Compute with Create derivative grid option.
Robbins and others (http://pubs.usgs.gov/ds/477/) describe this metric (a slope/roughness measure). You would get the same effect with a slope map using the Average neighbor slope algorithm, with some minor differences because rugosity does not account for differences in the diagonal distances.
This does not deal with different x and y spacing in geographic DEMs; MICRODEM computes it, and uses the Average DEM spacing.
We see no reason to use this option, and do not recommend it.
last revision 5/13/2011