Spectral pBRDF microfacet modeling for dicotyledonous leaves and a coefficient correction

The dimensions of physicochemical information about leaves can be broadened by spectral polarization detection. Traditional polarized bidirectional reflectance distribution function (pBRDF) microfacet models lack independent volumetric scattering in spite of mainly comprising specular and diffuse reflection. Additionally, they are not explicitly designed for leaves. Regarding the first aspect, a volumetric scattering BRDF microfacet model was proposed in previous research. In regard to the second aspect, this paper incorporates polarization into the microfacet model and puts forward a spectral pBRDF microfacet model designed explicitly for leaves. Spectral pBRDF measurements and comparative analyses were conducted on three dicotyledonous leaves and Firmiana simplex leaves with two different chlorophyll contents. The results indicated that volumetric scattering intensity, chlorophyll content, and leaf surface roughness (represented by the standard deviation of surface slope σ_g) are all correlated with the polarization information of reflected light. Based on these findings, the form of the Mueller matrix was obtained and combined with the BRDF microfacet model to construct the final pBRDF model and its matrix element expressions. The proposed model in this study demonstrates good performance in the fitting of the pBRDF matrix element f₀₀ compared with the traditional non-volumetric scattering pBRDF model.