2014 AK DOT Lidar: Bradfield to Behms Corridor, Alaska

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Bulk download of data files in LAZ format, geographic coordinates, orthometric heights. Note that the vertical datum (hence elevations) of the files here are different than described in this document.

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, from the Data Access Viewer (DAV), the raster Digital Elevation Model (DEM) data that were created from this lidar data set.

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 NOAA Office for Coastal Management (OCM) downloaded 110 laz files from the Alaska Division of Geological and Geophysical Surveys data Portal (https://elevation.alaska.gov/). The files contained classified elevation and intensity measurements for the 2014 Bradfield to Behms data set. The data were in Alaska State Plane, Zone 5001 coordinates (NAD83, US survey feet) and NAVD88 elevations (GEOID12A) in feet. The data were classified: Class 1: Unclassified, Class 2: Bare-earth ground, Class 3: Low vegetation, Class 4: Medium Vegetation, Class 5: High Vegetation, Class 7: Noise, Class 8: Ground Model Keypoints, Class 9: Water. OCM processed all points to the Digital Coast Data Access Viewer (DAV).

OCM performed the following processing on the data for Digital Coast storage and provisioning purposes:

1. The LAStools software scripts lasinfo and lasvalidate were run on the laz files to check for errors.

2. An internal OCM script was run to check the number of points by classification and by flight ID and the gps times and intensity ranges.

3. Internal OCM scripts were run on the laz files to convert from Alaska State Plane, Zone 5001 coordinates to geographic coordinates, to convert from NAVD88 elevations to ellipsoid elevations using the GEOID12A model, to convert from feet to meters, to assign the geokeys, to assign a lidar domain profile, to sort the data by gps time and zip the data to database and to http.