UPDATE 03.05.2011: Terrain shader preview: http://www.flightgear.org/forums/viewtopic.php?f=47&t=11274&start=30#p123287
UPDATE 14.03.2011: Links to patches and shaders: http://www.flightgear.org/forums/viewtopic.php?f=47&t=11274&p=117965#p117965
Hi all.
I've been doing an atmospheric scattering shader for few weeks now, mostly after Gpu Gems article, http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter16.html. I've modeled all those equations with python and found similar functions as O'Neil to make the shader runtime.
Some screenshots:
Skydome shader starting to work:

Skydome and ground shaders working, altitude is about 30km.

Same as above, but this time at around 250km.

I did this in a shader developing program, so it's not yet suitable for FG. It also is currently too slow as all calculations are done in fragment shader, but I might get it to work with FG in few weeks

Zan