159 APPLICATION OF MULTIFRACTAL FEATURE ANALYSIS TO THE SEA SURFACE J.M. Redondo, A.K. Platonov and J. Grau 1) Universitat Politècnica de Catalunya, Dept. de Física Aplicada, ( 1) UE Mecanica, EUETIB-CEIB) C/Jordi Girona Salgado s/n, Campus Nord, Modul B5, E-08034, Barcelona, Spain. e-mails: redondo@fa.upc.es , alexei@fa.upc.es , Joan.grau@upc.es . 1. Introduction In many geophysical phenomena of great environmental interest there appear simple processes at different scales that generate complexity (Mandelbrot 1967). This behaviour may be found in the growth of an ice crystal, the ramifications of a river basin or the self-similar dynamical structures in the ocean surface where the Reynolds number is high and the regime corresponds to a turbulent fluid flow. The energy enters in the system at the large scale and cascades following the theory of Richardson (1926) down to the Kolmogorov micro scale (Kolmogorov 1941), the large eddies break up in even smaller eddies. This is a typical self-similar process. An important topological analysis tool, the fractal analysis was also pioneered by Richardson (1926) and introduced formally by Mandelbrot (1967). The fractal dimension is a very useful indicator of the complex environmental flow dynamics (Turcotte 1988, Redondo 1990), but it only reflects the self-similar geometry, not the dynamics. Fig. 1. Examples of ERS-2 SAR images with oil spills in the Northwest Mediterranean near Barcelona on 05.07.98 (left) and on 28.09.97 (right). The image’s box size is near 100 Km. The oceans receive energy inputs at a wide range of scales, and the non-linear interac- tions that produce turbulent cascades of the type described by Richardson (1926) and Kraich- nan (1967) disperse the pollutants as well as the natural tracers in the ocean surface. The abil- ity of Synthetic Aperture Radar SAR equipped satellites to monitor a large sea area and the fact that Radar reflections are sensible to either surface tensioactives or pollutants that change the sea surface roughness which allows us to use remote sensing of the ocean surface even to police pollution. Man-made oil/water wash spills dampen the small-scale surface waves, these in turn are responsible for the radar backscattering from the water surface, and are visible as dark patches or lines in SAR images. We present several examples of the detected oil spills in the ocean surface and how the fractal analysis may be used to identify ocean surface pollution with SAR images (Fig. 1).