Thank you! I didn't have time to implement image-space occlusion queries, plus I wasn't sure of the level of support they have on mobile hardware (not that this demo will run on anything mobile for the time being :)). I'm shooting a grid of rays through the terrain instead (see relevant screenshots), using various techniques to accelerate that.

The result is used for modulating the intensity of both the lens flares layer and the glare layer.

Nice article!