2018 USGS Lidar DEM: Gulf Coast Islands (AL, FL, LA)

In October 2018, Quantum Spatial (QSI) was contracted by the United States Geological Survey (USGS) to collect high resolution topobathymetric Light Detection and Ranging (LiDAR) data in the winter of 2018 for the USGS Gulf Coast sites in the Gulf of Mexico. The USGS Gulf Coast project area covers approximately 174 square miles and is comprised of three main areas of interest; Chandeleur Island, Dauphin Island, and the Gulf Islands off the coast of Louisiana, Alabama, and Florida, respectively.

Original Product: These are Digital Elevation Model (DEM) data for the Florida Gulf Coast Topobathymetric LiDAR 2018 lidar project. Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 1 meter hydro-flattened Raster DEM.

Original Geographic Extent: This dataset and derived products encompass an area covering approximately 471 square kilometers of south Florida, Louisiana, and Alabama. Traditional near-infrared (NIR) LiDAR was fully integrated with green wavelength (bathymetric) LiDAR in order to provide a seamless topobathymetric LiDAR dataset.

Original Dataset Description: RAW flight line swaths were processed to create 2,272 classified LAS 1.4 files delineated in 500 m x 500 m tiles. Each LAS file contains LiDAR point information, which has been calibrated, controlled, and classified. Additional derived products include green and NIR intensity images, hydro-flattened breaklines, interpolated and clipped topobathymetric DEMs, and highest hit surface models of the study area. Ground Control Points were acquired and calibrated by Quantum Spatial, Inc. Data acquisition was coordinated by Quantum Spatial and all lidar data calibration, and follow-on processing were completed by Quantum Spatial.

Ground Conditions: Acquisition below aircraft 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 3DEP initiative. The raw lidar point cloud data were used to create classified lidar LAS files, NIR and Green Scanner intensity images, hydro-flattened DEMs, interpolated and clipped topobathymetric DEM's, highest hit surface models, and 3D hydroflattening breaklines of water bodies and lakes within the study area.

Raster File Type = TIFF Bit Depth/Pixel Type = 32-bit float Raster Cell Size = 1 meter Interpolation or Re-sampling 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.

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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 (ACCr) 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. Using a maximum flying height of 400m, this data set was produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 6.8 cm RMSEx / RMSEy Horizontal Accuracy Class which equates to Positional Horizontal Accuracy = +/- 11.8 cm at a 95% confidence level.

The project specifications require the accuracy (ACCz) of the derived DEM be calculated and reported in two ways: 1. The required NVA is: 19.6 cm at a 95% confidence level, derived according to NSSDA, i.e., based on RMSE of 10 cm in the “bare earth” and "urban" land cover classes. This is a required accuracy. The NVA was tested with 26 checkpoints located in bare earth and urban (non-vegetated) areas. 2. Vegetated Vertical Accuracy (VVA): VVA shall be reported for "brushlands/low trees" and "tall weeds/crops" land cover classes. The target VVA is: 29.4 cm at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for Lidar Data, i.e., based on the 95th percentile error in all vegetated land cover classes combined. This is a target accuracy. The VVA was tested with 14 checkpoints located in tall weeds/crops and brushlands/low trees (vegetated) areas. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. See survey report for additional survey methodologies. AccuracyZ has been tested to meet 19.6 cm or better Non-Vegetated Vertical Accuracy at 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA); assessed and reported using National Digital Elevation Program (NDEP)/ASRPS Guidelines. Specifications for this project also require that bathymetric accuracy meet the standard laid out in the National Coastal Mapping Strategy (NCMS) V1.0 for QL2b Bathy Lidar which was estimated to be 30cm at a 95% confidence level.

Tested 0.046 meters NVA at a 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA). The NVA of the derived raster DEM was calculated using 26 independent checkpoints located in the Bare Earth and Urban land cover categories with a resulting RMSE of 0.024 meters.

Tested 0.150 meters VVA at the 95th percentile. The VVA of the derived raster DEM was calculated using 14 independent checkpoints located in forest, shrub, and tall grass land cover classes.

Tested 0.093 meters Topobathymetric Submerged Vertical Accuracy at 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA). The Submerged Vertical Accuracy of the derived raster DEM was calculated using 66 independent submerged checkpoints with a resulting RMSE of 0.047 meters.

These LAS data files include all data points collected. No points have been removed or excluded. 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.

Data covers the entire area specified for this project.

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.