elevation - Calculating Topographic Ruggedness Index in ArcGIS Desktop?

Does anyone know how to calculate Topographic Ruggedness Index in ArcGIS Desktop without access to command line ArcInfo Workstation?

"The topographic ruggedness index (TRI) is a measurement developed by Riley, et al. (1999) to express the amount of elevation difference between adjacent cells of a digital elevation grid. The process essentially calculates the difference in elevation values from a center cell and the eight cells immediately surrounding it. Then it squares each of the eight elevation difference values to make them all positive and averages the squares. The topographic ruggedness index is then derived by taking the square root of this average, and corresponds to average elevation change between any point on a grid and it’s surrounding area." -- from an aml arcscript by Jeffrey Evans

Answer

I would recommend to look outside ArcGIS) Very easy using the free gdal software: http://www.gdal.org/gdaldem.html

gdaldem TRI input_dem output_TRI_map

Or if you'd prefer it in saga gis: http://www.saga-gis.org/saga_modules_doc/ta_morphometry/ta_morphometry_16.html