Beach Topography—Fire Island, New York, Post-Hurricane Sandy, April 2014: Ground Based Lidar (1-Meter Digital Elevation Model)

USACE-FRF Processing - 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 was post-processed using multiple software packages to produce the final digital elevation model product.

Terrestrial GPS data was post-processed with National Geodetic Survey's Continuously Operating Reference Stations (CORS) and integrated with post-processed IMU data through Applanix's POSPac GNSS software to derive a smoothed, best estimate of trajectory (SBET). After processing, quantitative quality-metrics were analyzed to ensure the trajectory accuracy met the manufacturer's specified values.

The SBET is imported into Riegl's RiProcess lidar software project where the lidar point cloud is rectified and geo-registered to a particular coordinate system, projection, and geoid model as well as applying boresight values for roll, pitch and yaw. Control monuments and previously validated datasets were used for comparison to determine the accuracy of the survey. These were measured by cutting cross-sections of the current survey overlayed on previously validated data within the software through stable structures such as houses, monuments, and road centerlines.

The processed point cloud was manipulated within RiProcess to delineate the shoreline, filter structures and vegetation, and classify points as water, vegetation, structures, and ground. The classified point cloud was exported as a .las (1.1) file.

The .las file was imported into 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 grid cells with no data were assigned a value of "null" - i.e., no data exists.

After gridding was completed, the raster digital elevation model (surface) was inspected for any remaining noise such as spikes and wells and these were removed prior to final export as an ASCII .xyz file.

SPCMSC Processing - The ASCII xyz file was converted to an ArcGIS multipoint feature using the 'ASCII 3D To Feature Class' tool within ArcCatalog 10.1. The output feature class was reprojected from the State Plane Coordinate System (NY, Long Island Zone) to NAD83 UTM Zone 18N.

An ArcGIS Digital Terrain Model was built from the xyz feature class using the 'Create Terrain' tool. A 1m raster grid was created from the terrain surface using the 'Terrain to Raster' tool.

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.