Fluvial and aquatic applications of Structure from Motion photogrammetry and unmanned aerial vehicle/drone technology

Abstract

Structure from motion (SfM) has seen rapid uptake recently in the fluvial and aquatic sciences. This uptake is not least due to the widespread availability of cheap unmanned aerial vehicles/drones, which help mitigate the challenging terrain and deliver efficient and reproducible and high‐accuracy images and topographical data. These data can have unprecedented spatio‐temporal coverage and includes measurements of fluvial and aquatic topography, hydraulics, geomorphology and habitat quality. SfM data also offer novel quantification of underwater archeology, structures and aquatic organisms. Studies are shifting from proof‐of‐concepts in topographic survey to genuine applications including grain‐size mapping, bathymetric surveys, geomorphological mapping, vegetation mapping, restoration monitoring, habitat classification, geomorphological change detection and sediment transport path delineation. Integrating point cloud analyses and orthophoto mosaics with digital elevation models has been shown to be effective in providing novel process understanding of fluvial and aquatic systems. Underwater and through‐water studies are beginning to overcome problems of accessibility, visibility and image distortion. Archival photographs and video (both above‐ and under‐water) are being reprocessed using a SfM workflow to generate three‐dimensional surfaces and objects from historical surveys, thereby extending the time period over which change can be detected. Recently, a SfM workflow has been developed to model free water surfaces with clear potential for future exploitation in hydraulics, sediment transport and river bed evolution studies. Future applications of SfM could seek to exploit the daily repeat coverage of high‐resolution satellite images but must be mindful of the necessary investment in this development versus the increasing availability and coverage of spaceborne light detection and ranging. This article is categorized under: Water and Life > Methods Science of Water > Methods Water and Life > Nature of Freshwater Ecosystems

Concept and Performance Evaluation of a Novel UAV-Borne Topo-Bathymetric LiDAR Sensor

“…More recently, Ref. [26,27] focused on fluvial and aquatic applications of SfM based on UAV imagery emphasising the unprecedented spatio-temporal coverage [27] and the necessity of automated procedures for refraction correction [26]. The latter is crucial for obtaining accurate depth measurements but is difficult to achieve because image-based reconstruction of natural water surfaces poses problems due to the general prerequisite of transparent water conditions.…”

Quantifying Below-Water Fluvial Geomorphic Change: The Implications of Refraction Correction, Water Surface Elevations, and Spatially Variable Error

“…Since 2015, a method which uses high resolution RPAS (or UAS/unmanned aerial system) imagery, processed using SfM, has been shown as a promising tool for measuring both above-water (bank and floodplain) and below-water (bathymetric) topography at the grain scale in fluvial environments, when paired with refraction correction post-processing [27]. Above-water use of the RPAS-SfM approach has already provided an important step-change in our ability to quantify exposed topography without the greater expense of a terrestrial laser scanning system (e.g., [34,[38][39][40]), but its use in submerged areas is less well established, due to the additional challenges posed by the presence of water and, in particular, the effects of refraction. Recently, two key RPAS-SfM methods have been proposed by the authors for use in submerged areas [27,28].…”

The Status of Earth Observation Techniques in Monitoring High Mountain Environments at the Example of Pasterze Glacier, Austria: Data, Methods, Accuracies, Processes, and Scales

“…Currently, UAV-based glacio-morphological analyses are increasingly conducted, e.g., the monitoring of glacier surface changes [113][114][115][116][117][118]. The use of UAVs is also increasing for monitoring fluvial systems [119]. UAV are the basis for data collection for requested bathymetry of river sections (for numerical modeling) and the observation of morphodynamic processes, such as quantifying erosion and accumulation or stream bank failure [105,120].…”