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
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
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.
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,