Sensitivity of roughness algorithms to sampling frequency for the characterization of weathered limestone specimens

Twenty-two weathered limestone specimens from various locations in Florida were profiled along their length to assess roughness and the sensitivity of computed roughness values to sampling frequency. A laser profilometer, with a data collection spacing of 0.05 mm, was used to obtain four profiles from each specimen. The profiles were then down-sampled to produce profiles of decreasing resolution. Seven common roughness algorithms were used analyze the profiles. Mean absolute angle, root mean square, and energy roughness values were not affected by down-sampling. Sinuosity roughness values decreased linearly for rough profiles but smooth profiles were unaffected. Number of turning points decreased linearly for both rough and smooth profiles with the rough profiles being more influenced by down-sampling. Z2 roughness values decreased logarithmically for rough profiles and very slightly decreased linearly for smooth profiles. The visual roughness classifications compared favorably with roughness values, most notably for the smooth and rough specimens. Rough specimens were less homogeneous then smooth specimens which indicates the whole specimens, not just portions of the specimen, should be used for roughness assessment.