2010 USACE NCMP Topobathy Lidar DEM: Atlantic Coast (NC - B)

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Information on the NOAA Office for Coastal Management (OCM)

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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 9 kHz, bathymetric lidar data at 1 kHz 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 GeoCue V7.0.34, which is a geospatial workflow production and management software tool employed by JALBTCX to perform and monitor production of data products. Upon import into GeoCue, the flightline LAS files are divided into a series of boxes, each of which are 1500 meters in length and width. To each box is assigned a customized classification macro, built upon the TerraScan V10 module within Microstation V8.0 that distinguishes ground points (2) and unclassified points (1). The macro is executed for all boxes within GeoCue. Upon completion of all boxes the classification results undergo quality control, 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 final classification results are comprised of individual lidar points with classifications of ground (2) or unclassified (1). They are partitioned into a series of 5km delivery boxes, one Classified LAS file per 5km box.

The points classified as ground in the Classified LAS files are exported from TerraScan V10 and converted to a grid by generating a Triangulated Irregular Network (TIN) and the 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,” “Smoothing filter Level 4 with a Max Roughness 2, and "Tiling Settings Snap to Grid (Expand).” The grid is exported from Quick Terrain Modeler as an ESRI ASCII Z grid file. Utilizing an in-house python script within ESRI ArcMapV9.3, the ASCII Z grid file is converted to a tiff-format raster file whose projection is defined as “The North American Datum of 1983.”

The NOAA Office for Coastal Management (OCM) received GeoTiff format files from USACE JALBTCX for the NC 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.