Combined use of UAV-SfM surveys, soil particle tracking with RFID tags and a sediment connectivity index to study...

To explore the processes of soil erosion at the plot scale, Digital surface model of Differences (DoD) maps (Unmanned Aerial Vehicle - Structure from Motion (UAV-SfM) method) and data from Radio Frequency Identification (RFID) tags were analysed. The comparison of differences in accuracy of UAV-SfM and 3D terrestrial laser scanner (TLS) measurements, and the integration of the UAV-SfM method and soil particle tracing with RFID tag locations were conducted to assess sediment transport in a plot in Fukushima prefecture, Japan. The Universal Soil Loss Equation (USLE) plot was installed and kept with no vegetation and no cultivation. Water and sediment discharges were measured at the outlet of the plot, and the topographic index of runoff and sediment connectivity (IC) -focused on surface roughness- was also estimated. Based on field surveys, four periods were defined. Locations of RFID tags were firstly determined by using orthoimages derived from the UAV-SfM method and then compared with those locations measured with a laser total station. The mean and standard deviation of difference amounts of UAV-SfM were of 1 and 3.3 mm, respectively. On average, the RFID tags were located with an accuracy of 3.1 cm (RMSE). Although data of tags tracing showed short transport distances with rill erosion, the results of the UAV-SfM surveys showed an increase of sediment connectivity (SC) over the study period that may explain the largest sediment discharge, especially of fine soil particles. The concurrence of higher values of SC as well as the development of new and longer rills demonstrated the important activity of net soil loss in our study site. The combination of distinct methods and techniques, all providing accurate measurements, shed light on the sediment transport process at short distances, which affects the net water and sediment discharge at larger scales.