Today I needed to drive the 16km from Halley VI back to Halley V in a snow cat. First thing in the morning was slightly foggy but with the sun nearly burning through - horizontal contrast poor, surface contrast good. This is the view from the snowcat, you can see clearly see the first drum of the drum line that I was following but the next drum and the horizon are very faint. The tracks of other vehicles that have driven the route are clearly visible.
Ok, I'll stop going on about contrast.