Why doesn the model read spectral reflectances?
The reason for this dates back to the origins of the DIRSIG model, which was originally written to perform strictly in the thermal infrared region of the spectrum. When the model was extended to the reflective regions of the EO spectrum, the concept of using emissivity as the primary optical property remained. The model assumes that surfaces are at thermodynamic equilibrium. Therefore, Kirchoff’s law holds and the reflectance can be computed as 1 – emissivity. In DIRSIG version 4, the user will be allowed to supply either reflectance, emissivity or both.
