Making 3D fog

Unity Engine
1

I want to make some fog which “stops” after a certain height above the ground, but when you look down you can see the fog. Sort of like fog on the ground in graveyards. Does anyone know how to do this?

2

There is a fog image effect in unity (Pro)

http://docs.unity3d.com/Documentation/Components/script-GlobalFog.html

Havnt used it so cant tell you much about it but sounds like what you want.