Abstract
This study presents an analysis of shoreline change on reef islands using unmanned aerial vehicle (UAV)-derived orthomosaics and digital surface models (DSMs) collected on Sipadan Island, Sabah, Malaysia, and Sasahura Ite Island, Isabel Province, Solomon Islands. The high resolution of UAV-derived orthomosaics enabled changes in the position of the base of beach to be detected with confidence. The accuracy of the UAV-derived DSMs was assessed against equivalent topographic profiles via root-mean-square error, and found to be <0.21 m in all but one case; this demonstrates the potential for using UAV-derived DSMs to interpret three-dimensional island beach morphology and detect patterns of geomorphic change. The correlation between planimetric and volumetric change along selected beach transects was also investigated and found to be variable, indicating that a multifaceted approach including both planimetric (two-dimensional) and volumetric (three-dimensional) metrics is of value when analysing reef-island change. However, interpretations of UAV-derived data must carefully consider errors associated with global positioning system (GPS) positioning, the distribution of ground control points, the chosen UAV flight parameters, and the data processing methodology. Further application of this technology has the potential to expand our understanding of reef-island morphodynamics and their vulnerability to sea-level rise and other stressors.
Highlights
Reef islands form through the accumulation of reef-derived carbonate sediment on coral reef platforms [1]
The root-mean-square error (RMSE) values calculated for the comparison of each digital surface models (DSMs)-derived profile with the surveyed topographic profiles ranged from 0.06 m to 0.17 m on Sipadan, and from
0.10 m to 0.21 m on Sasahura Ite (Table 2). These values are proportionate with the error range of the Trimble GeoXH global positioning system (GPS) used for positional corrections in Sipadan (±0.27 m) and the estimated vertical accuracy associated with correcting elevations to water level on Sasahura Ite (±0.2 m)
Summary
Reef islands form through the accumulation of reef-derived carbonate sediment on coral reef platforms [1]. Their social, economic, and environmental values are significant; in some areas, reef islands provide the only habitable land for settlement and infrastructure [2,3], as well as important habitat for endangered species such as sea turtles and nesting seabirds [4,5]. Some studies suggest that their geomorphic integrity is under threat [8], while others suggest they are resilient and adjust their form in response to changing environmental conditions [9,10].
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