Étude de la rétrodiffusion des surfaces d'eau en bande Ka à faible incidence

The evolution of the altimetric techniques from Ku-band to Ka-band and the wide swath al-timetry in the context of the SWOT mission (« Surface Water Ocean Topography », CNES/NASA) raises new scientific questions about the validity of the backscattering models from water sur-faces in such a frequency band and errors in estimating water heights from time-evolving water surfaces. A backscattering model (GO4) adapted to the SWOT configuration is introduced. It preserves the accuracy of the referencial Physical Optics model while maintaining the simplicity of the clas-sical Optical Geometrics model. In addition to the classical slope parameter, it introduces another parameter called as « effective curvature » (msc). This model allows the inverson of the surface slope and curvature parameters under certain conditions which are developped in this manus-cript. The joint validity of the backscattering models in Ka-band and from water surfaces is che-cked from controlled wind-wave tank radar measurements . In a last part, the temporal properties of the backscattered signal is studied, in particular the correlation time and the Doppler shift induced by waves motion. Influence of the latters on the non focused SAR synthesis is studied in the context of the SWOT system.L’évolution des techniques altimétriques de la bande Ku Nadir vers la bande Ka et l’interféro-métrie large fauchée proche Nadir dans le contexte de la mission SWOT (« Surface Water Ocean Topography », CNES/NASA) soulève de nouvelles questions scientifiques quant à la validité des modèles de rétrodiffusion des surfaces d’eau dans cette bande de fréquence et les erreurs sur les estimations de hauteurs d’eau dues aux mouvements de ces surfaces au cours du temps. Un modèle de rétrodiffusion (GO4) adapté à la configuration SWOT est présenté. Il conserve la précision du modèle de référence de l’Optique Physique tout en gardant la simplicité du modèle plus couramment employé de l’Optique Géométrique. En plus du paramètre classique de pente, il introduit un paramètre supplémentaire, dit de « courbure effective » (msc). Le modèle permet l’inversion des paramètres de pente et de courbure de la surface sous certaines conditions déve-loppées dans ce manuscrit. La validité des modèles conjoints de rétrodiffusion en bande Ka et de surface d’eau a été vérifiée sur des mesures radar effectuées en soufflerie dans un environnement contrôlé. Dans une dernière partie, les propriétés temporelles du signal rétrodiffusé ont été étudiées, en particulier le temps de corrélation et le décalage Doppler induit par le mouvement des vagues. Nous étudions l’influence de ces quantités sur les performances de la synthèse SAR non focalisée du système SWOT

Description statistique de la surface océanique et mesures conjointes micro-ondes (une analyse cohérente)

De plus en plus de données satellitales ou aéroportées acquises au dessus de la surface de la mer sont disponibles notamment dans la gamme micro-ondes. Pour interpréter correctement ces données, il est nécessaire de disposer d'une part d'un modèle de diffusion qui soit capable de prendre en compte l'aspect multi-échelles de la surface de mer et d'autre part une bonne représentation spectrale de la surface de mer. Ces dernières années, plusieurs modèles de diffusion électromagnétiques unifiés (capables de prendre en compte la diffusion électromagnétique pour les petites et grandes vagues) ont été développés sous statistiques gaussiennes de la surface de mer. Cependant, ces modèles sont insuffisants pour interpréter les observations lorsque différents jeux de données (multi-bande et multi-incidence) sont confrontés. Le plus de cette thèse est de progresser dans une modélisation cohérente de ces données radar.La première étape est d'incorporer les aspects non-gaussiens de la surface de mer, connus pour influer significativement sur la section efficace de rétrodiffusion (SER). Cela est réalisé dans le cadre du modèle électromagnétique "Weighted Curvature Approximation (WCA) en introduisant le kurtosis des pentes et en se limitant à la SER omnidirectionnelle et à la polarisation verticale.Ces corrections permettent une meilleure modélisation de la section efficace radar mais ne sont pas suffisantes pour obtenir un accord avec les données dans toutes les configurations (bande, incidence, vent). Cela suggère une amélioration nécessaire du spectre des vagues courtes, qui fait l'objet de la deuxième partie de ces travaux de recherche.Un nouveau spectre omnidirectionnel est calculé afin d'obtenir une meilleure modélisation de la SER omnidirectionnelle en polarisation verticale tout en respectant des contraintes a priori sur les pentes mesurées par des techniques optiques. Ce spectre s'avère assez semblable au spectre unifié d'Elfouhaily, avec quelques différences notables cependant dans la gamme des échelles décimétriques.More and more micro-wave data are available from spatial and airborne measurements over sea surface. An accurate backscattering model which is capable of taking the multi-scale aspect of the sea surface into account, is required to model correctly the data as well as a precise sea spectrum. Several unified backscattering models have been developed in recent years under Gaussian statistics. However, these models are not able to give a correct modelization of the backscattered signal when different data sets are studied together. One of the objectives of this study is to improve the modelization of the backscattered signal to get better agreement with the data.The first step of this study is to include non Gaussian statistics into backscattering model as it is well known they have a significant impact on the normalized radar cross section (NRCS). Then, a non Gaussian version of the Weighted Curvature Approximation was developed taking the kurtosis of slopes into account. This work was based only upon vertical polarization.It is then shown that the corrections allow a better agreement with the data but they are not sufficient to get a good estimation of the NRCS for all incidences and electromagnetic frequencies. This induces the hypothesis of a modification of the short wave sea spectrum.Then, a new parametrisation of the omnidirectional sea spectrum is suggested to get a better agreement with the multiband data sets and is based on the spectrum developed by Elfouhaily et al. The new omnidirectional short wave sea spectrum is quite alike the Elfouhaily s spectrum with some noticeable differences for the decimetric scales.TOULON-Bibliotheque electronique (830629901) / SudocSudocFranceF

Ocean Remote Sensing with Synthetic Aperture Radar

The ocean covers approximately 71% of the Earth’s surface, 90% of the biosphere and contains 97% of Earth’s water. The Synthetic Aperture Radar (SAR) can image the ocean surface in all weather conditions and day or night. SAR remote sensing on ocean and coastal monitoring has become a research hotspot in geoscience and remote sensing. This book—Progress in SAR Oceanography—provides an update of the current state of the science on ocean remote sensing with SAR. Overall, the book presents a variety of marine applications, such as, oceanic surface and internal waves, wind, bathymetry, oil spill, coastline and intertidal zone classification, ship and other man-made objects’ detection, as well as remotely sensed data assimilation. The book is aimed at a wide audience, ranging from graduate students, university teachers and working scientists to policy makers and managers. Efforts have been made to highlight general principles as well as the state-of-the-art technologies in the field of SAR Oceanography

The GO4 model in near-nadir microwave scattering from the sea surface

Abstract-We introduce a practical and accurate model, referred to as "GO4", to describe near-nadir microwave scattering from the sea surface and at the same time we address the issue of the filtered mean square slope (mss) conventionally used in the Geometrical Optics model. GO4 is a simple correction of this last model taking into account the diffraction correction induced by the rough surface through what we call an effective mean square curvature (msc). We evaluate the effective msc as a function of the surface wavenumber spectrum and the radar frequency and show that GO4 reaches the same accuracy as the Physical Optics model in a wide range of incidence and frequency bands with the sole knowledge of the mss and msc parameters. The key point is that the mss entering in GO4 is not the filtered but the total slope. We provide estimation of the effective msc on the basis of classical sea spectrum models. We also evaluate the effective msc from near-nadir satellite data in various bands and show that it is consistent with model predictions. Non-Gaussian effects are discussed and shown to be incorporated in the effective msc. We give some applications of the method, namely the estimation of the total sea surface mss and the recalibration of relative radar cross-sections

The GO4 Model in Near-Nadir Microwave Scattering From the Sea Surface

We introduce a practical and accurate model, referred to as "GO4," to describe near-nadir microwave scattering from the sea surface, and at the same time, we address the issue of the filtered mean square slope (mss) conventionally used in the geometrical optics model. GO4 is a simple correction of this last model, taking into account the diffraction correction induced by the rough surface through what we call an effective mean square curvature (msc). We evaluate the effective msc as a function of the surface wavenumber spectrum and the radar frequency and show that GO4 reaches the same accuracy as the physical optics model in a wide range of incidence and frequency bands with the sole knowledge of the mss and msc parameters. The key point is that the mss entering in GO4 is not the filtered but the total slope. We provide estimation of the effective msc on the basis of classical sea spectrum models. We also evaluate the effective msc from near-nadir satellite data in various bands and show that it is consistent with model predictions. Non-Gaussian effects are discussed and shown to be incorporated in the effective msc. We give some applications of the method, namely, the estimation of the total sea surface mss and the recalibration of relative radar cross sections