2010 USACE NCMP Topobathy Lidar DEM: Maryland (Post-Hurricane Earl)

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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.

This graphic displays the footprint for this lidar data set.

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.

These data were collected using the CHARTS system. It is owned by the Naval Oceanographic Office and operated through contract. The system collects topographic lidar data at 9kHz, bathymetric lidar data at 1kHz and RGB imagery at 1Hz. A CASI-1500 hyperspectral line scanner is integrated with the system as well. Aircraft position, velocity and acceleration information are collected through a combination of Novatel and POS A/V 410 equipment. All raw data streams are transferred to the office for downloading and processing in SHOALS GCS software. Aircraft position data are processed using POSPac software and the results are combined with the lidar data to produce 3-D positions for each lidar shot. Upon inspection and QA/QC in the software packages Fledermaus and PFM_ABE, anomalous data are flagged as invalid. PFM_ABE's chartsLAS module then converts all valid data from ellipsoid to orthometric heights based on the NGS' GEOID03 model and exports topographic data as a series of LAS files with a single file per flightline per 5km box.

The flightline LAS files are imported into the TerraScan V11 module within MicroStation V8.0. The resulting LAS files are thinned to eliminate duplicate points. A customized classification macro is used to distinguish ground points (2) and unclassified points (1). The classification results are QC'd and any misclassified points are manually edited. In areas of dense vegetation the bare ground points might be incorrectly classified due to the inability of the laser to penetrate the canopy and reach the bare ground. In these areas, JALBTCX defaults to the algorithm's "ground" surface instead of manually reclassifying those points. The points are exported to an ASCII file containing the following fields: longitude, latitude, elevation (orthometric), intensity, classification, mirror angle, time (GPS time), number of echos, and echo number. The ASCII file is converted to LAS using txt2las code from LAStools (http://www.cs.unc.edu/~isenburg/lastools/).

The points classified as ground in the Classified LAS files are converted to a grid by generating a Triangulated Irregular Network (TIN) and then extracting the grid node elevations from the TIN surface. The origin point of the grid is located at a horizontal position whose value is evenly divisible by the 1m grid resolution such that rasters from subsequent surveys have common cell boundaries. JALBTCX uses Quick Terrain Modeler V7.1.1 to perform this operation utilizing the following key parameters; "Max Sample Excursion 50," "Max Triangle Side 100," and "Smoothing filter Level 4 with a Max Roughness 2." The grid is exported as an ESRI ASCII Z grid formatted file, which is converted to a raster within ESRI ArcMap V10 using the ASCIIToRaster command within ArcToolbox. The resulting raster output is in TIFF format. The projection is defined as "The North American Datum of 1988" using the DefineProjection command within ArcToolbox. Horizontal positions, provided in decimal degrees of latitude and longitude, are referenced to the North American Datum of 1983 (NAD83). Vertical positions are referenced to the NAD83 ellipsoid and provided in meters. The National Geodetic Survey's (NGS) GEOID03 model is used to transform the vertical positions from ellipsoid to orthometric heights referenced to the North American Vertical Datum of 1988 (NAVD88).

The NOAA Office for Coastal Management (OCM) received GeoTiff format files from USACE JALBTCX for the Maryland coastline project area. The bare earth raster files were at a 1 m grid spacing. The data were in geographic NAD83 coordinates and NAVD88 (Geoid03) elevations in meters. OCM assigned the appropriate EPSG codes (Horiz - 4269, Vert - 5703) and copied the raster files to https for Digital Coast storage and provisioning purposes.