2025 NOAA OCS Topobathy Lidar DEM: Thunder Bay NMS (H14138), MI

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Bulk download of data files in UTM Zone 17N NAD83 (2011) meters coordinates and IGLD85 elevations in meters.

Information on the NOAA Office for Coastal Management (OCM)

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 NV5 lidar report.

Link to the BAG, GeoImage, and Reflectance Intensity data available from NCEI.

Lidar data for the NOAA Thunder Bay H14138 Topobathymetric survey was acquired by NV5 using Leica Chiroptera-5 and HawkEye-5 topobathymetric 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-IGLD85 LWD Vertical Units-meters NOAA provided NV5 with a project boundary for the NOAA Thunder Bay Topobathymetric project. The collected lidar data were processed in the field by NV5 to a level that allowed for immediate QA\QC measures to determine proper sensor function and assess the submerged topography coverage. NV5 reviewed all acquired flight lines to ensure complete survey area coverage and positional accuracy of the laser points. NV5 resolved kinematic corrections for the aircraft Global Navigation Satellite System (GNSS) data using static Global Positioning System (GPS) data from Continuously Operating Reference Stations (CORS) utilizing the Online Positioning User Service (OPUS) for precise positioning. Using raster-based QC methods, the output data was reviewed to ensure the refraction correction operated properly. After the resulting data was reviewed to ensure accurate positioning, custom classification algorithms were applied followed by manual classification editing using TerraSolid software packages and NV5’s proprietary LAS Monkey software to meet the contract specified ASPRS classification scheme listed below. Absolute vertical accuracy was assessed using ground survey data compared against the final H14138 dataset. The final lidar point cloud was provided in .LAS 1.4 file format, point record format 6 and delineated into 500 meter x 500 meter tiles and clipped to the 100 meter buffered project boundary. NV5's proprietary software LasMonkey was used to update LAS header information, including projection and coordinate reference system information. The final lidar data are in LAS format 1.4 and point data record format 6. The derived topobathymetric bare earth digital elevation model (DEM) raster mosaics were created from class 2 topographic ground, class 40 bathymetric bottom, and class 43 submerged object classified returns. The final bare earth rasters were provided in Cloud Optimized GeoTIFF format with 1 meter pixel resolution, IGLD85 Low Water Datum elevations, and were delineated into 52 - 5000 meter x 5000 meter DEM tiles clipped to the 100 meter buffered project boundary. A Bathymetric void shapefile was created to restrict interpolation in the final bare earth elevation model in areas of bathymetric voids greater than 9 square meters. The methodology used for the Thunder Bay H14138 product deliverables were further detailed in the NOAA Thunder Bay H14138 Topobathymetric final report. The final classification scheme is as follows: 1- Unclassified 1+Withheld- Edge Clip 1+Overlap+Withheld- Unrefracted Returns from Green Laser 2- Topographic Ground 7+Withheld- Low Noise 18+Withheld- High Noise 40- Bathymetric Bottom (Submerged Topography) 41- Water Surface 42+Synthetic- Synthetic Derived Water Surface 43- Submerged Object 45- Water Column 47+Withheld- Submerged (Bathymetric) Noise

NV5 transformed the vertical datum of the lidar datset from GRS80 ellipsoid to IGLD85 LWD elevations to create the final topobathymetric lidar products and resulting bare earth DEMs. The final bare earth digital elevation model (DEM) rasters were created using a triangulated irregular network (TIN) surface built from class 2 topographic ground, class 40 bathymetric bottom, and class 43 submerged feature classified points. A shapefile delineating bathymetric voids was created to limit the extent of triangulation (interpolation in the TIN) in the final bare earth topobathymetric elevation model to avoid potentially false interpolation across areas without mapped bathymetry. A threshold of 9 square meters was determined to restrict interpolation in areas lacking bathymetric bottom returns. Bathymetric void polygons were developed by calculating the maximum edge lengths of delineated triangles in the TIN surface model built from bathymetric bottom and submerged object classified returns. The maximum edge length that a 9 square meter equilateral triangle can have is 4.56 meters. Any TIN triangles with edge lengths greater than 4.56 meters were delineated into the bathymetric void shapefile and were used to clip out (exclude) interpolation areas from the bare earth DEM. Any TIN triangles with maximum edge lengths less than 4.56 meters were not delineated as a bathymetric void and remain as interpolation in the bare earth DEM.

The final topobathymetric bare earth DEMs were output at 1 meter resolution in GeoTIFF format into 26 - 5000 m x 5000 m tiles. The NOAA H14138 Thunder Bay Topobathymetric Lidar Bare Earth Model rasters were clipped to the extent of the project boundary and were named according to standard NOAA National Geodetic Survey (NGS), Remote Sensing Division naming schematics. (YYYY_{6-digit X coordinate value}e_{7-digit Y coordinate value}n_DEM) YYYY representing the year of project data acquisition and the XY coordinates representing the northwest corner of each respective DEM file.

The NOAA Office for Coastal Management (OCM) received GeoTIFF files from the NOAA Office of Coast Survey. The files were in UTM Zone 17N NAD83 (2011) meters coordinates and the elevations were in Low Water Datum (LWD) IGLD85 meters. The NOAA Great Lakes Low Water Datum (LWD) for Lake Huron is officially set at 176.0 meters IGLD85. In order to convert the data to IGLD85, 176.0 meters was added to each grid node. This was done with gdal_calc.py. The raster files were at a 1 m grid spacing. The GeoTIFF files were copied to NOAA OCM resources and made available for bulk and custom downloads from the NOAA Digital Coast Data Access Viewer (DAV).