The complex refractive index of crude oils determined by the combined Brewster–transmission method

•A new method for determining the complex refractive index was proposed.•The method is precise for both the strong and weak absorption medium.•The complex refractive index of two crude oils was determined.•The radiation properties of oil droplets and coated oil droplets were studied. The complex refractive index of crude oils is an essential parameter for the study of radiative properties, which has important and wide applications in remote sensing analysis and identification of oil pollution. In this paper, a combined Brewster–transmission method for determining the complex refractive index was proposed. The method has a good performance for both strong and weak absorption liquids. The root-means-square error is less than 0.2% for the refractive index, and 10.0% for the absorption index. Furthermore, the complex refractive index of two crudes was measured by this method and the radiative properties of oil droplets and coated oil droplets were calculated using MIE theory. The research shows that the droplets exhibit significant forward scattering characteristics, and the scattering develops to further forward with size parameter increase. The coating significantly affects the radiative properties of droplets, causing the absorption efficiency to increase, and the scattering efficiency to decrease.