The Evaluation of SfM Technique in the Determination of Surface Deformation on Skidding Roads Following Timber Harvesting

Forest roads are necessary engineering structures for accessing and managing forestry resources. Considering the difficult terrain and its numerous variable effects, it must be ensured that the capacity of forest roads function adequately and that the road platform is suitable for vehicle traffic. This study aimed to focus on the determination and evaluation of deformation on the surface of the soil roads in the forest using SfM (Structure from Motion) technique. The study focused on the usage opportunity of close-range photogrammetry in the analysis of surface deformation on skidding roads used for forestry operations. Field surveys were conducted on a newly constructed skidding road for forestry operations with a four-wheel farm tractor. The geo-spatial location of the road was obtained by a Total Station (TS) prior to harvesting operation. A digital camera mounted on a 3.5 m high pole was used as a carrier platform in the field survey. The photographs with front and side overlaps (approximately 60% and -80%) were obtained from 95 m segment of the unpaved road. The spatial (X, Y and Z) differences between field measurements- and SfM-based models were compared using Root Mean Square Error (RMSE), and the values of spatial error (SfMXY: 0.048; SfMZ: 0.010 for estimated model) were calculated. The change rate of stable, accumulations and abrasions on the road surface were calculated as 0.165%, 48.642% and 51.192%, respectively. The present study demonstrated that the use of semi-automatic measurement technique offers a promising potential for the evaluation of forest road surface deformation.