2011 USACE NCMP Topobathy Lidar DEM: California

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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 SHOALS-1000T and ALS60 systems. They are owned by Fugro and operated through contract. The ALS60 system collects topographic lidar data at maximum pulse rate of 200 kHz in a wavelength of 1064 nm with a CASI-1500 hyperspectral line scanner integrated with the system. The SHOALS collects bathymetric lidar data at 1kHz, RGB imagery at 1Hz and a CASI-2 hyperspectral line scanner integrated with the system as well. Aircraft position, velocity and acceleration information are collected through a Novatel and POS A/V 410 equipment (SHOALS) and the onboard GPS/IMU system (ALS60). SHOALS raw data streams are transferred to the office for downloading and processing in SHOALS GCS software. ALS60 raw data were also transferred to the office and processed in IPAS 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 (SHOALS), GeoCue and TerraScan (ALS60), anomalous data are flagged as invalid. FPI Workbench and Fugro's proprietary software convert all valid data from ellipsoid to orthometric heights based on the NGS' GEOID09 model and exports data as a series of first return topography and bathymetry ASCII files. The bathymetry files contain all of the returns from the bathymetric sensor which include returns both above and below the water.

An in-house script is run on the Hydrographic ASCII files to ensure that the file contains data from the same year. The resulting ASCII is then loaded into GeoCue to remove any valid topographic data collected with the hydrographic sensor. Then the data is converted into LAS format with a classification of 29. This LAS is then joined together with the Topographic Classified LAS to form one file that covers the entire NCMP box and contains both the bathymetry and topography of the given area. 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 V7.1.5 Beta to perform this operation utilizing the following key parameters; "Max Sample Excursion 50,” "Max Triangle Side 100, Radius of 4, Zero Tolerance of 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 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. 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) GEOID09 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 California project area. The bare earth raster files were at a 1 m grid spacing. The data were in geographic NAD83 coordinates and NAVD88 (Geoid09) 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.