Dissertations / Theses on the topic 'Imagerie par étude sismique'
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Cotton, Fabrice. "Imagerie de la source sismique par inversion des mouvements forts et étude des variations de contraintes associées aux séismes." Phd thesis, Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10218.
Full textLehujeur, Maximilien. "Étude d'un réservoir géothermique profond par corrélation de bruit sismique ambiant." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAH013/document.
Full textThis work focuses on the application of the ambient seismic noise correlation technique for the imaging and monitoring of deep geothermal reservoirs near Rittershoffen (ECOGI) and Soultz-sous-Forêts (GEIE-EMC). The strong spatial and temporal variability of the noise sources in the period range 0.2-7s limits the reconstruction of the Green’s functions. This results in significant errors in the velocity models. Two approaches are proposed to overcome the spatial non-uniformity of the noise and to improve the quality of the velocity models. Besides that, the temporal variability of the noise sources is a limiting factor for monitoring purposes. We estimate that the speed variations should be larger than 0.1% to 1% to be detected by the available networks. This threshold was not reached at Rittershoffen during the drillings or the stimulations. However, a probable change of the diffracting properties of the medium was observed following a hydraulic stimulation
Vernet, Kinson. "Imagerie densitométrique 3D des volcans par muographie." Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2022. http://www.theses.fr/2022UCFAC112.
Full textMuography is an imaging technique in particle physics where atmospheric muons passing through a target are used to determine information about the interior of the target : density distribution or chemical composition via the atomic number. Depending on the energy of the muons and the amount of matter they have to cross, some of them will survive and others will be stopped by the target. And, the diffusion of the muons depends, to a first approximation, on their momentum and the average atomic number along their flight path. Muography proposes, from the measurement of the transmission and/or diffusion of muons through a target, to provide information about its interior.There are currently two types of muography : transmission muography, where the transmitted flux of muons through the target is measured to infer the density distribution of that target, and diffusion muography, where the diffusion of muons through the target is used to determine the distribution of the atomic number of the target. This thesis discusses transmission muography in order to radiography volcanoes.In the case of transmission muography, a muon telescope is used to measure the transmitted flux of atmospheric muons through the target. This flux is, to a first approximation, a bijective function of the amount of matter encountered by the muons. The idea is to invert the measured number of muons into a density estimation of the target.There are other imaging methods in geophysics that can be used to reconstruct the density of a target. This is the case, for example, of gravimetry and seismic imaging. These so-called conventional methods have weaknesses. For these methods, the inversion problem is either ill-posed, i.e. there is no unique solution, or the solution presents large variations for small variations of the parameters on which it depends. A set of additional constraints are then added to remove the non-uniqueness.In muography however, the inversion problem is well posed and the solution is unique. Conventional geophysical methods alone cannot determine the density of a target. Combined with muography, they have great potential, either by providing other information on the rock and/or on the nature of the water, or by improving the accuracy of the target density reconstruction.Several experiments use the CSDA (Continuous Slowing Down Approximation) approximation to estimate the survival probability of muons through a target. Using this approximation, thus neglecting the stochastic character of the interaction of muons with matter, underestimates the muon survival probability and therefore induces systematic effects on the density reconstruction. In standard rock kilometers the effect is 3% - 8% depending on the modeling of the interaction of high energy muons with matter. In addition, a bad estimation of the background of the low momentum muons affecting the measurement of the signal results in an underestimation of the density of the target with respect to the gravimetry. This probably comes from the use of the analytical approximation to simulate the propagation of the muons through the target and the difficulty of rejecting in the measurement those with low momentum. For these reasons, in the Muon IMaging (MIM) experiment (where this thesis was conducted), we use a Monte Carlo treatment to simulate the muon transport through the target. In this case, we can accurately estimate the effet of these low momentum muons on the density reconstruction. One of the techniques used in our experiment, to make the low momentum muons scatter so that they can be statistically rejected, is to insert a thickness of lead between the telescope detection planes. (...)
Nguyen, Sylvain Laurent. "Imagerie par sismique réflexion : utilisations de la pente des données dans la migration de profondeur." Paris, ENMP, 2003. http://www.theses.fr/2003ENMP1177.
Full textSeismic reflection methods are based on the surface records of the seismic waves reflected on the discontinuities in the studied media. The seismic depth processing has two parts: the estimation of the velocities of the waves propagation, and then the depth migration repositions the reflectors. The velocity model is crucial for the quality of the migrated image. The tomography evaluates it using traveltimes picked in the seismic data. An extension of the tomography has been proposed for improving this picking: slope tomography which takes into account the local slope of the recorded reflection events without going along the entire reflectors in the data. Two technics of slope tomography been developped at the Ecole des Mines de Paris: Stereotomography and MVA (Migration Velocity Analysis). The first one has one picking process in the data, before an iterative optimization of the velocities. The MVA works with slopes obtained in the migrated domain, where the picking process is easier (better signal to noise ratio). But in this case, the picking occurs at each iteration. My purpose was to provide a technic of depth picking for the Stereotomography. I firstly studied the aliasing of the migration, which may imply some wrong picked events if it is not filtered. Moreover, I demonstrate that the slopes in the anti-aliasing filters lead to a more accurate focusing. Secondly, this work presents a quantitative method providing a tomographic picking data set in the migrated domain. Thus, I demonstrate a method based on a migration of attributes, whatever the velocity model is, which provides the locally coherent events for Stereotomography. Two real data applications
Hoxha, Fatmir. "Fonctions de Green et migration de Kirchhoff par imagerie optique." Pau, 1994. http://www.theses.fr/1994PAUU3020.
Full textVoutay, Olivier. "Mise au point d'attributs sismiques pour l'interprétation AVO et 4D des réservoirs pétroliers par analyse en composantes généralisée." Vandoeuvre-les-Nancy, INPL, 2003. http://www.theses.fr/2003INPL009N.
Full textGailler, Audrey. "Structure de la marge d'Équateur-Colombie par modélisation des données de sismique grand angle marines : influence sur le fonctionnement de la subduction et la sismicité." Nice, 2005. http://www.theses.fr/2005NICE4098.
Full textChalard, Emanuel. "Estimation de macro-modèles de vitesse en sismique réflexion par stéréotomographie 3D." Paris, ENMP, 2002. http://www.theses.fr/2002ENMP1094.
Full textAboville, Olivier d'. "Étude et mise en oeuvre d'un parallélisme multitache en sismique numérique." Toulouse, INPT, 1987. http://www.theses.fr/1987INPT112H.
Full textMoreaux, David. "Localisation de cavités souterraines par réflexion sismique haute résolution : étude numérique, étude de terrain." Lille 1, 1997. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1997/50376-1997-35.pdf.
Full textXu, Sheng. "Migration / inversion en milieu complexe par des méthodes asymptotiques haute fréquence." Paris, ENMP, 2001. http://www.theses.fr/2001ENMP0987.
Full textChami, Khazraji Soumia. "Étude de la zone Haltenbanken par la méthode de stratigraphie sismique." Paris 6, 1986. http://www.theses.fr/1986PA066456.
Full textJARDIN, ANNE. "Etude des sous-sols a structure complexe par interpretation sismique integree." Paris 6, 1993. http://www.theses.fr/1993PA066389.
Full textAsnaashari, Amir. "Imagerie sismique 4D quantitative en milieux complexes par l'inversion 2D de forme d'onde complète." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00932597.
Full textPop, Sorin. "Modèles de fusion et diffusion par équations aux dérivées partielles : application à la sismique azimutale." Thesis, Bordeaux 1, 2008. http://www.theses.fr/2008BOR13660/document.
Full textThis thesis focuses on developing new methods for image fusion based on Partial Differential Equations (PDE). The starting point of the proposed fusion approach is the enhancement process contained in most classical diffusion models. The aim of enhancing contours is similar to one of the purpose of the fusion: the relevant information (equivalent to the contours) must be found in the output image. In general, the contour enhancement uses an inverse diffusion equation. In our model of fusion, the evolution of each input image is led by such equation. This single equation must necessarily be accompanied by a global information detector useful to select the signal to be injected. In addition, an inverse diffusion equation, like any Gaussian deconvolution, raises problems of stability and regularization of the solution. To resolve these problems, a regularization term is integrated into the model. The general model of fusion is finally similar to an evolving cooperative system, where the information contained in each image starts moving towards relevant information, leading to a convergent process. The essential interest of PDE approach is to deal with noisy data by combining in a natural way two processes: fusion and diffusion. The fusion-diffusion proposed model is easy to adapt to different types of data by tuning the PDE. In order to adapt the fusion-diffusion model to a specific application, I propose 2 diffusion models: “Seismic fault preserving diffusion” and “3D directional diffusion”. The aim is to denoise 3D seismic data. These models are integrated into the fusion-diffusion approach. One of them is successfully transferred to the industrial partner: french oil company Total. The efficiency of our models (fusion and fusion-diffusion) is proven through an experimental plan in both noisy and noisy-free data
Stopin, Alexandre. "Détermination de modèle de vitesse anisotrope par tomographie de réflexion des modes de compression et de cisaillement." Université Louis Pasteur (Strasbourg) (1971-2008), 2001. http://www.theses.fr/2001STR13203.
Full textBaldassari, Caroline. "Modélisation et simulation numérique pour la migration terrestre par équation d'ondes." Phd thesis, Université de Pau et des Pays de l'Adour, 2009. http://tel.archives-ouvertes.fr/tel-00472810.
Full textKeresztes, Barna. "Segmentation de zones d'intérêt par processus objets : application à la détection des réseaux de failles sismiques." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13911/document.
Full textThis thesis presents a new approach for seismic fault detection. Its goal is to increase the detection accuracy by computing some classical attributes on a support founded on an a priori knowledge about the faults. Several forms of support are proposed: a linear filtering method using fixed length segments of variable direction, respectively using a stochastic algorithm: the marked point processes. To simulate this process we propose two object models, using a network of connected linear segments and a more complex curved support which aims to describe each fault using one object. One interest of this approach is the possibility of using a common support for different fault detection operators. Then a whole detection framework can be proposed which acts like a decision fusion process
Martin, Victor. "Structure et tectonique du prisme d'accrétion de Nankai dans la zone Tokai par imagerie sismique en trois dimensions." Phd thesis, Université Paris Sud - Paris XI, 2003. http://tel.archives-ouvertes.fr/tel-00008139.
Full textSingh, Vijay Pratap. "Application des algorithmes évolutionaires à la détermination de modèles de vitesse par inversion sismique." Paris, ENMP, 2006. http://www.theses.fr/2006ENMP1466.
Full textGoal of seismic data processing is to convert a recorded wave field into a structural or lithological image of the subsurface. This requires a model of the wave propagation velocities of the subsurface. Nevertheless obtaining this model is often the most difficult processing step, in areas of complex structure such as foothill or salt body. The goal of this thesis was to develop a robust and efficient migration velocity estimation technique that uses global optimisation methods and remains computationally tractable. We used e-MOEA (MultiObjective Evolutionary Algorithm) as an optimisation tool. We attempted to reduce the computational cost of EA by adding geological and geophysical knowledge to the component of the algorithms, at the representation level, in the variation operators and in the objective function. In this work, after some effort to design a concise and geologically meaningful representation, we finally concluded that the grid representation was the most flexible one, even though it implies a large number of unknown parameters and induces a high computational cost. We modified the differential semblance function and used it together with the semblance function to have a robust and accurate criterion. We hybridized e-MOEA using RMO (Residual MoveOut) and dip information. We first customize the e-MOEA algorithm itself, and also proposed a new exploitation operator and technique of optimal parent synthesis. The goal of the customization was to strive to have both the robustness of global methods and the efficiency of local optimisation methods. We presented examples of migration velocity analyses mainly on Marmousi model, together with a few results on the North-Sea L7 model. We demonstrated that our automatic velocity analysis technique is able to cope with large velocity errors and, in term of computation cost, it is as efficient as the gradient methods except in salt body. We expect that with some clever adoption this algorithm can be extended for 3D
Meric, Ombeline. "Étude de mouvements de terrain par méthodes géophysiques." Phd thesis, Université Joseph Fourier (Grenoble), 2006. http://tel.archives-ouvertes.fr/tel-00284215.
Full textNous avons mené des campagnes géophysiques sur cinq sites tests. Ces sites ont été choisis en milieu rocheux et de grande ampleur (Séchilienne, Isère, et La Clapière, Alpes Maritimes) ou de taille modérée (Ravin de l'Aiguille, Isère) et en contexte argileux (Super Sauze, Alpes de Hautes Provence, et Léaz, Ain). Nous montrons que, selon le degré de remaniement, l'étude des paramètres géophysiques tels que $\rho$ (tomographie électrique), $V_P$ (sismique réfraction et tomographie) et $V_S$ (sismique réfraction et analyse des ondes de surface) peut permettre de caractériser la géométrie du mouvement. Nous préconisons pour l'analyse des ondes de surface de contraindre la paramétrisation par $V_P$ si elle est connue en surface et par la fréquence du pic H/V. En outre, pour une géométrie régulière et des faibles gradients latéraux de $V_S$, nous montrons que la méthode H/V peut aider à obtenir rapidement des informations quantitatives sur la variation spatiale de la géométrie du substratum.
%Nous préconisons pour l'étude de la géométrie des mouvements rocheux, le déploiement de méthodes tomographiques (électrique et sismique) et l'analyse des ondes de surface enregistrées lors de prospection sismique et par des réseaux de bruit de fond, en tenant compte des informations sur $V_P$ en surface et de la fréquence de résonance du pic H/V. La caractérisation des écoulements au sein des mouvements est améliorée lorsque l'on associe l'interprétation des mesures de résistivité et de polarisation spontanée.
%Selon le degré de remaniement des argiles en mouvement, l'étude des paramètres géophy\-siques tels que $\rho$ (tomographie électrique), $V_P$ (sismique réfraction et tomographie) et $V_S$ (sismique réfraction et analyse des ondes de surface) peut permettre de caractériser la géométrie du mouvement. Pour une géométrie régulière et des faibles gradients latéraux de $V_S$, l'utilisation de la méthode H/V peut aider à obtenir rapidement des informations quantitatives sur la variation spatiale de la géométrie du substratum.
Enfin, nous avons déployé un réseau d'électrodes impolarisables pour le suivi temporel de la polarisation spontanée sur le mouvement de grande ampleur de Séchilienne. Ce réseau a permis de mettre en évidence les trajets préférentiels de circulation de fluide au sein du massif et de rendre compte de leur complexité.
Ker, Stéphan. "Développement de méthodes d'imagerie sismique par grand fond et d'analyse multiéchelle par ondelettes pour la caractérisation à haute résolution du sous-sol marin." Paris, Institut de physique du globe, 2012. http://www.theses.fr/2012GLOB0007.
Full textHigh Resolution marine seismic is a common tool to indirectly study the fine scale structures of the sub-seabed and its related geohazards. In water depths, ranging from the continental slope to deep oceanic basin, high resolution seismic imaging cannot be achieved with conventional near-surface system due to a number of shortcomings. Since the 90s, the acquisition strategy has therefore striven for lowering both seismic sources and receivers close to the seafloor. Ifremer has recently developed a deeptowed seismic system (SYSIF), based on piezoelectric transducer technology and dedicated to the study of superficial sediments up to 6000 m water depth. Our objective is to achieve seismic imaging and seismic characterization at small scales consistent with the accuracy of in situ geotechnical measurements. We aim at improving the seismic resolution of the deep-towed seismic data and proposing quantitative methods for the characterization of the sediments properties. The processing sequence of SYSIF data was first optimized by introducing the source signature deconvolution. We improve the vertical resolution by a factor 2 and reach 1 m and. 5 m resolution for the frequency ranges [220-1050 Hz] and [580-2200 Hz] respectively. In order to improve the lateral resolution, we assess the multioffset seismic imaging by setting up an experience based on the SYSIF source [220- 1050 Hz] and Ocean Bottom Hydrophones (OBHs). Such an acquisition requires precise positioning (which is achieved through acoustic relocation of sources and receivers) and the development of velocity analysis, processing and imaging methods suited to the acquisition geometry. We present a first application of this approach, performed during the ERIG3D cruise on a buried Mass transport Complex offshore Nigeria. The final seismic imaging has a 2. 5 m lateral resolution and demonstrates the feasibility of a high resolution depth imaging in deep-sea based on deep-towed seismic source. The former results allowed the development of a multichannel high resolution streamer to be started by Ifremer. To further improve the vertical resolution and to characterize the small scales structures of reflectors, we develop a multiscale analysis of deep-towed seismic data. This analysis relies on the wavelet response closely related to the continuous wavelet transform. The application of the wavelet response to broadband seismic data suffers from distortions generated by the bandpass filter effect of the seismic source. Two approaches have been proposed to account for these distortions. A first empirical approach is based on the wavelet transform of the seismic source. The second approach takes advantages of the properties of Lévy alpha-stable functions to obtain a family of effective dilated wavelets that enables the direct analysis of the medium’s Green functions. For the application on SYSIF data, gaussian derivatives are used which enable to merge information provided by both SYSIF sources (High and Very High Resolution) to obtain a wavelet response in the frequency range [220-2200 Hz]. We introduce new seismic attributes related to the wavelet response. These attributes are ridge functions of the wavelet response which constitute a sparse support of the multiscale information. Ridge function is an effective tool to characterize seismic reflector’s complexity and allow the determination of their characteristic size (in the range [24-115 cm] for SYSIF sources). Theoretical developments related to these new seismic attributes are applied on a case study associating seismic and ground truth data which enables to demonstrate the potential of the approach. Finally, we explore both the optimization of the source processing based on the fractional derivatives of the most adapted Lévy alpha-stable function and the acoustic impedance determination based on the inverse continuous wavelet transform. Thus, a first application of the inverse transform of the wavelet response related to SYSIF data provides an impedance profile with a vertical resolution of 25 cm
Pageot, Damien. "Imagerie de la lithosphère par inversion de formes d'ondes de données télésismiques." Nice, 2012. http://www.theses.fr/2012NICE4109.
Full textThis thesis follows a recent movement link to the design of more and more denser seismological networks et allow to evolve lithospheric imaging toward high resolution tomography methods initially design in the Framework of seismic exploration. Bostock et al. (2001) are pioneers in this movement with their adaption of ray + Born migration method to teleseismic configurations and by applying this method to real teleseismic data form CASC93. During this thesis, I adapted a Full Waveform Inversion algorithm, design for seismic exploration, to teleseismic configurations. This adaptation leads me to integrate plane wave sources, a scattered wave field approach and obliquity of plane waves in the original algorithm. In the first part, I present the method to model propagation of seismic waves which is the core engine of the algorithm of Full Waveform Inversion, its adaptation to teleseismic configurations and finally the inverse problem. In the second part, I present a parametric analysis of Full Waveform inversion method adapted to teleseismic configurations to assess the potential of the method and spot the differences with the parameterizations recommended in seismic exploration. The third part concerns the application of the methods to real teleseismic data recorded by the seismological network MASE deployed for imaging the subduction of the Cocos plate below Mexico
Martin, Laure. "Structure et évolution récente de la Mer Egée : apports d'une étude par sismique réflexion." Paris 6, 1987. http://www.theses.fr/1987PA066092.
Full textZhou, Tianyou. "Analyse de vitesse par migration : choix des paramètres utilisateurs et introduction des ondes transmises." Electronic Thesis or Diss., Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLM046.
Full textSeismic imaging is the technique used to determine the structures of the subsurface from seismic signals. One of the most important parameters is the velocity model, that can be split into the macromodel controlling the kinematics of wave propagation and velocity perturbations. Migration builds the image of velocity perturbation for a given macromodel. Migration Velocity Analysis estimates the quality of the macromodel with an objective function measuring the focusing in the image domain. The gradient of this objective function with respect to the macromodel allows to find the optimal macromodel in an iterative way. The method has been improved recently by replacing the migration operator by the asymptotic inverse in the subsurface offset domain. In this thesis, we show that the quality of the gradient is sensitive to the user parameters. We provide practical guidelines to ensure proper gradient. These guidelines are applied to the synthetic Marmousi model. Recent developments propose to take into account the transmitted waves. We compare different strategies for combining the two different kinds of waves and recommend to apply a separate workflow. We apply the method to a marine real data set provided by Total. We propose a two-step workflow: after a first try of several iterations, we adjust the parameters and restart the iterations
Deloison, Benjamin. "Imagerie fonctionnelle placentaire par résonance magnétique : étude de la perfusion placentaire." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112256.
Full textPlacental insufficiency is a serious medical condition with a diagnosis made usually too late to prevent introduction of effective therapies. The aim of this thesis is to develop, in pregnant rats and translate to humans, functional MRI (fMRI) tools allowing quantification of placental perfusion in clinical practice.Materials and Methods: Three studies using fMRI are part of this thesis. The first two were performed on a murine model. A dynamic sequence with injection of a contrast agent (DCE) has been developed with an iron oxide particle (SPIO) in a surgical model of chronic placental hypoperfusion with placental perfusion measurement (f) in ml / min / 100 ml and placental fractionnal volume (Vb) in %. Another technique of fMRI was developed with Arterial Spin Labeling (ASL) to estimate placental perfusion in ml / min / 100g without injection of contrast media.The latest study was a translational research. It consisted in the development of a dynamic sequence with injection of gadolinium chelate, in order to obtain perfusion (f) in ml / min / 100 ml and placental fractionnal volume (Vb) in %. We also studied maternal and fetal pharmacokinetics of gadolinium chelate.Results: In animals with SPIO DCE, our study allowed us to show that it is possible to use the T1 effect of SPIO to characterize the placental microcirculation by f = 159.4 ml / min / 100ml (+ / - 54.6) and Vb = 39.2% (11.9 +/-) for 31 « normal » placentas. In case of IUGR, f decreases significantly for the 23 examined placentas (f = 108.1 ml / min / 100ml +/- 41, p = 0.004), whereas the volume fraction placenta is not modified (Vb = 42 +/- 16.7 8 %, p = 0.24). ASL has allowed us to estimate placental perfusion for 47 placentas under physiological conditions, with an estimated perfusion of 146.8 ml / min / 100 g (70.1 +/-).In humans, 14 placentas were studied with an estimated perfusion of 183 ml / min / 100ml (+/- 144) and we also identified two types of placental kinetic enhancement (early and intense and later and less intense). Pharmacokinetics have allowed us to study quantitatively the transfer of gadolinium chelate in the fetus. This transfer is low compared to the initial concentration of Dotarem® : fetal blood concentration is 18.1x10-6%, concentration in amniotic fluid is 242.8 x10-6 % and 0.3% of the Dotarem® initial dose is present in the placenta approximately 70 hours after injection.Conclusion: This study illustrates the variety of functional MRI techniques available for placental study. Placental perfusion can be quantified by DCE with an iron oxide particle (SPIO) or without injection of contrast in ASL, in a rat model. The study of placental perfusion in humans is also possible in DCE with gadolinium chelates
Touma, Rita. "Approche matricielle de l’imagerie sismique passive par ondes de volume." Thesis, Université Grenoble Alpes, 2022. http://www.theses.fr/2022GRALU011.
Full textRevealing the structure of fault zones provides insights required to assess seismic hazards. Reflection imaging methods, in particular migration, are commonly used to image the subsurface. An accurate velocity model is often needed to properly locate the reflectors in depth.Imaging fault zones is challenging due to the complex distribution of velocity. Also, most reflection techniques image fault zones indirectly from the discontinuity of geological layers. Wave diffraction by small-scale heterogeneities, such as cracks and fractures is generally neglected.In this thesis, we propose a matrix imaging approach for geophysical exploration that handles the velocity variation in the crust and allows to resolve heterogeneities of the order of the wavelength throughout the fault zone.The reflection matrix approach is inspired from previous studies in ultrasound and optical imaging of complex media. First, ambient noise cross-correlations are used to retrieve the reflection matrix associated with a dense array of geophones. The body wave components of this matrix contains all the information available on the medium. Second, the presented approach does not require a detailed velocity model of the subsurface. A set of matrix operation is applied to compensate for the mismatch between the actual wave velocity model and its approximate model.In a first application, we use ambient noise records in the frequency band [10 20] Hz from a dense array in order image the San Jacinto Fault, California, at small scale with an horizontal resolution of 80 m. ZZ cross-correlations are computed and arranged as 2D matrix. By applying time delays, the response matrix is projected to depth, using a homogeneous velocity model. A focused reflection matrix is obtained, that contains the impulse response between virtual sources and receivers at depth. From this matrix, the image of the medium is built and the resolution of the image can be quantified.Variations between the considered model and the reality result in phase distortions, i.e aberrations, that have detrimental effects on the image of the medium.We develop an aberration correction process that allows to compensate for these distortions by introducing a novel operator, the distortion matrix. 3D images of the first 4 km of the crust are retrieved. These images reveal the backscattered intensity generated by the heterogeneities in the medium. The location and reflectivity of scatterers are retrieved with a resolution 8 times better than the one in free space. Differences in the scattering between the Northwest and the Southeast of the fault were reported with an intense localized damage zone in the Southeast.In a second application, we image the large scale structure of North Anatolian Fault using [0.1 0.5] Hz horizontal cross-correlations computed between 73 pairs of stations. A multi-layered velocity model is considered. A local correction of the phase distortions is performed. The scattering structure of the crust and the upper mantle is revealed. Differences in the Moho depth are reported, with a step below the northern branch. Strong scattering is observed in the region lying along the northern strand of the fault, coinciding with the limit of the lithospheric blocks. The scattering in the North extends to 60 km depth, suggesting a shear zone that penetrates in the upper mantle beneath the northern strand. The scattering also reveals the deep structure of the main geological blocks.In the last part of this thesis, we propose an approach that paves the route towards a 3D passive tomography of the body wave velocity. Finally, all the presented applications confirm the efficiency of the reflection matrix approach in revealing the structure of the subsurface. It provides new insights into the scattering distribution in the Earth. It can be applied to any scale, scattering regime, and frequency bandwith, if the spatial sampling of the geophones' array satisfies the Nyquist criterion
Brossier, Romain. "Imagerie sismique à deux dimensions des milieux visco-élastiques par inversion des formes d'ondes : développements méthodologiques et applications." Phd thesis, Université de Nice Sophia-Antipolis, 2009. http://tel.archives-ouvertes.fr/tel-00451138.
Full textWang, Yi. "Imagerie haute résolution des structures lithosphériques par inversion de formes d'ondes P télésismiques courte période." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30018.
Full textSeismic tomography allows us to image the Earth's interior based on surface observations of seismic waves. The full waveform inversion (FWI) method has the potential to improve tomographic images for the fine scale structures of the lithosphere. For this reason it receives a lot of attention of seismologists. FWI requires an efficient and precise numerical techniques to solve the elastic wave equation in 3D heterogeneous media. Its resolution potential is limited by the shortest wavelength in the seismic wavefield and the wavefield sampling density. Because of the high computational cost of modeling the propagation of seismic waves in heterogeneous media, FWI remains challenging. However, owing to the progress in high performance computational resources and numerical simulation techniques, as well as the deployment of permanent and temporary broadband arrays in the last two decades, this situation has changed dramatically. In this thesis, we focus on the high resolution imaging of lithospheric structure beneath the Pyrenean range by FWI, to quantify the highly controversial amount of convergence that occurred during the formation of this mountain range. In order to obtain finely resolved tomographic images, we exploit short period teleseismic P waves recorded by dense transects. We use a hybrid method that couples a global wave propagation method in a 1D Earth model to a 3D spectral-element method in a regional domain. A boundary coupling approach is used to match the global and regional wavefields on the boundaries of the regional domain. This hybrid method restricts the costly 3D computations inside the regional domain, which dramatically decreases the computational cost. The hybrid method can model teleseismic wavefields down to 1s period, accounting for all the complexities that may affect the propagation of seismic waves in the 3D regional domain. By using this hybrid method, the sensitivity kernels of the least square waveform misfit function with respect to elastic and density perturbations in the regional domain are computed with the adjoint state method. These waveform sensitivity kernels are used in an iterative L-BFGS algorithm to invert broad-band waveform data recorded by two dense transects deployed during the temporary PYROPE experiment across the Pyrenees mountains. We obtain the first high resolution lithospheric sections of compressional and shear velocities across the Pyrenean orogenic belt. The tomographic models provide clear evidence for the underthrust of the thinned Iberian crust beneath the European plate and for the important role of rift-inherited mantle structures during the formation of the Pyrenees
Kazantsev, Alexandre. "Perturbations d'amplitude du bruit ambiant au droit des hétérogéneités : étude de faisabilité pour l'exploration et la surveillance de réservoirs multi-fluide." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM075/document.
Full textThis PhD work investigates the possible elastic mechanisms behind the ambient noise amplification above multi-phase fluid reservoirs. Three datasets are analysed above different reservoirs. The observed spectral signature is different in the gas storage and geothermal contexts. A non-supervised algorithm for amplitude spectrum classification is developed, allowing to extract and map the relevant attributes of a multi-phase fluid presence. As a first modelling step, a wavefield characterisation methodology is applied to determine the composition of the ambient noise. It reveals the presence of strong Rayleigh overtones. Numerical 2D elastic modelling is used to simulate the propagation of overtones across a reservoir within a realistic geological structure. The modelled reservoir response is too small compared to the real data. However, the small amplitude perturbations arising in the numerical simulations are successfully inverted for the position of the reservoir, in simple background models. The developed method could in theory be used for imaging small time-lapse amplitude variations (monitoring), despite the obstacles remaining to be overcome before a real-data application. Neither visco-elastic nor 3D effects are adressed. Thus this work does not exclude the possibility of strong reservoir-specific spectral anomalies
Leleu, Claire. "Sismique très haute résolution tri-dimensionnelle : identification de la position du dispositif d'acquisition par une reformulation en temps." Paris 9, 2001. https://portail.bu.dauphine.fr/fileviewer/index.php?doc=2001PA090021.
Full textDéau, Estelle. "Saturne revisitée par la sonde Cassini : étude photométrique et dynamique des anneaux par imagerie spatiale." Paris 7, 2007. http://www.theses.fr/2007PA077193.
Full textIn the Solar system, the planetary rings represent a fantastic opportunity of studying a majority of phenomena taking place in the thin discs. One can find discs at all redshifts and on ail scales of the Universe. Planetary discs are very different : among the jovian rings, one finds a halo of fine and diffuse dust; the rings of Uranus are very compact, like radially confined strings and the System of rings of Neptune consists of azimuthally stable arcs. However our interest goes on Saturn which has the most complex and widest System of rings known to date : 484 000 km and a vertical extension which increases with the distance to Saturn (typically less than 1 km to 10 000 km). The interest of such a matter organization around Saturn plus its many moons (more than one forty including 8 of a size of several hundreds kilometers) gave birth to the exploration mission CASSINI, supposed to allow the development and the refinement of models set up at the flybies of the two interplanetary probes VOYAGER. The CASSINI Mission began its nominal tour on january, 15th 2005 after the orbital insertion the 15* july 2004 and the dropping of HUYGENS probe on january, 14th 2005 on Titan's surface. The purpose of this thesis consists to revisit two subjects unsolved of long date in the photometric and dynamic behaviours of the Saturn's rings. In a first part, we try to solve the problem of accretion of matter within the Roche limit by studying the F ring. This ring, since its discovery in 1979 by Pioneer 11, is involved in a most various dynamic theories to explain its complex multi-radial structure and its variable azimuthal structure. We showed that the multi-radial structure of this ring can be understood by the existence of a spiral which is rolled up around a central area, bright, eccentric and inclined : the core. The lifespan of this spiral is not the same one as the core, suggesting that the processes which create the spiral are periodic. Moreover, we showed that the structure of the core is roughly stable on a scale of one year, but is very unstable on a shorter spatial and temporal scales, which is explained by multiple interactions with the satellite Prometheus and the ephemeris satellites. May be that these satellites came from the core and re-interact with him. Additional observations are necessary to refine this theory. In a second part, we were interested in photometry of the Saturn's rings i. E. To the way that the ring particles reflect sunlight. We were interested on the one hand in the opposition effect, an intense brightness observed in the main rings for the first time in 1878 by Millier at zero phase angle (the angle between the Sun, the rings and the observer), and which since was vainly explained by geometric optics theories (in particular by the means of the theory of shadow hiding). The use of models combining geometric optics and quantum optics (thanks to the theory of the coherent backscattering which allow to Philip Anderson to receive the Physics Nobel Prize in 1977) made it possible to understand a part of the opposition effect observed in the Saturn's rings. We show that five generally assertions on the shadow hiding and the coherent backscattering used by the community are false. Our study of the opposition surge caused by the coherent backscattering also showed than the taking into account of vectorial nature of light is necessary to understand this quantum phenomenon. In addition, we studied the overall photometric behaviour of the Saturn's rings by obtaining for the first time the full phase curves, going from 0\textsuperscript{o} to 180\textsuperscript{o} of phase angle, at several optical wavelengths. We showed that the rings have the widest range of albedo and anisotropy of all planetary objects joined together. This could be explained by size distributions, compositions and very different filling factors, which we determined thanks to some photometric models and which are in agreement with dynamic simulations and hydrodynamic analytical computations
Abdelkhalek, Rached. "Accélération matérielle pour l’imagerie sismique : modélisation, migration et interprétation." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR15028/document.
Full textDuring the seismic imaging workflow, from seismic modeling to interpretation, processingseismic data requires a massive amount of computation. We show in this work that, at eachstage of this workflow, hardware accelerators such as GPUs may help reducing the time requiredto process seismic data while staying at reasonable energy consumption levels.In this work, the key programming considerations needed to achieve good performance are describedand discussed. The importance of adapted in-memory data access patterns is particularlyemphasised since data access is the main bottleneck for the considered algorithms. When usingGPUs, speedup ratios of 40× are achieved for FDTD seismic modeling, and 8× up to 113× forseismic attribute computation compared to CPUs
Broche, Ludovic. "Étude des lésions pulmonaires associées à la ventilation mécanique par imagerie synchrotron." Thesis, Amiens, 2015. http://www.theses.fr/2015AMIE0046/document.
Full textPatients treated with mechanical ventilation are exposed to lung damage leading to hypoxia or in the worst case multi organ failure. Using x-ray phase contrast synchrotron imaging of an animal model, we study the pulmonary micro-mechanic of the damage parenchyma. The relevance of the study lies in the characterisation of the dynamic of the alveoli and bronchi mechanic under constant pressure control ventilation. Thus, extent and magnitude of potential inflammatory regions were reported based on lung recruitment and derecruitment maps on each CT slice. It appears that lung instabilities remain non negligible despite the addition of a positive end expiratory pressure, which may explain the ineffectiveness of current protective ventilation protocols in intensive care units. One probable assumption is to consider one alveolus structural alteration as a consequence of shared stresses through the surrounding network of neighbouring alveoli. To support this hypothesis, a mathematical model mimicking injured lung ventilation was implemented in a realistic airway tree. The model short and long term behaviour shows a good correlation with experimental data, and provides a useful tool to evaluate new ventilation protocols
Yon, Jérôme. "Jet diesel haute pression en champ proche et lointain : étude par imagerie." Rouen, 2003. http://www.theses.fr/2003ROUES038.
Full textThe aim of the experimental study presented in this thesis is to improve the understanding of the atomization processes involved in a high injection pressure Diesel jet (up to 100 MPa, direct injection). The real Diesel jet structure and the processes involved are not yet fully understood. The great variety of models found in the literature confirms this state of affairs. This lack of knowledge is due to the difficulty of analyzing the Diesel jet caused by its optical density and the size of its characteristic scales of time ("1 ms) and space ("100 æm). During the work carried out for this thesis, new diagnostics based on image processing have been developed in order to analyze the phenomena occurring in the nozzle near field (first millimeters of the jet) and in the far field (spray formed at a long distance from the nozzle). Using several tomographic configurations with an unfocused imaging system, coupled with a shadowgraph imaging setup it was possible to observe, in the near field, cylindrical cavitation pockets located near the jet interface and to drawn a new model of the Diesel jet's internal structure. An entropic calculation applied to three-state-pictures (continuous liquid phase, dispersed liquid phase and gaseous phase) allows us to observe the evolution of a surface linked to the primary atomization. The morphological statistical analysis of the continuous liquid phase interface also enables us to describe the ligament detachment of the dense liquid jet as a function of the injection time and pressure
Coldefy, Hélène. "Contrôle non invasif de l'hyperthermie par imagerie microonde active : étude préliminaire sur fantôme homogène." Paris 11, 1986. http://www.theses.fr/1986PA112012.
Full textLi, Yubing. "Analyse de vitesse par migration quantitative dans les domaines images et données pour l’imagerie sismique." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM002/document.
Full textActive seismic experiments are widely used to characterize the structure of the subsurface. Migration Velocity Analysis techniques aim at recovering the background velocity model controlling the kinematics of wave propagation. The first step consists of obtaining the reflectivity images by migrating observed data in a given macro velocity model. The estimated model is then updated, assessing the quality of the background velocity model through the image coherency or focusing criteria. Classical migration techniques, however, do not provide a sufficiently accurate reflectivity image, leading to incorrect velocity updates. Recent investigations propose to couple the asymptotic inversion, which can remove migration artifacts in practice, to velocity analysis in the subsurface-offset domain for better robustness. This approach requires large memory and cannot be currently extended to 3D. In this thesis, I propose to transpose the strategy to the more conventional common-shot migration based velocity analysis. I analyze how the approach can deal with complex models, in particular with the presence of low velocity anomaly zones or discontinuous reflectivities. Additionally, it requires less memory than its counterpart in the subsurface-offset domain. I also propose to extend Inversion Velocity Analysis to the data-domain, leading to a more linearized inverse problem than classic waveform inversion. I establish formal links between data-fitting principle and image coherency criteria by comparing the new approach to other reflection-based waveform inversion techniques. The methodologies are developed and analyzed on 2D synthetic data sets
Verney, Philippe. "Interprétation géologique de données sismiques par une méthode supervisée basée sur la vision cognitive." Phd thesis, École Nationale Supérieure des Mines de Paris, 2009. http://pastel.archives-ouvertes.fr/pastel-00005861.
Full textSaidou, Adamou. "Étude du comportement en compression-cisaillement d'isolateurs sismiques en caoutchouc." Mémoire, Université de Sherbrooke, 2012. http://hdl.handle.net/11143/6209.
Full textLe, Bouteiller Philippe. "Approche eulérienne de l'équation de Hamilton-Jacobi par une méthode Galerkine discontinue en milieu hétérogène anisotrope : Application à l'imagerie sismique." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAU035/document.
Full textRecovering information on the structure and the composition of the Earth's interior is a fundamental issue for a large range ofapplications, from planetology to seismology, natural resources assessment, and civil engineering. Seismic waves are a very powerful tool for that purpose. Using a high-frequency approximation for the numerical modeling of seismic wave propagation is computationally advantageous when hundreds, thousands, or more of wavelengths have to be propagated. Instead of the linear wave equation, the high-frequency approximation yields three fundamental partial differential equations. The nonlinear Eikonal equation leads to traveltime. A second equation is derived for the take-off angle. Both Eikonal and angle equations belong to the wide Hamilton-Jacobi family of equations. In addition, the transport equation leads to the amplitude.As a Lagrangian approach, seismic ray tracing employs the method of characteristics to derive a set of ordinary differential equations from these partial differential equations. They can be easily integrated, thus yielding traveltime and amplitude along rays. Widely used in the geophysical community for their simplicity, the ray-tracing tools might not be the most efficient and robust ones for practical high-resolution imaging and inversion applications. Instead, it might be desirable to directly solve the partial differential equations in an Eulerian way. In the three last decades, plenty of Eikonal solvers have been designed, mostly based on finite-difference methods. Successive works try to find the best compromise between accuracy, computational efficiency, robustness, ease of implementation, and versatility.In this thesis, I develop a different approach, mainly based on the discontinuous Galerkin method. This method has been intensively used in the mathematical field for solving conservation laws and time-dependent Hamilton-Jacobi equations. Only few investigations have been done regarding its use for solving the static Eikonal equation in a geophysical context, despite the high level of accuracy allowed by this method. Therefore, improving upon mathematical studies, I propose a new Eikonal solver suitable for the geophysical context. Complex heterogeneous anisotropic media with non-flat topographies are correctly handled, with an unprecedented accuracy. Combined with a fast-sweeping strategy in a robust way, I show that this new solver exhibits a high computational efficiency, in two dimensions as well as in three dimensions.I also employ this solver for the computation of the take-off angle. I design an additional finite-volume solver for solving the transport equation, leading to the computation of amplitude. With this solver, I also consider the computation of the adjoint-state variable for seismic tomography, since it satisfies a similar transport equation. Eventually, I propose a whole set of consistent solvers to the geophysical community. These tools should be useful in a wide range of applications. As an illustration, I finally use them in advanced seismic imaging schemes, in order to demonstrate the benefit brought by the high-frequency approximation in this kind of schemes
Marcq, Emmanuel. "Prélude à la mission Venus Express : étude de l'atmosphère par spectro-imagerie infrarouge." Phd thesis, Université Paris-Diderot - Paris VII, 2006. http://tel.archives-ouvertes.fr/tel-00126105.
Full textLe début de la mission spatiale Venus Express, première mission spatiale dédiée à cette planète depuis la découverte de l'émission infrarouge nocturne, et notamment les données attendues du spectro-imageur VIRTIS ont donc motivé un travail préparatoire qui a fait l'objet de cette thèse. Grâce à l'acquisition de spectres obtenus avec le spectro-imageur SpeX à l'Infrared Telescope Facility d'Hawaii, nous avons disposé de données analogues à celles attendues de la part de l'instrument VIRTIS-H sur le plan de la résolution spectrale (R ~ 2000). Ces observations furent menées au cours de trois campagnes
lors des périodes de quadrature favorables à l'observation de Vénus, en février 2003, août 2004 et novembre 2005. Par la suite, grâce au modèle numérique de transfert radiatif développé par Bruno Bézard et simulant les spectres de l'émission nocturne de Vénus, nous avons développé des algorithmes permettant d'associer rapidement à un spectre donné divers paramètres atmosphériques compatibles avec les observations (abondances et gradients verticaux d'espèces minoritaires à une altitude donnée, rapport isotopique de la vapeur d'eau, opacité nuageuse inférieure).
Nous présentons ensuite les résultats obtenus, parmi lesquels la confirmation de l'enrichissement déjà soupçonné en monoxyde de carbone aux moyennes et hautes latitudes. Des variations anti-corrélées du sulfure de carbonyle ont également été détectées. Une variabilité associée des gradients verticaux de ces deux espèces a pu aussi être mesurée. Ces résultats ont en outre reçu une interprétation dynamique qualitative, basée sur la circulation verticale générale de l'atmosphère. De nouvelles contraintes plus précises concernant l'abondance globale en vapeur d'eau et son rapport isotopique ont également pu être dérivées.
Enfin, la dernière partie de ce mémoire porte sur l'analyse par des méthodes semblables des premières données issues de l'instrument VIRTIS, montrant ainsi l'applicabilité de nos méthodes et confirmant certains des résultats obtenus précédemment, ainsi que sur les perspectives futures, conciliant études spectroscopiques des composés mineurs et interprétation dynamique de leurs variations grâce aux modèles de circulation générale.
Cazala, Fadwa. "Les corrélats cérébraux de la pédophilie : étude en imagerie par résonance magnétique fonctionnelle." Thesis, Paris 5, 2014. http://www.theses.fr/2014PA05T073.
Full textIn contrast to the numerous studies about the neural underpinnings of normal sexual motivation, brain correlates of pedophilia are still largely unknown. The present thesis aimed to identify functional networks involved in pedophile sexual arousal. Therefore, we investigated with fMRI the activation profile of 13 heterosexual and 12 homosexual pedophiles, compared to each other and to 24 matched healthy subjects, in response to visual sexual stimuli depicted adult (women/men) and child (girls/boy) wearing swimsuits, while neutral ones depicted ordinarily dressed adult and dressed children. Results showed that brain responses of heterosexual and homosexual pedophiles were not statistically different from those of matched healthy subjects, in response to their respective preferred stimuli. They were located in occipital, temporal and parietal brain areas known to be involved in sexual arousal in healthy subjects. In the line of penile plethysmographic studies, analysis also showed that homosexual and heterosexual pedophiles may process non preferred child stimuli as relevant sexual stimuli. This could be explained by a bipolar dimension of morphological similarity, on which children are located near the middle, and adult men and women are located at opposite ends
Marcq, Emmanuel. "Prélude à la mission Vénus Express : étude de l'atmosphère par spectro-imagerie infrarouge." Paris 7, 2006. http://www.theses.fr/2006PA077205.
Full textThe opacity of CO2 in the atmosphere of Venus is weak enough for the thermal emission to escape from the deep (25-40 km) and hot layers in several spectral Windows. Its spectrum around 2. 3 microns is a unique way to investigate the composition in minor species (CO, OCS, H2O, SO2) under the thick clouds. Their local variations can inform us about the dynamics and chemistry of the lower atmosphere as well as the possible activity of the surface. The beginning of the first space mission since the discovery of this nightside thermal emission, Venus Express, has motivated this preliminary thesis work. Using SpeX at the IRTF in Hawaii, we obtained spectra similar to those expected from the VIRTIS instrument in orbit. We have led our observations during the quadratures from 2003 until 2005. Thanks to the radiative transfer mode! from B. Bézard, we could provide algorithms enabling the retrievals of abundances and vertical gradients, isotopic ratios of water vapor and lower cloud opacity. We could then confirm the suspected enrichment in CO towards higher latitudes, and detect anti-correlated variations in OCS as well as a variability in their vertical gradients. We also provided qualitative dynamical interpretations for these facts. Water abundance and its D/H ratio were also further precised. We finally applied similar methods to the first data from VIRTIS,. And confirmed some of the previous results
Pagliarulo, Francesca Romana. "Étude du photodétachement de petits agrégats de carbone par imagerie résolue en temps." Lyon 1, 2006. http://www.theses.fr/2006LYO10104.
Full textSeyed, Aghamiry Seyed Hossein. "Imagerie sismique multi-paramètre par reconstruction de champs d'ondes : apport de la méthode des multiplicateurs de Lagrange avec directions alternées (ADMM) et des régularisations hybrides." Thesis, Université Côte d'Azur (ComUE), 2019. http://www.theses.fr/2019AZUR4090.
Full textFull Waveform Inversion (FWI) is a PDE-constrained optimization which reconstructs subsurface parameters from sparse measurements of seismic wavefields. FWI generally relies on local optimization techniques and a reduced-space approach where the wavefields are eliminated from the variables. In this setting, two bottlenecks of FWI are nonlinearity and ill-posedness. One source of nonlinearity is cycle skipping, which drives the inversion to spurious minima when the starting subsurface model is not kinematically accurate enough. Ill-posedness can result from incomplete subsurface illumination, noise and parameter cross-talks. This thesis aims to mitigate these pathologies with new optimization and regularization strategies. I first improve the wavefield reconstruction method (WRI). WRI extends the FWI search space by computing wavefields with a relaxation of the wave equation to match the data from inaccurate parameters. Then, the parameters are updated by minimizing wave equation errors with either alternating optimization or variable projection. In the former case, WRI breaks down FWI into to linear subproblems thanks to wave equation bilinearity. WRI was initially implemented with a penalty method, which requires a tedious adaptation of the penalty parameter in iterations. Here, I replace the penalty method by the alternating-direction method of multipliers (ADMM). I show with numerical examples how ADMM conciliates the search space extension and the accuracy of the solution at the convergence point with fixed penalty parameters thanks to the dual ascent update of the Lagrange multipliers. The second contribution is the implementation of bound constraints and non smooth Total Variation (TV) regularization in ADMM-based WRI. Following the Split Bregman method, suitable auxiliary variables allow for the de-coupling of the ℓ1 and ℓ2 subproblems, the former being solved efficiently with proximity operators. Then, I combine Tikhonov and TV regularizations by infimal convolution to account for the different statistical properties of the subsurface (smoothness and blockiness). At the next step, I show the ability of sparse promoting regularization in reconstruction the model when ultralong offset sparse fixed-spread acquisition such as those carried out with OBN are used. This thesis continues with the extension of the ADMM-based WRI to multiparameter reconstruction in vertical transversely isotropic (VTI) acoustic media. I first show that the bilinearity of the wave equation is satisfied for the elastodynamic equations. I discuss the joint reconstruction of the vertical wavespeed and epsilon in VTI media. Second, I develop ADMM-based WRI for attenuation imaging, where I update wavefield, squared-slowness, and attenuation in an alternating mode since viscoacoustic wave equation can be approximated, with a high degree of accuracy, as a multilinear equation. This alternating solving provides the necessary flexibility to taylor the regularization to each parameter class and invert large data sets. Then, I overcome some limitations of ADMM-based WRI when a crude initial model is used. In this case, the reconstructed wavefields are accurate only near the receivers. The inaccuracy of phase of the wavefields may be the leading factor which drives the inversion towards spurious minimizers. To mitigate the role of the phase during the early iterations, I update the parameters with phase retrieval, a process which reconstructs a signal from magnitude of linear mesurements. This approach combined with efficient regularizations leads to more accurate reconstruction of the shallow structure, which is decisive to drive ADMM-based WRI toward good solutions at higher frequencies. The last part of this PhD is devoted to time-domain WRI, where a challenge is to perform accurate wavefield reconstruction with acceptable computational cost
Chevalier, Frédéric. "Le diagnostic assisté par ordinateur de l'image tomodensitométrique : étude de paramètres adaptés." Paris 12, 1991. http://www.theses.fr/1991PA120036.
Full textSchaeffer, Mathilde. "Lésions cérébrales induites par hypoxie ou hypoxie-ischémie prénatale : étude par immunohistochimie et imagerie par résonance magnétique nucléaire (IRM)." Paris 7, 2003. http://www.theses.fr/2003PA077112.
Full textBêche, Martin. "Architecture structurale de la ceinture de Gaspé (Canada) : Imagerie sismique intégrée et application à l'évaluation pétrolière." Phd thesis, Université de Cergy Pontoise, 2008. http://tel.archives-ouvertes.fr/tel-00441620.
Full textLeprêtre, Angélique. "Contraintes par imagerie sismique pénétrante sur l'évolution d'une marge Cénozoïque réactivée en compression (cas de la marge algérienne, secteur de Tipaza)." Phd thesis, Université de Bretagne occidentale - Brest, 2012. http://tel.archives-ouvertes.fr/tel-00861342.
Full textAït, Abdelmalek Radia. "Contribution à l'imagerie radiométrique microonde : étude de l'influence de la permittivité : inversion des images par déconvolution." Lille 1, 1996. http://www.theses.fr/1996LIL10025.
Full textLa campagne d'évaluation clinique, qui est en préparation, a pour but de mettre en évidence des volumes thermiques de l'ordre du centimètre cube, siège d'une élévation de température de quelques degrés. Un problème aussi ardu nécessite un procédé de traitement du signal adapté. Nous réalisions jusqu'alors des images dites brutes, obtenues par interpolation des mesures acquises sur la surface d'investigation. Le nouveau procédé que nous présentons consiste à réaliser une déconvolution des données, compte tenu de la fonction d'appareil, c'est-à-dire de la connaissance des paramètres de couplage. Ce procédé, associé à un filtrage de Wiener, est testé par des simulations et aussi appliqué à des mesures acquises sur des modèles physiques, dans des conditions approchant celles d'une évaluation clinique. Les conclusions qui en sont tirées sont précieuses en ce qui concerne l'évaluation des limites du procédé et aussi la mise en oeuvre de nouveaux perfectionnements