Innovative Technologies for Monitoring Interrill Erosion

Recent studies showed the suitability of the structure from motion (SfM) reconstruction for monitoring variations in soil surface characteristics and soil loss originating from low-intensity erosive events. This paper used a DJI Phantom 4 multispectral to obtain an SfM model of a plot 8 m × 22 m with bare soil and a slope of 16%. The plot, located at the SERLAB experimental site (central Italy), has devices for directly measuring soil loss. Therefore, Terrestrial laser scanning (TLS) was used to validate the SfM model. Two surveys of the soil surface, one before and one after a series of rainfall events, were carried out using the DJI Phantom 4 multispectral and TLS. The Agisoft Metashape software was used to process the images acquired using the DJI Phantom 4 multispectral, with a 0.5 cm/pixel resolution. For each survey, the point clouds obtained by the UAV were compared to the TLS point clouds (used as reference). Total runoff and soil loss were measured after each erosive event (i.e., any event producing measurable runoff). From the point clouds, digital surface and elevation models (DSMs and DEMs) (0.01 m × 0.01 m) were obtained. The differences between the DSMs/DEMs (DoDs) obtained from the two surveys for SfM and TLS were compared. To assess the uncertainty of the DEMs and DSMs, from the DoDs the minimum level of detection was derived. The soil loss was evaluated from DoDs (for SfM and TLS, respectively), considering negative values as erosion and positive values as deposition. SFM has demonstrated results consistent with those derived from TLS and capable of detecting soil losses due to moderate events.