Abstract
Structure from Motion with Multi-View Stereo photogrammetry (SfM-MVS) is increasingly used in geoscience investigations, but has not been thoroughly tested in gullied savanna systems. The aim of this study was to test the accuracy of topographic models derived from aerial (via Unmanned Aerial Vehicle, ‘UAV’) and ground-based (via handheld digital camera, ‘ground’) SfM-MVS in modelling hillslope gully systems in a dry-tropical savanna, and to assess the strengths and limitations of the approach at a hillslope scale and an individual gully scale. UAV surveys covered three separate hillslope gully systems (with areas of 0.412–0.715 km2), while ground surveys assessed individual gullies within the broader systems (with areas of 350–750 m2). SfM-MVS topographic models, including Digital Surface Models (DSM) and dense point clouds, were compared against RTK-GPS point data and a pre-existing airborne LiDAR Digital Elevation Model (DEM). Results indicate that UAV SfM-MVS can deliver topographic models with a resolution and accuracy suitable to define gully systems at a hillslope scale (e.g., approximately 0.1 m resolution with 0.4–1.2 m elevation error), while ground-based SfM-MVS is more capable of quantifying gully morphology (e.g., approximately 0.01 m resolution with 0.04–0.1 m elevation error). Despite difficulties in reconstructing vegetated surfaces, uncertainty as to optimal survey and processing designs, and high computational demands, this study has demonstrated great potential for SfM-MVS to be used as a cost-effective tool to aid in the mapping, modelling and management of hillslope gully systems at different scales, in savanna landscapes and elsewhere.
Highlights
Erosion is a globally significant land degradation process that has detrimental environmental, ecological and economic impacts across a range of landscape systems [1,2,3,4,5,6,7]
Results indicate UAV Structure from Motion with Multi-View Stereo photogrammetry (SfM-multi-view stereo (MVS)) can deliver topographic models with a resolution and accuracy suitable to define gully systems at a hillslope scale (e.g., ~0.1 m resolution with ~0.4–1.2 m elevation error), while ground-based SfM-MVS is more capable of quantifying gully morphology (e.g., ~0.01 m resolution with ~0.04–0.1 m elevation error)
Results from our study, conducted in a gullied dry-tropical savanna catchment in Upper Burdekin catchment, indicate UAV SfM-MVS can deliver topographic models with a resolution and accuracy suitable to define gully systems at a hillslope scale (e.g., ~0.1 m resolution with ~0.4–1.2 m elevation error), while ground-based SfM-MVS is more capable of quantifying individual gully morphology (e.g., ~0.01 m resolution with ~0.04–0.1 m elevation error)
Summary
Erosion is a globally significant land degradation process that has detrimental environmental, ecological and economic impacts across a range of landscape systems [1,2,3,4,5,6,7]. Effective management of gully erosion requires high-resolution topographic information that can be used to accurately quantify the spatial distribution and density of gully systems, gully morphology and morphologic change, and the catchment characteristics that influence gully evolution [2,8,9,10]. Recent advances in remote sensing techniques have greatly improved our ability to collect high-resolution topographic data at a range of scales [11,12,13]. A major limitation of LiDAR is the high instrument and survey costs [13]. Structure from Motion with Multi-View Stereo photogrammetry (hereafter referred to as SfM-MVS) is increasingly utilised as a cost-effective alternative method of rapidly acquiring very high resolution (sub-meter) and hyper-resolution (sub-centimetre) topographic data [13,16,17,18,19]
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