Beach Topography—Fire Island, New York, Post-Hurricane Sandy, April 2013: Ground Based Lidar (ASCII XYZ Point Data)

Data for the survey extents was collected along with a boresight to resolve subtle differences between the scanner and the inertial measurement unit (IMU). After collection, the data were post-processed with multiple software packages to produce the final digital elevation model product.

Terrestrial GPS data are post-processed with National Geodetic Survey's (NGS) continuously operating reference stations (CORS) and integrated with post-processed IMU and DMI data within Applanix's PosPac software to derive a smoothed best estimate of vehicle trajectory (SBET). After processing, quantitative quality-metrics were analyzed to ensure the trajectory accuracy met the manufacturer's specified values.

The SBET and bore-sight measurements are imported into Riegl's RiProcess lidar software where the lidar point cloud is geo-rectified. Control monuments and previously validated data are used for comparison to determine the accuracy of the survey. The processed point cloud is manipulated within RiProcess to delineate the shoreline, filter structures and vegetation, and classify points as water, vegetation, structures, and ground. The classified point cloud is exported as a .las file.

The .las file is imported into Applied Imagery's Quick Terrain Modeler software in which a mean-z (elevation) algorithm and an anti-aliasing filter are applied to the point-cloud data to grid the data at a 0.5 meter (m) resolution. After gridding is completed, the DEM (surface) is inspected for any remaining noise, such as spikes and wells, which are removed prior to final export as an American Standard Code for Information Interchange (ASCII) .xyz file. The .las file was imported in Applied Imagery's QTModeler software where a mean-z (elevation) algorithm was applied to the point cloud data to grid the data at 0.5 meter resolution. Anti-aliasing was also applied to increase the precision of the triangulation by subdividing each grid cell into 16 equal segments and recording which segment contained the point that was used to represent the elevation value of the grid cell. When triangulation occurs, this increased level of precision will enhance the accuracy of the triangles and the subsequent sampling that occurs. The sub-grid was not retained after the model was created. During the model triangulation, any Any grid cells with no data were assigned a value of "null" - i.e., no data exists.

Within Esri’s ArcCatalog, the ASCII xyz file was converted to an ArcGIS multipoint feature using the ASCII 3D To Feature Class tool and was projected from North American Datum of 1983 (NAD 83) State Plane New York Long Island (meters) to NAD 83, Universal Transverse Mercator (UTM) Zone 18N (meters). Using the 'Feature Class Z To ASCII' tool the point data was reverted back to ASCII xyz format for publication, in a non-proprietary format.

Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.

Added keywords section with USGS persistent identifier as theme keyword.