Unsupervised oil slick detection by SAR imagery using kernel expansion

Spaceborne synthetic aperture radar is well adapted to detect ocean pollution independently from daily or weather condition. In fact, oil slicks have specific impact on ocean wave spectra. Initial wave spectra may be characterized by three kinds of waves, big, medium and small, which correspond physically to gravity and gravity-capillary waves. The increase of viscosity due to the presence of oil damps gravity-capillary waves. This induces a damping of the backscattering to the sensor, but also a damping of the energy of the wave spectra. Thus, local segmentation of wave spectra may be achieved by the segmentation of a multiscale decomposition of the original SAR image. In this work, an unsupervised oil slick detection is proposed by using kernel-based novelty detection into the wavelet decomposition of a SAR image. It performs accurate detection with no consideration to signal stationarity nor to the presence of strong backscatters (such as ships). The algorithm has been applied on ENVISAT ASAR images. It yields accurate segmentation results, even for small slicks, with a very limited number of false alarms.