Data Management Plan

The Alaska Division of Geological & Geophysical Surveys (DGGS) used aerial lidar to produce a digital terrain model (DTM), surface model (DSM), and intensity model for the area surrounding the community of Kotlik, Alaska. Detailed bare earth elevation data for the Kotlik area support and inform potential infrastructure development and provide critical information required to assess geomorphic activity. Airborne data were collected on August 17, 2019, and subsequently processed in Terrasolid and ArcGIS. Ground control was collected between August 20-22, 2019, by the Alaska Division of Mining, Land, and Water. This data collection is released as a Raw Data File with an open end-user license. All files can be downloaded free of charge from the Alaska Division of Geological & Geophysical Surveys website (http://doi.org/10.14509/30561).

The NOAA Office for Coastal Management (OCM) downloaded this data set from this AK DGGS site:

https://elevation.alaska.gov/

These files were processed to the NOAA Digital Coast Data Access Viewer (DAV) and AWS S3. The total number of files downloaded and processed was 215.

During processing, it was noted that there are lidar points that fall in water areas and on structures that are classified as ground.

In addition to the lidar point data, the bare earth Digital Elevation Model (DEM) data at a 0.5 meter grid spacing, created from the lidar point data are also available from the NOAA Digital Coast. Links to these data are provided in the URL section of this metadata record.

Lineage Statement:
Data were collected by the Alaska Division of Geological and Geophysical Surveys (AK DGGS). OCM downloaded the data from the Alaska DGGS Elevation Portal and processed the data to be available for custom and bulk download from the NOAA Digital Coast Data Access Viewer (DAV).

Process Steps:

• 2019-08-17 00:00:00 - Airborne survey - DGGS operates a Riegl VUX1-LR lidar integrated with a GNSS and Northrop Grumman IMU system. The integration was designed by Phoenix LiDAR systems. The sensor is capable of collecting up to 820,000 points per second over a distance of 150 m. This survey was flown at a scan rate between 200,000 and 400,000 points per second at a scan rate between 80 and 150 lines per second. This survey was flown with an average elevation of 400 m above ground level and a ground speed of approximately 40 m/s with a fixed-wing aircraft configuration, using a Cessna 185 aircraft. The scan angle was set from 55 to 305 degrees. The total area surveyed was approximately 15 km2. The accompanying report provides additional detail regarding flight conditions.
• 2019-08-22 00:00:00 - Ground survey - The Alaska Division of Mining, Land, and Water acquired surveyed ground control August 20-22, 2019 in an approximate 2-mile radius around the town of Kotlik. Ninety-four points were collected, including 42 bare earth, 18 forested, 33 low-vegetation, and 1 urban surface points.
• 2020-01-01 00:00:00 - Lidar dataset processing - Point data were processed in SDCimport software for initial filtering and multiple-time-around (MTA) disambiguation. MTA errors, corrected in this process, are the result of imprecise interpretations of received pulse time intervals and occur more frequently with higher pulse refresh rates. IMU and GPS data were used to integrate flightline information with the point cloud in Spatial Explorer software. The point data were calibrated at an incrementally precise scale of sensor movement and behavior, incorporating sensor velocity, roll, pitch, and yaw fluctuations throughout the survey. Points were classified in accordance with ASPRS 2014 guidelines, using macros designed in Terrasolid software. Careful attention was given to the interpolation of the project's ground surface to compensate for inconsistent penetration through low vegetation as a function of the scan angle. Once classified, points underwent a geometric transformation and were converted from ellipsoidal heights to GEOID12B (Alaska) heights. Raster products were derived from the point cloud, using ArcMap. The DTM was interpolated from all ground class returns using a tin-based method. The DTM was also used to produce a separate hydroflattened raster, incorporating hydrography polygons from the AK SDMI IFSAR dataset. The DSM was likewise interpolated from only the first returns for all classes. An intensity image was also produced in ArcMap, using closest-to-mean binning.
• 2022-10-12 00:00:00 - The NOAA Office for Coastal Management (OCM) downloaded 215 laz files from the Alaska DGGS Elevation Portal at: https://elevation.alaska.gov/. The files were in UTM Zone 3 NAD83 (2011), meters coordinates and were in NAVD88 (Geoid12b) elevations in meters. During processing, it was noted that there are lidar points that fall in water areas and on structures that are classified as ground. The point classifications were: 1 - Unclassified , 2 - Ground, 3 - Low Vegetation, 4 - Medium Vegetation, 5 - High Vegetation, 6 - Buildings and 7 - Low Noise. Classes available on the DAV are: 1, 2, 3, 4, 5, 6, 7. OCM performed the following processing on the data for Digital Coast storage and provisioning purposes: 1. An internal OCM script was 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 orthometric (NAVD88) elevations to ellipsoid elevations using the Geoid12b model, to convert from UTM Zone 3 NAD83 (2011), meters coordinates to geographic coordinates, to assign the geokeys, to sort the data by gps time and zip the data to database and to AWS S3.

Data is available online for bulk and custom downloads.