Sky view factor from DEM please help!!

[JogglAber]

Hi,
I have a problem: I have a DEM and need as output a raster in the same resolution as the DEM with a value from 0 - 1 where 1 means that the whole hemisphere is visible and not obstructed by terrain.
For me that should be something like sky view factor.
Could you tell me how to calculate it?
I cant find any help in the forum.
Thanks,
JJJ

[DarrenWiens2]

Have you looked at Viewshed?

[JogglAber]

Thanks, but Viewshed seems to return the visible pixels from a point. However, I am looking for a raster with same extent and cell-size as DEM that gives instead of the z-value, a percentage of how much of the sky is visible.
I dont think viewshed does that or am I wrong??