Why is it divided into black, white and blue?

[showkeyjar]

rt.

I think albedo just decide by land material, solar angle, and air visibility.

if I miss something?

[showkeyjar]

I got it.
MCD43A1 homepage has describled.
but I'm still confused with white sky,
because the sufface is not one point angle, white sky will missing many informations.
and I think it is no need to distinguish between white and black,
why not use one unified reflection distribution function?
and black sky is a bit redundant.