Shrinking Coastlines: Use of uncrewed aerial systems to map and monitor rocky intertidal habitats

Climate change and associated sea-level rise (SLR) threaten rocky intertidal environments. The coarse temporal and spatial resolution of currently used field methods limit their use for studying SLR effects on rocky intertidal zones. Uncrewed aircraft systems (UAS), light detection and ranging (LiDAR), and structure from motion (SfM) photogrammetry offer options for comprehensive mapping and monitoring from a novel perspective and scale. We collected, processed and analysed UAS LiDAR and SfM photogrammetry datasets for three Multi-Agency Rocky Intertidal Network (MARINe) biological monitoring sites in Laguna Beach, California. Orthomosaics, point clouds, and digital surface models (DSM) were analysed and compared to assess the potential for UAS LiDAR and SfM technologies for monitoring rocky intertidal zones. The resultant data products are similar; the SfM products yield greater point density for DSM and slightly finer spatial resolution for orthoimage mosaics. Both approaches were useful in mapping intertidal substrates, zonation patterns, and barriers to sea-level rise, and in identifying several species monitored by MARINe. Work remains in SLR inundation modelling and in addressing the impacts of wave action and tides, and difficulty in image matching in optically homogenous areas.