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How to measure topographic roughness irrespective of slope in ArcGIS? I have used many methods to generate roughness layers, including TRI, VRM (which is supposed to be less correlated with slope), slope aspect index, slope variance, slope standard deviation etc.

So far, all of the output layers are extremely similar to each other and to my slope layer. They do not seem to be clearly differentiating between areas of steep and rugged terrain and those which are steep but smooth.

How can I generate a roughness layer which is not so dependent on slope?

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the difference between roughness and slope is a question of scale. I recommend that you think about the resolution of your raster at which you observe the slope but you don't see the roughness anymore, then you can smooth your surface (e.g. using a low pass, a mean filter or some spline) at this resolution. This will yield a new surface with zero roughness, only slope. You can then substract the original data and the smoothed raster to come out with a roughness layer on which you can apply your indices.

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