The ground-truth about lidar-derived digital elevation models in coastal wetland regions of the northern Gulf of Mexico

Recent advances in the quality and availability of lidar permit high spatial resolution in digital elevation models (DEMs). However, large-scale lidar acquisitions may be flown during high tides, storm events, and irregular tidal regimes leading to temporal change differences, but ultimately the uneven penetration through dense vegetation impacts the reality of ground surface positions. For the low-gradient coastal land margin of the northern Gulf of Mexico, even a small elevation bias (on the order of 0.1 m) can adversely affect surface hydrodynamic model accuracy. Therefore, ground-truthing with a vertical elevation adjustment is essential for robust biogeophysical modeling. This study assessed measurement errors of two lidar-derived DEM datasets (1 m and 3 m DEMs). The 1m and 3m topo-bathymetric DEMs were developed in 2021 and 2014, respectively. The DEMs were evaluated for distinct coastal wetlands, especially coastal marshes of Louisiana, Mississippi, and Alabama. Error analysis was conducted using Real-Time Kinematic (RTK) GPS to assess how well the lidar-derived elevations represent the actual marsh surface (ground surface). The performance of the temporally and spatially distinct lidar-derived elevation datasets was evaluated over 7,000 elevation points measured between 2011-2021. We also examined the relationship between measurement errors and vegetation characteristics (marsh type, height, and percent cover). This presentation will demonstrate our ongoing efforts to assess the high-resolution lidar-derived elevations in coastal wetlands and discuss the measurement errors.