Multiscale geostatistical estimation of gravel-bed roughness from terrestrial and airborne laser scanning

The aim of this study is to establish the link between the scaling behavior of gravel-bed roughness of Terrestrial Laser Scanning (TLS) and Airborne Laser Scanning (ALS) data. The fractal dimension calculated from the log-log variogram was used to represent the roughness at two gravel-bed sites with the extent of 6 m × 6 m. In situ digital surface models (DSMs) were generated from TLS. The 3-D point data were collected by ALS, which showed smoothed surfaces of the TLS counterparts. We used the regularization method to derive the variograms of the ALS footprint from the variograms of in situ DSMs and compared it with the variograms of ALS data in the directions of maximum and minimum continuity identified in the 2-D variogram surfaces. Our results confirm that the 2-D variogram surfaces of ALS data show similar anisotropy pattern as their respective TLS-derived DSMs. In addition, we demonstrate that the regularization method is able to establish the scaling relations between TLS-derived DSMs and the ALS data. The results will lead a better understanding of the scaling characteristics of the gravel-bed roughness on the change of measurement scale. To the best of our knowledge, this letter presents the first study of examining the grave-bed roughness of cluster bedforms derived from ALS data.