In the end, the simplest explanation for limb darkening lies in the recognition that directional spectral emissivity occurs naturally within condensed matter [66, 71-73].
Their complex radiative properties can be fully explained by considering directional spectral emissivity.
It elegantly accounts for solar emission using a single phenomenon (directional spectral emissivity in condensed matter) applicable across the full range of solar observations.
s] is given by multiplying the Planck function by spectral emissivity
[epsilon]([lambda]) (Zhengming, 1999).
To obtain a more accurate LST, roughness properties of the land surface, the amount and nature of vegetation cover, and the thermal properties and moisture content of the soil must be accounted for by correcting brightness temperatures using spectral emissivity values before computation occurs .
Since the temperature values obtained previously are referenced to a black body, corrections for spectral emissivity ([member of]) depending on the nature of land cover became necessary.
Since there was no means to measure the spectral emissivity
of the surface material (travertine rubble), the value of emissivity was estimated to be 0.
This calculation assumes that the spectral emissivity
of the black-body, determined essentially in the visible spectral range, is constant over the full spectral range.
Thus, the increased directional spectral emissivity in sunspots could only be explained with extreme difficulty using gaseous solar models and often attributed to the effect of "stray light" [41, p.
The directional spectral emissivity contrast of faculae, with respect to the photosphere, has long been known.
While faculae display CLV with respect to their spectral emissivity, their emissivity contrast remains highly associated with the magnetogram signal .
Their normal emissivity is typically higher than their directional spectral emissivity