I've fixed a few things up... new clouds with fixed lighting (including GI tweak) and added some low cloud for artistic licence... added some basic displacement, the only tricky thing I did was add progressively more displacement with distance. I liked the foreground so there is no extra displacement for 500m, then some mild displacement to 5km (covering the first range), and then some extra displacement beyond that. With the mountains being so rounded in this TER it seemed necessary to make things consistent across the terrain.
Running a render with high quality settings which might finish tonight.
And now for my first clues:
I approached the lighting of the atmosphere in the same way that I approach colouring surfaces. Rather than creating different surfaces with distinct colours, I rely on blending between the surfaces to create the final colour. A grass shader for example, will have a dark green base layer and the child layers of yellow, blue and white (and sometimes red). Colouring the atmosphere is a lot more complex because you have to use the lighting settings to provide colour tweaks without screwing up the lighting on the surfaces. It's quite easy to go around in circles. The other tricky part is that you don't have the same control over distribution. You are dependent on each settings effective "distribution". Furthermore, some of the effects you want to apply to the atmosphere will counter effects you may want to apply to surfaces.
From this I started with the Enviro Light settings where you have separate control over the colour and strength of GI on surfaces and the atmosphere. Take a detour to the Atmosphere TAB and note the Bluesky density and Redsky decay colours. Back in the Envro light section, apply the bluesky colour to the Colour on Surfaces and the Redsky colour to the Colour in atmosphere. Play around with the strengths and check out the preview render (wait for 40%)
The horizon colour will be influenced by atmospheric glow, so the GI colour will have less influence as you get closer to the sun. Try changing the hue of the Colour in atmosphere towards the red, and this will give you the variation you see along my horizon from left to right.
On the surfaces... the blue GI will a) fill the shadows and b) illuminate all surfaces with a blue light partly in proportion to how much sunlight it receives. To counter this in the surface highlights I made the sunlight a very light yellow. Previously when I had done this without GI it made everything look yuk, but with GI it works really well.
And of course there's the clouds. Clouds are incredible complex when it comes to lighting and I havea lot of tests to do before I can start to confidently control their lighting... but for now, in the lighting section of each cloud layer theres an Enviro light section to control the strength and colour for just that cloud layer. This is a really cool thing. In the first render above the clouds are still neutral in colour. In the next version they will have a similar variation to the horizon... ie. atmospheric glow will influence the balance between sunlight and GI. When I added the low level clouds they were pink which looked stupid. Editing their enviro light settings fixed this. Having this sort of control over individual cloud layers will make some awesome sunsets possible, where the lighting of the cloud will depend in part on its altitude.
There are some other bits I haven't included but this is the main crux of what I did for this image.
