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. Emulsifi cation is an important process aff ecting the thickness and normalized radar cross section (NRCS) of oil fi lm. Experiments of crude oil emulsifi cation 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 emulsifi ed oil spill experiments, to a certain extent, the NRCS of oil fi lm increased during the emulsifi cation process of crude oil. The backscattering mechanism of crude oil emulsifi cation was explored using a semi-empirical model (SEM); the change of oil fi lm NRCS was modulated by its dielectric constant and surface roughness, in which the dielectric constant showed a dominant eff ect. The relationship between thickness and NRCS of oil fi lm was studied under two experimental conditions. The diff erences of NRCS between oil fi lm and adjacent seawater (  σ 0 ) 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 emulsifi cation process. In the natural emulsifi cation process of continuous oil spill in which oil fi lm was mixed with both crude oil and emulsifi ed oil, an empirical equation of oil fi lm thickness is preliminarily established. The  σ 0 , DR, and the empirical equation of oil fi lm 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 fi lm.