LiDAR-based Digital Elevation Model for Northampton and Accomack Co., VA, 2010|数字高程模型数据集|环境科学数据集

This dataset contains a bare-earth digital elevation model (DEM) for Northampton and Accomack Counties, Virginia based on data collected March 25-30, 2010 and processed to yield bare-earth elevations. It was created using LiDAR by Sanborne Geosystems under a contract with the Virginia Information Technologies Agency (VITA) with funding from The Nature Conservancy, USGS and the Virginia Coast Reserve Long-term Ecological Research project of the University of Virginia. Original LiDAR point data (approximately 1 meter spacing) was used to create a digital elevation model (DEM) with a cell resolution of 10 ft. (3.048 m).  The DEM data layer is in the State Plane coordinate system (U.S. Feet) and uses the NAVD88 vertical datum with the 2009 Geoid for elevation in feet. As detailed in the included quality report, elevations are accurate to 0.65 feet or better. Water areas have been hydroflattened and may also include salt marsh areas that were inundated at the time of the flights.  As a result, water areas were given a default minimum elevation below the minimum elevation measured by LiDAR over a given area and dependent on tidal cycle.  Areas at or below this minimum elevation within the water mask may include salt marsh and tidal flats as well as open water.  The elevation of the hydroflattening varies spatially. Salt marsh areas within the water mask were later determined by VCRLTER staff based on the following factors: (1) present as marsh (code 18) in the NOAA CCAP 2006 land cover layer and not included as an open water feature in the 2010 USGS National Hydrography Dataset, (2) minimum contiguous area of 1800 square meters, approximately equal to two 30 meter resolution CCAP pixel cells, and (3) includes extensive areas of salt marsh within north-south flight line “stripesâ€, primarily the seaside lagoons and marshes south of Parramore Island and the town of Wachapreague plus Chesapeake Bay marshes immediately north of  Tangier Island (and excludes edge-only areas elsewhere). Two polygon shapefiles have been added to this dataset: one shapefile shows the region-specific water masks and includes the elevation of the masks (in meters, not feet); the other shapefile shows areas of saltmarsh hidden within the water mask and includes a recommended replacement elevation (0.404 meters) based on the average above-water-mask LiDAR elevations of all CCAP-minus-NHD-water-determined marshes of all seaside marshes south of Chincoteague Inlet.  The two polygon shapefiles have been reprojected to the WGS84 UTM zone 18N coordinate system, and the NAVD88 vertical elevations converted from feet to meters.