High-resolution monitoring of diffuse (sheet or interrill) erosion using structure-from-motion

• Published in: Geoderma 2020-10, Vol.375, p.114477, Article 114477
• Main Authors: Cândido, Bernardo M., Quinton, John N., James, Mike R., Silva, Marx L.N., de Carvalho, Teotônio S., de Lima, Wellington, Beniaich, Adnane, Eltner, Anette
• Format: Article
• Language: English
• Subjects: DEM of difference; Erosion plot; Photogrammetry; Sheet erosion; Structure-from-motion; UAV
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2020.114477

•UAV-SfM soil loss measurements were validated by direct sediment collection.•Photogrammetric precision estimates defined spatially variable levels of detection.•DEMs of difference illustrated the diffuse erosion patterns through time.•Accurate 3-D soil surface models were constructed from UAV-SfM data. Sheet erosion is common on agricultural lands, and understanding the dynamics of the erosive process as well as the quantification of soil loss is important for both soil scientists and managers. However, measuring rates of soil loss from sheet erosion has proved difficult due to requiring the detection of relatively small surface changes over extended areas. Consequently, such measurements have relied on the use of erosion plots, which have limited spatial coverage and have high operating costs. For measuring the larger erosion rates characteristic of rill and gully erosion, structure-from-motion (SfM) photogrammetry has been demonstrated to be a valuable tool. Here, we demonstrate the first direct validation of UAV-SfM measurements of sheet erosion using sediment collection data collected from erosion plots. Three erosion plots (12 m × 4 m) located at Lavras, Brazil, with bare soil exposed to natural rainfall from which event sediment and runoff was monitored, were mapped during two hydrological years (2016 and 2017), using a UAV equipped with a RGB camera. DEMs of difference (DoD) were calculated to detect spatial changes in the soil surface topography over time and to quantify the volumes of sediments lost or gained. Precision maps were generated to enable precision estimates for both DEMs to be propagated into the DoD as spatially variable vertical uncertainties. The point clouds generated from SfM gave mean errors of ~2.4 mm horizontally (xy) and ~1.9 mm vertically (z) on control and independent check points, and the level of detection (LoD) along the plots ranged from 1.4 mm to 7.4 mm. The soil loss values obtained by SfM were significantly (p