Comparison of roughness indices from weathered, differentially weathered and vuggy profiles obtained using laser scanning and photogrammetry

Surface profiles obtained from weathered limestone specimens using laser profiling and photogrammetry were assessed using three geometric and three fractal roughness algorithms. The specimens were visually classified as smooth, slightly rough, moderately rough, rough, differentially weathered, and vuggy. Comparisons of roughness indices from the two methods were made using a graphical qualitative assessment and semi-quantitative assessments using Bland-Altman plots with Kolmogorov-Smirnov tests. Profile roughness indices computed from laser profiling and photogrammetry methods compared favorably for smooth to rough weathering states. Profile roughness indices from using Sinuosity, Z2, Modified Division (a- and D-value), and Semi-Variance a-value did not compare favorably when assessing differentially weathered and vuggy profiles. Inspection of the profiles showed that photogrammetry profiles had segments containing high frequency perturbations which caused abnormally high roughness indices from the aforementioned algorithms. The perturbations are an artifact of the interpretation of the profiles obtained from specimen sections with pitted and vuggy surfaces. Care should be exercised when choosing profiling methods and assessing profile roughness when characterizing differentially weathered and vuggy specimens.