2012 USACE NCMP Topobathy Lidar DEM: Lake Michigan (IL, IN, MI, WI)

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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.

These data were collected using the RIEGL VQ-480 lidar system, operated by Fugro Pelagos through contract. The system collects topographic lidar data at maximum pulse rate of 150 kHz in a wavelength near infrared. Aircraft position, velocity and acceleration information are collected a POS AV 510 equipment. All logged raw data were transferred to the office and processed in RiPROCESS software. Aircraft position data are processed using POSPac software and the results combined with the lidar data to produce 3-D positions for each lidar shot. Upon processing and export to LAS format, QA/QC is performed with Fledermaus and FPI Workbench tools. Data are classified as 0 (valid topographic data), 21 (valid topographic data acquired with the bathymetric sensor), 27 (invalid topographic and bathymetric data), 29 (valid bathymetric data). The data are then shifted vertically to the International Great Lakes Datum of 1985 (IGLD85) using the VDatum program from NOAA (National Oceanic and Atmospheric Administration).

The flightline LAS files are imported into GeoCue V7.0.3.5, 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. A customized classification macro, built upon the TerraScan V12 module within Microstation V8i, classifies valid topographic data as ground points (2) and unclassified points (1). Upon completion the macro, the classification results undergo quality control and any misclassified points are manually edited. The resulting LAS file is then combined with valid bathymetric data (29). In areas of dense vegetation the bare earth 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), unclassified (1), water (9), and valid bathymetric data (29).

Data classified as ground (2) and valid bathymetric data (29) in the 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 [V7.1.5 Beta] to perform this operation utilizing the following parameters;” Legacy Triangulation”, 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 ArcMap [V10.0], 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 raster is then multiplied against a corresponding 1m Grid mask raster, a mask image produced from JALBTCX’s 1m Grid, in ESRI’s Raster Calculator to remove interpolated areas where data does not exist.

The NOAA Office for Coastal Management (OCM) received 95 1 meter bare earth raster files in GeoTiff format (IL - 11 files, IN - 7 files, MI - 26 files, WI - 51 files) from USACE JALBTCX along the Illinois, Indiana, Michigan and Wisconsin coastlines. The data were in geographic, NAD83 (2011) coordinates and IGLD85 elevations. OCM assigned the appropriate EPSG codes (Horiz - 6318, Vert - 5609) and copied the raster files to https for Digital Coast storage and provisioning purposes.