Les nuages sont une incertitude majeure pour l'étude du climat. Parmi eux, les cirrus en sont des modulateurs essentiels, par leur effet de serre élevé et leur effet d'albedo. Cependant, leur haute altitude et leur composition atypique compliquent leur étude. Les nombreuses campagnes de mesure des vingt dernières années ont montré la complexité de leur composition et la forte variabilité de leurs propriétés microphysiques : taille, forme et orientation des cristaux qui les composent. Ce manque de connaissance entraîne de graves lacunes dans leur modélisation, et une incohérence certaine dans les résultats des simulations climatiques à grande échelle. Les avantages des instruments de télédétection pourraient conduire à de nouvelles méthodes d'étude des cristaux dans les cirrus. Cette thèse analyse l'apport potentiel de mesures spatiales pour caractériser les nuages de glace, en prévision de l'Aqua-Train, une formation de satellites pour l'étude de l'atmosphère. La diffusion lumineuse dans les cristaux a été modélisée en prenant en compte leurs multiples propriétés, menant à plusieurs techniques de restitution de la microphysique des cirrus par des mesures de l'état de polarisation de la lumière par télédétection active et passive. Ces techniques ont été appliquées à des données sol pour évaluer leur pertinence, et leur application potentielle à des mesures spatiales envisagée. Combinées dans un cadre théorique homogène, elles ont conduit à la restitution cohérente des propriétés des cristaux dans les cirrus : orientation spatiale et angle maximum de déviation à partir de mesures polarisées (lidar à balayage, radiomètre) ; facteur de forme par observations lidar polarisées ; taille par synergie multi-instruments (lidar, radiomètre IR). La restitution de ces paramètres à l échelle globale conduira à une meilleure compréhension des propriétés radiatives des cirrus, et à une meilleure interprétation de leur importance dans le contexte du bilan radiatif terrestre.

The bidirectional reflectance distribution function (BRDF) that describes the scattered energy distribution is the most fundamental radiative property to calculate other properties. Although recent progress in surface metrology allows topography measurement in an atomic level, most studies still assume statistical distributions of roughness because of difficulty in roughness modeling. If the BRDF of rough silicon wafers is modeled with assumptions, predicted radiative properties may be inaccurate because non-Gaussian and anisotropic roughness of some wafers cannot be approximated with known statistics. Therefore, this thesis focuses on development of BRDF modeling that accounts for anisotropic roughness to accurately predict radiative properties of rough silicon surfaces with thin-film coatings. Monte Carlo ray-tracing methods are developed to consider multiple scattering and the change of polarization states and to satisfy physical laws such as the reciprocity principle. Silicon surface topographic data measured with an atomic force microscope are incorporated into the ray-tracing algorithms to model anisotropic roughness statistics. For validation, BRDF and emittance predictions are compared with measurements using an optical scatterometer and an integrating sphere. Good agreement between prediction and measurement demonstrates that the incorporation of topography measurement into BRDF modeling is essential for accurate property prediction. Roughness effects on the BRDF are so strong that BRDFs also reveal anisotropic features regardless of the presence of coating. Anisotropic roughness increases multiple scattering although first-order scattering is dominant, and thus enhances emittance noticeably. Silicon dioxide coating changes the magnitude of BRDF and emittance and reduces the anisotropic roughness effect on emittance enhancement. The research in this thesis advances the method to predict radiative properties by incorporating anisotropic rough statistics into BRDF modeling.

The effects of coupling parameters of active-passive and passive-passive coupling components on the coupling efficiency and signal mixed proportion for polymer optical fiber (POF) communication are investigated. A high sensitivity and easy fabricated POF displacement sensor is proposed by using cycling bending POF. Also, light sources for both Laser diode (LD) and light emitting diode (LED) are employed in this study. Experimental approaches and numerical analysis of rays tracing method and finite element method are performed to investigate the effects of coupling scheme and bent deformation on the optical power attenuation. Experimental results also illustrate the feasibility of using numerical analysis in coupling components and POF displacement sensor design. The effect of V-grooved array¡¦s POF on the coupling efficiency and signal mixed proportion are presented in active-passive components. The results indicate that the effect of the V-groove¡¦s shape and size on the coupling efficiency is very significant for all designed parameters of V-grooved array¡¦s POF. Compared with the parallel V-grooved array, the skew V-grooved array reduces the length of the coupling component and increases the output power between light source and POF. In the Y-branch POF coupler for passive-passive components, both the excess loss and the output power ratio of the Y-branch couplers are very sensitive to the couple angle, the coupling distance and the refractive index of the filling medium between the emitting-end and receiving-end of fibers. The results also show that the proposed model can be used to analyze the coupling efficiencies in the asymmetrical Y-branch or axial symmetrical couplers with acceptable accuracy. In the POF displacement sensor using by cycling bending loss, the results show that the effect of roller¡¦s number, interval and wavelength on light power attenuation is very significant. Based on the experimental data, a linear equation is derived to estimate the relationship between the power loss and the relative displacement. The difference between the estimated results and the experimental results is less than 8%.

The graphics hardware have evolved from simple feed forward triangle rasterization devices to flexible, programmable, and powerful parallel processors. This evolution allows the researchers to use graphics processing units (GPU) for both general purpose computations and advanced graphics rendering. Sophisticated GPUs hold great opportunities for the acceleration of computationally expensive photorealistic rendering methods. Rendering of photorealistic images in real-time is a challenge. In this work, we investigate efficient ways to utilize GPUs for real-time photorealistic rendering. Specifically, we studied uniform grid based ray tracing acceleration methods and GPU friendly traversal algorithms. We show that our method is faster than or competitive to other GPU based ray tracing acceleration techniques. The proposed approach is also applicable to the fast rendering of volumetric data. Additionally, we devised GPU based solutions for real-time stereoscopic image generation which can be used in companion with GPU based ray tracers.

Ray tracing is a computationally complex global illumination algorithm that is used for producing realistic images. In addition to parallel implementations on commodity PC clusters, recently, Graphics Processing Units (GPU) have also been used to accelerate ray tracing. In this thesis, ray tracing is accelerated on a GPU cluster where the viewing plane is divided into unit tiles. Slave processes work on these tiles in a task parallel manner which are dynamically assigned to them. To decrease the number of ray-triangle intersection tests, Bounding Volume Hierarchies (BVH) are used. It is shown that almost linear speedup can be achieved. On the other hand, it is observed that API and network overheads are obstacles for scalability.

Understanding and modeling seismic wave propagation is important in regional and exploration seismology. Ray tracing is a powerful and popular method for this purpose. Wavefront construction (WFC) method handles wavefronts instead of individual rays, thereby controlling proper ray density on the wavefront. By adaptively controlling rays over a wavefront, it efficiently models wave propagation. Algorithms for a quasi-P wave wavefront construction method and a new coordinate system used to generate wavefront construction mesh are proposed and tested for numerical properties and modeling capabilities. Traveltimes, amplitudes, and other parameters, which can be used for seismic imaging such as migrations and synthetic seismograms, are computed from the wavefront construction method. Modeling with wavefront construction code is applied to anisotropic media as well as isotropic media. Synthetic seismograms are computed using the wavefront construction method as a new way of generating synthetics. To incorporate layered velocity models, the model based interpolation (MBI) ray tracing method, which is designed to take advantage of the wavefront construction method as well as conventional ray tracing methods, is proposed and experimental codes are developed for it. Many wavefront construction codes are limited to smoothed velocity models for handling complicated problems in layered velocity models and the conventional ray tracing methods suffer from the inability to control ray density during wave propagation. By interpolating the wavefront near model boundaries, it is possible to handle the layered velocity model as well as overcome ray density control problems in conventional methods. The test results revealed this new method can be an effective modeling tool for accurate and effective computing.

Modern rendering systems require fast and efficient acceleration structures in order to compute visibility in real time. I present several novel data structures and algorithms for computing visibility with high performance. In particular, I present two algorithms for improving heuristic based acceleration structure build. These algorithms, when used in a demand driven way, have been shown to improve build performance by up to two orders of magnitude. Additionally, I introduce ray tracing in perspective transformed space. I demonstrate that ray tracing in this space can significantly improve visibility performance for near-common origin rays such as eye and shadow rays. I use these data structures and algorithms to support a key hypothesis of this dissertation: “There is no silver bullet for solving the visibility problem; many different acceleration structures will be required to achieve the highest performance.” Specialized acceleration structures provide significantly better performance than generic ones and building many specialized structures requires high performance build techniques. Additionally, I present an optimization-based taxonomy for classifying acceleration structures and algorithms in order to identify which optimizations provide the largest improvement in performance. This taxonomy also provides context for the algorithms I present. Finally, I present several novel cost metrics (and a correction to an existing cost metric) to improve visibility performance when using metric based acceleration structures. / text

Three related electromagnetic scattering problems, namely, high frequency electromagnetic (EM) ray tracing, scattering feature extraction, and inverse scattering are studied in this dissertation. New approaches are presented to advance the state of the art in each of the areas. The presented study in electromagnetic ray tracing leads to an alternative ray tracing algorithm which can outperform the traditional algorithms for complex targets. The performance of the proposed techniques demonstrates their potential application to the study of high-frequency EM scattering prediction. Second, a genetic algorithm (GA)-based algorithm with an adaptive-feeding technique is developed to simultaneously extract both scattering centers and resonances. Scattering feature extraction algorithms are then developed with the consideration of the visibility of scattering centers. Inverse scattering problems with strong multiple scattering effects are also studied. A GA-based method is presented to invert the shapes with multiple scattering effects. An approach combining hybrid GA with the tabu list idea are then developed to further improve the performance of the GA-based inversion algorithms. / text

Spindulių trasavimas ir padalijimo paviršiai yra svarbūs įrankiai realistiškai atrodantiems vaizdams generuoti. Padalijimas – tai algoritmas, leidžiantis gauti glotnius paviršius pakartotinai dalijant gardeles. Spindulių trasavimas yra technologija, kuri remiasi apšvietimo skaičiavimu. Jos dėka galima gauti atspindžius, permatomumą, spindulių lūžimą kertant skaidrius objektus, taipogi realistiškus šešėlius. Mūsų darbo tikslas buvo suderinti šiuos du metodus, kuriant programinę priemonę, kuri leistų gauti sudėtingų objektų idealiai glotnius aukštos kokybės realistiškus vaizdus. Siekdami to, mes pritaikėme ir tokias kompiuterinės grafikos technologijas, kaip dengimas tekstūromis ir tūrių algebra. / Ray tracing and subdivision surfaces are important tools for generating realistic looking images. Subdivision is an algorithmic technique to generate smooth surfaces as a sequence of successively refined polyhedral meshes. Ray tracing is a technique that performs global calculations of lighting and shading, reflection and transmission of light, casting of shadows, and other effects. The basic idea behind ray tracing is to follow the paths of light rays around a 3-D scene. Our goal is generation of a high-quality realistic images by combining these two techniques. We also implemented other computer graphics methods designed to increase image realism (Texture Mapping) and to simplify modeling process (Boolean operations with solids).

This thesis develops and demonstrates an approach for estimating the three-dimensional (3D) location of a vocalizing underwater marine mammal using acoustic arrival time measurements at three spatially separated receivers while providing rigorous location uncertainties. To properly account for uncertainty in the measurements of receiver parameters (e.g., 3D receiver locations and synchronization times) and environmental parameters (water depth and sound speed correction), these quantities are treated as unknowns constrained with prior estimates and prior uncertainties. While previous localization algorithms have solved for an unknown scaling factor on the prior uncertainties as part of the inversion, in this work unknown scaling factors on both the prior and arrival time uncertainties are estimated. Maximum a posteriori estimates for sound source locations and times, receiver parameters, and environmental parameters are calculated simultaneously. Posterior uncertainties for all unknowns are calculated and incorporate both arrival time and prior uncertainties. Simulation results demonstrated that, for the case considered here, linearization errors are generally small and that the lack of an accurate sound speed profile does not necessarily cause large uncertainties or biases in the estimated positions. The primary motivation for this work was to develop an algorithm for locating underwater Pacific walruses in the coastal waters around Alaska. In 2009, an array of approximately 40 underwater acoustic receivers was deployed in the northeastern Chukchi Sea (northwest of Alaska) from August to October to record the vocalizations of marine mammals including Pacific walruses and bowhead whales. Three of these receivers were placed in a triangular arrangement approximately 400 m apart near the Hanna Shoal (northwest of Wainwright, Alaska). A sequence of walrus knock vocalizations from this data set was processed using the localization algorithm developed in this thesis, yielding a track whose estimated swim speed is consistent with current knowledge of normal walrus swim speed. An examination of absolute and relative walrus location uncertainties demonstrated the usefulness of considering relative uncertainties for applications where the precise location of the mammal is not important (e.g., estimating swim speed). / Graduate