Evaluation of LiDAR vertical accuracy in Delaware's tidal salt marshes
Date
2020
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Publisher
University of Delaware
Abstract
Accurate elevation data of tidal salt marshes is necessary for understanding how marshes will respond to future environmental conditions. Light Detection and Ranging (LiDAR) is a remote sensing technique that collects high resolution, high accuracy elevation data across large spatial extents. In tidal salt marshes, the LiDAR pulses are unable to penetrate through the dense vegetation to reach the marsh surface leading to a vertical bias in LiDAR-derived Digital Elevation Models (DEM). A 1 m resolution bare-earth DEM was derived from LiDAR collected by aircraft during leaf-off conditions in 2014. In this study, we evaluated and corrected the LiDAR vertical bias of the salt marsh platform and mosquito ditches across three salt marshes in Delaware. ☐ Real-time kinematic (RTK) global positioning system (GPS) points were collected across the Blackbird, St. Jones, and Murderkill watersheds to evaluate and reduce the LiDAR vertical bias. Results show that the LiDAR vertical bias depends on the vegetation community. An overall 0.08 to 0.20 m vertical bias exists between the DEM and the RTK-GPS elevations for the salt marsh platform, and an overall 0.06 to 0.029 m vertical bias is present for the mosquito ditches. A total of six DEM correction methods were assessed for reducing the LiDAR vertical bias. Based on the lowest error criterion utilized to assess the DEM correction methods, the mean bias per vegetation community method was selected to correct the DEM for the salt marsh platform and mosquito ditches. . The LiDAR vertical bias after applying the mean bias per vegetation community correction was -0.016 to 0.009 m depending on the vegetation community. ☐ Finally, the uncorrected and corrected DEMs were applied to a tidal inundation bathtub model to evaluate the change in inundation from the uncorrected DEM to the corrected DEM. Following correction, the area inundated under mean high water (MHW) and mean higher high water (MHHW) for the salt marsh platform DEM increased from 36 to 65% and 57 to 85% for all watersheds, respectively. Area inundated under MHW and MHHW for the mosquito ditch corrected DEM did not change. Water volume increased under MHW and MHHW for the salt marsh platform corrected DEM compared to the uncorrected DEM. The volume of water increased or decreased depending on the study watershed for the mosquito ditch corrected DEM.
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Keywords
Light Detection and Ranging, Vertical accuracy, Tidal salt marshes, Delaware