Study On Polarization Characteristics Of Scattered Light From Sea Surface And Oil Film

Oil spill on the sea is one of the factors that threaten the ecological environment,and timely detection and identification of it is very necessary.Compared to traditional light intensity based detection of oil spills on the sea surface,polarization detection is more popular because it is not limited by surface contrast.Condensate is one of the commonly used crude oils in industry.This article studies the scattering characteristics of the sea surface and condensate film,as well as the scattering Stokes vector in hemispherical space.The specific work is as follows:(1)Gaussian random rough surfaces and random sea surfaces were established using linear filtering method,and the scattering of single-layer random rough surfaces was analyzed using Kirchhoff approximation method and spatial scattering field expressions were obtained.An improved method of traditional masking effect algorithm,ray tracing method,was proposed,which significantly improved the computational efficiency.The simulated distribution of scattered light intensity from random rough surfaces is in good agreement with the results in the literature,proving the effectiveness of this method.The distribution of scattered light intensity in the incident plane of S-wave and P-wave incident on the sea surface was numerically calculated.Based on the rough surface scattering mechanism,the reason for the appearance of two peaks of scattered light in the Brewster angle incident P-wave was explained.(2)We studied the scattering of layered random rough surfaces and calculated the indirect transmission field of layered rough surfaces using ray tracing method.On the basis of the improved ray tracing method,unnecessary ray tracing surface elements caused by the thickness of the upper layer medium are removed,further improving the efficiency of ray tracing.Comparing the simulated layered rough surface scattering coefficient with the literature results,it is in good agreement.Numerical calculations were conducted on the distribution of scattered light intensity in the incident plane of the sea surface and condensate oil film.It was found that when S waves were incident at 30°,56°,and P waves were incident at 30°,the scattered light intensity of the oil film was greater than that of the sea surface.The peak appeared in the mirror direction of the incident light,and as the wind speed increased,the peak of S wave scattered light intensity shifted to the right,while P wave scattered light intensity shifted to the left;When the P-wave is incident at 56°,the scattered light intensity has two peaks,distributed on both sides of the Brewster angle mirror direction.When the wind speed is low,the values of the two peaks of the oil film are close.As the wind speed increases,the right peak increases faster,and the difference between the left and right peaks gradually increases.(3)The hemispherical spatial Stokes vectors of scattered light on the sea surface and condensate oil film at different incident angles and polarizations were numerically calculated under different wind speeds.Analyzed the effects of polarization state of incident light,incident angle,and wind speed on the Stokes vector of scattered light.The results show that when linearly polarized light is incident on the sea surface,the V component of the Stokes vector of the scattered light is almost zero.However,when incident on the oil film,there is a more obvious V component,especially when the P-wave is incident at 56°,the V component shows a clear two lobe antisymmetric distribution on both sides of the incident plane.When the 45°polarized light is incident at 56°,the V component shows a clear two lobe antisymmetric distribution on both sides of the incident light mirror direction in the incident plane,Therefore,the V component can be used to distinguish between seawater and oil film.This result can provide a certain theoretical basis for detecting oil spills on the sea surface.