2019 AK DGGS Lidar: Kotlik, Alaska

The Alaska Division of Geological & Geophysical Surveys (DGGS) used aerial lidar to produce a digital terrain model (DTM), surface model (DSM), and intensity model for the area surrounding the community of Kotlik, Alaska. Detailed bare earth elevation data for the Kotlik area support and inform potential infrastructure development and provide critical information required to assess geomorphic activity. Airborne data were collected on August 17, 2019, and subsequently processed in Terrasolid and ArcGIS. Ground control was collected between August 20-22, 2019, by the Alaska Division of Mining, Land, and Water. This data collection is released as a Raw Data File with an open end-user license. All files can be downloaded free of charge from the Alaska Division of Geological & Geophysical Surveys website (http://doi.org/10.14509/30561).

The NOAA Office for Coastal Management (OCM) downloaded this data set from this AK DGGS site:

https://elevation.alaska.gov/

These files were processed to the NOAA Digital Coast Data Access Viewer (DAV) and AWS S3. The total number of files downloaded and processed was 215.

During processing, it was noted that there are lidar points that fall in water areas and on structures that are classified as ground.

In addition to the lidar point data, the bare earth Digital Elevation Model (DEM) data at a 0.5 meter grid spacing, created from the lidar point data are also available from the NOAA Digital Coast. Links to these data are provided in the URL section of this metadata record.

Detailed bare earth elevation data for the Kotlik area support and inform potential infrastructure development and provide critical information required to assess geomorphic activity. This data release is one of a series of DGGS publications to present elevation data.

>classified point cloud data: Classified point cloud data is provided in this collection in compressed .laz format. Data are classified in accordance with ASPRS 2014 guidelines and contain return and intensity information. The average pulse spacing was 24.8 cm and the average density was 16.25 pts/m^2. Elevation surfaces interpolated from areas with a point density of fewer than 4pts/m2 were classified as nodata.

>digital surface model: The DSM represents surface elevations, for example, heights of vegetation, buildings, bridges, etc. The DSM is a single band, 32-bit GeoTIFF file, with a ground sample distance of 0.5 meters. No Data value is set to -3.40282306074e+038. >digital terrain model: The DTM represents surface elevations of ground surfaces, excluding vegetation, bridges, buildings, etc. The DTM is a single-band, 32-bit float GeoTIFF file, with a ground sample distance of 0.5 meters. No Data value is set to -3.40282306074e+038.

>lidar intensity image: The lidar intensity image describes the relative amplitude of reflected signals, contributing to the point cloud. Lidar intensity is largely a function of scanned object reflectance in relation to the signal frequency, is dependent on ambient conditions, and is not necessarily consistent between separate scans. The intensity image is a single-band, 32-bit float GeoTIFF file with a ground sample distance of 0.5 meters. No Data value is set to -3.40282306074e+038 (32-bit, floating-point minimum).

>hydro-enforced digital terrain model: The hydro-enforced DTM represents bare earth surfaces which have undergone a selective "flattening" process, where elevation values for any hydrologic features, as well as any hydrologic obstacles (bridges, culverts, etc.), are replaced with neighboring pixel values. The hydro-enforced DTM is a single-band, 32-bit float GeoTIFF file, with a ground sample distance of 0.5 meters. No Data value is set to -3.40282306074e+038.

The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity, whether from the use of the electronic services or products, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requestor or anyone else exceed the fee paid for the electronic service or product.

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

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.

Horizontal accuracy was not measured for this collection.

Forty-two bare earth checkpoints were used to determine the non-vegetated vertical accuracy (NVA) of the point cloud ground class, using a tin-based approach. Project NVA was calculated to have a root mean square error (RMSE) of 8.2 cm. Using the same approach, fifty-two vegetated points were used to determine the vegetated vertical accuracy (VVA) of the point cloud ground class. Project VVA was evaluated at 25.2 cm RMSE, with an average elevation difference of +21.2 cm.

This data release is complete, and there is no over collect except for the aircraft turns that were eliminated from the dataset.

The data quality is consistent throughout the survey. The accompanying report provides additional detail regarding tests used to determine data fidelity.

Data were collected by the Alaska Division of Geological and Geophysical Surveys (AK DGGS). OCM downloaded the data from the Alaska DGGS Elevation Portal and processed the data to be available for custom and bulk download from the NOAA Digital Coast Data Access Viewer (DAV).