The Bidirectional Reflectance Distribution Function (BRDF) describes the directional dependence of the reflected energy of a target as a function of illumination and viewing geometries. The BRDF also depends on wavelength and is determined by the structural and optical properties of the surface, such as shadow-casting, mutiple scattering, mutual shadowing, transmission, reflection, absorption, and emission by surface elements, facet orientation distribution, and facet density.Relevance to remote sensing of the environment:
The BRDF is needed in remote sensing for the correction of view and illumination angle effects (for example in image standardization and mosaicking), for deriving albedo, for land cover classification, for cloud detection, for atmospheric correction and other applications. It gives the lower radiometric boundary condition for any radiative transfer problem in the atmosphere and is hence of relevance for climate modeling and energy budget investigations.
View of the tested soil surfaces: (A) rough surface; (B) smooth surface; (C) uncultivated, relatively smooth; and (D) cultivated with furrows.
Distributions of the Normalized Hemispherical–Directional Reflectance Function (NHDRDF) of the tested surfaces obtained from the measured data for the wavelengths of 850 nm for chosen illumination conditions defined by the solar zenith angle θs and additionally by the angle fc-s describing illumination of the furrows as a distance angle between the direction of the furrows and the sun position.
Illustration of the effect of BRDF can be viewed for the following conditions (press the arrows to run the simulations)
Simulations created by the group of Prof. Jerzy Cierniewski, Adam Mickiewicz University
|qs = 35o||fc-s = 264o||t = 2.00||l = 850nm|
|qs = 35o||fc-s = 264o||t = 0.10||l = 850nm|
|qs = 70o||fc-s = 264o||t = 2.00||l = 850nm|
|qs = 70o||fc-s = 264o||t =0.10||l = 850nm|