2018 - 2019 USGS QL1 Lidar DEM: North Slope, AK

Product: QL1 Hydroflattened Digital Elevation Model (DEM). Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 1.5 foot hydro-flattened Raster DEM.

Geographic Extent:

AK_NorthSlope_B1 - This block includes the Kaktovik AOI.

AK_NorthSlope_B2 - This block includes the Nuiqsut AOI.

AK_NorthSlope_B3 - This block includes the Utqiagvik and Atqasuk AOIs.

AK_NorthSlope_B4 - This block includes the Wainwright AOI.

AK_NorthSlope_B9 - This block includes the Anaktuvuk Pass AOI.

AK_NorthSlope_B10 - This block includes the Point Lay AOI.

AK_NorthSlope_B11 - This block includes the Point Hope AOI.

Dataset Description: The North Slope Borough 3DEP LiDAR project called for the planning, acquisition, and processing of LiDAR data collected at an aggregate nominal pulse spacing (ANPS) of 0.35 meters. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base LiDAR Specification, Version 1.3. LiDAR data was delivered as processed Classified LAS 1.4 files, formatted to individual 1500 ft x 1500 ft tiles. Derived products include: tiled Intensity Imagery, tiled and mosaicked bare earth DEMs and shaded relief rasters, tiled and mosaicked Highest Hit Digital Surface Models and shaded relief rasters, tiled 2 ft contour shapefiles, 3D building footprints, and 3D waters edge breaklines.

Ground Conditions: LiDAR was collected in the summer 2018 and the summer of 2019, while the presence of snow on the ground was at a minimum and rivers were at or below normal levels. In order to post process the LiDAR data to meet task order specifications and meet ASPRS vertical accuracy guidelines, UMIAQ established the ground control points distributed throughout the North Slope Borough 3DEP, Alaska project area. LiDAR data was calibrated to these known ground locations. Additional independent accuracy checkpoints in Bare Earth and Urban landcovers (NVA points) and in Tall Grass, Tundra and Shrubbery categories (VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.

In July 2018, Quantum Spatial (QSI) was contracted by the United States Geological Survey (USGS) to collect Light Detection and Ranging (LiDAR) data in the summer of 2018 for several areas of interest (AOIs), comprising the North Slope Borough Communities 3DEP LiDAR project in Alaska. Data were collected to aid USGS in assessing the topographic and geophysical properties of the study area, to support its mission to gather high quality 3D elevation data over the state of Alaska.

This metadata record supports the data entry in the NOAA Digital Coast Data Access Viewer (DAV). For this data set, the DAV is leveraging the GeoTIFF files hosted by USGS on Amazon Web Services.

The purpose of the lidar data was to produce a high accuracy 3D dataset that meets all necessary standards laid out by the 3DEP initiative. The raw lidar point cloud data were used to create classified lidar las files, hydroflattened DEMs, highest hit DSMs, intensity images, 2 foot contours, 3D hydro breaklines, and 3D building footprints.

CONTRACTOR: Quantum Spatial, Inc. Ground Control Points were acquired by Umiaq. Quantum Spatial coordinated the data acquisition and performed all calibration, follow up processing, and creation of the final derived products. Raster File Type = IMG and GRID Bit Depth/Pixel Type = 32-bit float Raster Cell Size = 1.5 ft (QL1) Interpolation or Resampling Technique = Triangulated Irregular Network Required Vertical Accuracy = 19.6 cm NVA

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the Office for Coastal Management or its partners.

AK_NorthSlope_B1 - This block includes the Kaktovik AOI.

AK_NorthSlope_B2 - This block includes the Nuiqsut AOI.

AK_NorthSlope_B3 - This block includes the Utqiagvik and Atqasuk AOIs.

AK_NorthSlope_B4 - This block includes the Wainwright AOI.

AK_NorthSlope_B9 - This block includes the Anaktuvuk Pass AOI.

AK_NorthSlope_B10 - This block includes the Point Lay AOI.

AK_NorthSlope_B11 - This block includes the Point Hope AOI.

Data is available online for bulk and custom downloads.

None

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

LiDAR horizontal accuracy is a function of Global Navigation Satellite System (GNSS) derived positional error, flying altitude, and INS-derived attitude error. The obtained RMSEr value is multiplied by a conversion factor of 1.7308 to yield the horizontal component (ACCr) of the National Standards for Spatial Data Accuracy (NSSDA) reporting standard where a theoretical point will fall within the obtained

radius 95 percent of the time. Using a flying altitude of 1,750 meters, an IMU error of 0.005 decimal degrees, and a GNSS positional error of 0.032 meters, the horizontal accuracy (ACCr) for the LiDAR collection is 1.54 feet (0.48 meters) at the 95% confidence level.

Absolute accuracy was assessed using Non-Vegetated Vertical Accuracy (NVA) reporting designed to meet guidelines presented in the FGDC National Standard for Spatial Data Accuracy. NVA compares known ground check point data that were withheld from the calibration and post-processing of the LiDAR point cloud to the triangulated surface generated by the unclassified LiDAR point cloud as well as the derived gridded bare earth DEM. NVA is a measure of the accuracy of LiDAR point data in open areas where the LiDAR system has a high probability of measuring the ground surface and is evaluated at the 95% confidence interval (1.96 * RMSE).

The mean and standard deviation (sigma ) of divergence of the ground surface model from quality assurance point coordinates are also considered during accuracy assessment. These statistics assume the error for x, y and z is normally distributed, and therefore the skew and kurtosis of distributions are also considered when evaluating error statistics. For the North Slope Borough Communities survey, 56 ground check points were withheld from the calibration and post processing of the LiDAR point cloud, with resulting non-vegetated vertical accuracy of 0.140 feet (0.043 meters) as compared to unclassified LAS, and 0.139 feet (0.042 meters) as compared to the bare earth DEM, with 95% confidence.

NVA of the DEM files is RMSE = 0.071 ft (0.022 m).

VVA (Vegetated Vertical Accuracy) of the DEM files 14.1 cm at 95th Percentile.

Datasets contain complete coverage of tiles. No points have been removed or excluded. A visual qualitative assessment was performed to ensure data completeness. There are no void areas or missing data. The raw point cloud is of good quality and data passes Non-Vegetated Vertical Accuracy specifications.

Data covers the entire area specified for this project area.

Data is backed up to tape and to cloud storage.

The NOAA Office for Coastal Management (OCM) ingested references to the USGS GeoTIFF files that are hosted on Amazon Web Services (AWS), into the Digital Coast Data Access Viewer (DAV). The DAV accesses the raster data as it resides on AWS.