2021 USGS Lidar DEM: Central Eastern Massachusetts

Original Product: Hydroflattened Digital Elevation Model (DEM) data covering the Central Eastern Massachusetts project area.

Original Dataset Geographic Extent: This dataset and derived products encompass an area covering approximately 5,246 Square Miles of Massachusetts.

Original Dataset Description: Lidar flight line swaths were processed to create 6,038 classified LAS 1.4 files delineated in 1,500m x 1,500m 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 6,038 0.5 meter hydro-flattened Raster DEMs delineated in 1,500m x 1,500 m tiles. Non-Vegetated Vertical Accuracy (NVA) was assessed using 129 check points located on bare earth in clear, unobstructed areas. Vegetated Vertical Accuracy (VVA) was assessed using 95 check points in Tall Grass, Forest, and Shrub landcover types. Additional products include classified LAS files, intensity images, highest hit surface models, and 3D breaklines of rivers and lakes within the study area.

Original Dataset Ground Condition: Ground condition was free of snow and acquisition occurred free of smoke, fog and cloud cover, and occurred in coordination with low tide windows.

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 Central Eastern Massachusetts contract. The lidar point cloud data were used to create classified lidar LAS files, intensity images, hydro-flattened DEMs, highest hit DSMs, 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 = 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.

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be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions.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.

Applanix PosPac 8.5, PofImport 1.7.4, Georun v.6.1.1, BayesMap-StripAlign v.2.19, Microstation CONNECT version 10, 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 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. All areas surveyed at a flying altitude of 1500 meters, with an IMU error of 0.002 decimal degrees, and a GNSS positional error of 0.015 meters, were produced to meet 0.16 meters horizontal accuracy at the 95% confidence level (or 0.09 m RMSEr). All areas using a flying altitude of 1,829 meters, an IMU error of 0.002 decimal degrees, and a GNSS positional error of 0.015 meters, were produced to meet 0.20 meters horizontal accuracy at the 95% confidence level (or 0.11 m 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. Specifications for this project require that the NVA be 0.196 meters or better AccuracyZ at 95% confidence level.

USGS Determined DEM Vertical Accuracy

Non-Vegetated Vertical Accuracy (NVA) = 7.51 cm at 95% Confidence Level (3.8 cm RMSE)

Vegetated Vertical Accuracy (VVA) = 12.54 cm at 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 Geospatial 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.