Analysis of Evolving Oil Spills in Full-Polarimetric and Hybrid-Polarity SAR

Oil spill detection using a time series of images acquired off Norway in June 2015 with the uninhabited aerial vehicle synthetic aperture radar is examined. The relative performance of a set of features derived from quad-polarization versus hybrid-polarity (HP) modes in detection of various types of slicks as they evolve on a high wind driven sea surface is evaluated. It is shown that the HP mode is comparable with the full-polarimetric mode in its ability to distinguish the various slicks from open water (OW) for challenging conditions of high winds (9-12 m/s), small release volumes (0.2-0.5 m(3)), and during the period 0-9 h following release. The features that contain the cross-polarization component are better for distinguishing the various slicks from open water at later and more developed stages. Although these features are not available in the HP mode, we identify alternative features to achieve similar results. In addition, a clear correlation between the results of individual features and their dependence on particular components within the two-scale Bragg scattering theory is identified. The features that show poor detectability of the oil slicks are those that are independent of the small-scale roughness, while the features resulting in good separability were dependent on several factors in the two-scale Bragg scattering model. We conclude that the HP mode is a viable alternative for SAR-based oil spill detection and monitoring that provides comparable results to those from the quad-polarimetric SAR.