Experimental investigation of spectral mueller matrix and polarimetric radiative characteristics of multi-phase emulsified oil spills in the UV–vis-NIR range

Polarimetric analysis provides an effective optical pathway for identifying and characterizing marine oil spill emulsions; however, experimental Mueller matrix data for oil–water emulsions over a broad spectral range remain limited. To enhance marine oil spill identification and emulsion type discrimination, this study utilized spectroscopic ellipsometry to measure the Mueller matrices of light crude oil emulsions across a 200–1690 nm spectral range at a 45° incidence angle. Samples included seawater, pure crude oil, and emulsions with varying oil contents (0.1%–6% O/W and 80%–98% W/O). Through Lu-Chipman decomposition, the polarimetric radiative characteristics of oil-in-water (O/W) and water-in-oil (W/O) emulsions were systematically analyzed. The results indicate that the depolarization index (DI) is governed by the competition between crude oil absorption and multiple scattering; W/O emulsions exhibit higher DI values, indicating a weaker depolarization capability compared to O/W emulsions. Linear and circular polarization parameters (LB, LD, CB, CD) reveal a mechanistic transition from localized Mie scattering to collective multiple scattering in O/W emulsions, whereas W/O emulsions reach scattering saturation due to the strong absorption of the continuous phase. Furthermore, the difference in the m₁₂ element (Δm₁₂) between seawater and emulsions reveals a characteristic peak around 370–380 nm that exhibits an increasing trend with oil content, providing a robust spectral window for polarimetric detection. Additionally, the degree of polarization (DOP) peaks are found to be determined by the continuous phase's Brewster angle, showing negligible sensitivity to oil content. These findings quantitatively reveal the intrinsic correlation between polarization parameters and microstructure of emulsions, provide important experimental data in relevant fields, and provide critical experimental support and characteristic bands for the polarimetric monitoring and characterization of emulsified oil spills.