Structure From Motion
Coastal topographic and bathymetric (topobathymetric) data with high spatial resolution (1-meter or better) and high vertical accuracy are needed to assess the vulnerability of Pacific Islands to climate change impacts, including sea-level rise. According to the Intergovernmental Panel on Climate Change reports, low-lying atolls in the Pacific Ocean are extremely vulnerable to king tide events, storm surge, tsunamis, and sea-level rise.
The lack of coastal topobathymetric data has been identified as a critical data gap for climate vulnerability and adaptation efforts in the Republic of the Marshall Islands (RMI). For Majuro Atoll, home to the largest city of RMI, the only elevation dataset currently available is the Shuttle Radar Topography Mission data which has a 30-meter spatial resolution and 16-meter vertical accuracy (expressed as linear error at 90%).
To generate high-resolution digital elevation models (DEMs) in the RMI, elevation information and photographic imagery have been collected from field surveys using Global Navigation Satellite System (GNSS) / total station and unmanned aerial vehicles (UAS) for Structure-from-Motion (SfM) point cloud generation. DigitalGlobe
WorldView II imagery was processed to create SfM point clouds to fill in gaps in the point cloud derived from the higher resolution UAS photos. The combined point cloud data is filtered and classified to bare-earth and georeferenced using the GNSS data acquired on roads and along survey transects perpendicular to the coast. A total station was used to collect elevation data under tree canopies where heavy vegetation cover blocked the view of GNSS satellites. A subset of the GPS / total station data was set aside for error assessment of the resulting DEM.
Additional information regarding SfM development and analysis is available at https://fallmeeting.agu.org/2016/
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Imagery of Majuro, Republic of Marshall Islands, created from Structure From Motion. Imagery created by Monica Palaseanu-Lovejoy.
Imagery of Djarrit, Majuro, Republic of Marshall Islands, created from Structure From Motion. Imagery created by Monica Palaseanu-Lovejoy.