Characteristics of 13.9 GHz radar scattering from oil films on the sea surface

An aircraft remote sensing project to study the response of a number of active and passive microwave and optical remote sensors to an oil-covered sea surface was conducted by NASA Langley Research Center in 1979. Included was a 13.9-GHz Doppler scatterometer, with a fan beam antenna and coherent detection, to measure radar backscatter as a function of incidence angle. The purpose of this paper is to present a comparison between the radar scattering signature of the clear surface and signatures of the surface while covered with a variety of crude oil films. The films were deposited on the surface from ships. Both in situ data and infrared aerial photography provided surface truth. Scattering changes were observed over a range of incidence angles from nadir to approximately 60°. Results show up to 14-dB reduction in backscattered power between the clear surface and the films for horizontal polarization at an incidence angle of approximately 30°. In all cases, the greatest reduction in backscatter due to the oil was observed at approximately 30°, which suggests an optimum incidence angle for oil detection and mapping at 13.9 GHz (λ0 = 2.16 cm). Maximum reduction in backscatter also appears to occur where the oil is the thickest.