Parameterization of Bidirectional Reflection from Maize Leaves with Measurement in the Principal Plane

Characterization of bidirectional reflectance distribution of individual leaf is essential in canopy radiative transfer modeling. Measuring bidirectional reflection over reflectance hemisphere is a very complex and time-consuming work. Considering that leaf's reflection is a linear combination of specular and diffuse component, where specular reflection is centered on mirror direction in the principal plane and diffuse reflection is uniform regardless of directions, we made an attempt to parameterize Bidirectional Reflectance Distribution Function (BRDF) over reflectance hemisphere from angular distribution of reflection in its principal plane. Angular reflection of maize (Zea mays L) leaves over reflectance hemisphere was measured with a custom-designed device. The leaves were illuminated with two wavelengths of 650 nm and 830 nm, at three incidence angles of 0deg, 30deg and 60deg. Reflection measured in the principal plane was used to model BRDF with a physically based BRDF model. They were used to predict the reflection in other directions outside the principal plane. The predicted reflection was in a good agreement with those measured. It indicates that reflection distribution in the principal plane carries sufficient information to characterize the BRDF over hemisphere.