Problems & some Solutions

Albedo Variations 
Large-scale variations normalized via high-pass filtering.
Images with large albedo variations should not be measured.
Some small-scale variations are unavoidable. However, they
    will contribute to steepening slopes, and contribute to an
    upper limit.

Haze
Unavoidable
We process two versions of each image:
No haze removed
            (slopes shallower than reality, h = 0)

Minimum pixel value subtracted as the haze
            (slopes steeper than reality, h = minimum pixel value in scene)