CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Dunas costeiras exercem um importante papel na manutenÃÃo do fluxo de sedimentos da zona costeira. O Parque Nacional de Jericoacoara, localizado no estado do CearÃ, regiÃo Nordeste do Brasil, possui uma morfologia pouco frequente, trata-se de um promontÃrio associado com um campo de dunas mÃveis denominadas barcanas, dunas individuais, de grande porte com formato de ferraduras que se deslocam em direÃÃo L â O. Elas realizam o by-pass, o transporte de sedimentos, essencial para a manutenÃÃo da linha de costa. Neste trabalho, foi priorizada a definiÃÃo da evoluÃÃo morfodinÃmica de dunas mÃveis isoladas (dunas Papai Noel, PÃr-do-Sol e Arraia), tendo como referencial teÃrico a anÃlise das paisagens e como procdimento tÃcnico principal a anÃlise espaÃo-temporal do recobrimento de imagens multitemporais dos satÃlites Landsat e Quickbird entre os anos de 1973 a 2014. AtravÃs da comparaÃÃo da distribuiÃÃo espaÃo temporal das morfologias dunares, nesse perÃodo de 41 anos, evidenciaram-se mudanÃas significativas na Ãrea, perÃmetro e deslocamento das dunas. Foi possÃvel constatar a aÃÃo dos fluxos de matÃria e energia vinculados com migraÃÃo continuada direcionada para a faixa de praia (setor de bypassing de sedimentos). A dinÃmica de migraÃÃo das dunas, quando analisadas apÃs as imagens de 2000, evidenciou possibilidades de alteraÃÃes dos aspectos morfolÃgicos influenciados pelo incremento do fluxo turÃstico, quando instituÃdo o PARNA de Jericoacoara. As mudanÃas foram mais significativas, sobretudo, entre os anos de 2001 a 2005, o que pode estar relacionado a uma maior intervenÃÃo humana (fluxo de turistas). A utilizaÃÃo das tÃcnicas de geoprocessamento para o mapeamento da evoluÃÃo morfodinÃmica do campo de dunas do Parque Nacional de Jericoacoara constituiu- se uma ferramenta essencial para a produÃÃo de informaÃÃes que certamente subsidiarÃo a continuidade do planejamento ambiental da referida, que se constitui como uma Unidade de ConservaÃÃo de ProteÃÃo Integral. / Coastal dunes play an important role in the sediment flow of the coastal zone. The unique morphology of the Jericoacoara National Park in the northeastern Brazilian state of Cearà consists of a promontory covered by a mobile dune field consisting of large, horseshoe-shaped dunes known locally as barcanas that migrate from east to west. These dunes are responsible for the by-pass, the transport of sediments essential for the maintenance of the coastline. The present study focused on the morphodynamic evolution of these isolated mobile dunes through the recovery of multitemporal Landsat and Quickbird satellite images from the years between 1975 and 2014. The comparison of the spatio-temporal distribution of the morphology of these dunes over this 41-year period revealed significant shifts in their area, perimeter, and movement. It was possible to confirm that the flow of material and energy were linked to a process of continuous migration in the direction of the beach (sediment bypassing sector). The dynamics of the dune migration in the years following 2000, when the national park was established, indicate possible impacts of the increase in tourism within the area on the morphology of the dunes. The changes were most significant between 2001 and 2005, possibly reflecting a greater influx of tourists and thus more intense anthropogenic impacts. The different geoprocessing techniques applied to the mapping of the morphodynamic evolution of the dune field of the Jericoacoara National Park proved to be an essential tool for the production of information that will guarantee the long-term environmental planning of this integral conservation unit.

Made available in DSpace on 2014-07-29T15:06:28Z (GMT). No. of bitstreams: 1 Dissertacao Daniel Rodrigues.pdf: 929080 bytes, checksum: da4db89bfdec7ec99ff5836ad5b5327e (MD5) Previous issue date: 2009-07-02 / The together-belongingness (Zusammengehörigkeit) of Be-ing and man is discussed in this dissertation in the style of a Phenomenological reflection the together-belongingness (Zusammengehörigkeit) of Be-ing and man. It treats of a concept which appears explicitily in the phenomenological thought of Martin Heidegger, especially, beginning in the 30s, when he questioned the meaning of Truth according to the history of Be-ing, that is, as enowning (Ereignis). The reflection, however, begins with the presupposition together-belongingness is a notion present in the thought of Heidegger from the outset of the fundamental-ontological development of the question of Be-ing, represented principally by the primary work of 1927, Sein und Zeit. For this reason, the reflection begins discussing the unity of the thought itinerary of Heidegger, showing that the reversal of the thinking (Kehre) of the 30s is responsible for the transformation which establishes the same question of Be-ing in a more originating extent than that of Sein und Zeit. Admitting from the beginning that together-belongingness translates the mutual reference between Be-ing and man, coming from the primordial unity, in dependence upon which both bring about historically their essence, and not a secondary and posterior relation between two self-subsisting poles, the discussion proceeds determining the structures of human existence, by which together-belongingness is considered in the different levels of elaboration of the question of Be-ing. Consequently, the central thrust of the dissertation is summarized in limiting the spatial-temporal ambience of the common reference. In the first place, attention is given to the analyses of the comprehension-interpretation project of human existence and language, according to Sein und Zeit. Then, according to Beiträge zur Philosophie, the same ambience is limited taking into consideration the grounding of Da-sein as the intermediary dimension between man and Be-ing, it being the instance of supportability of happening of Truth. Finally, the projection of human existence is revealed as the leap of Be-ing, in such a manner that movement of realization of the essence of Be-ing is shown as being the same as the consummation of the historical existence of men. Thus, the coming about of the Truth, by which Be-ing is experienced as abysmal grounding, is coordinated with the historical coming about of human existence, granting it, in virtue of the depth of its grounding, a unitary movement of revealing and of hiding the mystery of Be-ing. Being that this coordination is the manifestation of the originating space and time, human existence appears as the establishment of the space-time dimension of the abyss of Being, always in agreement with an historical possibility. In this way, the together-belongingness appears as an historical sending-forth, in the form of a questioning which Be-ing directs to man, but which is consumed in the measure which man responds, or as it may be, assumes the responsibility for the destiny of his existence according to the appeals of Be-ing. Thus, thought, understood as a human faculty during all of the history of metaphysics, is reduced to its essence: that by which man corresponds to the historical appeals of Be-ing. To think consumes the intimate reference of man to Be-ing and, therefore, is the privileged manner of placing in operation human existence in union with Be-ing. By means of thought, therefore, man has understood himself separated from and in front of Be-ing. For that reason, the reflection of this dissertation is a path in search of the forgotten unity between man and Be-ing. / Discute-se nessa dissertação, ao modo de uma reflexão fenomenológica, a co-pertinência (Zusammengehörigkeit) entre Ser e homem. Trata-se de um conceito que aparece explicitamente no pensamento fenomenológico de Martin Heidegger, sobretudo a partir dos anos 30, quando o pensamento heideggeriano interroga o sentido da Verdade segundo a história do Ser, isto é, como Ereignis. A reflexão, entretanto, parte do pressuposto de que a co-pertinência é uma noção presente no pensamento de Heidegger desde o desenvolvimento fundamental-ontológico da questão do Ser, representado principalmente pela obra capital de 1927, Sein und Zeit. Por essa razão, a reflexão principia discutindo a unidade do itinerário de pensamento de Heidegger, mostrando que a viragem (Kehre) dos anos 30 é responsável por uma transformação que instaura a mesma questão do Ser em um âmbito mais originário que aquele de Sein und Zeit. Admitindo desde o início que a co-pertinência traduz a mútua referência entre Ser e o homem, advinda da unidade primordial, em dependência da qual ambos realizam historicamente sua essência, e não uma relação secundária e posterior entre dois pólos subsistentes em si, a discussão prossegue explicitando as estruturas da existência humana, pelas quais a co-pertinência é abordada nos diferentes níveis de elaboração da questão do Ser. Nesse sentido, o esforço central da dissertação se resume em circunscrever a ambiência espaço-temporal da mútua referência. Primeiramente, privilegiam-se as análises do projeto compreensivo-interpretativo da existência humana e da linguagem, conforme Sein und Zeit. Depois, conforme os Beiträge zur Philosophie, a mesma ambiência é circunscrita tendo em vista a fundação do Da-sein como a dimensão intermediária entre homem e Ser, por ser a instância de suportabilidade do acontecimento da Verdade. Ao final, o projetar-se da existência humana se desvela como um lance do Ser, de tal maneira que o movimento de realização da Essência do Ser se mostra como sendo o mesmo da consumação da existência histórica dos homens. Assim, o acontecer da Verdade, pelo qual o Ser se dá como fundamento abissal, conjuga-se com o acontecer histórico da existência humana, conferindo a ela, em virtude da abissalidade de seu fundamento, um movimento unitário de abrir e de velar o mistério do Ser. Sendo essa conjunção a manifestação do espaço e tempo originários, o existir humano aparece como a instauração do espaço-temporal do abismo do Ser, sempre em consonância com uma possibilidade histórica. Desse modo, a co-pertinência aparece como um envio histórico, na forma de uma interpelação que o Ser dirige ao homem, mas que se consuma à medida que o homem responde, ou seja, responsabiliza-se pela destinação de sua existência segundo os apelos do Ser. Assim, o pensamento, compreendido como uma faculdade humana durante toda a história da metafísica, é reconduzido a sua essência: aquilo pelo qual o homem corresponde aos apelos históricos do Ser. Pensar consuma a íntima referência do homem ao Ser e, portanto, é o modo privilegiado de pôr em obra a existência humana em unidade com o Ser. Pelo pensamento, porém, o homem tem se compreendido separado e diante do Ser. Por isso, a reflexão dessa dissertação é um caminho em busca da unidade esquecida entre homem e Ser.

In this thesis, we investigated modes of intraseasonal variability (ISV) observed in the Indian monsoon rainfall and how these modes modulate rainfall over India. We identified a decreasing trend in the intensity of low-frequency intraseasonal mode with increasing strength in synoptic variability over India. We also made an attempt to understand the reason for these observed trends using numerical simulations. In the first part of the thesis, satellite rainfall estimates are used to understand the spatiotem-poral structures of convection in the intraseasonal timescale and their intensity during boreal sum-mer over south Asia. Two dominant modes of variability with periodicities of 10–20-days (high-frequency) and 20–60-days (low-frequency) are found, with the latter strongly modulated by sea surface temperature. The 20–60-day mode shows northward propagation from the equatorial In-dian Ocean linked with eastward propagating modes of convective systems over the tropics. The 10–20-day mode shows a complex space-time structure with a northwestward propagating anoma-lous pattern emanating from the Indonesian coast. This pattern is found to be interacting with a structure emerging from higher latitudes propagating southeastwards. This could be related to ver-tical shear of zonal wind over northern India. The two modes exhibit variability in their intensity on the interannual time scale and contribute a significant amount to the daily rainfall variability in a season. The intensities of the 20–60-day and 10–20-day modes show significantly strong inverse and direct relationship, respectively, with the all-India June–September rainfall. This study also establishes that the probability of occurrence of substantial rainfall over central India increases significantly if the two intraseasonal modes simultaneously exhibit positive anomalies over the region. There also exists a phase-locking between the two modes. In the second part of the thesis, we investigated the changing nature of these intraseasonal modes over Indian region, and their association with extreme rainfall events using ground based observed rainfall. We found that the relative strength of the northward propagating 20–60-day mode has a significant decreasing trend during the past six decades, possibly attributed to the weakening of large-scale circulation in the region during monsoon. This reduction is compensated by a gain in synoptic-scale (3–9 days) variability. The decrease in the low-frequency ISV is associated with a significant decreasing trend in the percentage of extreme events during the active phase of the monsoon. However, this decrease is balanced by a significant increasing trend in the percentage of extreme events in break phase. We also find a significant rise in occurrence of extremes during early- and late-monsoon months, mainly over the eastern coastal regions of India. We do not observe any significant trend in the high-frequency ISV. In the last part of the thesis, we used numerical simulations to understand the observed changes in the ISV features. Using the atmospheric component of a global climate model (GCM), we have performed two experiments: control experiment (CE) and heating experiment (HE). The CE is the default simulation for 10 years. In HE, we prescribed heating in the atmosphere in such a way that it mimics the conditions for extreme rainfall events as observed over central India during June– September. Heating is prescribed primarily during the break phase of the 20–60-day mode. This basically increases the number of extremes, majority of which are in break phase. The design of the experiment reflects the observed current scenario of increased extreme events during breaks. We found that the increased extreme events in the HE decreased the intensity of the 20–60-day mode over the Indian region. This reduction is associated with a reduction of rainfall in active phase and increase in the length of break phase. A reduction in the seasonal mean over India is also observed. The reduction of active phase rainfall is linked with an increased stability of the atmosphere over central India. Lastly, we propose a possible mechanism for the reduction of rainfall in active phase. We found that there is a significant reduction in the strength of the vertical easterly shear over the northern Indian region during break–active transition phase. This basically weakens the conditions for the growth of Rossby wave instability, thereby elongating break phase and reducing the rainfall intensity in the following active phase. This study highlights the redistribution of rainfall intensity among periodic (low-frequency) and non-periodic (extreme) modes in a changing climate scenario, which is further tested in a modeling study. The results presented in this thesis will provide a pathway to understand, using observations and numerical model simulations, the ISV and its relative contribution to the Indian summer monsoon. It can also be used for model evaluation.

Cette thèse concerne l’étude de la propagation d’ondes acoustiques dans des structures hétérogènes. Le but essentiel de ces travaux est de confronter des résultats d’expériences numériques effectuées dans le domaine physique (espace, temps) à des prédictions analytiques pour la propagation des ondes de surface SH le long d’un demi-espace stratifié périodique produisant des spectres discontinus de dispersion pour les ondes, ainsi que pour la diffusion multiple dans des milieux aléatoires inclusionnaires (fissures, cavités). Le code numérique FDTD développé lors de cette étude a permis, en autres choses, de corroborer quantitativement les fenêtres spectrales théoriques d’existence des ondes de surface dans les demi-espaces périodiques,ainsi que de montrer des zones de validité fréquentielles des approches analytiques de diffusion multiple concernant les propriétés effectives de milieux aléatoires. / The study is concerned with acoustic waves in elastic media with a different nature of in homogeneity consisting in either periodically continuous or piece wise variation of material properties, or in random sets of defects embedded into a homogeneous matrix, with a given statistical distribution. The scope of problems is topical in non-destructive testing and other applications of ultrasound.Theoretical methods describing involved acoustic phenomena (complex dispersion features, coherent wave in random media, ensemble average techniques) often rely on certain a priori assumptions which render numerical verification especially important.The thesis presents results of analytical modelling of the propagation of surface acoustic waves along periodic half-space, for which the dispersion spectrum is rather complex (discontinuous spectrum of propagation for the surface waves). A 2nd order FDTD numerical code has been developed in order to perform numerical experiments in the space and time domains, and to corroborate the analytical predictions in the frequency domain. A good agreement of simulated results with analytical modelling demonstrates applicability and consistency of the numerical tool. Finally, the code has been used for extracting numerically the coherent wave regime (mean wave over ensemble averaging of the positions of scatterers) for the acoustic propagation in different types of populations of randomly distributed scatterers. The results indicate ranges of validity of some multiple scattering analytical techniques.

No description available.

Depuis le succès croissant des systèmes mobiles au cours des années 1990, les nouvelles technologies sans fil ont été développées afin de répondre à la demande croissante de services multimédias de haute qualité avec des taux d'erreur les plus faibles possibles. Un moyen intéressant pour améliorer les performances et obtenir de meilleurs taux de transmission consiste à combiner l'utilisation de plusieurs diversités avec un accès de multiplexage dans le cadre des systèmes MIMO. L'utilisation de techniques de sur-échantillonnage, d'étalement et de multiplexage, et de diversités supplémentaires conduit à des signaux multidimensionnels, au niveau de la réception, qui satisfont des modèles tensoriels. Cette thèse propose une nouvelle approche tensorielle basée sur un codage spatio-temporel tensoriel (TST) pour les systèmes de communication sans fil MIMO. Les signaux reçus par plusieurs antennes forment un tenseur d'ordre quatre qui satisfait un nouveau modèle tensoriel, modèle PARATUCK-(2,4) (PT-(2,4)). Une analyse de performance est réalisée pour le système TST ainsi que pour un système spatio-temporel-fréquentiel (STF) récemment proposé dans la littérature, avec l'obtention du gain maximum de diversité dans le cas d'un canal à évanouissement plat. Un système de transmission basé sur le codage TST est proposé pour les systèmes MIMO avec plusieurs utilisateurs. Une nouvelle décomposition tensorielle est introduite, appelée PT-(N1,N). Cette thèse établit les conditions d'unicité du modèle PT-(N1,N). À partir de ces résultats, différents récepteurs semi-aveugles sont proposés pour une estimation conjointe des symboles transmis et du canal, pour les systèmes TST et STF. / Since the growing success of mobile systems in the 1990s, new wireless technologies have been developed in order to support a growing demand for high-quality multimedia services with low error rates. An interesting way to improve the error performance and to achieve better transmission rates is to combine the use of various diversities and multiplexing access techniques in the MIMO system context. The incorporation of oversampling, spreading and multiplexing operations and additional diversities on wireless systems lead to multidimensional received signals which naturally satisfy tensor models. This thesis proposes a new tensorial approach based on a tensor space-time (TST) coding for MIMO wireless communication systems. The signals received by multiple antennas form a fourth-order tensor that satisfies a new tensor model, referred to as PARATUCK-(2,4) (PT-(2,4)) model. A performance analysis is carried out for the proposed TST system and a recent space-time-frequency (STF) system, which allows to derive expressions for the maximum diversity gain over a at fading channel. An uplink processing based on the TST coding with allocation resources is proposed. A new tensor decomposition is introduced, the so-called PT-(N1,N), which generalizes the standard PT-2 and our PT-(2,4) model. This thesis establishes uniqueness conditions for the PARATUCK-(N1,N) model. From these results, joint symbol and channel estimation is ensured for the TST and STF systems. Semi-blind receivers are proposed based on the well-known Alternating Least Squares algorithm and the Levenberg-Marquardt method, and also a new receiver based on the Kronecker Least Squares (KLS) for both systems.

A new combination of techniques for the numerical computation of incompressible flow is presented. The temporal discretization bases on the discontinuous Galerkin-formulation. Both constant (DG(0)) and linear approximation (DG(1)) in time is discussed. In case of DG(1) an iterative method reduces the problem to a sequence of problems each with the dimension of the DG(0) approach. For the semi-discrete problems a Galerkin/least-squares method is applied. Furthermore a non-overlapping domain decomposition method can be used for a parallelized computation. The main advantage of this approach is the low amount of information which must be exchanged between the subdomains. Due to the slight bandwidth a workstation-cluster is a suitable platform. Otherwise this method is efficient only for a small number of subdomains. The interface condition is of the Robin/Robin-type and for the Navier-Stokes equation a formulation introducing a further pressure interface condition is used. Additionally a suggestion for the implementation of the standard k-epsilon turbulence model with special wall function is done in this context. All the features mentioned above are implemented in a code called ParallelNS. Using this code the verification of this approach was done on a large number of examples ranging from simple advection-diffusion problems to turbulent convection in a closed cavity.

In the present work we deal with the stability of the space-time discontinuous Galerkin method applied to non-stationary, nonlinear convection - diffusion problems. Discontinuous Galerkin method is a very efficient tool for numerical solution of partial differential equations, combines the advantages of the finite element method (polynomial approximations of high order of accuracy) and the finite volume method (discontinuous approximations). After the formulation of the continuous problem its discretization in space and time is described. In the formulation of the discontinuous Galerkin method the non-symmetric, symmetric and incomplete version of discretization of the diffusion term is used and there are added penalty terms to the scheme also. In the third chapter are estimated individual terms of the previously derived approximate solution by special norms. Using the concept of discrete characteristic functions and the discrete Gronwall lemma, it is shown that the analyzed scheme is unconditionally stable. At the end, in the fourth chapter, are given some numerical experiments, which verify theoretical results from the previous chapter.

Esta investigación tiene como propósito desentrañar la sociedad española que sedescribe en la novela Tierra de campos del autor español David Trueba, con elobjetivo de cartografiarla y encontrar en ella rasgos comunes y propios de unasociedad posmoderna.Para ello se recurrirá a los postulados de la teoría de la posmodernidad deFredrik Jameson y se centrará especialmente en los conceptos de espacio y tiempo.De la novela se extraerán los rasgos distintivos de los personajes, de los lugares ydel contexto en el que esta acontece para poder configurar un paisaje amplio de lasociedad a la que pertenecen y de esta forma acercarse al objetivo del estudio.Como resultado de la investigación se ha podido definir la sociedadespañola descrita en la novela como de carácter posmoderno, pero con unaspeculiaridades propias derivadas de la herencia de las antiguas estructuras deltardofranquismo. / The following research is intended to ascertain and furthermore describe in depththe way in which David Trueba’s fictional novel Tierra de campos reflects thecontemporary Spanish society. And by so doing, an analysis of whether Spanishsociety can genuinely be considered postmodern, will be presented.The analysis will be supported by a focus on the space-temporal scope asit is asserted in Fredrik Jameson’s theory on post-modernism. Taking the novel byTrueba as a main source, reference characters, places, setting as well as context, willplay an important role in the mapping out of all shared features of the society thatthe novel describes in order to approach the purpose of the study.As a result of this research, we have been able to properly define the societydepicted in the novel as one clearly pertaining to the post-modern timeline,nonetheless bearing some of the inherent traces derived from the rusty structurescharacteristic of the last period of Franco’s dictatorship.

Une des finalités du traitement d’antenne est la détection et la localisation de cibles en milieu bruité. Dans la plupart des cas pratiques, comme par exemple le RADAR ou le SONAR actif, il faut estimer dans un premier temps les propriétés statistiques du bruit, et plus précisément sa matrice de covariance ; on dispose à cette fin de données secondaires supposées identiquement distribuées. Dans ce contexte, les hypothèses suivantes sont généralement formulées : bruit gaussien, données secondaires ne contenant que du bruit, et bien sûr matériels fonctionnant parfaitement. Il est toutefois connu aujourd’hui que le bruit en RADAR est de nature impulsive et que l’hypothèse Gaussienne est parfois mal adaptée. C’est pourquoi, depuis quelques années, le bruit et en particulier le fouillis de sol est modélisé par des processus elliptiques, et principalement des Spherically Invariant Random Vectors (SIRV). Dans ce nouveau cadre, la Sample Covariance Matrix (SCM) estimant classiquement la matrice de covariance du bruit entraîne des pertes de performances très importantes des détecteurs / estimateurs. Dans ce contexte non-gaussien, d’autres estimateurs de la matrice de covariance mieux adaptés à cette statistique du bruit ont été développés : la Matrice du Point Fixe (MPF) et les M-estimateurs.Parallèlement, dans un cadre où le bruit se décompose sous la forme d’une somme d’un fouillis rang faible et d’un bruit blanc, la matrice de covariance totale est structurée sous la forme rang faible plus identité. Cette information peut être utilisée dans le processus d'estimation afin de réduire le nombre de données nécessaires. De plus, il aussi est possible d'utiliser le projecteur orthogonal au sous espace fouillis à la place de la matrice de covariance ce qui nécessite moins de données secondaires et d’être aussi plus robuste aux données aberrantes. On calcule classiquement ce projecteur à partir d'un estimateur de la matrice de covariance. Néanmoins l'état de l'art ne présente pas d'estimateurs à la fois être robustes aux distributions hétérogènes, et rendant compte de la structure rang faible des données. C'est pourquoi ces travaux se focalisent sur le développement de nouveaux estimateurs (de covariance et de sous espace), directement adaptés au contexte considéré. Les contributions de cette thèse s'orientent donc autour de trois axes :- Nous présenterons tout d'abord un modèle statistique précis : celui de sources hétérogènes ayant une covariance rang faible noyées dans un bruit blanc gaussien. Ce modèle et est, par exemple, fortement justifié pour des applications de type radar. Il à cependant peu été étudié pour la problématique d'estimation de matrice de covariance. Nous dériverons donc l'expression du maximum de vraisemblance de la matrice de covariance pour ce contexte. Cette expression n'étant pas une forme close, nous développerons différents algorithmes pour tenter de l'atteindre efficacement.- Nous développons de nouveaux estimateurs directs de projecteur sur le sous espace fouillis, ne nécessitant pas un estimé de la matrice de covariance intermédiaire, adaptés au contexte considéré.- Nous étudierons les performances des estimateurs proposés et de l'état de l'art sur une application de Space Time Adaptative Processing (STAP) pour radar aéroporté, au travers de simulations et de données réelles. / One purpose of array processing is the detection and location of a target in a noisy environment. In most cases (as RADAR or active SONAR), statistical properties of the noise, especially its covariance matrix, have to be estimated using i.i.d. samples. Within this context, several hypotheses are usually made: Gaussian distribution, training data containing only noise, perfect hardware. Nevertheless, it is well known that a Gaussian distribution doesn’t provide a good empirical fit to RADAR clutter data. That’s why noise is now modeled by elliptical process, mainly Spherically Invariant Random Vectors (SIRV). In this new context, the use of the SCM (Sample Covariance Matrix), a classical estimate of the covariance matrix, leads to a loss of performances of detectors/estimators. More efficient estimators have been developed, such as the Fixed Point Estimator and M-estimators.If the noise is modeled as a low-rank clutter plus white Gaussian noise, the total covariance matrix is structured as low rank plus identity. This information can be used in the estimation process to reduce the number of samples required to reach acceptable performance. Moreover, it is possible to estimate the basis vectors of the clutter-plus-noise orthogonal subspace rather than the total covariance matrix of the clutter, which requires less data and is more robust to outliers. The orthogonal projection to the clutter plus noise subspace is usually calculated from an estimatd of the covariance matrix. Nevertheless, the state of art does not provide estimators that are both robust to various distributions and low rank structured.In this Thesis, we therefore develop new estimators that are fitting the considered context, to fill this gap. The contributions are following three axes :- We present a precise statistical model : low rank heterogeneous sources embedded in a white Gaussian noise.We express the maximum likelihood estimator for this context.Since this estimator has no closed form, we develop several algorithms to reach it effitiently.- For the considered context, we develop direct clutter subspace estimators that are not requiring an intermediate Covariance Matrix estimate.- We study the performances of the proposed methods on a Space Time Adaptive Processing for airborne radar application. Tests are performed on both synthetic and real data.