2023 USGS Lidar: Southwest Central Alabama

Create custom data files by choosing data area, product type, map projection, file format, datum, etc. A new metadata will be produced to reflect your request using this record as a base. Change to an orthometric vertical datum is one of the many options.

Bulk download of data files in LAZ format, UTM Zone 16N NAD83(2011), meters coordinates and NAVD88 (GEOID18) elevations in meters.

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 USGS Project Report that provides information about the project, vertical accuracy results, and the point classes and sensors used.

Link to the reports, breaklines, metadata, and spatial metadata.

Link to the lidar report

Entwine Point Tile (EPT) is a simple and flexible octree-based storage format for point cloud data. The data is organized in such a way that the data can be reasonably streamed over the internet, pulling only the points you need. EPT files can be queried to return a subset of the points that give you a representation of the area. As you zoom further in, you are requesting higher and higher densities. A dataset in EPT will contain a lot of files, however, the ept.json file describes all the rest. The EPT file can be used in Potree and QGIS to view the point cloud.

Link to view the point cloud, using the Entwine Point Tile (EPT) format, in the 3D Potree viewer.

Aerial LiDAR Acquisition: LiDAR acquisition was done using H.L Sonny Callahan Airport (KCQF), Bay Minette Municipal Airport (1R8) and Bessemer Airport (KEKY), as the base airport. DAS used dedicated GPS base stations located at the respective airports to support the aerial LiDAR acquisition. DAS used Leica's Terrain LiDAR Sensor (SN90524) for the acquisition. The project consisted of 247 flightlines totaling 7699.47 nautical miles. The acquisition was completed in 27 lifts from January 9th, 2023 - March 5th, 2023.

Ground Control Survey: A survey was performed to support the acquisition of Light Detection and Ranging (LiDAR).The checkpoints were a combination of the following ground cover classification: Open Terrain, Urban Terrain, Bare Earth, High Grass, and Low Trees. All field survey observations were completed March 5th, 2023 with Leica GS18.

LiDAR Data Processing: Inertial Explorer 8.9 software was used to compute inertial solution file (*.sol) for each mission using ground GPS base station. The resulting solution was checked to ensure a minimum accuracy of +/- 0.05m, combined separation, for horizontal and vertical positions. Inertial Explorer methodology integrates Inertial Navigation Solution by processing the GPS data and Inertial Measurement Unit (IMU). The software applies the reference lever arms for the GPS and IMU during the process to determine the trajectory (position and orientation) of the LiDAR sensor during the acquisition mission. Inertial Explorer generated graphical results was reviewed to ensure that the IMU data was healthy. These results are found in Appendix C.

Raw LiDAR sensor ranging data and the final solution sensor trajectory (*.sol), from Inertial Explorer, were processed in Leica’s HxMap software to produce LiDAR point cloud swath for each flight line in LAS version 1.4 file format.Quality control of the swath point cloud was performed to validate proper functioning of the sensor system, full coverage of the project area and point density of the LiDAR data. Swath point clouds were assigned unique file source identification. The data was found to be complete and consistent with the sensor calibration parameters.

LiDAR Calibration:HxMap is the common workflow platform for Leica airborne sensors. The processing workflow involves; Ingest, Block Creation, LiDAR Matching, Quality Assurance (QA) and Product Generation.

LiDAR is processed in HxMap by generating point clouds from raw sensor data during the Ingest step. Noise filtering, sensor installation calibration and atmospheric condition parameters are also applied during the ingest process. Once all data is processed through ingest, they are assembled into a block for LiDAR Matching. The LiDAR Matching step resolves LiDAR registration errors which remain in the point clouds after sensor and installation calibration parameters are applied in the ingest step. QA tool is run on the Block after LiDAR Matching to verify quality of results. QA results are reviewed to ensure that, 95% of patches less than 5cm for Vertical Scan Direction and Vertical Line Separation. Ground control points are also included to assess absolute accuracy for the point cloud data. LiDAR products are finally generated in the Product Generation step as LAS swaths (LAS 1.4). Vertical (Z) shift (calculated from QA step) is also applied during the product generation. Flood inundations were identified in low lying areas within the project DPA. The inundation conditions in these areas resulted in poor returns in ground classification, resulting in thinning in bare earth digital elevation models (DEM) generated for these areas. A total of 438 Low confidence polygons were delineated and submitted as deliverables to help in data QC. Nine LAS tiles (16RCU682360, 16RCU802347, 16RCU817356, 16RDV072408, 16RDV087414, 16RDV087440, 16RDV102426, 16RDV147485 , 16SDC762705) are located in deep water bodies and therefore had no LiDAR returned data.

Original point clouds in LAS/LAZ format were restructured as Entwine Point Tiles and stored on Amazon Web Services. The data were re-projected horizontally to WGS84 web mercator (EPSG 3857) and no changes were made to the vertical (NAVD88 GEOID18 meters).

The NOAA Office for Coastal Management (OCM) created references to the Entwine Point Tiles (EPT) that were ingested into the NOAA Digital Coast Data Access Viewer (DAV). No changes were made to the data. The DAV will access the point cloud as it resides on Amazon Web Services (AWS) under the usgs-lidar-public container.

This is the AWS URL being accessed:

https://s3-us-west-2.amazonaws.com/usgs-lidar-public/AL_SWCentral_1_B22/ept.json