2018 - 2019 USGS Lidar DEM: GA Statewide

Dates of collection for B1.

Dates of collection for B2.

Dates of collection for B3 (Block 3).

Dates of collection for B6 (Block 7).

Dates of collection for B8 (Block 5).

Dates of collection for B9 (Block 6).

Dates of collection for B10 (Block 9).

Dates of collection for B11(Block 8).

Dates of collection for B4 (Block 4A).

Date of collection for B5 (Block 11).

Dates of collection for B7 (Block 4B).

Dates of collection for B12 (Block 10).

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Bulk download of data files in GeoTIFF format, based on a horizontal datum/projection of Albers Conic, NAD83(2011), meters (EPSG: 6350) and a vertical datum of NAVD88 (GEOID12B) and units in meters (EPSG: 5703).

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

Link to the additional information available for this data set from the USGS. This information includes reports, tile index shapefiles, and hydro breaklines.

Link to the USGS work package report that provides project information, vertical accuracy results, classifications used, sensors used, and work unit information.

There is misclassification of vegetation as ground. These misclassified points are marked as overlap. Including the overlap flagged points when deriving ground products can have poor and unusable results.

Aircraft and Sensor Information and Flight Plan Execution:

Atlantic operated a Cessna (N732JE) outfitted with a Leica ALS70-HP LiDAR system during the collection of the project area. Atlantic acquired 212 passes of the AOI as a series of perpendicular and/or adjacent flight-lines executed in 25 flight missions conducted between February 8, 2019 and April 23, 2019. Onboard differential Global Navigation Satellite System (GNSS) unit(s) recorded sample aircraft positions at 2 hertz (Hz) or more frequency. LiDAR data was only acquired when a minimum of six (6) satellites were in view.

Twenty-two (22) Continuously Operating Reference Stations (CORS) were used to control the LiDAR acquisition for the defined project area.

Ground Control Survey:

A total of 124 ground survey points were collected in support of this project, including 31 LiDAR Control Points (LCP), 46 Non-vegetated Vertical Accuracy (NVA) and 47 Vegetated Vertical Accuracy (VVA).

Point cloud data accuracy was tested against a Triangulated Irregular Network (TIN) constructed from LiDAR points in clear and open areas. A clear and open area can be characterized with respect to topographic and ground cover variation such that a minimum of five (5) times the Nominal Pulse Spacing (NPS) exists with less than 1/3 of the RMSEZ deviation from a low-slope plane. Slopes that exceed ten (10) percent were avoided.

Each land cover type representing ten (10) percent or more of the total project area were tested and reported with a VVA. In land cover categories other than dense urban areas, the tested points did not have obstructions forty-five (45) degrees above the horizon to ensure a satisfactory TIN surface. The VVA value is provided as a target. It is understood that in areas of dense vegetation, swamps, or extremely difficult terrain, this value may be exceeded.

The NVA value is a requirement that must be met, regardless of any allowed “busts” in the VVA(s) for individual land cover types within the project. Checkpoints for each assessment (NVA and VVA) are required to be well-distributed throughout the land cover type, for the entire project area.

LiDAR Point Cloud Generation:

Atlantic used Leica software products to download the IPAS ABGNSS/IMU data and raw laser scan files from the airborne system. Waypoint Inertial Explorer is used to extract the raw IPAS ABGNSS/IMU data, which is further processed in combination with controlled base stations to provide the final Smoothed Best Estimate Trajectory (SBET) for each mission. The SBETs are combined with the raw laser scan files to export the LiDAR ASCII Standard (*.las) formatted swath point clouds.

LiDAR Calibration:

Using a combination of GeoCue, TerraScan and TerraMatch; overlapping swath point clouds are corrected for any orientation or linear deviations to obtain the best fit swath-to-swath calibration. Relative calibration was evaluated using advanced plane-matching analysis and parameter corrections derived. This process was repeated interactively until residual errors between overlapping swaths, across all project missions, was reduced to ≤2cm. A final analysis of the calibrated lidar is preformed using a TerraMatch tie line report for an overall statistical model of the project area. Individual control point assessments for this project can be found in Section VI of this report. Upon completion of the data calibration, a complete set of elevation difference intensity rasters (dZ Orthos) are produced. A user-defined color ramp is applied depicting the offsets between overlapping swaths based on project specifications. The dZ orthos provide an opportunity to review the data calibration in a qualitative manner. Atlantic assigns green to all offset values that fall below the required RMSDz requirement of the project. A yellow color is assigned for offsets that fall between the RMSDz value and 1.5x of that value. Finally, red values are assigned to all values that fall beyond 1.5x of the RMSDz requirements of the project.

LiDAR Classification:

Multiple automated filtering routines are applied to the calibrated LiDAR point cloud identifying and extracting bare-earth and above ground features. GeoCue, TerraScan, and TerraModeler software was used for the initial batch processing, visual inspection and any manual editing of the LiDAR point clouds. Atlantic utilized collected breakline data to perform classification for class 9 (Water). Code Description 1 Processed but unclassified 2 Bare-earth ground 3 Low Vegetation (0.5 - 5 feet) 4 Medium Vegetation (5 - 20 feet) 5 High Vegetation (>20 feet) 6 Building footprints 7 Low Noise 9 Water 17 Bridge Decks 18 High Noise 20 Ignored ground (breakline proximity) 21 Snow (where reliable identifiable) 22 Temporal Exclusion (typically non-favored data in intertidal zones) .

LiDAR Intensity Imagery LiDAR intensity imagery was created from the final calibrated and classified lidar point cloud. Intensity images were produced from all classified points and posted to a 1-meter cell size. Intensity images were cut to match the tile index and its corresponding tile names and delivered in GeoTIFF format.

Hydro-line Collection/Conflation Hydro breaklines were compiled using LiDAR intensity data and surface terrain models of the entire project area. After the collection, all delineated hydro features were validated for monotonicity and vertical variance. This procedure ensures that no points were floating above ground. Hydro-lines were then encoded into the LiDAR surface and used to hydro-enforce/flatten all significant water bodies. These final hydro-lines were then used in the production of bare Earth digital models to hydro flatten significant water bodies. This product was delivered as an ESRI geodatabase for the entire project area.

Bare-Earth Surface Digital Elevation Model (DEM) Bare earth Digital Elevation Models (DEMs) were derived using the hydro-lines and bare earth (ground) LiDAR points. All DEMs were created with a grid spacing of 1 meter. DEMs for this project were cut to match the tile index and its corresponding tile names and delivered in 32-bit floating point .img format.

The NOAA Office for Coastal Management (OCM) extracted the GeoTIFF files URL references and ingested them into the NOAA Digital Coast Data Access Viewer (DAV). No changes were made to the data. The DAV will access the DEM as it resides on Amazon Web Services (AWS) under the pr-tnm container.