| Popis: |
Salt marshes are transitional wetlands placed between ocean and land, which act as natural defenses against coastal hazards. The amount of organic and inorganic deposition, which is strongly influenced by vegetation characteristics, is one of the main drivers for the survival of salt marshes. Vegetation also favors the dissipation of wind waves and storm surges. For these reasons, an accurate description of canopy characteristics in salt marshes is critical for their preservation and management. For this purpose, airborne LiDAR (Light Detection And Ranging) has become an accessible and cost-efficient tool to map large wetland areas. However, the limited horizontal resolution of airborne-derived point clouds (~1 m) prevents the direct extraction of ground elevation and vegetation height if not coupled with other data sources, such as RGB or hyperspectral images. Uncrewed Aerial Vehicles (UAV) have become an affordable and cost-efficient tool to map targeted salt marshes quickly. Although LiDAR is capable of measuring surface elevations, laser penetration is limited in dense salt marsh vegetation. The limited ability of the laser to penetrate dense vegetation hinders its usefulness for surveying tidal marsh platforms. For UAV-borne LiDAR, a reliable method to extract ground elevation and vegetation height from high-resolution point clouds is yet not available. Here we derive a new formulation for converting the 3D distribution of UAV-derived points into vegetation height and ground-level elevation without the support of other data sources. Our formulation has been calibrated on the surveyed vegetation height in a Spartina alterniflora marsh in Little Sapelo Island, Georgia, USA, and successfully tested on an independent dataset. Our method produces high-resolution (40×40 cm2) maps of ground elevation and vegetation height, thus capturing the large gradients in the proximity of tidal creeks. |
