2023 USGS Topobathy Lidar DEM: Chehalis River, WA

Original Product: Topobathymetric Digital Elevation Model (DEM) data covering the Chehalis River Topobathy project area.

Original Dataset Geographic Extent: Lidar flight line swaths were processed to create 248 classified LAS 1.4 files delineated in 1000m x 1000m tiles tiles. Each LAS file contains lidar point information, which has been calibrated, controlled, and classified. Class 2 (ground) and class 40 (bathymetric bottom) lidar points were used to create a 248 1.0 meter topobathymetric Raster DEMs delineated in 1000m x 1000m tiles tiles. This version of the topobathymetric model has been clipped. Areas of bathymetric voids were identified through utilization of a raster-based point count approach, wherein continuous cells exceeding 9 square meters were represented as voids. Users should be aware that bathymetric voids can indicate deeper areas beyond the penetration capabilities of the laser and view these as low confidence areas. Non-Vegetated Vertical Accuracy (NVA) was assessed using 23 check points located on bare earth in clear, unobstructed areas. Submerged Topography accuracy was assessed using 283 check points collected as feasible in depths up to 1m. Vegetated Vertical Accuracy (VVA) was assessed using 9 check points in Tall Grass, Forest, and Shrub landcover types. Additional products include classified LAS files, intensity images, maximum surface height rasters, and a bathymetric void shape.

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

This metadata supports the data entry in the NOAA Digital Coast Data Access Viewer (DAV). The NOAA Office for Coastal Management (OCM) downloaded the GeoTIFF files from the USGS AWS S3 site and processed the data to make it available for bulk and custom downloads from the NOAA Digital Coast Data Access Viewer (DAV).

The 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 Chehalis River Topobathy contract. The lidar point cloud data were used to create classified lidar LAS files, intensity images, void interpolated topobathymetric DEMs, void clipped topobathymetric DEMs, highest hit DSMs, 3D breaklines of rivers and lakes within the study area, and a bathymetric void shape.

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 Mapping Suite 2.4, Applanix PosPac 7.1, Microstation CONNECT version, TerraScan Version 20, TerraModeler Version 20, TerraMatch Version 20, ESRI ArcGIS 10.3, Windows 10 Operating System

Lidar horizontal accuracy is a function of Global Navigation Satellite System (GNSS) derived positional error, flying altitude, and inertial navigation system (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 500 meters, an IMU error of 0.002 decimal degrees, and a GNSS positional error of 0.008 meters, this project was produced to meet 0.056 meters horizontal accuracy at the 95% confidence level.

Some flightlines throughout the area of interest were flown at an AGL of 600 meters. With the same IMU and GNSS error as above, but adjusting the altitude to 600 meters, the horizontal accuracy at the 95% confidence level was 0.066 meters.

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

NV5 Determined Vertical Accuracy:

The NVA was tested with 23 independent check points located in open terrain and distributed throughout the project as feasible. These check points were not used in the calibration or post processing of the lidar point cloud data. Specifications for this project require that the NVA be 0.196 meters or better AccuracyZ at 95% confidence level.

The 23 independent NVA check points were surveyed using the closed level loop technique. Elevations interpolated from the ground-classified lidar surface were compared to the elevation values of the surveyed NVA check points. NVA AccuracyZ has been tested and meets the required 0.196 meter NVA at 95% confidence level using (RMSEz * 1.9600) for the ground-classified lidar point cloud as defined by the National Standards for Spatial Data Accuracy (NSSDA) and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines.

Submerged topography was also tested with 283 check points. These check points were withheld from the calibration and post processing of the lidar point cloud data and distributed throughout the project area as feasible. Submerged topography points are typically collected in depths up to 1m. Project specifications require submerged topography shall meet a vertical RMSE of QL2b specified in the Draft National Coastal Mapping strategy 1.0 which is equivalent to 0.363 m RMSE at a depth of 1m.

The 283 independent BAP check points were surveyed using the closed level loop technique. Elevations interpolated from the bathy classified lidar surface were compared to the elevation values of the surveyed submerged topography check points. Submerged Topographic AccuracyZ has been tested and meets the required 0.363 m RMSE at a depth of 1m for the derived bare earth DEMs as defined by the Draft National Coastal Mapping strategy 1.0 and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines.

USGS DEM Determined Vertical Accuracy:

Non-Vegetated Vertical Accuracy (NVA) = 2.98 cm RMSE

Vegetated Vertical Accuracy (VVA) = 24.26 cm at the 95th Percentile

Bathymetric Vertical Accuracy (BVA) = 15.42 cm at the 95th Percentile

A visual qualitative assessment was performed to ensure data completeness. A bathymetric void shape has been provided as a separate deliverable. The classified 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 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.