| Concept definition: |
The ratio, for a particular material <SURFACE> and unit solid angle about a particular reflection <DIRECTION>, of the reflected <<RADIANCE>> into that solid angle to the purely diffuse, total incident <<RADIANCE>> from the hemisphere above that <SURFACE>; hemispherical directional reflectivity. This quantity is also defined as the integral over the incident hemisphere of the BRDF times the cosine of the angle between the surface normal and the incidence <DIRECTION> times the differential incident solid angle. It is a function of the <<REFLECTANCE_ZENITH_ANGLE_LOCAL>> and <<REFLECTANCE_AZIMUTH_LOCAL>> of the reflected <<RADIANCE>> and is spectral (a distribution function in <<WAVELENGTH>>), therefore the quantity is measured in terms of inverse <<WAVELENGTH>> bin size. |
