2019 - 2020 USGS Lidar DEM: Matanuska - Susitna Borough, AK

Original Dataset Description: The Matanuska - Susitna Borough 3DEP LiDAR project called for the planning, acquisition, and processing of LiDAR data collected at an aggregate nominal pulse spacing (ANPS) of 0.71 meters. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base LiDAR Specification, Version 1.3. The data was developed based on the NAD83 horizontal datum and NAVD88 (GEOID12B) vertical datum. Data was projected in Alaska State Plane Zone 4. All units are in US Survey Feet. LiDAR data was delivered as processed Classified LAS 1.4 files, formatted to 4236 individual 3,000 ft x 3,000 ft tiles.

Original Dataset Product: Hydroflattened Digital Elevation Model (DEM). Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 3.0 foot hydro-flattened Raster DEM.

Original Dataset Geographic Extent: This dataset and derived products encompass an area covering approximately 1099 square miles in south west Alaska.

Delivery 1/B1: (Work Unit 180695) - 951 square miles

Delivery 2/B2: (Work Unit 213376) - 148 square miles

Derived products include: tiled Intensity Imagery, tiled DZ orthos, tiled bare earth DEMs and shaded relief rasters, tiled Highest Hit Digital Surface Models and shaded relief rasters, tiled 1 ft contour shapefiles, 2D building footprints, and 3D waters edge breaklines.

Original Dataset Ground Conditions:

Delivery 1/B1: (Work Unit 180695)

LiDAR was collected in summer 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, McClintock and Associates established a total of 57 ground control points distributed throughout the Matanuska - Susitna Borough 3DEP, Alaska project area. LiDAR data was calibrated to these known ground locations. An additional 93 independent accuracy checkpoints, 52 in Bare Earth and Urban landcovers (NVA points) and 41 in Tall Grass, Tundra and Shrub categories (VVA points), were used to assess the vertical accuracy of the project data. These checkpoints were not used to calibrate or post process the data.

Delivery 2/B2: (Work Unit 213376)

Lidar was collected in summers of 2019 and 2020, 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, McClintock Land Associates established a total of 13 ground control points distributed throughout the Matanuska - Susitna Borough 3DEP, Alaska project area. Lidar data was calibrated to these known ground locations. An additional 34 independent accuracy checkpoints, 25 in Bare Earth and Urban landcovers (NVA points) and 9 in Tall Grass, Forest and Shrub categories (VVA points), were used to assess the vertical accuracy of the project 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.

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, dz orthos, 1 foot contours, 3D hydro breaklines, and 2D building footprints.

CONTRACTOR: Quantum Spatial, Inc. Ground Control Points were acquired by McClintock and Associates. Quantum Spatial coordinated the data acquisition and performed all calibration, follow up processing, and creation of the final derived products Raster File Type = GeoTIFF Bit Depth/Pixel Type = 32-bit float Raster Cell Size = 3.0 ft 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.

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. Acknowledgment of the U.S. Geological Survey would be appreciated for products derived from these data.

Waypoint Inertial Explorer v.8.7; Leica Cloudpro v.1.2.4; TerraScan v.19; Terramatch v.19; TerraModeler v.19;Las Product Creator v.3.4 (QSI proprietary); Las Monkey 2.4.3 (QSI proprietary); Windows 10 Operating System

Delivery 1/B1:

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 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. Based on a flying altitude of 1,750 meters, an IMU error of 0.002 decimal degrees, and a GNSS positional error of 0.070 meters, this project was compiled to meet 0.0008 meters (0.0029 ft) horizontal accuracy at the 95% confidence level.

During processing of the data to the NOAA Digital Coast Data Access Viewer, NOAA OCM noted that this value did not sound correct. The horizonal accuracy information was copied from the Quantum Spatial (QSI) lidar report. An email was sent to the QSI project manager for clarification. As of June 2023, there has been no response.

Delivery 2/B2:

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 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.

For the ALS80 sensor acquisition based on a flying altitude of 1,750 meters, an IMU error of 0.005 decimal degrees, and a GNSS positional error of 0.032 meters, this project was compiled to meet 0.476 meters (1.562 ft) horizontal accuracy at the 95% confidence level.

The VQ1560ii sensor acquisition based on a flying altitude of 2,305 meters, an IMU error of 0.002 decimal degrees, and a GNSS positional error of 0.015 meters, this project was compiled to meet 0.250 meters (0.822 ft) horizontal accuracy at the 95% confidence level.

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 checkpoints located in bare earth and urban (non-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.

USGS Determined Vertical Accuracy:

Digital Elevation Model

Non-Vegetated Vertical Accuracy (NVA) = 8.08 cm at 95% Confidence Level or 4.12 cm RMSE

Vegetated Vertical Accuracy (VVA) = 24.76 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 in the contract.

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.