2014 AK DOT Lidar DEM: Bradfield to Behms Corridor, AK

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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.

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Information on the NOAA Office for Coastal Management (OCM)

Link to custom download the lidar point data from which these raster Digital Elevation Model (DEM) data were created.

The LiDAR data for the Bradfield to Behms corridor was acquired on June 26 and 27 and July 11 of 2014. SBET and shapefile of the trajectory are located with the point cloud data. The data was post processed through PosPac, Waypoint’s GPS and IMU (inertial measurement unit) post processing software, and LMS, Optech’s LiDAR post processing software. PosPac is used to generate the trajectory file which contains the position (X, Y, Z) from differential GPS observations and the plane’s attitude (roll, pitch, heading) from the IMU. LMS is used to join the discreet point range information to the trajectory information through a common time stamp and to calibrate the data. The calibration is achieved by first identifying common features in the overlap of adjacent flight lines, and then adjustments are applied to the IMU’s angular offsets to align the data. Once finished, LMS refines the calibration further through a bundle adjustment to create the final calibrated data set.

Classification of the calibrated LiDAR data set is achieved through the use of TerraScan, the industry standard software from TerraSolid for classifying LiDAR. Individual macros were defined that derive and refine a ground surface, vegetation, and buildings. These macros are also used to eliminate spurious points below the surface and high point artifacts. The Bradfield to Behms area was then manually checked and edited to eliminate low and high points as well as to ensure that points are classified appropriately.

Breaklines were derived from LiDAR and imagery and help define water classes in the LiDAR data.

The DEM was created using ESRI 3DAnalyst. The individual steps included:

1.Importing all las files into the geodatabase as multipoint, all returns, classes 8 and 9.

2. Importing the breaklines as a feature layer.

3. Creating a terrain in 3D Analyst from all mass-points.

4. Creating a 3’ spacing grid, using the NATURAL_NEIGHBORS interpolation method

5. The ERDAS Imagine mosaic tool was then used to clip and tile the DEM at the same time into individual geotiff tiles

The NOAA Office for Coastal Management (OCM) downloaded 117 tif files from the Alaska Division of Geological and Geophysical Surveys data Portal (https://elevation.alaska.gov/). The data were in Alaska State Plane, Zone 5001 coordinates (NAD83, US survey feet) and NAVD88 elevations (GEOID12A) in feet. The bare earth raster files are at a 3 ft grid spacing.

OCM converted the files to Cloud Optimized GeoTiffs and set the vertical georeferencing using GeoTiff 1.1 format.