2015 NOAA NGS Topobathy Lidar: Puerto Rico

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This graphic shows the lidar footprint for the 2015 NOAA NGS topobathy lidar project along the coast of Puerto Rico.

Date that the source FGDC record was last modified.

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Data for the Puerto Rico Topobathy LiDAR project was acquired by NOAA using a Riegl VQ-820G Topobathy LiDAR systems. All delivered LiDAR data is referenced to:

Horizontal Datum-NAD83 (2011) epoch: 2010

Projection-UTM Zone 19

Horizontal Units-meters

Vertical Datum-NAD83 (2011) epoch: 2010 (ellipsoid heights)

Vertical Units-meters

This dataset encompasses 5,721 500m x 500m tiles in Puerto Rico. Both green LiDAR data and NIR LiDAR data (used for water surface model creation that is incorporated during refraction of the green bathymetric data) was acquired.

NOAA acquired and calibrated the LiDAR data.

Dewberry received the calibrated green and NIR data and verified complete coverage. Relative accuracy of the green swaths compared to overlapping and adjacent green swaths as well as the relative accuracy of green swaths compared to overlapping and adjacent NIR swaths was verified through the use Delta-Z (DZ) orthos created in GeoCue software.

Dewberry used E-Cognition to create 2D breaklines representing land/water interfaces. These 2D breaklines were manually reviewed and adjusted where necessary to ensure all well-defined hydrographic features (at 1:1200-scale) were represented with breaklines. Using TerraScan, all green LiDAR data within breaklines are classified as water column and a sub-set of these points meeting specific criteria are classified as green water surface points. Using TerraScan, all NIR LiDAR data within breaklines are classified as water column and a sub-set of these points meeting specific criteria are classified as NIR water surface points.

Dewberry used the green water surface points and NIR water surface points to create water surface models. These models are used in the refraction tool to determine the depth of bathymetric points and 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.

Using the SBET data and the water surface models, all green LiDAR data classified as water column (data within the breaklines) is refracted using Dewberry's LiDAR Processor (DLP). 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 position (change of angle/direction) of the green LiDAR data. Using statistics and limited manual review, the output data is verified to ensure the refraction tool functioned properly.

Once all green data has been refracted by flight lines, all flight lines covering each tile are combined into a single 500 m x 500 m tile. As the various flight lines may include data collected at Mean Lower Low Water (MLLW) and higher water (HW), which includes everything that is outside the range of MLLW, any HW refracted data points landward of the MLLW land/water interface were classified to class 18 to ensure these HW bathymetric points were not used when MLLW exposed ground points exist in those locations.

Dewberry used algorithms in TerraScan to create the initial ground/submerged topography surface. Dewberry then performed manual editing to review and improve the final topobathy surface. Locations of temporal differences were resolved using the Temporal Difference Decision Tree approved by NOAA. Polygons marking the locations of large temporal differences are provided as part of the deliverables.

All LiDAR data was peer-reviewed. Dewberry's internal QC also included creating void polygons for use during review. All necessary edits were applied to the dataset. GeoCue software was used to update LAS header information, including all projection and coordinate reference system information. The final LiDAR data are in LAS format 1.2 and point data record format 3.

The final classification scheme is as follows:

1-Unclassified

2-Ground

7-Topo Noise

25-Water Column

26-Bathymetric Bottom or Submerged Topography

27-Water Surface

29-Submerged Object

30-International Hydrographic Organization (IHO) S-57 objects

Dewberry then produced the final void layer and final set of DZ orthos using the final ground (2) and submerged topography (26) classes.

All data is then verified by an Independent QC department within Dewberry. The independent QC is performed by separate analysts who do not perform manual classification or editing. The independent QC involves quantitative and qualitative reviews.

The NOAA Office for Coastal Management (OCM) received files in las format. The files contained lidar elevation and intensity measurements along the coast of Puerto Rico. The data were in UTM Zone 19 coordinates and ellipsoid elevations in meters. The data classifications for the data are: 1 - unclassified, 2 - ground, 7 - topo noise, 25 - water column, 26 - bathymetric bottom or submerged topography, 27 - water surface, and 30 - International Hydrographic Organization (IHO) S-57 objects. OCM performed the following processing on the data for Digital Coast storage and provisioning purposes: 1. Eliminated elevation outliers below -100 meters ellipsoid height 2. Converted from UTM Zone 19 to geographic coordinates 3. Sorted by gps time 4. Compressed the data using laszip