Have you tried simply making an animation of sequentially numbered tif files with no background? That should give you your alpha channel and I don't remember the ground ever rendering, however there are settings (perhaps under View) that allow you to shut off things like the groundplane and groundplane shadows (which are different than rendered shadows. You then just import the sequence of files into your next application which will create the animation. You may have to invert the alpha during import. I know the Avid needs that box checked for the alpha channel to come in properly for some reason.

HTH

 
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