Seafloor Elevation Change From 2016 to 2017 at Looe Key, Florida Keys-Impacts From Hurricane Irma (version 2.0)

Step 1: The original 2016 NOAA NGS Topography Lidar DEM: Florida Keys Outer Reef Block 01 tagged image file format (TIFF) DEM was downloaded from https://inport.nmfs.noaa.gov/inport/item/48373 using the "Customized Download" capability of NOAA’s DigitalCoast website. The data were downloaded with the following parameters: UTM Zone: Zone 17 Range 084W-078W; Horizontal Datum: NAD83; Horizontal Units: Meters; Vertical Datum: NAVD88; Vertical Units: Meters; File Format: Tiff 32-bit Float; Bin Method: TIN; Bin Size: 1.0; Bin Units: Meters; Data Classification: Bathymetric Lidar Points; Data Returns: Any Points; Ancillary Data: No Ancillary Data; and Geoid Name: GEOID12B. Using VDatum version 3.9, a publicly available software from NOAA (https://vdatum.noaa.gov/), the lidar TIFF was transformed from the North American Datum of 1983 (NAD83) to NAD83 (2007) horizontal datum, the vertical datum and geoid model were kept the same.

Step 2: The original 2017 Looe Key XYZ multibeam data were downloaded from https://coastal.er.usgs.gov/data-release/doi-P9P2V7L0. Using VDatum v.3.9, the data were transformed from their native WGS84 horizontal datum and ellipsoid heights to the NAD83 (2007) horizontal datum and North American Vertical Datum 1988 (NAVD88) vertical datum, applying the GEOID12B model. The transformed XYZ points were loaded into Blue Marble Global Mapper version 18.2 and gridded using the "Create Elevation Grid from 2D Vector/Lidar Data" tool in the Analysis menu. Grid spacing was manually set to 1 m for the X- and Y-axes and the 'Elevation Grid No Data Distance Criteria' was set to 3.0. The resultant 2017_LooeKey_Multibeam_Clip DEM was exported as a TIFF with the following parameters: 32-bit floating point samples, Sample Spacing of 1 m for both X- and Y-axes, Always Generate Square Pixels, LZW Compression, Generate TFW (World) File, and Generate PRJ File.

Step 3: Using Esri ArcGIS Desktop Advanced version 10.6, footprints of the original 2016 lidar and 2017 multibeam TIFF's were created with the "Reclassify (Spatial Analyst)" tool in ArcToolbox. To create each raster file, all old data values were replaced with 1 and the 'No Data' value with 0 to create the raster files. Then, the "Raster to Polygon (Conversion)" tool was used to create a footprint of the original lidar and original multibeam data by converting the raster files to polygon shape (SHP) files.

Step 4: Due to edge effects, additional areas were removed from the 2016 lidar. Polygons encompassing the regions of error were created using Global Mapper 18.2 with the "Digitizer" tool and the 'Create Area/Polygon Features'. The polygons were exported as a single SHP file, see Lidar_EdgeEffects_Removed_Areas SHP file.

Step 5: A polygon SHP file of the geometric intersection between the lidar and multibeam was created with the "Intersect (Analysis)" tool by adding the lidar and multibeam footprint SHP files (Step 4) as 'Input features'. Additional areas were deleted from the Intersect_footprint SHP file because of lidar edge effects using the "Erase (Analysis)" tool by specifying the Intersect_footprint SHP file as the 'Input features' and the Lidar_EdgeEffects_Removed_Areas SHP file as the 'Erase Features'. Then, the lidar and multibeam TIFF's (Step 1, 2) were clipped to the extent of the Intersect_footprint SHP file using the "Clip (Data Management)" tool by specifying the lidar or multibeam TIFF as the 'Input Features' and the Intersect_footprint SHP file as the 'Clip Features,' creating the 2016_LooeKey_Lidar_Clip TIFF and the 2017_LooeKey_Multibeam_Clip TIFF.

Step 6: A 2-m grid was created using the "Create Fishnet (Data Management)" tool with the following parameters: Template extent: Intersect_footprint SHP file (Step 5); Cell size width: 2; Cell size height: 2; Number of Rows: left blank, Number of Columns: left blank; Geometry type: POLYLINE and box checked for 'Create Label Points'. The 2-m grid label points SHP file was clipped to the extent of the Intersect_footprint SHP file using the "Clip (Analysis)" tool by specifying the 2-m grid label points SHP file as the 'Input features' and the Intersect_footprint SHP file as the 'Clip features.' XY coordinates were added to the 2-m grid SHP file using the "Add XY Coordinates (Data Management)" tool, to create the 2m_grid point SHP file.

Step 7: Values from the 2016_LooeKey_Lidar_Clip TIFF (Step 5) and 2017_LooeKey_Multibeam_Clip TIFF (Step 5) were extracted at the location of the 2m_grid points using the "Extract Values to Points (Spatial Analyst)" tool by specifying the 2m_grid point SHP file as the 'Input point features' and the 2016_Lidar_Clip TIFF as the 'Input', creating the Lidar_Extract_Points SHP file. This step was repeated with the Lidar_Extract_Points SHP file as the 'Input point features' and the 2017_LooeKey_Multibeam_Clip TIFF as the 'Input', creating the LooeKey_IntersectPoints SHP file.

Step 8: The elevation difference (Diff_m) between the multibeam (RASTERVALU) and the lidar data (RASTERVA_1) were calculated by adding a field to the attribute table of the LooeKey_IntersectPoints SHP file using the "Field Calculator" and the expression Diff_m = [RASTERVALU] – [RASTERVA_1].

Step 9: The original Unified Florida Reef Tract Map version 2.0 SHP file was downloaded from http://ocean.floridamarine.org/IntegratedReefMap/UnifiedReefTract.htm. Using Esri ArcGIS, the original habitat SHP file was modified using the "Clip (Analysis)" tool to clip the habitat SHP file to the extent of the Intersect_footprint SHP file (Step 4) by specifying the habitat SHP file as the 'Input Features' and the Intersect_footprint SHP file as the 'Clip Features', creating the LooeKey_Habitat_Clip. Using the "Select by Attribute" tool, individual habitat SHP files were created from the LooeKey_Habitat_Clip SHP file using the "Select by Attribute" tool to select one ClassLv2 habitat and exporting as a separate SHP file.

Step 10: Elevation change statistics were determined by habitat type using the XYZ points from the LooeKey_IntersectPoints SHP file. The "Select Layer by Location (Data Management)" tool was used to extract points within or on the boundary of a specific habitat type by using the following parameters: Input Feature Layer: LooeKey_IntersectPoints; Relationship: INTERSECT; Selecting Features: Habitat SHP file; Search Distance: left blank; and Selection type: NEW_SELECTION. An ArcMap model was created to automate the process, because these steps had to be repeated for 10 habitat types. Elevation change statistics from Looe Key were compiled by habitat type into a comma separated values (CSV) file using Microsoft Excel 2016, see LooeKey_Elevation_Statistics.csv.

Step 11: An elevation change surface model was created using the "Create TIN (3D Analyst)" tool by specifying the LooeKey_IntersectPoints SHP file (Step 7) as the 'Input Feature Class', Diff_m as the 'Height Field' and Mass_Points as the 'Type', creating the Intersect_TIN file. Then, the Intersect_TIN file was delineated using the "Delineate TIN Data Areas (3D Analyst)" tool by specifying the Intersect_TIN as the 'Input TIN', a 'Maximum Edge Length' of 2.828428 (hypotenuse of a 2-m grid) and the 'Method' set to ALL. The delineated Intersect_TIN was clipped to the extent of the Intersect_footprint SHP file (Step 5) using the "Edit TIN (3D Analyst)" tool with the following parameters: Input TIN: Intersect_TIN; Input Features Class: Intersect_footprint SHP file; Height Field: None, Tag Field: None; and Type: Hard clip.

Step 12: In addition to elevation-change statistics, volume-change statistics per habitat type were calculated using the final TIN (Step 10). Surface volume changes were calculated for four cases using the "Surface Volume (3D Analyst)" tool. To calculate the net erosion lower limit (case 1) the 'Reference Plane' was set to BELOW and the 'Plane Height' set to -0.212 m. For the net erosion upper limit (case 2) the 'Reference Plane' was set to BELOW and the 'Plane Height' set to 0 m. For the net accretion lower limit (case 3) the 'Reference Plane' was set to ABOVE and the 'Plane Height' was set to 0.212 m. For the net accretion upper limit (case 4) the 'Reference Plane' was set to ABOVE and the 'Plane Height' was set to 0 m. A 0.212 m threshold was determined by vertical error analysis using the uncertainties reported in the metadata of the original lidar (0.15 m) and multibeam (0.15 m) products to calculate the Root Mean Square Error (RMSE) of 0.212 m. Minimum net volume was calculated by summing results from cases 1 and 3. Maximum net volume was calculated by summing results from cases 2 and 4. Area normalized volume change lower limit was calculated by dividing the minimum net volume change for each habitat by the habitat's total area. The area normalized volume change upper limit was calculated by diving the maximum net volume for each habitat by the habitat's total area. An ArcMap model was created to automate the process, because these steps had to be repeated for 10 habitat types. Volume change statistics from Looe Key were compiled by habitat type in CSV format using Microsoft Excel 2016, see LooeKey_Volume_Statistics.csv.

The elevation and volume statistics files and elevation change points SHP file were revised in July 2020 and version 2.0 of the data release was created. Using ArcMap version 10.6, points with 'No Data' were removed from the LooeKey_IntersectPoints SHP file using the "Select by Attribute" tool to select points from the attribute table where the RASTERVALU (multibeam) or the RASTERVA_1 (lidar) equaled -9999. The "Editor Toolbox" was used to delete a total of 2,548 points prior to the final file being saved as, LooeKey_IntersectPoints_v2 SHP file. The elevation and volume statistics were recalculated using the updated LooeKey_IntersectPoints_v2 SHP file, creating the LooeKey_Elevation_Statistics_v2.csv and LooeKey_Volume_Statistics_v2.csv files.