Marine pollution has been highlighted thanks to the advances in detection techniques as well as increasing coverage of catastrophes (e.g. the oil tankers Amoco Cadiz, Exxon Valdez, Erika, and Prestige) and of smaller oil spills from ships. The new satellite based sensors SAR and ASAR and new methods of oil spill detection and analysis coupled with self-similar statistical techniques allow surveys of environmental pollution monitoring large areas of the ocean. We present a statistical analysis of more than 700 SAR images obtained during 1996-2000, also comparing the detected small pollution events with the historical databases of great marine accidents during 1966-2004 in European coastal waters. We show that the statistical distribution of the number of oil spills as a function of their size corresponds to Zipf's law, and that the common small spills are comparable to the large accidents due to the high frequency of the smaller pollution events. Marine pollution from tankers and ships, which has been detected as oil spills between 0.01 and 100 km 2 , follows the marine transit routes. Multi-fractal methods are used to distinguish between natural slicks and spills, in order to estimate the oil spill index in European coastal waters, and in particular, the north-western Mediterranean Sea, which, due to the influence of local winds, shows optimal conditions for oil spill detection.

Abstract. The use of synthetic aperture radar (SAR) to investigate the ocean surface provides a wealth of useful information that is very seldom used to its full potential. Here we will discuss the application of multifractal techniques to detect oil spills and the dynamic state of the sea regarding turbulent diffusion. We present different techniques in order to relate the shape of the multifractal spectral functions and the maximum fractal dimension to the behaviour of the ocean surface. We compare eddy and sheared dominated flows with convective driven flows and discuss the different features and observation methods. We also compare the scaling of different oil spills detected by means of SAR images. Recent spills and weathered ones are selected and compared to investigate their behaviour in different spatial and temporal ranges. We calculate the partition function based on the grey intensity value of each SAR pixel deriving several types of multifractal spectra as a function of spill residence time estimated for each image. Image manipulations are seen to reduce the speckle noise and thus distinguish much better the texture of the oil spill images. The results are used to discuss how eddy diffusivity may be estimated and used in a description of the ocean surface using a simple turbulence kinematic simulation model to predict the shape of oil spills. Differences in the multifractal spectrum among SAR images may detect the slicks due to plankton and also provide information on the age of the oil spills, on the Lagrangian turbulent structure and on ocean surface diffusivity.

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The advances in radar sensors may be applied to study the flow in the Region of Fresh Water Influence (ROFI) region of the ocean. The Synthetic Aperture Radar (SAR) is a useful tool that may be used to study both marine water dynamics and its pollution. Oil spills and natural slicks may be detected and processed with advanced computer techniques to reveal vortex dynamics and turbulence spectral characteristics of the complex eddy and current interaction in the ocean surface, more than 300 SAR images of the North-west Mediterranean Sea area taken between December 1996 and December 1998 were analyzed. A total of 255 eddies were detected under convenient environmental conditions and we analyzed statistically the appearance, size, shape and position of vortices in the test area. We find that the maximum size of the eddies detected near the coast is limited by the Rossby deformation radius and that there is a decrease in size in the coastal waters in the direction of the Liguro-Provenzal current with the largest eddies occurring near the cape of Rosas. Near the Rhone and Ebro rivers, high discharges also contribute to eddy forcing, coastal radar measurements confirm the SAR observations. The role of submarine canyons in the vortex generation is also confirmed due to the asymmetry of their distribution with respect to the thalwegs. It is demonstrated that useful information of a geometrical nature obtained by SAR satellite images may be used to estimate relevant dynamical parameters of coastal flows

Se presenta una continuación temática del artículo “Aplicación de las imágenes SAR en el estudio de la dinámica de las aguas y de la polución del Mar Mediterráneo cerca de Barcelona”, publicado en la Revista “Ingeniería del Agua”, Vol. 8, N1 en marzo de 2001. Ahora el área de estudio se amplió y comprende toda la zona del Mediterráneo Noroccidental MN, es decir incluye el Mar Balear y el Golfo de León. Los resultados del análisis de cerca de 330 imágenes del Radar de Apertura Sintética, obtenidas mediante los proyectos Clean Seas, ERS-1/2 SAR Exploitation Study in Catalonia y Oil Watchnos permitieron obtener una visión general, pero estadísticamente justificada, sobre el estado del ambiente marino del MN en los años 1996 – 1998. Se constata que las rutas marítimas cercanas a Marseille están más limpias que cerca de Barcelona. Se evalúa la contaminación total del área, la contribución de los penachos de aguas residuales procedentes de los ríos regionales y de los pequeños pero “habituales” derrames causados por los petroleros. Los derrames de productos petroquímicos durante el período 1996-1998 en el MN ocupan un área estimada de diámetro de 150 km., con un peso de 4,5x103 Tm.