Radar signatures of marine mineral oil spills measured by an airborne multi-frequency radar

Radar signatures of mineral oil spills consisting of heavy and light fuel w ere measured by an airborne five-frequency (L- S- C- X- and K-u-band) multi polarization microwave scatterometer flown on a helicopter during a control led oil spill experiment in the North Sea. The damping ratio, defined as th e ratio of the backscattered radar power from an oil-free and an oil-covere d sea surface, was measured at different radar frequencies and incidence an gles such that the Bragg wavenumbers, k(B), between 20 rad m(-1) and 500 ra d m(-1) were covered. The following results were obtained: for the five oil spills deployed in the experiment the damping ratio, in general, increases monotonically from k(B) = 20 rad m(-1) to k(B) = 500 rad m(-1). At S- C- X - and K-u-band, the damping ratio is larger for heavy fuel than for light f uel spills, while at L-band it is almost the same. For heavy fuel, the damp ing ratio increases with increasing thickness of the oil layer. Furthermore , for wind speeds between 6 ms(-1) and 10 ms(-1) the damping of the backsca ttered radar power is independent of the polarization of the radar and its look direction relative to the wind. The results obtained in the present in vestigation agree well with those obtained from similar measurements with h eavy fuel under high wind conditions.