effect of the oceans on the generation and variability of the earth's magnetic field may be nontrivial. We estimate the form and magnitude of these forces and make comparisons with observations. Despite many uncertainties, we find evidence to suggest the ocean forcing mechanism may be significant and conclude that this process should be further investigated in the context of a larger study.
This work indicates that it is likely that the geomagnetic record has captured oceanic signals. From a preliminary data analyses we find that aside from the oceanic tidal signals, the magnetic record shows other signals of possible oceanic origin including an apparent correlation between magnetic records from the equatorial Pacific and the Southern Oscillation Index. We discuss the prerequisites that are necessary to extract information about ocean circulation variability from the geomagnetic record.
Lu, Xinyou. "Inversion of controlled-source audio-frequency magnetotelluric data /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/6799.
Full textKing, Joshua David. "Using a 3D finite element forward modeling code to analyze resistive structures with controlled-source electromagnetics in a marine environment." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/1371.
Full textStalnaker, Jack Lee. "A finite element approach to the 3D CSEM modeling problem and applications to the study of the effect of target interaction andtopography." Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/2770.
Full textThunell, Rasmus. "Groundwater flow paths in fractured crystalline bedrock : Electromagnetic VLF measurements and modelling of a groundwater basin in Svanberga, Sweden." Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231983.
Full textTestbädd dricksvatten är ett pågående projekt och testanläggning där tester och utveckling av filter och småskaliga tekniker för rening av dricksvatten samt kvalitetscertifiering för effektivitets och hållbarhetstester kommer utföras. Testanläggningen består av ett nedlagt grundvattenverk med tre tillhörande bergborrade brunnar i Svanberga utanför Norrtälje. Grundvattensystemet och flödesvägar för grundvattnet i området är relativt okända och bättre förståelse av hydrogeologin skulle kunna bidra till framtida arbete med att identifiera och bedöma risker för föroreningstransporter i området samt till grundvattenverkets brunnar. Detta examensarbete har genom beprövade metoder i form av sprick-kartering, geofysiska undersökningar (VLF) och grundvattenmodellering med COMSOL Multiphysics identifierat flera möjliga flödesvägar i berggrunden kopplade till grundvattenverket. Resultatet från studien visar att ett antal sprickzoner i öst-västlig riktning utgör en större risk för föroreningstransport av ämnen från trafik och jordbruk samt att en större del av det vatten som tillförs grundvattensystemet troligen har sitt ursprung från tjockare morän-lager i de norra delarna av området. Provpumpningar och verifiering av de identifierade sprick-zonerna genom spårämnestester och geofysiska undersökningar bör utföras för att stärka resultaten från detta arbete och möjligen utöka kunskapen om hydrogeologin i området kring Svanberga gamla grundvattenverk.
Wilson, Glenn Andrew, and glenn wilson@griffith edu au. "Plane Wave Propagation Problems in Electrically Anisotropic and Inhomogeneous Media with Geophysical Applications." Griffith University. School of Microelectronic Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20030325.210206.
Full textWilson, Glenn Andrew. "Plane Wave Propagation Problems in Electrically Anisotropic and Inhomogeneous Media with Geophysical Applications." Thesis, Griffith University, 2003. http://hdl.handle.net/10072/365776.
Full textThesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Microelectronic Engineering
Full Text
Carsillo, Vincent John. "MONITORING STORMWATER INFILTRATION IN A VACANT LOT COMPARING TIME-LAPSE ELECTROMAGNETIC INDUCTION AND ELECTRICAL RESISTIVITY TOMOGRAPHY." Master's thesis, Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/518905.
Full textM.S.
Vacant lots in cities and surrounding urban areas can potentially be used for stormwater management because they are pervious. However, the extent to which vacant lots provide pervious cover to increase infiltration and reduce stormflow is poorly understood. The goal of this study was to develop faster methods for monitoring stormwater infiltration to improve characterization of heterogeneous urban systems. Geophysical techniques are capable of mapping and characterizing subsurface materials, but are often limited by time and sensitivity constraints. In this study, the infiltration characteristics of a vacant lot created by the demolition of a house was characterized using a series of modeling, field and lab experiments. Site characterization under background conditions with an EM Profiler was used to map zones of different fill materials. Three zones were identified in the study site: grass area, driveway area, and a former house area. Transient soil moisture conditions were monitored during irrigation tests using two geophysical methods (electrical resistivity tomography [ERT] and electromagnetic induction [EM]) to evaluate method sensitivity and differences between the three zones. ERT proved more sensitive than EM profiling at detecting changes in the three zones. Soil moisture changes in the driveway area were particularly difficult to detect using EM. The EM Profiler showed a reduction rather than increase in conductivity at the start of irrigation and storms, which was attributed to flushing of high conductivity pore fluids by dilute irrigation or rain water. This explanation was supported using Archie’s Law to model the response of apparent conductivity under highly conductive pore fluid conditions. The EM Profiler was also used under natural precipitation conditions to quickly monitor areas too large for the ERT to reasonably survey. The results suggested that EM instrument drift needs to be corrected to make the method more sensitive. It was difficult to detect differences in hydrologic characterization between areas of the vacant lot using traditional soil point measurements because of the inherent spatial variability. The most useful point measurement was soil moisture loggers. Data from soil moisture loggers was used to parameterize the model; in addition, the soil moisture loggers showed a slow drying period. By combining the EM Profiler method with soil moisture data and applying corrections for drift, some improvement in sensitivity might be achieved. Quantitative characterization of fill material was shown by ERT, which detected more heterogeneous infiltration in the area of the former house than in the grass area.
Temple University--Theses
McGarr, Jeffery T. "Geophysical Imaging of Hyporheic Mixing Dynamics Within Compound Bar Deposits." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1617109253147661.
Full textBarrett, Brian Edward. "Water-borne geophysics for Murray River salt-load detection." Title page, contents and abstract only, 2003. http://web4.library.adelaide.edu.au/theses/09SM/09smb2741.pdf.
Full textKruske, Montana L., and Dr Eileen G. Ernenwein. "Paleochannel or Palisade? Preliminary Geophysical Investigations of a Linear Feature at the Runion Archaeological Site, Washington County, Tennessee." Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/asrf/2019/schedule/74.
Full textGaliana, Blanch Savitri. "Two-dimensional modeling and inversion of the controlled-source electromagnetic and magnetotelluric methods using finite elements and full-space PDE-constrained optimization strategies." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400616.
Full text[cat] El mètode de font electromagnètica controlada (CSEM) i el mètode magnetotel.lúric (MT) són tècniques geofísiques usades habitualment per obtenir una imatge de les propietats elèctriques del subsòl terrestre i s'utilitzen independentment, conjuntament i en combinació amb altres tècniques geofísiques. Per poder interpretar les dades, ambdós mètodes necessiten la modelització directa i inversa de la conductivitat elèctrica del subsòl amb l'objectiu final d'obtenir un model coherent per al qual les dades simulades s'ajustin de forma raonable a les observacions. Naturalment, la qualitat d'aquest ajust no només depèn de l'error en les dades mesurades i de l'error numèric, sinó també del grau en l'aproximació física inferit per la modelització numèrica. D'aquesta manera, les recerques actuals se centren a investigar noves metodologies per a la modelització i inversió, per tal d'obtenir models acurats i fiables de les estructures de la Terra en escenaris cada cop més complexos. Un primer pas és millorar les aproximacions en la modelització tenint en compte factors físics com ara l'anisotropia, la topografia o fonts més realistes. En segon lloc, per tal d'acomodar aquests factors en un programa de modelització i inversió i per poder tractar els conjunts de dades típicament llargs, els mètodes numèrics han de ser avaluats en termes de la precisió de la solució, l'eficiència en temps i la demanda en memòria. Els mètodes de modelització en elements finits (FE) són coneguts per oferir una major flexibilitat en la modelització de la geometria i contenen mecanismes de control de la solució, com ara l'ordre de les funcions forma i la tècnica de refinament adaptatiu de la malla. La majoria de programes de modelització emergents estan basats en els FE, i mostren avantatges significatius, però gairebé tots els programes de modelització inversa, encara avui dia, estan basats en el mètode de les diferències finites (FD) o en el mètode de l'equació integral (IE). A més a més, la modelització inversa desenvolupada per a dades electromagnètiques (EM) es basa generalment en mètodes del gradient i es formula en un espai reduït, on les úniques variables d'optimització són els paràmetres del model, és a dir, la conductivitat elèctrica del subsòl. Originalment, el problema invers es formula per als camps EM i per al paràmetre conductivitat, i està constret per les equacions diferencials en derivades parcials (PDEs) que governen les variables camps EM. L'estratègia d'espai reduït elimina les variables camps aplicant lligams d'igualtat i soluciona, doncs, el problema no constret en l'espai reduït dels paràmetres del model. Un desavantatge general d'aquests mètodes és la costosa repetició del càlcul de la solució del problema directe i de la matriu jacobiana de sensibilitats (per mètodes basats en Newton). D'altra banda, també és possible de solucionar el problema invers en l'espai complet de les variables camps EM i del paràmetre conductivitat. Solucionar-hi el problema d'optimització constret per les PDEs té l'avantatge que només és necessari de solucionar exactament el problema directe al final del procés d'optimització, però això comporta el cost addicional de tenir moltes més variables d'optimització i de la presència de lligams d'igualtat. També, en particular, en el marc dels FE, el problema d'optimització constret per les PDEs té l'avantatge afegit d'incloure tècniques sofisticades pròpies dels FE en el procés d'inversió, com ara el refinament adaptatiu de la malla. Aquesta tesi desenvolupa un programa robust i versàtil amb FE i malles irregulars adaptatives per modelar numèricament el camp total de dades CSEM i MT bidimensionals (2D) i anisòtropes, que permet l'ús de fonts tridimensionals (3D) orientades arbitràriament. Per tal de representar fonts CSEM 3D en un model físic 2D, s'utilitza una aproximació dos i mig dimensional (2.5D). Les formulacions FE es deriven per a ambdós mètodes, per a estructures de conductivitat del subsòl isòtropes i anisòtropes. Encara que el cas anisòtrop no és general, inclou anisotropia vertical i de cabussament. La precisió en la solució es controla i millora amb un algoritme de refinament adaptatiu de la malla utilitzant mètodes d'estimació de l'error a posteriori. Una sèrie exhaustiva d'experiments numèrics valida el programa de FE adaptatius per ambdós mètodes, CSEM i MT, i en escenaris terrestres i marins. S'estudia la influència de les dimensions del model, del disseny de la malla i de l'ordre de les funcions forma en l'exactitud de la solució i es troba un comportament notablement superior de les funcions forma quadràtiques comparades amb les lineals o cúbiques. Diferents exemples mostren l'efecte d'escenaris complexos sobre les dades EM, en particular, un model amb batimetria, un model terrestre i un de marí amb fonts orientades i de dimensió finita, un medi amb anisotropia vertical amb un reservori encastat i un altre amb un reservori encastat en una estructura anticlinal. Aquests exemples demostren la importància de considerar adequadament (en termes de modelització directa) característiques físiques com la topografia, l'orientació i geometria de la font i l'anisotropia del medi, que sovint es troben en mesures reals. Juntament amb això, es deriva una formulació per al problema invers 2.5D CSEM com una optimització constreta per les PDEs en l'espai complet i en un marc de FE, seguint dues estratègies diferents: discretització-optimització i optimització-discretització. L'estratègia de discretització-optimització considera que el problema invers es troba en forma discretitzada i deriva les condicions d'optimitat de la Lagrangiana i el pas de Newton. Contràriament, l'aproximació optimització-discretització deriva primer les condicions d'optimitat i el pas de Newton o una aproximació d'aquest, i després discretitza les equacions resultants. La implementació de la formulació discretització-optimització es mostra en dos exemples, un model canònic de reservori i un model marí més realista amb topografia, utilitzant un programa d'optimització de propòsit general, que és una implementació d'un algoritme de programació quadràtica seqüencial (SQP). Encara que no s'utilitza una regularització explícita, l'ús de diferents malles per al paràmetre del model i per a les variables camps, permet recuperar les principals estructures del model i obtenir un ajust de les dades acceptable. Cal dir, però, que l'eficiència en temps i memòria del programa hauria de millorar-se. Finalment, el problema invers 2.5D CSEM es formula com un problema d'optimització constret per les PDEs en l'espai complet i en un marc de FE utilitzant una estratègia d'optimització-discretització i com un primer pas per al desenvolupament d'un esquema d'inversió que utilitzi malles adaptatives de FE.
Kalscheuer, Thomas. "Improvement and Assessment of Two-Dimensional Resistivity Models Derived from Radiomagnetotelluric and Direct-Current Resistivity Data." Doctoral thesis, Uppsala universitet, Geofysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9366.
Full textBörner, Jana H. "Electrical phenomena during CO2–rock interaction under reservoir conditions : experimental investigations and their implications for electromagnetic monitoring applications." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-206674.
Full textShan, Chunling. "Natural and Controlled Source Magnetotelluric Data Processing and Modeling." Doctoral thesis, Uppsala universitet, Geofysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-229917.
Full textDowns, Christine Marie. "Imaging Wetland Hydrogeophysics: Applications of Critical Zone Hydrogeophysics to Better Understand Hydrogeologic Conditions in Coastal and Inland Wetlands and Waters." Scholar Commons, 2017. https://scholarcommons.usf.edu/etd/7397.
Full textDevi, Maureen. "Etudes expérimentales et numériques de la propagation d'ondes couplées sismiques et électromagnétiques dans des matériaux saturés non consolidés." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAU022/document.
Full textThe first few hundred meters of the subsurface is the seat of important issues related to fluids which society still has to face, such as the detection and monitoring of water ressources and pollution as well as the role of fluids in various types of hazard assessment or in geotechnics. This depth scale is highly complex and heterogeneous in terms of lithology and fluid content. Among the available geophysical methods, seismo-electric (or electro-seismic) coupling phenomena have the potential to emerge as a new high-resolution imaging technique, naturally sensitive to fluid contrasts. Two seismo-electric signals have been predicted and sometimes observed: co-seismic electric signals (high amplitude) and weak electromagnetic (EM) disturbances generated at depth when seismic waves cross an interface. This second phenomenon is the most promising in terms of imaging due to its sensitivity to original contrasts compared to seismic reflection. The emergence of the seismo-electric method was however slowed down due to difficulties in recording these weak seismo-electric signals. Based on the combination of experimental and numerical approaches, this PhD thesis aims at addressing practical questions concerning the acquisition and processing of seismo-electric and electro-seismic data.In the first part, in order to increase the signal-to-noise (S/N) ratio of seismo-electric signals, we theoretically and experimentally study their sensitivity to various electrode arrangements. For this, we developed a filter theory designed to assess the influence of complex electrode arrays for seismo-electric signals acquisition. This theory was successfully confronted to experimental seismo-electric data acquired using various electrode arrangements (namely the spacing between the electrodes, the number of the electrodes and the apparent seismic velocity) and to full waveform numerical simulations. This combined analysis shows that electrode configuration properties strongly influence seismo-electric amplitudes and waveforms. In particular, this approach explains the difficulty in recording depth-generated seismo-electromagnetic waves converted at an interface, when the conventional dipole configuration is used as receivers. We then promote the use of a 3-electrode configuration in seismo-electric measurements, since: 1) it reduces ubiquitous man-made electric noise, and 2) its filtering properties do amplify the EM waves originating from interfaces at depth with respect to dominant coseismic events.In the second part, we focus on the reciprocal electro-osmotic phenomena, i.e. the generation of seismic signals by an electric source in poroelastic saturated media. We first performed numerical investigations to assess the nature and properties of the different seismic arrivals generated by an electrical source in a homogeneous and an heterogeneous material, at the field scale. Then we tried to acquire electro-seismic laboratory data in a homogeneous material, data that we again confronted with numerical full waveform computations. The results show that electro-seismic waves can be observed and that they are locally generated around the electric source. We finally show that these electro-seismic signals are influenced by the fluid conductivity
Caudillo, Mata Luz Angélica. "Multiscale and upscaling methods for geophysical electromagnetic forward modeling." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63343.
Full textScience, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
Maris, Virginia. "Electromagnetic geophysical surveys of geo-environmental targets in southern Manitoba." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq54231.pdf.
Full textNghiem, Son V. (Son Van). "Electromagnetic wave models for polarimetric remote sensing of geophysical media." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13879.
Full textVita.
Includes bibliographical references (p. 239-245).
by Son V. Nghiem.
Ph.D.
Dickey, Kira Ann. "Geophysical Investigation of the Yellowstone Hydrothermal System." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/84922.
Full textMaster of Science
Knaak, Allison. "3D synthetic aperture for controlled-source electromagnetics." Thesis, Colorado School of Mines, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3682006.
Full textLocating hydrocarbon reservoirs has become more challenging with smaller, deeper or shallower targets in complicated environments. Controlled-source electromagnetics (CSEM), is a geophysical electromagnetic method used to detect and derisk hydrocarbon reservoirs in marine settings, but it is limited by the size of the target, low-spatial resolution, and depth of the reservoir. To reduce the impact of complicated settings and improve the detecting capabilities of CSEM, I apply synthetic aperture to CSEM responses, which virtually increases the length and width of the CSEM source by combining the responses from multiple individual sources. Applying a weight to each source steers or focuses the synthetic aperture source array in the inline and crossline directions. To evaluate the benefits of a 2D source distribution, I test steered synthetic aperture on 3D diffusive fields and view the changes with a new visualization technique. Then I apply 2D steered synthetic aperture to 3D noisy synthetic CSEM fields, which increases the detectability of the reservoir significantly. With more general weighting, I develop an optimization method to find the optimal weights for synthetic aperture arrays that adapts to the information in the CSEM data. The application of optimally weighted synthetic aperture to noisy, simulated electromagnetic fields reduces the presence of noise, increases detectability, and better defines the lateral extent of the target. I then modify the optimization method to include a term that minimizes the variance of random, independent noise. With the application of the modified optimization method, the weighted synthetic aperture responses amplifies the anomaly from the reservoir, lowers the noise floor, and reduces noise streaks in noisy CSEM responses from sources offset kilometers from the receivers. Even with changes to the location of the reservoir and perturbations to the physical properties, synthetic aperture is still able to highlight targets correctly, which allows use of the method in locations where the subsurface models are built from only estimates. In addition to the technical work in this thesis, I explore the interface between science, government, and society by examining the controversy over hydraulic fracturing and by suggesting a process to aid the debate and possibly other future controversies.
Yang, Dikun. "Geophysical survey decomposition and efficient 3D inversion of time-domain electromagnetic data." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50471.
Full textScience, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate