Radar signatures of mineral oil spills measured by an airborne multi-frequency radar and the ERS-1 SAR

Radar signatures of different mineral oil spills were measured by an airborne five-frequency (L-, S-, C-, X-, and K_u-band) microwave scatterometer during a controlled oil spill experiment in the North Sea. Furthermore, signatures of oil spills on C-band SAR images obtained by the First European Remote Sensing Satellite (ERS-1) were analysed. The radar contrast or damping ratio, defined as the ratio of the backscattered radar power from an oil-free and an oil-covered sea surface, increases monotonically for Bragg wavenumbers from k=20 m^-1 to k=500 m^-1. The radar contrast depends on the oil type and the thickness of the oil layer but was found to be independent of the polarization of the radar and the look direction of the radar relative to the wind for wind speeds between 6 m/s and 10 m/s