2018-2019 NOAA NGS Topobathy Lidar DEM Hurricane Irma: Miami to Marquesas Keys, FL

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Bulk download of data files in geotiff format, geographic coordinates, orthometric heights. Note that the vertical datum (hence elevations) of the files here are different than described in this document. They will be in an orthometric datum.

This graphic displays the footprint for this lidar data set.

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Acquisition and processing report

Data for the NOAA Hurricane Irma project area was acquired by Quantum Spatial (QSI) using Riegl VQ-880-GII, Riegl VQ-880-GH, and Riegl VQ-880-G+ Topobathy LiDAR systems. All derived DEM data is referenced to:

Horizontal Datum-NAD83(2011) epoch: 2010.00

Projection-UTM Zone 17N

Horizontal Units-meters

Vertical Datum-NAVD88 (Geoid12b)

Vertical Units-meters

The collected LiDAR data were immediately processed in the field by QSI to a level that will allow QA\QC measures to determine if the sensor is functioning properly and assess the coverage of submerged topography. An initial SBET was created in POSPAC MMS 8.3 SP3 and loaded into RiProcess which applies pre-calibrated angular misalignment corrections of scanner position to extract the raw point cloud into geo-referenced LAS files. These files were inspected for sensor malfunctions and then passed through automated raster generation using LAStools to develop an initial assessment of bathymetric coverage. QSI reviewed all acquired flight lines to ensure complete coverage and positional accuracy of the laser points. These rasters were also used to create an initial product - Quick Look Coverage Maps. These Quick Look files are not fully processed data or final products but provide rapid assessment of approximate coverage and depth penetration.

QSI resolved kinematic corrections for aircraft position data using aircraft GNSS and Applanix' proprietary PP-RTX solution. When PP-RTX was not used QSI conducted static Global Navigation Satellite System (GNSS) ground surveys (1 Hz recording frequency) using base stations over known monument locations during flights. After the airborne survey, static GPS data were triangulated with nearby Continuously Operating Reference Stations (CORS) using the Online Positioning User Service (OPUS) for precise positioning. Multiple independent sessions over the same base station were performed to confirm antenna height measurements and to refine position accuracy.

This data was used to correct the continuous onboard measurements of the aircraft position recorded throughout the flight. A final smoothed best estimate trajectory (SBET) was developed that blends post-processed aircraft position with attitude data. Using the SBETs, sensor head position and attitude were then calculated throughout the survey.PosPac MMS 8.3 SP3 was used for these processes.

Following final SBET creation, QSI used RiProcess 1.8.5 to calculate laser point positioning by associating SBET positions to each laser point return time, scan angle, and intensity. Terra 19 and LasTools were used to classify water surface and create a water surface model. They are created for single swaths to ensure temporal differences and wave or water surface height variations between flight lines do not impact the refraction of the bathymetric data. These models are used in QSI's LasMonkey refraction tool to determine the accurate positioning of bathymetric points. All LiDAR data below water surface models were classified as water column to be refracted. Light travels at different speeds in air versus water and its direction of travel or angle is changed or refracted when entering the water column. The refraction tool corrects for this difference by adjusting the depth (distance traveled) and horizontal positioning (change of angle/direction) of the LiDAR data. Using raster-based QC methods, the output data is verified to ensure the refraction tool functioned properly.

Once all data was refracted by flight line data was exported to LAS 1.4 format and combined into 500 m x 500 m tiles. Data were then further calibrated using TerraMatch. QSI used custom algorithms in TerraScan to classify the initial ground/submerged topography surface points. Relative accuracy of overlapping swaths was compared and verified through the use Delta-Z (DZ) orthos created using QSI's Las Product Creator. Absolute vertical accuracy of the calibrated data was assessed using ground survey data and complete coverage was again verified.

Post automated classification QSI then performed manual editing to review all classification and improve the final topobathymetric surface. QSI's LasMonkey was used to update LAS header information, including all projection and coordinate reference system information. The final LiDAR data are in LAS format 1.4 and point data record format 6.

The final classification scheme is as follows:

1 - Unclassified

2 - Ground

7 - Noise

40 - Bathymetric Bottom or Submerged Topography

41 - Water Surface

43 - Submerged feature

45 - Water Column

46 - Temporal Bathymetric Bottom

71 - Overlap Default

72 - Overlap Ground

81 - Overlap Water Surface

85 - Overlap Water Column

1-Overlap - Edge Clip

QSI transformed the final LiDAR data from ellipsoid heights to orthometric heights referenced to NAVD88, Geoid12B to create the final topobathymetric DEMs. The topobathymetric bare earth DEMs were output at 1 meter resolution in IMG format into 300 5,000 m x 5,000 m tiles. The NOAA Hurricane Irma Project rasters are clipped to the extent of the project boundary and named according to project specifications.

A bathymetric void shapefile was created to indicate areas where there was a lack of bathymetric returns. This shape was created by triangulating bathymetric bottom points with an edge length maximum of 4.56m to identify all areas greater then 9 square meters without bathymetric returns. This shapefile was used to clip and exclude interpolated elevation data from these areas in the bathymetric void clipped topobathymetric bare earth model.

The NOAA Office for Coastal Management (OCM) received img format files from Quantum Spatial. Horizontal positions were provided in UTM Zone 17 NAD83(2011), meters coordinates. Vertical positions were provided in NAVD88 (Geoid12b) elevations and in meters. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The data were converted to GeoTiff format and the projection and vertical datum EPSG codes were assigned..

2. The data were copied to https