Implement option to use a MODTRAN LUT based on the 'Fontenla' solar irradiance model.
Currently, OHB and GFZ use a MODTRAN LUT based on the 'New-Kurucz' solar irradiance model. However, DLR applies MODTRAN simulations calculated with the 'Fontenla 2011' solar irradiance model. To enable consistency with their radiance data, SICOR should provide the option to use a LUT calculated with 'Fontenla'. A simple multiplicative spectrum should suffice to convert the 'New-Kurucz' LUT to 'Fontenla'.