Radar signatures of mineral oil spills measured by an airborne multi-frequency multi-polarization microwave scatterometer

Radar signatures of different mineral oil spills were measured by an airborne five-frequency, (L-, S-, C-, X-, and K_u-band) four-polarization (HH, HV, VV and VH), microwave scatterometer during a controlled oil spill experiment in the North Sea. The 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_B=20 m^-1 to k_B=500 m ^-1. The damping ratio depends on the oil type and the thickness of the oil layer, but was found to be independent of the polarization and the look direction of the radar relative to the wind direction for wind speeds between 6 m/s and 10 m/s. These experimental results are interpreted in terms of a theoretical model on the damping of short gravity-capillary waves by surface films