Abstract
We conducted topographic measurements using unmanned aerial vehicles and by terrestrial laser scanning at inaccessible sea cliffs with an overhanging complex shape in eastern Japan. From the repeated measurements, we constructed multitemporal three-dimensional point clouds of the sea cliffs to quantitatively evaluate the volumetric changes in the cliffs with a high spatial resolution (in centimeter). As potential main triggers of rockfalls and slope failures, high sea waves and strong earthquakes were examined with the time series of eroded volumes. It is suggested that sea waves have a greater impact than earthquakes on sea-cliff erosion. The approaches provided in this study have great potential for a wide range of applications including high spatial monitoring of other inaccessible, complex-shaped sea cliffs with high data accuracy and low acquisition and operational costs.
Highlights
Monitoring rapid erosion along a bedrock coast is crucial for the management of infrastructure and conservation of natural landscapes (Sunamura 1992; Hutchinson 2002)
Long-term, decadal changes in the bedrock coastlines can be detected by time series of aerial photographs if coastal erosion is sufficiently rapid
As the reference for the Unmanned aerial vehicle (UAV)-Structure from motion (SfM) point clouds, the terrestrial laser scanning (TLS)-derived point clouds at different times of measurement were aligned to one another based on a reference period whose coordinates are provided with the highest georeferenced accuracy
Summary
Monitoring rapid erosion along a bedrock coast is crucial for the management of infrastructure and conservation of natural landscapes (Sunamura 1992; Hutchinson 2002). The TLS data could be obtained only for the land side of the island (i.e., not the entire island), it enabled robust measurements of the relative coordinates of this area with better accuracies than the UAV-SfM clouds.
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