Bidirectional Reflectance Factor Analysis from Field Radiometry and HyMap data

Vegetation canopies like most of the natural surfaces reflect the incoming radiation flux in an anisotropic way. Thereby, for an adequate interpretation of the reflectance, we should geometrically characterise the reflecting properties of the surfaces. The basic function that characterises the angular dependence of the reflectance is the Bidirectional Reflectance Distribution Function (BRDF), which is -by definitiona non-measurable quantity due to involving infinitesimal solid angle, and therefore without measurable radiation, for all existing geometries [1]. However, we can estimate the BRDF of natural surfaces by means of the Bidirectional Reflectance Factor (BRF), which is defined for conical solid angle, and so involves measurable radiation quantities, for a limited set of all possible geometries.