[verycuriousguy (OP)]

Sometimes, in skiing, there is flat light, when clouds completely cover the sky.  In flat light, it is very hard to see surface features, e.g. small features or curves in snow.

Yet if you ski near the trees, visibility is much improved.

Why is this?  Doesn't seem like it could be about shade.

[chris]

Lovely question, but can you please edit the thread title to format it as a question, in line with forum policy? Otherwise the thread will be deleted. Thanks.

[Bogie_smiles]

The optics of the flat light that you refer to are the monotony of the snowscape and the lack of any features that stand out. Add the presence of tree trunks and the monotony is broken, and you have something that allows you to gage the scale of differences in the shading of the snowscape, don't you think?

[verycuriousguy (OP)]

I had no idea as to the cause, not even a guess. but your response sounds plausible. 

The flat light situation I'm talking about is quite odd....you look down and you can see your feet, but if you're not around trees you really have difficulty seeing the surface.

[evan_au]

Our eyes detect the edges of objects by changes in color and brightness.
- Snow is a uniform color
- When there is an overcast sky, lighting is uniform, there are no shadows, and there is little variation in brightness

If we are close enough to objects (15 feet or 5 meters), our eyes can pick out additional cues due to binocular vision - but you need some variation in color, brightness or texture to allow your eyes to "converge" properly.

However, if you are near trees, that provides:
- A strong difference in color
- A shadowing effect, so that objects are no longer uniformly illuminated
- Some clear edges to assist convergence