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NOAA - NMAO personnel and R/V NANCY FOSTER
"...rugosity derivation relies, in part, on a neighborhood analysis using a 3 grid cell by 3 grid cell neighborhood. An algorithm is passed through the Raster Map Algebra Operation object within Spatial Analyst that calculates the planar distance between the center point of the center cell and of each of the eight surrounding cells in the neighborhood. Next, using the Pythagorean Theorem, the surface distance is calculated for each planar distance using the difference in elevation between the cells. The result of this function is sixteen separate grid data sets with each cell value equal to this surface distance. The next step in the process is to calculate the area formed by three adjacent sides. The result is eight triangular surface area grids. These grid datasets are combined to obtain a surface area data set for the input bathymetric data set. The final step in the process is to create a data set that represents the ratio of surface area to planar area. This final data set represents rugosity for the study area."
More information on the specific algorithms used, and contact points for questions, can be found in the BTM's documentation.
Rugosity values near 1 represent flat smooth terrain, while higher values reflect increasing rugosity or terrain roughness. For rugosity grid interpretation, is recommended that the grid be reclassified according to standard deviation divisions.