In this thesis, target induced glint error phenomenon is analyzed and the glint reduction techniques are evaluated. Glint error reduction performance of the methods is given in a comparative manner. First, target glint is illustrated with the dumbbell model which has two point scatterers. This illustration of the glint error builds the basic notion of target scattering centers and effect of scattering characteristics on glint error. This simplest approach is also used to understand the glint reduction methods. In an effort to evaluate the glint reduction techniques, a model based upon the concept of coherent summation of scattering complexes is used . The model is also used for introducing the basic properties of glint phenomenon. Basics of the glint phenomenon and glint reduction techniques are discussed with particular emphasis on diversity methods. Frequency diversity and spatial diversity techniques are described and investigated with generated simulation data. The diversity selection methods which are used to eliminate the erroneous data are introduced and their performances are investigated. Glint error reduction results of various scenarios including both reduction techniques and selection methods are evaluated in comparison with each other. The results indicate that significant reduction of glint error is possible by the appropriate utilization of diversity techniques in radar systems.

Le rendu de micro-reflets, utile pour simuler l'apparence de matériaux pailletés, de métal brossé ou de plastique rayé, est un défi théorique et technique en informatique graphique. Il implique l'utilisation de fonctions de distribution de réflectance bidirectionnelles surfaciques (P-BRDFs) hautes fréquences et qui varient spatialement. Dans cette thèse, nous proposons deux nouvelles P-BRDFs basées sur des cartes de normales presque parfaitement spéculaires. La première empêche toute création d'énergie grâce à une normalisation dépendante de l'empreinte du rayon, contrairement à la méthode précédente [YHMR16]. Cette normalisation est possible grâce à une nouvelle représentation d'une carte de normales en une mixture de NDFs de Beckmann décentrées et non-alignées sur les axes. La deuxième méthode améliore la première et empêche, pour la première fois, toute création et perte d'énergie, en simulant du multi-rebonds dans la micro-géométrie du matériau. Elle permet donc un rendu sans artefacts de surfaces opaques possédant des micro-reflets. De plus, nous donnons un algorithme d'échantillonnage optimal, utilisant la visibilité des normales. L'idée clé de cette méthode est la définition d'une V-cavité en chaque point de la surface. Pour simuler le multi-rebonds à l'intérieur, nous compensons l'énergie perdue par une modélisation simple rebond, en la réintégrant à l'aide d'une BRDF de compensation d'énergie. Nos méthodes ont le même ordre de grandeur que la méthode précédente en matière de temps de rendu et d'empreinte mémoire. / Glint rendering, useful for simulating the appearance of glittery materials, brushed metal or scratched plastic, is a theoretical and technical challenge in computer graphics. It involves the use of spatially varying patch bidirectional reflectance distribution functions (P-BRDFs) with high frequencies. In this thesis we propose two new P-BRDFs based on specular normal maps. Unlike the previous method [YHMR16], our first BRDF prevents any creation of energy through footprint-dependent normalisation. This normalisation is possible thanks to a new representation of the normal map based on a mixture of non-centered and non-axis aligned Beckmann NDFs. The second method improves the first one and prevents, for the first time, any creation and loss of energy, by simulating multiple scattering in the microgeometry. It enables artifact-free rendering of opaque and sparkling surfaces. In addition, we provide an optimal sampling algorithm using the visibility information of the normals. The key idea of this method is the definition of a V-cavity for each point of the surface. To simulate multiple scattering inside it, we compensate for the energy lost by a single scattering model, by reintegrating lost energy with an energy compensation BRDF. The rendering time and memory footprint of our methods are in the same order of magnitude than previous methods.

No description available.

Remote sensing is a powerful tool for studying the marine environment; however, many images are contaminated by sun glint, the specular reflection of light from the water surface. Improved radiative transfer modelling could lead to better methods for estimating and correcting sunglint. This thesis explores the effect of using detailed numerical models of the sea surface when investigating the transfer of light through the atmosphere-ocean system. New numerical realisations that model both the shape and slope of the sea surface have been created; these contrast with existing radiative transfer models, where the air-water interface has slope but not elevation. Surface realisations including features on a scale from 3 mm to 200 m were created by a Fourier synthesis method, using up to date spectra of the wind-blown sea surface. The surfaces had mean square slopes and elevation variances in line with those of observed seas, for wind speeds up to 15 m/s. Ray-tracing using the new surfaces gave estimates of reflected radiance that were similar to those made using slope statistics methods, but significantly different in 41% of cases tested. The mean difference in the reflected radiance at these points was 19%, median 7%. Elevation-based surfaces give increased sideways scattering and reduced forward scattering of light incident on the sea surface. The elevation-based models have been applied to estimate pixel-pixel variation in ocean colour imagery and to simulate scenes viewed by three types of sensor. The simulations correctly estimated the size and position of the glint zone. Simulations of two ocean colour images gave a lower peak reflectance than the original values, but higher reflectance at the edge of the glint zone. The use of the simulation to test glint correction methods has been demonstrated, as have global Monte Carlo techniques for investigating sensitivity and uncertainty in sun glint correction. This work has shown that elevation-based sea surface models can be created and tested using readily-available computer hardware. The new model can be used to simulate glint in a variety of situations, giving a tool for testing glint correction methods. It could also be used for glint correction directly, by predicting the level of sun glint in a given set of conditions.