INFLUENCE OF SURFACE OIL ON C- AND KU-BAND OCEAN BACKSCATTER.

A comparative study of ocean backscatter depression due to surface oil has been carried out using Ku- and C-band scatterometers supported by some X- and C-band synthetic-aperture radar (SAR) imagery. The depression of radar backscatter for both C-band and Ku-band horizontally polarized radiation was measured for the incidence angle range from 20 degree to 50 degree on two days for which the average wind and wave height conditions were 3-6 m/s, 0. 3 m and 10-14 m/s, 1. 2 m, respectively. Results show that the depression in Ku-band backscatter increases from approximately 3-5 dB at 20 degree to approximately 10 dB or more at 30 degree -40 degree and then decreases at larger incidence angles. Generally, the angular dependence of C-band backscatter depression was similar to that at Ku-band, but the peak depression was shifted to slightly larger angles and usually exceeded the Ku peak by 1-2 dB. The Ku-band results are in good agreement with previous work that tentatively explained the angular results of backscatter depression on the basis of a selective damping of the first-order Bragg resonant waves by the oil film. This explanation, however, is inconsistent with the results of the present work when both C- and Ku-band are considered. The significance of the data is discussed in the context of present and future radar systems.