Planck's Radiation Law Planck's Radiation Law describes the spectral distribution of the radiation emitted by a blackbody as a smooth curve with a single maximum. It gives the complete solar spectrum leaving the sun. Emissivity is the ratio of the radiant exitance of a surface or element to that of a blackbody at the same temperature. Stefan Boltzman Law Stefan-Boltzman Law integrates Planck's equation between 0 and infinity. Transmitted and reflected energy are unaltered spectrally, whereas absorbed energy is irreversibly transformed.
Most surface have anisotropic reflectance characteristics.
This is what really is measured in the field. The fundamental and intrinsic property governing the complete reflectance behavior of a target. Earth surface irradiance is made up of a direct and diffuse component. This energy again may be absorbed, transmitted, or reflected by a vegetated canopy layer. Energy that passes through this layer may again be absorbed or reflected by the soil background layer.