Table 1.

Summary of surface roughness properties

Material	$S_a$, $\mathrm{\mu }$m	$R_a$, $\mathrm{\mu }$m	Maximum height, $\mathrm{\mu }$m
Glass*	0.02	0.01	0.19
Wood (pine)	10.60	0.68	212.07
Sandstone	75.13	1.16	581.12
Mesh (steel)	174.26	1.15	665.39

The arithmetic mean area roughness, S_a (asperities), arithmetic mean line roughness discretized by the average spine tip radius of 23 _m, R_a (friction), and height range of each material.

^*The transparency and reflectivity may have added noise to the measurements.