2020 DC OCTO Lidar DEM: Washington, DC

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Information on the NOAA Office for Coastal Management (OCM)

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

Link to custom download, from the Data Access Viewer (DAV), the lidar point data from which these raster Digital Elevation Model (DEM) data were created.

This graphic displays the footprint for this lidar data set.

The lidar acquisition was flown on 6/26/2020, 6/29/2020, and 6/30/2020, at an altitude of 9,022 feet above mean sea level and composed of 28 flight lines, 26 primary lines and two cross ties. All lidar data was collected with a Cessna 441, tail# N93HC and a Leica ALS80 lidar sensor, #130. Due to the known difficulties flying over DC, the ALS80 sensor was selected to take advantage of its flight altitude and speed, minimizing the number of lifts for the various flight restrictions. All lidar was collected in conjunction with airborne GPS.

The hydro-flattened bare earth DEM was generated using the lidar bare earth points and 3D hydro breaklines to a resolution of 1 m. The bare earth points that fell within 1NPS along the hydro breaklines were excluded from the DEM generation process and put into class 20 – ignored ground. This is analogous to the removal of mass points for the same reason in a traditional photogrammetrically compiled DTM. This process was done in batch using proprietary software. The technicians then used Fugro proprietary software for the production of the lidar-derived hydro-flattened bare earth DEM surface in initial grid format at 1 m GSD. Water bodies (inland ponds and lakes), inland streams and rivers, and island holes were hydro-flattened within the DEM. Once the initial, hydro-flattened bare earth DEM was generated, the tiles were checked to ensure that the grid spacing met specifications. The surface was also checked to ensure proper hydro-flattening. The entire dataset was reviewed for complete project coverage and then converted to Geotiffs.

The NOAA Office for Coastal Management (OCM) downloaded a single GeoTiff format file from the DC Open Data site (https://opendata.dc.gov/datasets/DCGIS::2020-lidar-hydro-enforced-digital-terrain-model) for the Washington DC project area. The bare earth raster files were at a 1 m grid spacing. The data were in MD State Plane (FIPS 1900) NAD83, meters coordinates and NAVD88 (Geoid12B) elevations in meters. OCM assigned the appropriate EPSG codes (Horiz - 26985, Vert - 5703) and copied the raster files to https for Digital Coast storage and provisioning purposes.