Hello Dr Heydar ,

Thanks for your attention, it's irradiance (radiance)

The first-order approximation of solar irradiance can be obtained from creating a DEM shaded relief image. Please try "Topographic Modelling" tool of ENVI.

Dear Imran Rahimi,

So far I know there is no direct process of getting/estimate/extract solar radiation from any satellite image. There are many methods (statistical or physical models) for estimation of solar radiation from satellite images. For that some other data also needed. You can find many papers regarding estimation of solar radiation from satellite images from internet. You can follow my papers also to have a look.

Hope that helps.

u can also follow the paper of bisht. et.al.