2024 - 2025 USGS Lidar DEM: Typhoon Merbok, AK (Part 3 of 4)

Product: Hydro-flattened Digital Elevation Model (DEM) data covering the Typhoon Merbok Alaska Topographic Lidar 2024 project area.

Geographic Extent: This dataset and derived products encompass an area covering approximately 894,095 acres on the western coast of Alaska along Norton Sound.

AK_TyphoonMerbokNV5_1 - covers approximately 685,389 acres on the western coast of Alaska along Norton Sound

AK_TyphoonMerbokNV5_2 - covers approximately 208,706 acres on the western coast of Alaska along Norton Sound

Dataset Description: Lidar flight line swaths were processed to create classified LAS 1.4 files delineated in 750 m x 750 m 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 0.5 meter hydro-flattened Raster DEMs delineated in 750 m x 750 m tiles. Additional products include classified LAS files, intensity images, maximum surface height rasters, swath separation RGB images, and 3D breaklines of water bodies within the study area.

Ground Conditions: 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 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 3D Elevation Program and the Typhoon Merbok Alaska Topographic Lidar 2024 contract. The lidar point cloud data were used to create classified lidar LAS files, intensity images, hydro-flattened DEMs, maximum surface height rasters, swath separation RGB images, and 3D breaklines of water bodies within the study area.

Raster File Type = TIFF

Bit Depth/Pixel Type = 32-bit float

Raster Cell Size = 0.5 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.

AK_TyphoonMerbok_NV5_1 (Work Unit 300810)

AK_TyphoonMerbok_NV5_2 (Work Unit 301214)

To the extent possible under law, the U.S. Government has waived all copyright and related or neighboring rights to this dataset.

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.

AK_TyphoonMerbokNV5_1 (Work Unit 300810)

Based on a flying altitude of 2016 meters, an IMU error of 0.003 decimal degrees, and a GNSS positional error of 0.023 meters, this project was produced to meet 0.329 meters horizontal accuracy at the 95% confidence level.

AK_TyphoonMerbokNV5_2 (Work Unit 301214)

Based on a flying altitude of 2016 meters, an IMU error of 0.002 decimal degrees, and a GNSS positional error of 0.023 meters, this project was produced to meet 0.222 meters 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 Determined DEM Vertical Accuracy

Non-Vegetated Vertical Accuracy (NVA) = 2.63 cm RMSE

Vegetated Vertical Accuracy (VVA) = 18.97 cm at the 95th Percentile

Refer to the USGS Project Report. A link to this report is provided in the URL section of this metadata record.

A visual qualitative assessment was performed to ensure data completeness. No void areas or missing data exist. 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.

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.