Wave Breaking in Slicks: Impacts on C-Band Quad-Polarized SAR Measurements

Abstract

Radarsat-2 C-band quad-polarization SAR observations of crude oil, emulsion, and plant oil slicks acquired in the wind speed range from 4 to 8 m/s and incidence angles from 30° to 50° are analyzed to yield new insights into the attenuation of short waves and breaking waves by surface slicks in real conditions. To provide a direct quantitative assessment of the surface wave damping, the measurements are decomposed into polarization difference (PD), polarization ratio (PR), nonpolarized (NP), and cross-polarized (CP) components. The PD signals relate to the extent of Bragg damping in the slick areas, over which the PR is systematically higher than over the ambient sea surface. Attenuation of the breaking waves is revealed to affect both the CP and the NP signals, with distinct but weaker contrasts compared to that of the PD. A revised physical model description is proposed to provide consistent interpretation of the polarized and NP signals. The results suggest that the different slick types and look-alikes can be efficiently discriminated and classified.