2021 USACE NCMP Topobathy Lidar DEM: Alaska

Original Data: These files contain rasterized topobathy lidar elevations generated from data collected by the Coastal Zone Mapping and Imaging Lidar (CZMIL) system. CZMIL integrates a lidar sensor with simultaneous topographic and bathymetric capabilities, a digital camera and a hyperspectral imager on a single remote sensing platform for use in coastal mapping and charting activities. Native lidar data is not generally in a format accessible to most Geographic Information Systems (GIS). Specialized in-house and commercial software packages are used to process the native lidar data into 3-dimensional positions that can be imported into GIS software for visualization and further analysis.

The original data's horizontal positions were provided in UTM Zones 2, 3, 4, 5, 7, and 8 referenced to the North American Datum of 1983 National Adjustment of 2011 (NAD83 (2011)). Vertical positions were in NAVD88 (Geoid12B) heights in meters. The 3-D position data are sub-divided into a series of LAS files, which are tiled into 1-km by 1-km boxes defined by the Military Grid Reference System. The following list indicates which blocks of data fall into each UTM Zone:

1. UTM Zone 2N - Blk 21215 Gambell, Blk 21216 Savoonga

2. UTM Zone 3N - Blk 21207 Point Lay, Blk 21208 Point Hope, Blk 21209 Point Hope, Blk 21210 Kivalina, Blk 21211 Cape Blossom, Blk 21212 Cape Blossom, Blk 21213 Shishmaref, Blk 21217 Nome, Blk 21218 Elim, Blk 21225 Cold Bay, Blk 21226 Cold Bay, Blk 21227 Akun

3. UTM Zone 4N - Blk 21204 Elson, Blk 21205 Utkiagvik, Blk 21206 Wainwright, Blk 21219 Shaktoolik, Blk 21228 Unalakleet

4. UTM Zone 5N - Blk 21220 Ninilchik, Blk 21221 Homer

5. UTM Zone 7N - Blk 21201 Kaktovik

6. UTM Zone 8N - Blk 21251 Gustavus, Blk 21252 Hoonah, Blk 21253 Tenakee, Blk 21254 Angoon, Blk 21255 Kake, Blk 21256 Petersburg, Blk 21257 Wrangell, Blk 21258 Whale Pass, Blk 21259 Coffman, Blk 21260 Nautaki, Blk 21261 Klawock, Blk 21262 Craig, Blk 21263 Thorne Bay, Blk 21264 Kasan, Blk 21265 Hydaburg

The data were provided to the NOAA Office for Coastal Management (OCM) by the USACE Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX) to make the data publicly available for bulk and custom downloads from the NOAA Digital Data Access Viewer (DAV).

In addition to these bare earth Digital Elevation Model (DEM) data, the lidar point data that these DEM data were created from, are also available from the NOAA Digital Coast. A link to the lidar point data is provided in the URL section of this metadata record. DEMs at a 1 meter grid spacing, created from all classifications, are available by request at coastal.info@noaa.gov.

This data was collected by the USACE in support of the National Coastal Mapping Program to assess changes in elevation above and below water along the coast of Alaska.

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the Office for Coastal Management or its partners.

Data is available online for bulk and custom downloads.

None

These data depict the heights at the time of the survey and are only accurate for that time. Acknowledgement of the Joint Airborne Lidar Bathymetry Technical Center of eXpertise (JALBTCX) would be appreciated in any publications or derived products. The data herein, including but not limited to geographic data, tabular data, analytical data, electronic data structures or files, are provided "as is" without warranty of any kind, either expressed or implied, or statutory, including, but not limited to, the implied warranties or merchantability and fitness for a particular purpose. The entire risk as to the quality and performance of the data is assumed by the user. No guarantee of accuracy is granted, nor is any responsibility for reliance thereon assumed. In no event shall the U.S. Army Corps of Engineers, Mobile District Office, Spatial Data Branch be liable for direct, indirect, incidental, consequential or special damages of any kind, including, but not limited to, loss of anticipated profits or benefits arising out of use of or reliance on the data. The Spatial Data Branch does not accept liability for any damages or misrepresentation caused by inaccuracies in the data or as a result of changes to the data caused by system transfers or other transformations or conversions, nor is there responsibility assumed to maintain the data in any manner or form.

These data have been developed from the best available sources. Although efforts have been made to ensure that the data are accurate and reliable, errors and variable conditions originating from physical sources used to develop the data may be reflected in the data supplied. Users must be aware of these conditions and bear responsibility for the appropriate use of the information with respect to possible errors, scale, resolution, rectification, positional accuracy, development methodology, time period, environmental and climatic conditions and other circumstances specific to these data. The user is responsible for understanding the accuracy limitations of the data provided herein. The burden for determining fitness for use lies entirely with the user. The user should refer to the accompanying metadata notes for a description of the data and data development procedures.

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

Every effort within operational constraints was made to acquire data that meets specifications as outline in this project's Statement of Work. Per flight block, elevations in areas of swath overlap are internally consistent and meet CZMIL specifications. Anomalous high and/or low elevation values have been removed, and point cloud classification algorithms have been validated via manual review and QC. Temporal differences in elevation exist in areas of active near shore processes from the dune to the depth of closure. JALBTCX conducts operations in a manner to ameliorate temporal differences, to include the collection of entire flight blocks within single missions. For a given flight block, it's adjacent flight blocks are captured within 3 days as weather and airspace permit.

CZMIL topographic data - Compiled to meet 1 m horizontal accuracy at 95% confidence level. CZMIL bathymetric data - Compiled to meet 3.5 + 0.05d m horizontal accuracy at 95% confidence level, d is depth.

CZMIL topographic data - Compiled to meet 20 cm vertical accuracy at 95% confidence level (10 cm RMSE). CZMIL bathymetric shallow FOV data - Compiled to meet SQRT((0.25^2) +((0.0075d)^2)) m vertical accuracy at 95% confidence level, d is depth. CZMIL bathymetric deep FOV data - Compiled to meet SQRT((0.30^2) +((0.013d)^2)) m vertical accuracy at 95% confidence level, d is depth.

Planned data coverage for this dataset includes the shoreline along the coast of Alaska. Lidar and imagery data acquisition was focused on a 1500 meter swath of the shoreline that generally extends from the shoreline onshore 500 meters and from the shoreline offshore to 1000 meters or laser extinction, whichever occurs first. The planned point spacing is 70 centimeters on land and in shallow water. In deeper water the planned point spacing is 2 meters. Gaps or data holidays exist in the bathymetric portion of the data coverage due to a number of operational and environmental conditions, including by not limited to, active surf, low-reflectivity bottom substrate materials and turbidity in the water column. Please see the Report of Survey for additional details.

Every effort within operational constraints was made to achieve the intended data coverage and planned point densities.

JALBTCX evaluates final data coverage using techniques that are common to the lidar industry. These techniques are performed in a 3D environment for visual review of the final data coverage and verification of data alongside lidar waveforms and imagery collected concurrent with the lidar. Data reviewers perform checks to verify (1) extreme high and/or low elevation values have been invalidated, (2) elevations in areas of swath overlap are internally consistent, (3) binned standard deviation values meet CZMIL specifications, (4) point cloud classifications are valid, and (5) CZMIL processing modes are valid.

Data is backed up to cloud storage.

CZMIL data is processed from raw lidar waveforms to point clouds using the CZMIL HydroFusion software package. Point clouds are then classified and edited in industry-standard software packages. Derivative data products are generated through the application of gridding and contouring algorithms in a GIS environment. The data processing workflow, including software packages, algorithms and parameters are provided in detail, herein this metadata as Process Steps.

The NOAA Office for Coastal Management (OCM) received the data from the USACE Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX). NOAA OCM processed the data to the NOAA Digital Coast Data Access Viewer (DAV) to make the data publicly available for bulk and custom downloads.