2024 NOAA Lidar DEM: AK Coastal Communities (Kachemak Bay)

Original Product: Hydroflattened Digital Elevation Model (DEM) data covering the NOAA AK Communities 2025 project area.

Original Geographic Extent: This dataset and derived products encompass an area covering approximately 286,327 acres of Southwest Alaska.

Original Dataset Description: Lidar flight line swaths were processed to create 2,299 classified LAZ 1.4 files delineated in 750m x 750m tiles. Each LAZ 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 2,299 - 0.5 meter hydro-flattened Raster DEMs delineated in 750m x 750m tiles. Non-Vegetated Vertical Accuracy (NVA) was assessed using 43 check points located on bare earth in clear, unobstructed areas. Vegetated Vertical Accuracy (VVA) was assessed using 19 check points in Tall Grass, Forest, and Shrub landcover types. Additional products include classified LAZ files, intensity images, maximum surface height rasters, and 3D breaklines of water bodies within the study area.

Ground Condition: Ground conditions contained snow at high elevations and acquisition occurred free of smoke, fog and cloud cover

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 NOAA AK Communities 2023 contract. The lidar point cloud data were used to create classified lidar LAZ files, intensity images, hydro-flattened DEMs, MSHRs, 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.

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be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions.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 Mapping Suite 2.4, Applanix PosPac 9.1, Microstation CONNECT version, TerraScan Version 20, TerraModeler Version 20, TerraMatch Version 20, ESRI ArcGIS 10.8, Windows 10 Operating System

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 2478 meters for UTM Zone 5, an IMU error of 0.003 decimal degrees, and a GNSS positional error of 0.023 meters, this project was produced to meet 0.200 m horizontal accuracy at the 95% confidence level. The horizontal accuracy for UTM Zone 5 was 0.233 meters RMSEr.

This data set was produced to meet ASPRS Positional Accuracy Standard for Digital Geospatial Data (2014) for a 10-cm RMSEz Vertical Accuracy Class. The specifications require that classified Non-vegetated Vertical Accuracy (NVA) be computed from the derived DEMs. The NVA was tested with 43 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. Vegetated Vertical Accuracy (VVA) is also to be computed from the derived DEMS. The VVA was tested with 19 check points in Tall Grass, Forest, and Shrub land cover types. These check points were also withheld from the calibration and post processing of the lidar point cloud data and distributed throughout the project area as feasible. Specifications for this project require that the VVA be 0.300 meters or better AccuracyZ at the 95th percentile.

The 43 independent NVA check points were surveyed using real-time kinematics (RTK). Elevations of the derived bare earth DEMs were compared to the elevation values of the surveyed NVA check points. The RMSE was computed to be 0.048 meters resulting in an AccuracyZ of 0.095 meters at the 95% confidence level. NVA AccuracyZ has been tested and meets the required 0.196 meter NVA at 95% confidence level using (RMSEz * 1.9600) for the derived bare earth DEMs as defined by the National Standards for Spatial Data Accuracy (NSSDA) and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines.

The 19 VVA check points were surveyed using real-time kinematics (RTK). Elevations for these points were compared to the elevations of the derived bare earth DEMs resulting in an AccuracyZ of 0.258 meters at the 95th percentile (0.129 m RMSE). AccuracyZ has been tested on the derived bare earth DEMs and meets the required 0.300 meter VVA using the 95th percentile of the absolute value of all vertical errors in all combined vegetation classes as defined by the National Standards for Spatial Data Accuracy (NSSDA); and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines.

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 cloud storage.

This data was collected by NV5 Geospatial for the NOAA Office for Coastal Management (OCM).