LiDAR Vertical Bias Assessment and Digital Elevation Model Correction in Delaware's Tidal Salt Marshes

In tidal wetlands, small changes in elevation can have significant impacts on hydrology, vegetation, and habitat. LiDAR data were collected in Delaware during leaf off conditions in early 2014 to produce a statewide Digital Elevation Model (DEM). The 2014 LiDAR-derived DEM provides accurate elevation measurements over large spatial extents, but suffers from increased errors in areas with dense vegetation, reducing its effectiveness in wetland applications. Dense vegetation in tidal salt marshes prevent LiDAR pulses from penetrating the vegetation to reach the marsh surface, resulting in a positive vertical elevation bias. RTK-GPS measurements and GIS analysis of vegetation communities were used to reduce the DEM bias across Delaware's National Estuarine Research Reserve. Depending on the vegetation community, the 2014 DEM had a difference of 13 to 26 cm from the collected RTK-GPS points. Multiple correction methods were evaluated including: overall mean bias, mean bias per vegetation community, multiple regression, and minimum value grid cells extracted from the LiDAR point cloud. Bias correction factors calculated from each method were subtracted from the original DEM to produce a new corrected DEM. The methods above will be applied to additional tidal marshes in a future study, in an effort to produce a corrected DEM for all tidal marshes in Delaware, while providing researchers and coastal managers with a more precise tool for future tidal wetland applications.