2017 USGS Lidar DEM: Prince of Wales Island, AK

Product: These are Digital Elevation Model (DEM) data for the Prince of Wales, AK 2017 QL1 LiDAR project AOI. Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 0.5-meter hydro-flattened raster DEM.

Geographic Extent: Partial coverage of Prince of Wales-Hyder Census Area in southeastern Alaska, covering approximately 2055.6 total square miles over Prince of Wales Island.

Dataset Description: The Prince of Wales, AK 2017 QL1 LiDAR project called for the planning, acquisition, processing, and derivative products of LiDAR data to be collected at a nominal pulse spacing (NPS) of 0.35 meters. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base LiDAR Specification, Version 1.2. LiDAR data were delivered as flightline-extent unclassified LAS swaths, as processed Classified LAS 1.4 files formatted to 6333 individual 1,000-meter x 1,000-meter tiles. Tiled intensity imagery, tiled bare earth digital elevation models (DEMs), tiled first return digital surface models (DSMs), tiled shaded relief rasters, and tiled 1-foot contours were produced using a 2,000-meter x 2,000-meter schema for 1705 tiles. Continuous breaklines were produced in Esri file geodatabase format. Building footprints were created in Esri file geodatabase format.

Ground Conditions: LiDAR was collected in the spring, summer, and fall of 2017, when the least amount of snow was on the ground 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, Quantum Spatial, Inc. established a total of 79 ground control points that were used to calibrate the LiDAR to known ground locations established throughout the project area. An additional 127 independent accuracy checkpoints, 74 in Bare Earth and Urban landcovers (74 NVA points), 53 in Forested, Shrubs, and Tall Weeds categories (53 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.

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.

To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments and elevation modeling, etc. Classified LAS files are used to show the manually reviewed bare earth surface. This allows the user to create intensity images, breaklines and raster DEMs. The purpose of these LiDAR data was to produce high accuracy 3D hydro-flattened digital elevation models (DEMs) with a 0.5-meter cell size. These raw LiDAR point cloud data were used to create classified LiDAR LAS files, intensity images, 3D breaklines, hydro-flattened DEMs, and building footprints as necessary.

Raster File Type = TIFF Bit Depth/Pixel Type = 32-bit float Raster Cell Size = 0.5 Meters Interpolation or Resampling Technique = Triangulated Irregular Network (TIN), Linear Interpolation, Proprietary

In no event shall the creators, custodians, or distributors of these data be liable for any damages arising out of its use, or from the inability of the customer to use these data for their intended application. In no event shall the creators, custodians, or distributors of these data be liable for any damages arising out of its use, or from the inability of the customer to use these data for their intended application.

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

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.

The project specifications require the accuracy (ACCz) of the derived DEM be calculated and reported in two ways: 1. The required NVA is: 19.6 cm at a 95% confidence level, derived according to NSSDA, i.e., based on RMSE of 10 cm in the "bare earth" and "urban" land cover classes. This is a required accuracy. The NVA was tested with 74 checkpoints located in bare earth and urban (non-vegetated) areas. 2. Vegetated Vertical Accuracy (VVA): VVA shall be reported for "forested", "shrubs", and "tall weeds" land cover classes. The target VVA is: 29.4 cm at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for LiDAR Data, i.e., based on the 95th percentile error in all vegetated land cover classes combined. This is a target accuracy. The VVA was tested with 53 checkpoints located in forested, shrubs, and tall weeds (vegetated) areas. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. AccuracyZ has been tested to meet 19.6 cm or better Non-Vegetated Vertical Accuracy at 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA); assessed and reported using National Digital Elevation Program (NDEP)/ASRPS Guidelines. Refer to the FOCUS on Accuracy Report listed in the URL section of this metadata record.

DEM NVA = 5.42 cm RMSE

DEM VVA = 28.77 cm at the 95th Percentile

All files are inspected to ensure that they conform to the specified file naming conventions, all files load in their correct geographic position, all files conform to the project specifications for file standard and content.

Data covers the entire area specified for this project.

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.