Adding my 2 cent to the discussion: I believe this photo best illustrates what the paper is attempting to do: notice that the more distant a shadow is, the brighter and bluer it is.
That's generally true with distance, but in absolute numbers it's greatly dependent upon the precise atmospheric conditions at the time, even to the point that I'd suspect that even a highly calibrated instrument might give a different reading from top to bottom of its vertical field of view: think of ground-hugging bands of moist air, for example. The concept, although nicely illustrated by the large distances seen in your mountain photo, doesn't seem like a thing designed to work with a small, close sighting of an insect. And of course comparing shadows requires conditions that produce shadows.
I don't have your expertise with cameras; I'm just suggesting some limiting conditions that might make such methodology problematic.