2020 USGS Topobathy Lidar DEM: Nisqually River Basin, WA

Original Data Product: Hydroflattened Digital Elevation Model (DEM) data covering the Nisqually River Basin 2020 project area.

Original Geographic Extent: This dataset and derived products encompass an area covering approximately 13,189 acres of Western Washington.

Original Dataset Description: Lidar flight line swaths were processed to create 85 classified LAS 1.4 files delineated in 1,000m x 1,000m tiles. Each LAS file contains lidar point information, which has been calibrated, controlled, and classified. Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create 85 1.0 meter hydro-flattened Raster DEMs delineated in 1,000m x 1,000m tiles. Non-Vegetated Vertical Accuracy (NVA) was assessed using 22 check points located on bare earth in clear, unobstructed areas. Vegetated Vertical Accuracy (VVA) was assessed using 14 check points in tall grass, forest, and shrubland landcover types. Additional products include classified LAS files, intensity images, topobathymetric bare earth DEMs, highest hit surface models, and 3D breaklines of rivers and lakes within the study area.

Ground Condition: Ground condition was free of snow and acquisition occurred free of smoke, fog and cloud cover.

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 USGS GeoTIFF files hosted by USGS on Amazon Web Services.

he purpose of the lidar data was to produce a high accuracy 3D dataset that meets all necessary standards laid out by the 3D Elevation Program and the Nisqually River Basin 2020 contract. The lidar point cloud data were used to create classified lidar LAS files, intensity images, hydro-flattened DEMs, topobathymetric DEMs, highest hit surface models, and 3D breaklines of rivers and lakes within the study area.

Raster File Type = TIFF Bit Depth/Pixel Type = 32-bit float Raster Cell Size = 1.0 meter 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be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions.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.

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 400 meters, an IMU error of 0.002 decimal degrees, and a GNSS positional error of 0.015 meters, this project was compiled to meet 0.050 m horizontal accuracy at the 95% confidence level.

This data set was produced to meet ASPRS Positional Accuracy Standard for Digital Geospatial Data (2014) for a 10-cm RMSEz Vertical Accuracy Class.

USGS DEM Determined Vertical Accuracy

Non-Vegetated Vertical Accuracy (NVA) = 2.5 cm RMSE

Vegetated Vertical Accuracy (VVA) = 16.71 cm at the 95th Percentile

A visual qualitative assessment was performed to ensure data completeness. No void areas or missing data exist. The raw point cloud is of good quality and data passes Non-Vegetated Vertical Accuracy specifications.

DEM files were tested by NV5 for vertical accuracy. All data is seamless from one tile to the next, no gaps or no data areas.

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.