This thesis presents a new template for multidisciplinary habitat mapping that combines the analyses of seafloor geomorphology, oceanographic proxies and modelling of associated biologic features. High resolution swath bathymetry of the Faial and western Pico shelves is used to present the first state-of-the-art geomorphologic assessment of submerged island shelves in the Azores. Solid seafloor structures are described in previously unreported detail together with associated volcanic, tectonic and erosion processes. The large sedimentary expanses identified in the area are also investigated and the large bedforms identified are discussed in view of new data on the local hydrodynamic conditions. Coarse-sediment zones of types hitherto unreported for volcanic island shelves are described using swath data and in situ imagery together with sub-bottom profiles and grainsize information. The hydrodynamic and geological processes producing these features are discussed. New oceanographic information extracted from satellite imagery is presented including yearly and seasonal sea surface temperature and chlorophyll-a concentration fields. These are used as proxies to understand the spatio-temporal variability of water temperature and primary productivity in the immediate island vicinity. The patterns observed are discussed, including onshore-offshore gradients and the prevalence of colder/more productive waters in the Faial-Pico passage and shelf areas in general. Furthermore, oceanographic proxies for swell exposure and tidal currents are derived from GIS analyses and shallow-water hydrographic modelling. Finally, environmental variables that potentially regulate the distribution of benthic organisms (seafloor nature, depth, slope, sea surface temperature, chlorophyll-a concentration, swell exposure and maximum tidal currents) are brought together and used to develop innovative statistical models of the distribution of six macroalgae taxa dominant in the infralittoral (articulated Corallinaceae, Codium elisabethae, Dictyota spp., Halopteris filicina, Padina pavonica and Zonaria tournefortii). Predictive distributions of these macroalgae are spatialized around Faial island using ordered logistic regression equations and raster fields of the explanatory variables found to be statistically significant. This new approach represents a potentially highly significant step forward in modelling benthic communities not only in the Azores but also in other oceanic island shelves where the management of benthic species and biotopes is critical to preserve ecosystem health.

La zone économique exclusive Mauritanienne est le siège d’upwelling et constitue une zone de transition où cohabitent des espèces d’affinités tempérée et tropicale. Pour comprendre le comportement spatio-temporel des assemblages démersaux du point de vue de leur composition, structuration, distribution de probabilité et diversité face aux préoccupations écologiques. Les facteurs abiotiques contribuent à la structuration des assemblages démersaux persistants au cours du temps. Les effets de la pêche étaient relativement faibles. Les trajectoires temporelles entre les assemblages et les conditions environnementales ont été mises en évidence pour certaines années et des zones. Dans les types d’habitats, un groupe minoritaire d’espèces très agrégatives obéissant au modèle de distribution en log-séries de Fisher et un autre majoritaire peu ou pas du tout agrégatives obéissant au modèle de distribution binomiale négative tronquée ont été identifiés. La diversité spécifique peut être divisé en deux groupes distincts et complémentaires : la richesse spécifique et l'autre associé à l’équitabilité. Un seul composant de la diversité ne peut donc pas représenter la diversité des poissons démersaux de la zone étudiée. Les GLM des indices complémentaires ont montré essentiellement un effet temporel et l’interaction Année-Strates bathymétriques. Aucun effet de l’effort de pêche n’a été observé sur la richesse spécifique, ni de la concentration en chlorophylle sur l’équitabilité. Ce travail pourrait fournir aux gestionnaires et aux scientifiques des connaissances complémentaires sur la dynamique spatio-temporelle des assemblages démersaux exploités dans des écosystèmes d’upwelling. / The Mauritanian exclusive economic zone is the seat of an upwelling phenomenon and constitutes a transition zone where species of temperate and tropical affinities coexist. To understand the spatio-temporal behavior of demersal assemblages from the point of view of their composition, structure, distribution of probability and diversity faced to ecological concerns. Abiotic factors contribute in the structuring of persistent groundfish assemblages over time. The fishing effects were relatively low, although significant in some years and in some specific geographic areas. Temporal trajectories between groundfish assemblages and environmental conditions have been highlighted for some years and in some specific areas. In each type habitats, two species groups were identified: a minority group of species very aggregative well fitted by Fisher’s log-series distribution and another majority of species little or not aggregative well fitted by the truncated negative binomial distribution. Diversity indices analyzed reveal that this set can be split into two distinct and complementary groups: a group associated with the species richness and another group associated with evenness. One component of diversity may not represent the diversity of the groundfish in the study area. GLMs of complementary indices showed essentially a temporal effect and Bathymetric strata-Year interaction. No effect of fishing effort was observed on the species richness and neither was the concentration of chlorophyll a on the evenness. This work could provide managers and scientists to further knowledge on the spatio-temporal dynamics of groundfish species assemblages exploited in upwelling ecosystems.

Dans cette thèse, nous avons abordé plusieurs thématiques liées aux modes de variabilité climatique dans l'Atlantique tropical à l'échelle interannuelle. Les analyses statistiques nous ont permis dans un premier temps de mettre en évidence les deux principaux modes dominants de cette variabilité interannuelle: un mode équatorial et un mode méridien. Le mode équatorial est responsable d'anomalies de température de surface de la mer (SST) principalement dans le Golfe de Guinée et est identifié par des variations de la pente du niveau de la mer dans la bande équatoriale. Il est dû à des rétroactions dynamiques entre le vent, le niveau de la mer et la SST. Quant au mode méridien, il se manifeste par des fluctuations inter-hémisphériques de SST et est contrôlé par des rétroactions dynamiques et thermodynamiques entre le vent, l'évaporation et la SST. L'évaluation du couplage de ces variables clés du mode méridien nous a permis de proposer un modèle conceptuel pour expliquer les principaux mécanismes responsables des oscillations du mode méridien. Le modèle a montré que le mode méridien résulte de la superposition d'un mécanisme auto-entretenu basé sur les rétroactions positives et négatives générant des oscillations régulières de haute fréquence (2-3 ans) et d'un autre mécanisme d'oscillation basse fréquence (4-9 ans) lié à l'influence d'ENSO du Pacifique Est. Comme l'évolution de ces deux modes est fortement liée au déplacement méridien de la zone de convergence intertropicale (ITCZ) qui transporte les pluies, nous avons ensuite identifié la signature de ces modes sur la salinité de la surface de la mer à l'aide observations in situ et d'une simulation numérique régionale. Les processus océaniques et/ou atmosphériques responsables de la signature de chaque mode ont été également identifiés grâce à un bilan de sel dans la couche de mélange du modèle validé. Le bilan de sel a révélé que le forçage atmosphérique, lié à la migration de l'ITCZ, contrôle la région équatoriale tandis que l'advection, due à la modulation des courants, du gradient vertical et le mélange à la base de la couche de mélange, explique les variations de SSS dans les régions sous l'influence des panaches. [...] / In this thesis, we investigate several topics related to the interannual climatic modes in the tropical Atlantic. Statistical analyses allows us to extract the two main dominant modes of interannual variability: an equatorial mode and a meridional mode. The equatorial mode is responsible for Sea Surface Temperature (SST) anomalies mainly found in the Gulf of Guinea and is linked to variations of the sea-level slope in the equatorial band. It is due to dynamic feedbacks between zonal wind, sea level and SST. The meridional mode is characterised by inter-hemispheric SST fluctuations and is controlled by dynamic and thermodynamic feedbacks between the wind, evaporation and SST. After quantifying the coupling between key variables involved in the meridional mode, we develop a conceptual model to explain the main mechanisms responsible for meridional mode oscillations. The model shows that the meridional mode results from the superposition of a self-sustaining mechanism based on positive and negative feedbacks generating regular oscillations of high frequency (2-3 years) and another low frequency oscillation mechanism (4-9 years) related to the influence of ENSO. As the evolution of these two modes is strongly linked to the meridional shift of the Intertropical Convergence Zone (ITCZ) and associated rainfall maximum, we identify the signature of these modes on Sea Surface Salinity (SSS) using in situ observations and a regional numerical simulation. Oceanic and/or atmospheric processes responsible for the signature of each mode are also identified through a mixed-layer salt budget in the validated model. The salt balance reveals that the atmospheric forcing, related to the ITCZ migration, controls the equatorial region while the advection, due to the modulation of current dynamics, the vertical gradient and mixing at the base of the mixed layer, explains SSS variations in regions under the influence of plumes. Finally, we study the Equatorial Kelvin wave characteristics and influences on the density that are involved in the meridional and equatorial mode connection processes, using a very simplified model of gravity wave propagation along the equator. After a brief description of this model, which was initially constructed to study dynamics in the equatorial Pacific, we apply it to the specific case of the equatorial Atlantic by validating its analytical and numerical solutions under adiabatic conditions. [...]

The quantification and description of sea surface temperature (SST) is critically important because it can influence the distribution, migration, and invasion of marine species; furthermore, SSTs are expected to be affected by climate change. Recent research indicates that there has been a warming trend in ocean temperatures over the last 50 years. Hence, we sought to identify and demonstrate how a particularly germane SST dataset can be used within the scope of global climate change research. For this project we assembled a 29-year nearshore time series of mean monthly SSTs along the North Pacific coastline, as well as mean monthly SSTs for ice-free regions of the Arctic, using remotely-sensed satellite data collected with the Advanced Very High Resolution Radiometer (AVHRR) instrument. By providing detailed information concerning both dataset generation and data limitations, we aimed to make these data comprehensible to an expanded audience concentrating on life sciences rather than the traditionally physical science-based community. Furthermore, by making these data freely and publically available in multiple formats, including GIS (geographic information systems) layers, we expand their visibility and the extent of their use. We then used the dataset to describe SST patterns of nearshore (< 20 km offshore) regions of 16 North Pacific ecoregions, and of ice-free regions of 20 Arctic ecoregions, as delineated by the Marine Ecoregions of the World (MEOW) hierarchical schema. Our work creates a better understanding of present temperature regimes in these critically sensitive areas, from which we can draw several basic conclusions. 1) AVHRR SST measurements alone are sufficient to identify temperature patterns pertinent to determining health of ecosystems; 2) Within the nearshore North Pacific, ecoregions along the California Current System are most vulnerable to habitat-altering SST changes; 3) sea ice distribution is a major factor affecting SSTs in Arctic ecoregions, causing concern for the welfare of Arctic species. / Graduation date: 2012

No description available.

Exchange of mass (water vapor), momentum, and energy between atmosphere andocean has profound influence on weather and climate. This exchange takes place at the air-sea interface, which is part of the marine atmospheric boundary layer. Various empirical relations are being used for estimating these fluxes in numericalweather and climate models but their accuracies are not sufficiently verified or tested over the Indian Ocean. The main difficulty is that vast areas of open oceans are not easily accessible. The marine environment is very corrosive and unattended long term and accurate measurements are extremely expensive. India has research ships that spend most of their time over the seas around India but that opportunity is yet to be exploited. To address this, an air-sea flux measurement system for operation on board research ships was planned. The system was tested on board Indian Research Vessels ORV SagarKanya during its cruise SK-296 in the Bay of Bengal (BoB) in July-August 2012, and NIO ship Sindhu Sadhana in June-July 2016. The complete set included instruments for measuring wind velocity, windspeed and direction, air and water temperature, humidity, pressure, all components of radiation and rainfall. In addition, ship motion was recorded at required sampling rate to correct for wind velocity. The set up facilitates the direct computation of sensible and latent heat fluxes using the eddy covariance method. In this thesis, design and installation of meteorological and ship motion sensors onboard research ships, data collection and quality control, computation of fluxes of heat, moisture and momentum using eddy covariance method and their comparison with those derived from bulk method are described. A set of sensors (hereafter, flux measuring system) were mounted on a retractable boom, ~7 m long forward of the bow to minimize the flow disturbance caused by the ship superstructures. The wind observed in the ship frame was corrected for ship motion contaminations. During the CTCZ cruise period true mean wind speed was over 10 m/s and true wind direction was South/South-Westerly. True windspeedis computed combiningdata from the anemometer a compass connected to AWS and a GPS. Turbulent fluxes were computed from motion-corrected time-series of high frequency velocity, water vapor, and air temperature data. Covariance latent heat flux, sensible heat flux, and wind stress were obtained by cross-correlating the motion-corrected vertical velocity with fast humidity fluctuations measured with anIR hygrometer, temperate fluctuation from sonic anemometer and motion-corrected horizontal windfluctuations from sonic anemometer, respectively. During the first attempt made in July-August 2012 as part of a cruise of CTCZ monsoonresearch program, observations were mainly taken in the North Bay of Bengal. The mean air-temperature and surface pressure were ~28 Deg C and ~998 hPa, respectively. Relative humidity was ~80%. Average wind speed varied in the range 4-12 m/s. The mean latent heat flux was 145 W/m2 , sensible heat flux was ~3 W/m2 and average sea-air temperature difference was ~ 0.7°C. The Bay of Bengal boundary layer experiment (BoBBLE) was conducted during June-July 2016 and the NIO research ship Sindhu Sadhana was deployed. The same suite of sensors installed during CTCZ were used during BoBBLE. During daytime, peaks of hourly net heat fluxes (Qnet ) were around 600 Wm-2(positive if into the sea), whereas, night time values were around -250 W m-2. Sea surface temperature was always >28°C and maximum air temperature exceeded 29°C. During the experimental period the mean Qnet was around -24 Wm-2 from both eddy covariance and conventional bulk methods, but there are significant differences on individual days.The new flux system gives fluxes which are superior to what was available before.

Made available in DSpace on 2015-02-24T19:48:45Z (GMT). No. of bitstreams: 1 AndersonTSF_TESE_ Capa_ate_pag22.pdf: 11459625 bytes, checksum: fd30a979bc39cf6180f782c772106ee3 (MD5) Previous issue date: 2013-09-16 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This paper presents models of parameters of Sea Surface Layer (SSL), such as chlorophyll-a, sea surface temperature (SST), Primary Productivity (PP) and Total Suspended Matter (TSM) for the region adjacent to the continental shelf of Rio Grande do Norte (RN), Brazil. Concentrations of these parameters measured in situ were compared in time quasi-synchronous with images AQUA-MODIS between the years 2003 to 2011. Determination coefficients between samples in situ and bands reflectance sensor AQUA-MODIS were representative. From that, concentrations of SSL parameters were acquired for the continental shelf of the RN (eastern and northern) analyzing the geographic distribution of variation of these parameters between the years 2009-2012. Geographical and seasonal variations mainly influenced by global climate phenomena such as El Ni?o and La Ni?a, were found through the analysis of AQUA-MODIS images by Principal Components Analysis (PCA). Images show qualitatively the variance and availability of TSM in the regions, as well as their relationship with coastal erosion hotspots, monitored along the coast of the RN. In one of the areas identified as being of limited availability of TSM, we developed a methodology for assessment and evaluation of Digital Elevation Models (DEM) of beach surfaces (emerged and submerged sections) from the integration of topographic and bathymetric data measured in situ and accurately georeferenced compatible to studies of geomorphology and coastal dynamics of short duration. The methodology consisted of surveys with GNSS positioning operated in cinematic relative mode involved in topographic and bathymetric executed in relation to the stations of the geodetic network of the study area, which provided geodetic link to the Brazilian Geodetic System (GBS), univocal , fixed, and relatively stable over time. In this study Ponta Negra Beach, Natal / RN, was identified as a region with low variance and availability of MPS in the region off, as characterized by intense human occupation and intense coastal erosion in recent decades, which presents potential of the proposed methodology for accuracy and productivity, and the progress achieved in relation to the classical methods of surveying beach profiles / Este trabalho apresenta modelos de par?metros da Camada Superficial do Mar (CSM), tais como: Clorofila-a, Temperatura da Superf?cie do Mar (TSM), Produtividade Prim?ria (PP) e Material Particulado em Suspen??o (MPS), para a regi?o adjacente a plataforma continental do Rio Grande do Norte (RN), Brasil. Concentra??es desses par?metros medidos in situ foram comparadas em tempo quase-s?ncronos com imagens AQUAMODIS entre os anos de 2003 at? 2011. Coeficientes de determina??o foram representativos entre as amostras in situ e as bandas de reflect?ncia do sensor AQUAMODIS. A partir disso, concentra??es de par?metros da CSM foram adquiridos para a plataforma continental do RN (Plataforma Oriental e Setentrional) analisando a distribui??o geogr?fica da varia??o desses par?metros entre os anos de 2009-2012. Varia??es geogr?ficas e sazonais influenciadas principalmente por fen?menos clim?ticos globais como o fen?meno El Ni?o e La Ni?a, foram constatadas atrav?s das an?lises das imagens AQUA-MODIS por an?lise de Principais Componentes (PC). As imagens apontam de maneira qualitativa a vari?ncia e disponibilidade do MPS nas regi?es, assim como sua rela??o com hotspots de eros?o costeira, monitorados ao longo do litoral do RN. Em uma das regi?es identificadas como sendo de pouca disponibilidade de MPS, foi desenvolvida uma metodologia para levantamento e avalia??o de Modelos Digitais de Eleva??o (MDE) de superf?cies praiais (setores emersos e submersos) a partir da integra??o de dados topogr?ficos e batim?tricos mensurados in situ e georreferenciados com precis?o compat?vel aos estudos de geomorfologia e din?mica costeira de curta dura??o. A metodologia desenvolvida consistiu de levantamentos com posicionamentos GNSS operados no modo relativo cinem?tico envolvidos nos levantamentos topogr?ficos e batim?tricos executados em rela??o ?s esta??es da rede geod?sica da ?rea de estudo, que forneceram referencial geod?sico vinculado ao Sistema Geod?sico Brasileiro (SGB), o qual ? un?voco, fixo e relativamente est?vel no tempo. No estudo foi apresentado a Praia de Ponta Negra, Natal/RN, identificada como uma regi?o com baixa vari?ncia e disponibilidade de MPS ao largo, assim como, caracterizada por intensa ocupa??o antr?pica e intensa eros?o costeira nas ?ltimas d?cadas, no qual s?o apresentadas as potencialidades da metodologia proposta, quanto ? acur?cia e produtividade, al?m dos avan?os alcan?ados em rela??o aos m?todos cl?ssicos de levantamento de perfis de praia

Made available in DSpace on 2015-03-13T17:08:24Z (GMT). No. of bitstreams: 1 AndersonTSF_1_60pdf.pdf: 1582556 bytes, checksum: e1053ad83e14cdcdf0d10a9b5dcbdbbf (MD5) Previous issue date: 2009-10-14 / Orbital remote sensing has been used as a beneficial tool in improving the knowledge on oceanographic and hydrodynamic aspects in northern portion of the continental shelf of Rio Grande do Norte, offshore Potiguar Basin. Aspects such as geography, temporal and spatial resolution combined with a consistent methodology and provide a substantial economic advantage compared to traditional methods of in situ data collecting. Images of the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard NASA's AQUA satellite were obtained to support systematic data collections related to the campaign of environmental monitoring and characterization of Potiguar Basin, held in May 2004. Images of Total Suspension Matter (TSM) and values of radiance standard were generated for the calculation of concentrations of total suspension matter (TSM), chlorophyll-a and sea surface temperature (SST). These data sets were used for statistical comparisons between measures in situ and satellite estimates looking validate algorithms or develop a comprehensive regional approach empirically. AQUA-MODIS images allowed the simultaneous comparison of two-dimensional water quality (total suspension matter), phytoplankton biomass (chlorophyll-a) variability and physical (temperature). For images of total suspension matter, the generated models showed a good correlation with the field data, allowing quantitative and qualitative analysis. The images of chlorophyll-a showed a consistent correlation with the in situ values of concentration. The algorithms adjusted for these images obtained a correlation coefficient fairly well with the data field in order that the sensor can be having an effect throughout the water column and not just the surface. This has led to a fit between the data of chlorophyll-the integration of the average sampling interval of the entire water column up to the level of the first optical depth, with the data generated from the images. This method resulted in higher values of chlorophyll concentration to greater depths, due to the fact that we are integrating more values of chlorophyll in the water column. Thus we can represent the biomass available in the water column. Images SST and SST measures in situ showed a mean difference DT (SST insitu - SST sat) around -0.14 ? C, considered low, making the results very good. The integration of total suspension matter, chlorophyll-a, the temperature of the sea surface (SST) and auxiliary data enabled the recognition of some of the main ways to fund the continental shelf. The main features highlighted were submerged canyons of rivers Apodi and A?u, some of the lines and beachrocks reefs, structural highs and the continental shelf break which occurs at depths around -60 m. The results confirmed the high potential for use of the AQUA-MODIS images to environmental monitoring of sea areas due to ease of detection of the field two-dimensional material in suspension on the sea surface, temperature and the concentration of chlorophyll-a / O sensoriamento remoto orbital tem sido utilizado como ferramenta vantajosa na melhoria do conhecimento sobre os aspectos hidrodin?micos e oceanogr?ficos na por??o norte da plataforma continental do Estado do Rio Grande do Norte, regi?o offshore da Bacia Potiguar. Aspectos como a cobertura geogr?fica e resolu??es temporal e espacial, somados a uma metodologia consistente garantem uma substancial vantagem e economia em rela??o aos m?todos tradicionais de coletas de dados in situ. Em apoio ?s coletas sistem?ticas referentes ? campanha de caracteriza??o e monitoramento ambiental da Bacia Potiguar, realizada em maio de 2004, foram obtidas imagens do sensor Moderate-Resolution Imaging Spectroradiometer (MODIS) instalado a bordo do sat?lite AQUA da NASA. Foram gerados imagens de material partitulado em suspens?o e valores de radi?ncias normalizadas para o calculo de concentra??es do material particulado em suspens?o (MPS), clorofila-a e temperatura da superf?cie do mar (TSM). Estes conjuntos de dados foram utilizados para compara??es estat?sticas entre medidas in situ e estimativas por sat?lite buscando validar algoritmos globais ou desenvolver uma abordagem regional empiricamente. As imagens AQUA-MODIS permitiram a compara??o bidimensional simult?nea da qualidade da ?gua (material particulado em suspens?o, da biomassa fitoplanct?nica (clorofila-a) e variabilidade f?sica (temperatura). Para as imagens de material particulado em suspens?o, os modelos gerados apresentaram uma boa correla??o em rela??o aos dados de campo, permitindo uma an?lise quantitativa e qualitativa dessas imagens. As imagens de clorofila-a apresentaram correla??o consistente com os valores das concentra??es in situ. Os algoritmos ajustados para essas imagens obtiveram um coeficiente de correla??o razoavelmente bom em rela??o aos dados de campo, tendo em vista que o sensor possa estar tendo influ?ncia de toda a coluna d ?gua e n?o apenas da superf?cie. Esse fato levou a um ajuste entre os dados de clorofila-a da integra??o das m?dias dos intervalos de coleta de toda a coluna ?gua at? o n?vel da primeira profundidade ?ptica, em rela??o aos dados gerados das imagens. Tal m?todo resultou em valores mais altos de concentra??o de clorofila para maiores profundidades, devido ao fato de se estar integrando mais valores de clorofila na coluna d ?gua. Dessa maneira pode-se representar a biomassa dispon?vel na coluna d ?gua. As imagens TSM e as medidas de TSM in situ mostraram uma diferen?a m?dia v DT (TSM insitu TSM sat) em torno de -0,14 ?C, considerada baixa, tornando os resultados muito bons. A integra??o de imagens de sedimentos em suspens?o, de clorofila-a e de temperatura da superf?cie do mar possibilitaram o reconhecimento de algumas das principais formas de fundo da plataforma continental. As principais fei??es destacadas foram os canyons submersos dos rios Apodi e A?u, algumas das linhas de beachrocks e recifes, altos estruturais e a quebra da plataforma continental que ocorre a profundidades em torno de 60 m. Os resultados confirmaram o alto potencial de uso das imagens AQUA-MODIS no monitoramento ambiental de ?reas oce?nicas devido ? facilidade na detec??o do campo bidimensional material em suspens?o na superf?cie do mar, de temperatura e da concentra??o de clorofila-a

Le travail réalisé dans cette thèse s'intègre globalement dans le cadre de I'observation et la surveillance maritime.Afin d'améliorer la reconnaissance et I'identification automatique de cibles noyées dans un environnement perturbé, nous avons opté à la fusion de différentes connaissances et informations concernant une scène observée à distance par des capteurs micro-ondes. En effet, plusieurs phénomènes physiques co-existent et perturbent la propagation des ondes électromagnétiques au-dessus d'une surface et notamment au-dessus d'une surface maritime hétérogène (la réfraction due aux gradients d'indice, la rugosité de la surface de mer, les effets hydrodynamiques non linéaires du type vagues déferlantes, la présence d'objets, les polluants, sillage de navires, zones côtières, ...). Dans ce contexte, le travail présenté dans cette thèse porte sur l'étude de la signature électromagnétique (coefficients de diffusion) d'une surface maritime hétérogène avec la prise en compte des phénomènes hydrodynamiques (linéaires : vagues de capillarité et de gravité, non linéaires : vagues déferlantes). Cette estimation de la signature électromagnétique est effectuée en configuration bistatique (monostatique et propagation avant) et en bande X. L'étude complète de cette problématique est difficile. En effet, le déferlement est un processus dissipatif de l'énergie qui correspond à la dernière étape de la vie d'une vague et qui a donc le plus souvent lieu à I'approche du rivage. Ce phénomène non linéaire produit un pic de mer qui est une augmentation rapide des coefficients de diffusion et qui peut dépasser 10 dB dans une période de 100 ms. Ce pic peut conduire à des échos parasites, qui peuvent être identifiés comme des cibles virtuelles, et par la suite elles peuvent perturber le système de détection radar (fausses alarmes). Par conséquent, pour améliorer le processus de détection et pour réduire le taux de fausses alarmes, il est important de distinguer entre les cibles et les pics de mer générés par des vagues déferlantes. Ceci constitue I’une des motivations et aussi I'intérêt d'étudier la signature électromagnétique des vagues déferlantes dans différentes configurations d'observation de sorte que nous puissions facilement indiquer la présence voir I'identification des pics de mer. Pour contribuer à cette problématique, nous avons proposé une méthodologie basée sur un modèle électromagnétique hybride basé sur une combinaison d'une part de méthodes asymptotiques(SPMI utilisée dans le cadre de ce travail) pour simuler la réponse radar des vagues linéaire (vagues de capillarité et de gravité décrites via le spectre de mer d'Elfouhaily), et d'autre part de méthodes exactes (MoM, FB < Forward-Backward ) retenue dans le travail présenté dans ce manuscrit) pour calculer la réponse électromagnétique des vagues non-linéaires (profils considérés sont issus des résultats du code LONGTANK). Afìn de compléter l'étude théorique et les simulations réalisées, nous avons effectué une phase d'évaluation et de validation par des mesures de signature radar réalisées dans la chambre anéchoïque de I'Ensta Bretagne. / The work done in this thesis fits generally under the observation and maritime surveillance. To improve the detection and automatic identification of targets embedded in a noisy environment targets, we opted for the fusion of different knowledge and information regarding a remotely observed scene by microwave sensors. Indeed, several physical phenomena co-exist and interfere with the propagation of electromagnetic waves over a heterogeneous sea surface (the refraction due to the index gradients, the roughness of the sea surface, nonlinear hydrodynamic effects like waves breaking, the presence of objects, pollutants, ship wake, coastal areas,..). In this context, the work presented in this thesis focuses on the study of electromagnetic signature (diffusion coefficients) of a heterogeneous sea surface with consideration of hydrodynamic phenomena (linear: capillary and gravity waves, nonlinear: breaking waves). The electromagnetic signature is performed in bistatic configuration (monostatic and forward propagating) and in X-band. The complete study of this problem is difficult.Indeed, the breaking wave is a dissipative process of energy that corresponds to the last stage of the life of a wave and therefore has most often held in the shore. This nonlinear phenomenon produces a sea peak which is a rapid increase of the diffusion coefficients and can exceed l0 dB in a 100 ms period. This peak can lead to clutter, which can be identified as virtual targets, and then they can disrupt the detection radar system (false alarms). Therefore, to improve the detection process and reduce the false alarm rate, it is important to distinguish between targets and sea peaks generated by breaking waves. This represents one of the motivations and also the interest to study the electromagnetic signature of breaking waves in different observation configurations so that we can easily detect and identify the sea peaks. To solve this problem, we proposed a methodology based on a hybrid electromagnetic model which is on a combination of asymptotic methods (SPMI used in this work) to simulate the radar response of linear waves (capillary and gravity waves described via the Elfouhaily sea spectrum) and an exact methods, the method of moment (the FB "Forward-Backward" method is used in this work), to calculate the electromagnetic response of nonlinear waves (profiles are produced by the LONGTANK code). To complement the theoretical study and simulations, we carried out an evaluation and validation phase by measuring the radar signature of breaking wave profiles in the ENSTA Bretagne anechoic chamber.