Retrieving Oil-Water Mixture Ratios of Marine Oil Spills From L-Band SAR Imagery

Abstract

Retrieving the oil-water mixture ratio (M, the proportion of oil in an oil-water mixture) of the marine oil spill is of vital importance for the emergency treatment of oil pollution, which can be achieved by a copolarization ratio (PR) method. In the framework of the PR method, it is assumed that Bragg scattering dominates at moderate incidence angles, and the relative contribution of non-Bragg scattering to total scattering (RCNT) is typically neglected. However, in this work, it is found that the RCNT cannot be neglected for L-band, especially for HH polarization at higher wind speeds (the RCNT is approximately 0.6-0.8 for wind speeds of 10-12 m/s). The significant impact of non-Bragg scattering results in the PR method not being accurate enough for retrieving M. After separately investigating the influences of the damping effect and effective dielectric constant reduction on the RCNT, a novel approach is proposed for more accurately estimating the M of marine oil spills by eliminating the impact of non-Bragg scattering. The proposed method was applied to uninhabited aerial vehicle synthetic aperture radar (UAVSAR) images collected during the Deepwater Horizon (DWH) oil spill accident. The inversion results of our approach show that the M of most oil spill areas ranges from approximately 0.3 to 0.6, which matches the reality better than that of a traditional PR method (ranging from approximately 0.6 to 0.8).

The evidentiary challenges of using satellite technologies to enforce ship-source marine pollution standards on the high seas

“…The prominence of SAR, an active, coherent, band-limited microwave high resolution sensor, is attributed to its ability to penetrate atmospheric conditions, providing near-time 24-h visibility under all-weather conditions [ 30 , 31 ]. More importantly, when such microwaves pulses encounter the ocean surface, the existence of a surface oil layer reduces the intensity of SAR backscattering by damping small-scale waves and reducing the effective dielectric constant, thereby creating a noticeable dip in the backscattered signal when compared to the surrounding ocean surface [ 32 , 33 ]. Since its inception, several technological developments such as polarimetric SAR and improved algorithmic techniques have been implemented to further improve the detection and feature attraction aspects of oil detection using SAR [ 27 , 34 , 30 ].…”