2023 NOAA USGS Lidar DEM: Hawaii (Big Island)

Dates of collection for the big Island of Hawaii

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Bulk download of data files in NAD83 (PA11), UTM 5 (EPSG 6635), meters coordinates and elevations in NAVD88 (GEOID12B), meters.

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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 lidar report.

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

After acquisition QC was complete, a formal reduction process was performed. Boresight calibrations (omega, phi, kappa) are performed, and a block adjustment is made to ensure relative accuracy. The laser point position was then calculated by associating the SBET position to each laser point return time, scan angle, intensity, etc. Raw laser point cloud data was created for the whole project area in LAS format with each point containing the corresponding scan angle, return number (echo), intensity, and x, y, and z information. Automated line-to-line calibrations were then performed for system attitude parameters (pitch, roll, heading), mirror flex (scale) and GPS/IMU drift to test the relative calibration. Calibrations were performed on ground classified points from paired flight lines. Every flight line was used for relative accuracy calibration. Statistical reports were generated for comparison and used to make the necessary adjustments to remove any residual systematic error.

Lidar Point Cloud Classification: The point cloud underwent a classification process to determine bare-earth points and non-ground points utilizing "first and only" as well as "last of many" lidar returns. This process determined Processed, but Unclassified (Class 1), Bare Earth Ground (Class 2), Low Noise (Class 7), Water (Class 9), Bridge Decks (Class 17), High Noise (Class 18), and Ignored Ground (Class 20). The bare-earth (Class 2 - Ground) lidar points underwent a manual QA/QC step to verify the quality of the DEM as well as a peer-based QC review. This included a review of the DEM surface to remove artifacts and ensure topographic quality. After the bare-earth surface is finalized, it is then used to generate all hydro-breaklines through a semi-automated process. All ground (Class 2) lidar data inside of the Lake Pond and Double Line Drain hydro flattening breaklines were then classified to water (Class 9) using TerraScan/LP360 macro functionality. A buffer of 0.35 meters was also used around each hydro-flattened feature to classify these ground (Class 2) points to Ignored Ground (Class 20). All Lake Pond Island and Double Line Drain Island features were checked to ensure that the ground (Class 2) points were reclassified to the correct classification after the automated classification was completed. All data was manually reviewed and any remaining artifacts removed using functionality provided by TerraScan and TerraModeler. Global Mapper was used as a final check of the bare earth dataset. GeoCue was then used to create the deliverable industry-standard LAS files. Woolpert proprietary software and LP360 was used to perform final statistical analysis of the classes in the LAS files, on a per tile level to verify final classification metrics and full LAS header information.

During the initial quality check, the lidar data was processed immediately following acquisition to verify the coverage has appropriate density, distribution, and no unacceptable data voids. The spatial distribution of the geometrically usable first return lidar points was reviewed for density by verifying the points spaced so that 90% of the cells in a 2*NPS grid placed over the data contain at least one lidar point. The Nominal Point Spacing (NPS) assessment was conducted against single swath, first return data located within the geometrically usable center portion (typically ~90%) of each swath. The data coverage was reviewed for unacceptable data voids to determine no area greater than or equal to (4 x ANPS)² exhibited data coverage gaps.

Maximum Surface Height Rasters (MSHR) is a proof of performance check that the withheld bit flag was used properly in the point cloud. Using all returns in the point cloud and excluding any points flagged as withheld, a raster is generated at twice the pixel size as the DEM deliverable using the same delivery tile index. This raster is generated as a 32-bit floating-point GeoTIFF with each pixel being generated as highest-hit elevation. The raster is then visually reviewed for anomalies that might indicate improperly classified noise. Any issues encountered are then corrected in the point cloud and a new/updated raster is generated. 5,044 files were produced and clipped to the DPA. The GSD for the surface is 1 meter, which is two times the DEM cell size.

The Swath Separation Imagery (SSI) was generated to visualize the DZ between the overlapping areas of the flight lines. To generate this surface a point insertion method was applied as the primary algorithm. Last returns were used, and points flagged as withheld or classified as noise were excluded. A GeoTIFF was generated, and the color ramp is based on a QL1 data product. The GSD for the raster is 1 meter, which is two times the DEM post spacing. Intensity values were modulated to 50% to ensure that there is no oversaturation of intensities values throughout the surface. After all calculations and surfaces were made, 5,044 files were produced and clipped to the data extent. The color ramp for the swath separation image is as follows: Less than 8-cm: Green, 8 to 16-cm: Yellow, 16-24-cm: Orange, Greater than 24-cm: Red.

Hydro-Flattened Digital Elevation Models (DEMs): Class 2 (ground) lidar points in conjunction with the hydro breaklines as well bridge breaklines were used to create a 0.5-meter, hydro-flattened bare-earth raster DEM. Using automated scripting routines within ArcMap, a GeoTIFF file was created for each tile. Each surface is reviewed using Global Mapper to check for any surface anomalies or incorrect elevations found within the surface.

The NOAA Office for Coastal Management (OCM) received 3450 GeoTIFF files for the NOAA USGS Hawaii lidar project from Woolpert. The bare earth raster files were at a 0.5 m grid spacing. The data were in UTM Zone 5N NAD83 (PA11), meters coordinates and NAVD88 (Geoid12B) elevations in meters. OCM assigned the appropriate EPSG codes (Horiz - 6635, Vert - 5703) and copied the raster files to AWS S3 for Digital Coast storage and provisioning purposes.