La compréhension et la simulation des mécanismes de déformation dans la croûte supérieure sont des enjeux scientifiques et techniques importants. La calcite étant un minéral commun de la croûte supérieure se déformant essentiellement par maclage sous 200 °C, c'est pour cette raison que l'on s'intéresse plus particulièrement au maclage de la calcite dans le cadre de cette thèse. L'utilisation du maclage de la calcite n'en est pas à son coup d'essai et de nombreuses méthodes d'inversions existent que ce soit pour remonter aux tenseurs des contraintes comme aux tenseurs des déformations. Cette thèse propose une nouvelle méthode d'inversion basée sur l'inversion d'Etchopar permettant de reconstruire 5 sur 6 paramètres du tenseur des contraintes avec une quantification fine des incertitudes. Cette méthode permet de détecter automatiquement l'existence d'un ou de plusieurs évènements tectoniques enregistrés par le maclage de la calcite. Un deuxième volet de la thèse consiste en l'amélioration de la méthode d'acquisition des données de macles en utilisant un EBSD (electron backscatter diffraction). En effet, l'utilisation traditionnelle de la platine universelle a des limitations techniques et amène aussi à un doute visuel sur l'appréciation du statut non-maclé de certains plans, en plus du côté long et fastidieux. Le dernier volet de la thèse consiste à déterminer le seuil de maclage de la calcite pour différentes tailles de grains à l'aide de tests mécaniques sous une presse uniaxiale. Qui plus est, le suivi en continu des déformations sur les monocristaux de calcite a permis de mettre en évidence le comportement macroscopique d'un cristal de calcite et la séquence de maclage. / The understanding and modelling of deformation mechanics in the upper crust are important scientific and technical issues. The calcite is a common mineral in the upper crust and mainly deforms by twinning under 200°C. That is why we are interested by calcite twinning as part of this thesis. It is not the first time that calcite twinning is used to reconstruct paleostress or paleostrain tensors. This thesis propose a new inversion method based on the Etchecopar’s one allowing to reconstruct 5 among 6 parameters of the stress tensor with an accurate quantification of the uncertainties. This method allows to automatically detect the realness of one or several tectonic events recorded by calcite twinning. A second part of the thesis consists in the improvement of the data acquisition by using EBSD (electron backscatter diffraction). In fact, the traditional use of the universal stage has technical limitations and brings some optical doubt about the untwinned status of few planes in addition to the long and tedious side. The last part of the thesis consists in the establishing the threshold of calcite twinning for different grain sizes by mechanical tests under a uniaxial press. Moreover, the continuous monitoring of the experiments using single crystals of calcite allowed to highlight the macroscopic behavior of a single crystal and the sequence of twinning.

Os órgãos de saúde internacionais e nacionais, como o Ministério da Saúde na portaria 453/98 da Vigilância Sanitária, exigem que a Dose de Entrada na Pele seja avaliada para cada equipamento mamográfico através da leitura de um sistema câmara de ionização-eletrómetro corrigida pelo fator de retroespalhamento. Ao não existir menção explícita na portaría de valores utilizáveis para o fator de retroespalhamento, este trabalho visa à determinação experimental do fator de retroespalhamento, através da utilização dos dosímetros termoluminescentes TLD-100. No estudo são verificadas as dependências geométricas e espectrais do fator de retroespalhamento, assim como do valor da Dose de Entrada na Pele, e da Dose em Profundidade, correspondentes com as técnicas radiográficas empregadas nos exames mamográficos convencionais de rotina. Foram avaliados feixes na faixa de 0,35 mmAl até 0,43 mmAl, tensões do tubo de 25kV, 28kV, 30kV, e 32kV, assim como os três tamanhos de campo disponíveis no Mamógrafo Senographe DMR utilizado, e distancias focofilme iguais a 56cm, 61cm e 66cm. Os resultados obtidos foram comparados com publicações existentes, as quais apresentam resultados obtidos através de Simulação Monte Carlo, câmaras de ionização, e dosímetros TLD-100. Os resultados obtidos neste trabalho permitem estabelecer e discutir as dependências das grandezas dosimétricas estudadas com a Camada Semi-Redutora, tensão do tubo, combinação ânodo-filtro, tamanho de campo, distância foco-filme e espessura da mama. / National and international health organizations such as the Brazilian Ministry of Health, through its Secretary of Health Surveillance establishes in the publication Nº 453/98 that in all mammographic equipments must be evaluated the entrance-skin dose through the readings of an ionization chamber-electrometer system corrected by the backscatter factor, among others factors. Nevertheless, there is no explicit mention for useful values of backscatter factor in this document; the main aim of this work is the experimental determination of backscatter factor through the use of TLD-100 dosimeters. In this study, the geometric and spectral dependencies of the backscatter factor, entrance-skin dose and the in-depth dose were evaluated, corresponding to the most radiographic techniques employed in conventional mammographic procedures, i.e., beam qualities in the range of 0.35 mmAl to 0.43 mmAl, tube voltages from 25kV to 32kV, focus-film distances from 56cm to 66cm, and three field sizes were evaluated. Our results were compared with those previously published obtained through Monte Carlo simulation, ionization chambers and TLD dosimeters. The results obtained in this work allow studying the dependency of the mentioned dosimetric quantities with the half-value layer, tube voltage, anode-filter combination, field size, focusfilm distance and breasting thickness of the breast.

Made available in DSpace on 2014-06-12T15:59:32Z (GMT). No. of bitstreams: 2 arquivo5160_1.pdf: 4852221 bytes, checksum: 00af0b636289f3973abc1f5ce9bce923 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2004 / O ru´ıdo speckle aparece em imagens com iluminac¸ ao coerente, tais como, sonar, laser, ultra-sonografia e radar de abertura sint´etica (Synthentic Aperture Radar SAR). Existem diversas t´ecnicas para reduc¸ ao de ru´ıdo speckle. Este trabalho propoem uma metodologia que permite a utilizac¸ ao destas t´ecnicas a fim de produzir uma imagem filtrada. Esta imagem filtrada ´e obtida combinando pontualmente de forma linear as t´ecnicas j ´a dispon´ıveis. Os coeficientes da combinac¸ ao linear s ao encontrados tal que satisfac¸am aproximadamente as expectativas do usu´ario. A t´ecnica ´e denominada Filtragem Interagente, desde que as expectativas do usu´ario s ao expressas atrav´es das especificac¸ oes das regi oes de interesse e dos valores desejados associados a cada regi ao de interesse. A t´ecnica ´e implementada na linguagem IDL e integrada ao ENVI, uma plataforma de processamento de imagens. A proposta ´e avaliada em imagens sint´etica e real SAR utilizando duas medidas de qualidade, o erro m´edio quadr ´atico normalizado (NMSE - Normalized Mean Square Error) e o n ´umero equivalente de visadas (ENL - Equivalent Number of Looks), sob o crit´erio da relac¸ ao sinal-ru´ıdo (SNR Signal-to-Noise Ratio). Os resultados quantitativos e qualitativos obtidos s ao superiores aos obtidos com filtros cl ´assicos redutores de ru´ıdo speckle e as imagens obtidas satisfazem as expectativas do usu´ario.

This work focuses on detection of denial of service (DoS) attacks which utilize random spoofing of source IP address in attack packets. These types of attacks lead to generation of side effect in a form of backscatter that can be used to identify victims of such attacks. Backscatter analysis has so far been limited to unused address space ranges referred to as network telescopes. This work therefore proposes a new method of DoS attack detection via backscatter outside of network telescope environment where legitimate user traffic is also present. Furthermore proposed approach uses only abstracted traffic in a form of network flows. Presented method was implemented as part of NEMEA system and tested on real flow data capture provided by CESNET.

This thesis deals with snow cover mapping by using time-series of SAR images of the sensors ENVISAT ASAR and TerraSAR-X. The methodology is based on the so-called Nagler's algorithm, which is based on determination of the change of absorption of radar signal due to the liquid water content in the snow cover. The resulting ratio image is classified into the areas with wet snow or without it according to the selected threshold value. The results are compared with the maps of snow cover derived from MODIS optical data and with data from meteorological stations of CHMI. The main aims of this work are to suggest most suitable conditions (time of the year, weather) for acquisition of reference images, to find the change of the threshold value with respect the chosen reference image and the type of land cover. The same methodology should then be applied on the radar data of shorter wavelength. The obtained results will be further used for improving the methodology of snow cover mapping from SAR data in the Czech Republic.

The present thesis deals with a number of challenges in the field of large eddy simulation (LES). These include the performance of subgrid-scale (SGS) models at fairly high Reynolds numbers and coarse resolutions, passive scalar and stochastic modeling in LES. The fully-developed turbulent channel flow is used as the test case for these investigations. The advantage of this particular test case is that highly accurate pseudo-spectral methods can be used for the discretization of the governing equations. In the absence of discretization errors, a better understanding of the subgrid-scale model performance can be achieved. Moreover, the turbulent channel flow is a challenging test case for LES, since it shares some of the common important features of all wall-bounded turbulent flows. Most commonly used eddy-viscosity-type models are suitable for moderately to highly-resolved LES cases, where the unresolved scales are approximately isotropic. However, this makes simulations of high Reynolds number wall-bounded flows computationally expensive. In contrast, explicit algebraic (EA) model takes into account the anisotropy of SGS motions and performs well in predicting the flow statistics in coarse-grid LES cases. Therefore, LES of high Reynolds number wall-bounded flows can be performed at much lower number of grid points in comparison with other models. A demonstration of the resolution requirements for the EA model in comparison with the dynamic Smagorinsky and its high-pass filtered version for a fairly high Reynolds number is given in this thesis. One of the shortcomings of the commonly used eddy diffusivity model arises from its assumption of alignment of the SGS scalar flux vector with the resolved scalar gradients. However, better SGS scalar flux models that overcome this issue are very few. Using the same methodology that led to the EA SGS stress model, a new explicit algebraic SGS scalar flux model is developed, which allows the SGS scalar fluxes to be partially independent of the resolved scalar gradient. The model predictions are verified and found to improve the scalar statistics in comparison with the eddy diffusivity model. The intermittent nature of energy transfer between the large and small scales of turbulence is often not fully taken into account in the formulation of SGS models both for velocity and scalar. Using the Langevin stochastic differential equation, the EA models are extended to incorporate random variations in their predictions which lead to a reasonable amount of backscatter of energy from the SGS to the resolved scales. The stochastic EA models improve the predictions of the SGS dissipation by decreasing its length scale and improving the shape of its probability density function. / QC 20110615

YSCAT is a unique ultrawideband microwave scatterometer developed to investigate the sea surface under a variety of environmental and radar parameters. The YSCAT94 experiment consisted of a six month deployment on the WAVES research tower operated by the Canada Center for inland Waters (CCIW). Over 3500 hours of data were collected at 2Γ 3.05Γ 5.3Γ 10.02Γ and 14 GHz and at a variety of wind speeds, relative azimuth angles, and incidence angle. A low wind speed "rolloff" of the normalized radar cross section (σ°) in YSCAT94 data is found and quantified. The rolloff wind speedΓ γΓ is estimated through regression estimation analysis using an Epanechnikov kernel. For YSCAT94 data, the rolloff is most noticeable at mid-range incidence angles with γ values ranging from 3 to 6 m/s. In order to characterized YSCAT94 backscatter distributions, a second order polynomial in log space is developed as a model for the probability of the radar cross sectionΓρ(σ°). Following Gotwols and ThompsonΓρ(σ°) is found to adhere to a log-normal distribution for horizontal polarization and a generalized log-normal distribution for vertical polarization. If ρ(α|σ°) is assumed to be Rayleigh distributed, the instantaneous amplitude distribution ρ(α) is found to be the integral of a Rayleigh/generalized log-normal distribution. A robust algorithm is developed to fit this probability density function to YSCAT94 backscatter distributions. The mean and variance of the generalized log-normal distribution are derived to facilitate this algorithm. Over 2700 distinct data cases sorted according to five different frequencies, horizontal and vertical polarizations, upwind and downwind, eight different incidence angles Γ1-10 m/s wind speeds, and 0.1-0.38 mean wave slope are considered. Definite trends are recognizable in the fitted parameters a1Γ a2Γ and C of the Rayleigh/generalized log-normal distribution when sorted according to wind speed and mean wave slope. At mid-range incidence angles, the Rayleigh/generalized log-normal distribution is found to adequately characterize both low and high amplitude portions of YSCAT94 backscatter distributions. However, at higher incidence angels (50°and 60°) the more general Weibull/generalized log-normal distributions is found to better characterized the low amplitude portion of the backscatter distributions.

In May of 2000 Jason-1, a joint project between NASA and the French space agency CNES, will be launched. Its mission is to continue the highly successful gathering of data which TOPEX/Poseidon has collected since August of 1992. The main goal of Jason-1 is to achieve higher accuracy in measuring the mean sea level (MSL). In order to do so, the electromagnetic (EM) bias must be estimated more accurately because it is the largest contributing error. This thesis presents two different studies which add to the knowledge and improve estimation of the EM bias, and thus assists Jason-1 in achieving its primary goal. Oceanographic data collected from two different experiments are analyzed; on in the Gulf of Mexico (GME) and the other in Bass Strait, Australia (BSE). The first study is a spatial analysis of the backscattered power versus the phase of the wave. Its purpose is to determine why the normalized EM bias stops increasing and levels out at high wind speeds (about 11 m/s) and then decreases at higher wind speeds. Two possible causes are investigated. First, it could be due to a shift in the backscatter power modulation to the forward or rear face of the wave crests. Second, it may be due to the backscatter power becoming more homogeneous throughout the wave profile. This study is novel because it uses the knowledge of the spatial distribution of both the backscatter and wave displacement for the study of the EM bias. Both contribute to the EM bias decrease, but the latter cause seems to be the dominant effect. This study is performed on GME data. The second study uses two different nonparametric regression (NPR) techniques to estimate the EM bias. A recent study of satellite data from the TOPEX/Poseidon altimeter supports that the bias is modeled better using NPR regression. A traditional parametric fit is compared to two NPR techniques with GME data. The parametric fit is a variation of NASA's equation used to estimate EM bias for their Geophysical Data Records (GDRs). The two NPR techniques used are the Nadaraya-Watson Regression (NWR) and Local Linear Regression (LLR) estimators. Two smoothing kernel functions are used with each NPR technique, namely the Gaussian and the Epanechnikov kernels. NPR methods essentially consist of statistically smoothing the measured EM bias estimates are compared in the wind and significant wave height plane. Another recent study has shown that wave slope is strongly correlated to EM bias. With this knowledge, EM bias is estimated over several two-dimensional planes which include wave slope in attempt to reduce the residual bias. This portion of the study is performed on GME and BSE data. It is shown that a combination of slope, significant wave height, and wind speed used in conjunction with these NPR methods produces the best EM bias estimate for tower data.

Ku-band dual-polarization radar backscatter measurements from the SeaWinds on QuikScat scatterometer and microwave radiometer measurements from the Special Sensor Microwave/Imager (SSM/I) are used to determine periods of surface melt and freeze in the Antarctic ice-shelves. The normalized radar backscatter (sigma-0) and backscatter polarization ratio (PR) are used in the maximum likelihood estimation of the ice-state. This method is used to infer the daily ice-surface conditions for 25 selected study points located on the Ronne, Ross, Larsen, Fimbul, Amery, and Shackleton Ice-shelves. The temporal and spatial variations of the radar response are also observed for various neighborhood sizes surrounding each given point during the study period. Criteria for determining the dates of melt-onset and freeze-up for each Austral summer are also presented. Validation of the ice-state and melt-onset date estimates is performed by analyzing corresponding brightness temperature (Tb) measurements from radiometers. QuikScat sigma-0 measurements from 1999 through 2003 are analyzed and it is shown that Ku-band scatterometers are very useful for determining periods of melt in Antarctic ice-sheets and provide high temporal and spatial resolution ice-state estimates. These estimates can be important for long-term studies of the climatic effects of the seasonal and inter-annual melting of the Antarctic ice-sheets. The SeaWinds on QuikScat (QuikScat) and SeaWinds on ADEOS-2 (SeaWinds) scatterometers are identical radar sensors on different spaceborne platforms traversing similar orbits. QuikSCAT and SeaWinds data are used to infer near-surface wind vectors, polar sea-ice extent, polar-ice melt events, among others. In order to verify the relative calibration of these two sensors a simple cross-calibration method is implemented based on land measurements. A first-order polynomial model for the incidence angle dependence of sigma-0 is used to account for biases in the sigma-0 measurements. This model is applied to selected regions of the Amazon rainforest and the Sahara desert. It is shown that the two sensors are well calibrated. Additionally, evidence of a previously presumed diurnal cycle in the Amazon rainforest backscatter is given.

The presence of rain over oceans interferes with the measurement of sea surface wind speed and direction from the Sea Winds scatterometer and as a result wind measurements contain biases in rain regions. In past research at the Central Florida Remote Sensing Lab, it has been observed that rain has multi-fractal behavior. In this report we present an algorithm to detect the presence of rain so that rain regions are flagged. The forward and aft views of the horizontal polarization σ0 are used for the extraction of textural information with the help of multi-fractals. A single negated multi-fractal exponent is computed to discriminate between wind and rain. Pixels with exponent value above a threshold are classified as rain pixels and those that do not meet the threshold are further examined with the help of correlation of the multi-fractal exponent within a predefined neighborhood of individual pixels. It was observed that the rain has less correlation within a neighborhood compared to wind. This property is utilized for reactivation of the pixels that fall below a certain threshold of correlation. An advantage of the algorithm is that it requires no training, that is, once a threshold is set, it does not need any further adjustments. Validation results are presented through comparison with the Tropical Rainfall Measurement Mission Microwave Imager (TMI) 2A12 rain retrieval product for one whole day. The results show that the algorithm is efficient in suppressing non-rain (wind) pixels. Also algorithm deficiencies are discussed, for high wind speed regions. Comparisons with other proposed approaches will also be presented.