Experimental research on oil film thickness and its microwave scattering during emulsification

Abstract

Synthetic Aperture Radar (SAR) plays a major role in identifying oil spills on the sea surface. However, obtaining information of oil spill thickness (volume) is still a challenge. Emulsification is an important process affecting the thickness and normalized radar cross section (NRCS) of oil film. Experiments of crude oil emulsification with C-band fully-polarized scatterometer were conducted combining airborne hyperspectral imaging spectrometer and 3D laser scanner observation data, to provide experimental parameters and method to support accurate remote sensing monitoring on marine oil spill. It is further proved that through quantitative homogeneous emulsified oil spill experiments, to a certain extent, the NRCS of oil film increased during the emulsification process of crude oil. The backscattering mechanism of crude oil emulsification was explored using a semi-empirical model (SEM); the change of oil film NRCS was modulated by its dielectric constant and surface roughness, in which the dielectric constant showed a dominant effect. The relationship between thickness and NRCS of oil film was studied under two experimental conditions. The differences of NRCS between oil film and adjacent seawater (Δσ0) and the damping ratio (DR) were found to have a linear relationship with oil thickness, which were best in the vertical polarization mode (VV) at 45° incident angle during the quantitative crude oil homogeneous emulsification process. In the natural emulsification process of continuous oil spill in which oil film was mixed with both crude oil and emulsified oil, an empirical equation of oil film thickness is preliminarily established. The Δσ0, DR, and the empirical equation of oil film thickness were applied to the marine continuous oil spill incident on a 19–3 oil platform with spaceborne SAR image and successfully explained the distribution of the relative thickness of the oil film.