Comparing Near-Coincident C- and X-Band SAR Acquisitions of Marine Oil Spills

In this paper, we compare satellite-borne C-and X-band synthetic aperture radar (SAR) data for marine oil spill observation. During large-scale oil-on-water exercises in the North Sea, quad-polarization Radarsat-2 (C-band) and dual-polarization TerraSAR-X (X-band) data were acquired with temporal distances of less than 24 min. The objective is to characterize and quantify differences in the Radarsat-2 and TerraSAR-X measurements. Three scene pairs are compared in terms of data quality and signal characteristics, including statistical properties and selected multipolarization (HH, VV) parameters. The signal characteristics are also compared among low-backscatter features of various origin within the individual pairs. No viable argument for selecting one sensor above the other is identified in the data quality study. In the statistical analysis, investigation of log-cumulants indicates a larger deviation from Gaussian statistics in the TerraSAR-X data compared with Radarsat-2 measurements. Log-cumulant diagrams are also shown to be a useful tool for discrimination between oil spills and a simulated biogenic slick in both sensors. Multipolarization features show enhanced slick-sea contrasts and a better discrimination between mineral oil spills and other low-backscatter features in Radarsat-2 compared with TerraSAR-X. The presence of a non-Bragg scattering component in the data is revealed for both sensors. The relative contribution of non-Bragg scattering to the total backscatter is found to be higher in the TerraSAR-X data than in the Radarsat-2 data. In general, the non-Bragg component is found to account for a larger part of the backscatter in slick-covered areas compared with clean sea.