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Oil Spill Detection and Prediction from SAR multiscale analysis

Jose Manuel Redondo(1,2)

(1) Univ. Politecnica de Catalunya, B5 Campus Nord UPC, 08034, Spain
(2) University of Cambridge, Wimberforce Rd. C, Cambridge, United Kingdom

Abstract

The statistical analysis of larger data sets (1996-2005) from the collection of the SAR images, including new images obtained from ESA (ENVISAT and ERS-2) as well as further SAR/ASAR images obtained directly from ESA(C1P.2240) (2000-2007)has been used both to analyse the Sea Surface features, such as slicks and vortices as well as oil spills. Images during a 9 yr period have been analysed, using at the same time a more comprehensive identification of the topology associated to patterns and eddies detected in the ocean surface. More than 2000 synthetic aperture radar (SAR and ASAR) as well as other types of images have been compared over the test site used by the Clean Seas proyect in the NW Mediterranean sea. We have analyzed these SAR images with respect to radar signatures of (natural and man-made) oil pollution and other surface features. The extension of most of the SAR detected vortices (63 %) is less than 100 Km2. 33% of vortices occupy an area between 100 to 500 Km2 and only 4% of the vortices possess a large area between 500 and 1200 Km2. About a 93% of vortices have a diameter less than 20 Km. Most detected vortices (79%)have elipticities between 1.125 – 1.625. The vortices in the NW Mediterranean exhibit a bi-normal distribution of the vortices and we consider that there exist two main types of mechanisms related to their orientation: Dynamical, mostly due to the influence of the Liguro-Provenzal current (about 50% of the detected vortices have direction angles between 250 and 750 and bathymetrical, due to the influence of the submarine canyons situated mostly perpendicularly to the coast line (25% of the cases the detected vortices have azimuth angles between 125 and 145 degrees near Barcelona. The oil spills and slicks in the ocean surface exhibit a distinct parabolic multifractal shape when they have been weathered, their statistic and comparative analysis with in situ and laboratory image analysis provides important assimilation tools in order to improve numerical models of turbulent diffusion in the ocean surface at different scales. In particular the role of the Rossby deformation radius on mesoscale turbulent diffusion will be shown. The ability to discriminate between oil spills and natural slicks thanks to multiscale analysis is an important tool to develop realistic turbulent diffusivity parametrizations including the role of the wind in dispersing asymetrically the oil spills. It is possible to find predictive empirical relationships that can be used to parameterise the sub-grid turbulence in terms of generalized diffusivities that take into account the topology and the self-similarity of the sea surface environment. Multifractal analysis can be used to distinguish fresh oil spills and natural slicks in the ocean surface, with residence time of the oil spill, the diference in multifractality for the lower SAR reflectivity diminishes, but nevertheless using a non dimensional Time similar to the Damkholer number corresponding to oil in a turbulent environment, the calibration of a numerical model matching the turbulent diffusivity to that observed in the ocean may be used to estimate how long ago was the spill released.

References

Redondo, J. M., Platonov, A. 2001. Aplicación de las imágenes SAR en el estudio de la dinámica de las aguas y de la polución del mar Mediterráneo cerca de Barcelona. Ingeniería del Agua, Vol. 8 1-22.

Redondo, J.M., Platonov A.K., Grau, J. 2004. Aplication of multifractal feature analysis to the sea surface. Proceedings of the Fluxes and Structures in Fluids International Conferece (2003). Eds.Chashechkin and Baydulov; Russian Academy of Sciences RAS, Moscow.

Redondo J.M. (2004)The topology of Stratified Rotating Flows in Topics in Fluid Mechanics, 129-135. Ed. Prihoda & K.Kozel, CAS, Praga.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry