2018 AK DGGS Lidar: Turnagain Pass, Alaska

Create custom data files by choosing data area, product type, map projection, file format, datum, etc. A new metadata will be produced to reflect your request using this record as a base. Change to an orthometric vertical datum is one of the many options.

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. They will be in an orthometric datum.

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.

Link to the lidar report.

Link to view the point cloud (using the Entwine Point Tile (EPT) format) in the 3D Potree viewer.

Entwine Point Tile (EPT) is a simple and flexible octree-based storage format for point cloud data. The data is organized in such a way that the data can be reasonably streamed over the internet, pulling only the points you need. EPT files can be queried to return a subset of the points that give you a representation of the area. As you zoom further in, you are requesting higher and higher densities. A dataset in EPT will contain a lot of files, however, the ept.json file describes all the rest. The EPT file can be used in Potree and QGIS to view the point cloud.

This graphic displays the footprint for this lidar data set.

Airborne survey - This lidar survey was flown at an average elevation of 200 m above ground level and a ground speed of approximately 40 meters per second with a fixed-wing Cessna 180. Elevation data were acquired with a Riegl VUX1-LR laser scanner integrated with a GNSS and Northrop Grumman IMU system. The integration was designed by Phoenix LiDAR systems. Lidar data were acquired at a pulse rate ranging from 50,000 pulses per second in the alpine areas to 400,000 pulses per second over forested areas, a scan rate of 200 revolutions per second, and a scan angle range of 80-280 degrees. The accompanying report provides additional detail regarding flight conditions.

Ground survey - Ground control and check points were collected on September 2, 2018. A Trimble R7 GNSS receiver with Zephyr-2 antenna was deployed near the center of the study area and provided a base station occupation and real-time kinematic (RTK) corrections to points surveyed with a rover Trimble R8-4 GNSS receiver (internal antenna). 78 total ground control points and check points were collected to be used for calibration and assessment of the vertical accuracy of the point cloud. All points were collected on a paved road surface.

Lidar dataset processing - Raw data were processed using Terrasolid software to produce integrated files for navigation correction and a point cloud for calibration. The navigation was corrected using Inertial Explorer software, where the GNSS and IMU data are integrated to establish correct flight path and orientation of the lidar sensor. Internal consistency of the dataset was improved by calibrating the point cloud data using global, flight line, and fluctuation (within individual flightlines) tielines in Terrasolid software. The point cloud was classified for ground points as well as low, medium, and high vegetation (0.01-0.5 m, 0.5-3 m, and 3-60 m heights above the ground, respectively, in accordance with ASPRS lidar classification codes). Some manual processing was required to eliminate erratically placed points and misclassified ground points. All low points and air points were eliminated from the dataset. A LAS dataset was created in ArcMAP, from which a 50 cm DTM, DSM, and intensity image were produced. The DTM was derived from elevation values of ground-classified points only, and built using the binning technique of minimum elevation and linear void fill. The DSM was derived from elevation values from first returns from all point classes, and built using the binning technique of average elevation values and linear void fill. The intensity image was derived from intensity values of first return points.

The NOAA Office for Coastal Management (OCM) downloaded 229 laz files from the Alaska Division of Geological and Geophysical Surveys Elevation Portal (https://elevation.alaska.gov/). The files contained classified elevation and intensity measurements for the 2018 Turnagain Pass project. The data were in UTM Zone 6 NAD83 (2011), meters coordinates and NAVD88 (GEOID12B) elevations in meters. The data had the following classifications: 1 - Unclassified, 2 - Ground, 3- Low Vegetation, 4 - Medium Vegetation, 5 - High Vegetation, 7 - Noise, 8 - Model Key Point. 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. Internal OCM scripts were run to check the number of points by classification and by flight ID and the gps and intensity ranges.

2. Internal OCM scripts were run on the laz files to convert from UTM Zone 6 NAD83 (2011) meters coordinates to geographic coordinates, to convert from NAVD88 elevations to ellipsoid elevations using the GEOID12B model, to assign the geokeys, to sort the data by gps time and zip the data to database and to the AWS S3 bucket.