2013 NOAA Topographic Lidar DEM: U.S. Virgin Islands (St. Croix, St. John, St. Thomas)

The United States Virgin Islands Topographic LiDAR Task Order involved collecting and delivering topographic elevation point data derived from multiple return light detection and ranging (LiDAR) measurements on the islands of St. Thomas, St. John, St. Croix and numerous smaller islands and islets in the United States Virgin Islands. The data collected for the project area will exhibit Hydro Flattened DEMs (1m resolution) for inclusion into the NED. The purpose of the data is for use in coastal management decision making, including applications such as flood plain mapping and water rights management. LiDAR was collected at an average of 0.7 meter point spacing for all acquired project areas.

Overall the DEMs were acceptable, but appear oversampled as a result of low ground point density (heavy vegetation), and is not a contractor issue as a 1 m DEM was specified. Incremental improvements to the DEMs were earned through breakline adjustments. Another characteristic of the USVI lidar data that was observed on all islands is the appearance of divots where there is a single tree or a narrow line of trees that lie in areas of open, bare terrain. The cause appeared to be sub-canopy points that were lower than the surrounding land. In most cases these low points were lower than the true ground surface at those locations, but were classified as ground and retained in the point cloud for use in DEM generation. This issue was not addressed during revisions.