Roughness
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Method of Shadow Profilometry:

wpe1.jpg (16104 bytes) Consider a piece of corrugated cardboard, as an example.
wpe2.jpg (25407 bytes) If we cast a shadow using a remote light source and straightedge, we create a shadow edge that follows the contours of the "rough" surface.  The shadow post is used to calculate the exact angle of the lighting.
wpe3.jpg (21200 bytes) The image is digitized, and the shadow profile is identified.
wpe4.jpg (6199 bytes) The edge of the shadow profile (roughness profile) is isolated.

The above profile is analyzed for any of the traditional roughness parameters.

wpe5.jpg (31032 bytes)

This techniques works on any rough or smooth surface.

 

REFERENCES:

Maerz, N. H., Franklin, J. A, and Bennett, C. A., 1990. Joint roughness measurement using shadow profilometry. Int. J. of Rock Mech. Min. Sci. & Geomech. Abst, v 27, pp. 329-343.

Maerz, N. H., and Franklin, J. A., 1990. Roughness scale effect and fractal dimension. Proc. 1st Int. Workshop on Scale Effects in Rock Masses, Loen, Norway, pp. 121-126.