2007 USACE NCMP Topobathy Lidar DEM: Niagara (NY)

Bulk download of data files.

Information on the NOAA Office for Coastal Management (OCM)

This graphic displays the footprint for this lidar data set.

Link to custom download 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. Once converted to orthometric heights, the data were then converted to IGLD85 using the VDatum program from NOAA (National Oceanic and Atmospheric Administration).

The flightline LAS files are imported into the TerraScan V10 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 with the 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 V7.0.3 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 <V9.3> 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.

The NOAA Office for Coastal Management (OCM) received 13 tif files from USACE JALBTCX. The bare earth raster files were at a 1 m grid spacing. The data were in geographic coordinates and IGLD85 elevations in meters. OCM assigned the EPSG codes of 4269 and 5609 to the files using gdal_translate. OCM copied the raster files to https for Digital Coast storage and provisioning purposes.