Analytical forms of eigenvalues are given based on the coherence matrix simplified under the hypothesis of reflection symmetry, and three parameters , , and representing the individual contribution of single, double, and multiple scattering mechanisms to the total backscattering are defined. The single scattering is confirmed as a direct description of the Bragg scattering while the double and multiple scatterings are supposed to be classified as non-Bragg scattering. Experiments using quad-polarization single look complex C-band RADARSAT-2 SAR images indicate that the oil slick mainly dampens the Bragg scattering, due to the reduction of single scattering over oil-covered sea surfaces. The decrease of results in the corresponding increase of and , and the values of over clean sea surfaces are higher than those of oil slicks on the image. Therefore, can be selected to discriminate oil slicks from clean sea surfaces. By comparing the two imagery experiments, we also note that the relative contribution of Bragg scattering to the backscattering over oil-covered surfaces is highly dependent on the local wind field.