Modelling And Analysis Of Polarised Light Reflection Off Layered Rough Surfaces

Light gets reflected by objects during its propagation.The distribution and the intensity of the reflected light are highly dependent on the optical and geometrical properties of the object surface.By modelling the light reflection off rough surfaces,we can evaluate the optical information of reflected light(incident light)effectively,with given incident light(reflected light).So,rough surface reflectance modelling has long been a hot topic in the research of remote sensing,object detection,and photo-realistic rendering in computer graphics.Many researchers made a lot of efforts to increase the accuracy of models,and to make models more adaptive to different surfaces.Currently,most of the works still focuses on the light reflection process on single layered surfaces.However,layered surfaces are almost everywhere in our daily life,as well as in military scenes,modelling reflectance on layered surfaces remains to be a hard problem,due to the difficulty of simulating all possible light-matterinteractions when light propagates in layered surfaces.Polarisation is a property of light wave.One can describe a polarised light with its light intensity and polarisation state.However,the effect of polarisation is usually ignored in traditional reflectance model for layered surfaces.As polarisation state of light will affect the intensity of its scattered light,including polarisation effect intoreflectance model will serve as a way to increase its accuracy.At the same time,considering polarisation in reflectance model will bring us the polarisation state of the reflected light as well.As such polarisation state of reflected light is a reflection of object that the incident light interacts with,this will provide extra information in its application of object detection and classification.In summary,modelling polarisation light reflection on layered rough surfaces is important and meaningful.In this thesis,we divided the problem of reflectance modelling on layered surface with polarisation effect into three key problems:1.the calculation and tracing of polarised light;2.the effective expression of the structure of layered surface and the reflectance model with given surface structure;3.the calculation of multi-scattering effects on surfaces.Focusing on these three key problems,with the micro-facet theory,Monte Carlo methods and the technique of polarisation ray-tracing,we propose two polarisation reflectance models on layered surface,and solve the all of the three key problems step by step.The work in this paper is as follows:(1)Focusing on the first two key problems,we proposed a single-facet based polarisation reflectance model for layered surfaces.Micro-facet theory is applied in this model,which allow us to represent random rough surface with single facet approximately.The single facet is randomly oriented but statistically follows Gaussian distribution,and a layered surface is then formed by adding single facet on the other single facet.In this model,we also discussed the method of the rotation operation for polarisation reference frame alignment,which is important in polarisation ray-tracing.Finally,we build up our single-facet model with Monte Carlo method and polarisation ray-tracing techniques.Validations are conducted against published measured data and the data from theoretical model.The limitations of this model are summarized in the end as well.(2)Based on the single-facet reflectance model for layered surfaces,we presented a mesh surface based reflectance model for layered surface,which include polarisation and multi-scattering effects into a layered surface reflectance model at the same time.By applying procedural modelling techniques,layered rough surfaces are represented by several meshes with known statistical properties.The model incorporates light-object intersection test on the mesh based surface to deal with multi-scattering,and applies importance sampling scheme which improves the efficiency of the model.A large amount of experiments was carried out for model validation,we compare our simulated data with the state-of-art model to prove the theoretical correctness of our model.We also conduct real measurement on gold coated sandpaper samples with scanning electron microscope(SEM)and ellipsometer,and achieve good matches with the measured data,which showed that our model could serve as reference data generator for layered surface reflectance model.(3)We carried out a large amount of simulation experiments to investigate the impact of polarisation on the reflectance on layered surfaces.First,we investigate the impact of polarisation on the accuracy of layered surface BRDF modelling,i.e.how many errors it will brings to the BRDF value if we ignore polarisation.Based on the simulations,we discussed the how the incident angle,surface materials and roughness affect the magnitude of the error from ignoring polarisation,and lead to a discipline to predicting the impact of polarisation on layered BRDF model,which is useful in the application when highly accurate BRDF data is needed,for example in photo-realistic rendering.Second,we investigate how the surface materials,incident wavelength,and incident polarisation state affect the polarisation states of the reflected light.As the polarisation states of the reflected light reflect the characteristics of the object surface,analysing reflected polarised light is useful in the tasks like object detection and recognition.In the meantime,the simulated BRDF data are published on Figshare.