QUOTE (Bill Harris @ Jan 31 2006, 03:51 AM)
Now that we're approaching the Homeplate basin, I've noticed something odd. From the color images of the Inner Basin taken from atop Husband Hill or from Comanche, I see many large dark boulders and a few large light-toned boulders the size of the Rover or larger on Mitcheltree Ridge. But now that Spirit is climbing that ridge I haven't seen any large boulders. I had assumed that this was a blurring phenomenon, but blurring tends to bleed over from the light areas (sand) into the dark spots (rocks) and not vice versa, so the dark rocks should be made less visible.
Any thoughts? Not a big deal, this just bugs me...
I would have thought my embarrassment about The Big Black Rock
would have made the answer obvious. Objects (rocks or the sun or moon) on a horizon are expanded in size by the brain. This optical illusion has been studied in depth by many researchers. (While a graduate student, I actually served as a volunteer subject in one of these studies.) When moved significantly above or below the horizon (especially if other objects for reference are nearby), the object 'shrinks' in our perception. No, I can't tell you why.
In the MER example, the different cameras and their lenses and locations on the rover seem to enhance this effect. So many times I've looked at a bunch of 'boulders' in a pancam image, thinking: We'll never get past those!
Then when I see the same rocks in the fish-eye hazcam,with the wheels in the frame, it's obvious that we can just roll over those 'pebbles'.
I'm much more cautious now about judging rock sizes, but I'd be willing to wager that those "rover-size" rocks on Mitcheltree were nowhere near that big. A parallax estimate is the only technique I would trust until we're sitting on the thing.
Ain't science wonderful?