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Sea Oil Spill Observation by means of Analysis of Spatial Statistics in Polarimetric SAR Data Using Wavelet Signatures

Attilio Gambardella(1), Gianfranco De Grandi(2), Tom Ainsworth(3) and Maurizio Migliaccio(1)

(1) Università degli Studi di Napoli Parthenope, Centro Direzionale, Isola C4., 80100 Napoli, Italy
(2) European Commission, DG Joint Research Centre, Via Enrico Fermi, 21027, Ispra (VA), Italy
(3) Naval Research Laboratory, 4555 Overlook Ave SW, 20375, Washington, DC, United States

Abstract

Oil spills in the sea are dramatic environmental events that can be effectively monitored by means of remote sensing. Synthetic Aperture Radar (SAR) has been shown to be most useful sensor. Oil spill detection by means of SAR images is possible because of the damping effect of the short wind waves caused by the presence of oil on the sea surface. As a consequence, an oil spill is physically a low backscatter and appears as a dark patch over SAR images. Unfortunately, other physical phenomena, known as look-alikes, may generate dark patches over SAR images. A widely adopted approach to characterize natural targets on SAR images is based on the texture statistics analysis. Moreover, in last years great attention has been paid on the use on polarimetric SAR data to achieve additional information. The Wavelet Polarization Signature (WASP) is a formalism, recently introduced in the literature, for analyzing in SAR imagery the dependences of texture measures afforded by wavelet frames on scale and polarization state. In detail, WASP encapsulates in graphical form the dependencies of texture measures on polarization and scale. These measures are a proxy of the structure function statistics. As such, they are related to the autocorrelation function for stationary processes, and to the fractal dimension for non-stationary processes with stationary increments. As a matter of fact, spatial variations of SAR backscatter from natural targets bear information on structural and geometric properties of the target, and therefore can be potentially useful in detection and segmentation problems. In this study WASP analysis is applied for the spatial statistics characterization of dark areas over marine scenes. The data set (C-band multi-look complex) used in this study was acquired during the SRL-2 SIR-C/X-SAR mission. The images include features related to oil spills, biogenic look-alikes and low wind areas. Experimental results show that the different response to polarimetric state, spatial scale and directional features of the oil surfactants and the look-alikes can be documented through polarimetric texture analysis.

 

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