2018 AK DGGS Lidar DEM: Chilkat Ridge, Alaska

The State of Alaska Division of Geological & Geophysical Surveys (DGGS) used lidar to produce a digital terrain model (DTM) and digital surface model (DSM) over ridgelines along the Chilkat River just north of Haines, Alaska. The lidar and Global Navigation Satellite System (GNSS) data were collected on November 15-16, 2018, and processed using Terrasolid. This data collection is being released as a Raw Data File with an open end-user license. The complete report and digital data are available from the DGGS website: http://doi.org/10.14509/30224.

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

https://elevation.alaska.gov/

This file was processed to make the data available for custom and bulk download from the NOAA Digital Coast Data Access Viewer (DAV) . The total number of files downloaded and processed was 1.

This dataset includes point cloud data, a 32-bit digital terrain model, and an intensity image covering a study area near the Chilkat Ridge region of southeast Alaska. The data release is one of a series of Alaska Division of Geological & Geophysical Surveys (DGGS) publications to present elevation data. The goal is to provide information for the Alaska Division of Forestry on the ground conditions and tree cover on Chilkat Ridge.

>point_cloud_data: Classified (ASPRS standard) lidar values for all returns; File format: LAS 1.4.

>dtm: DTMs represent surface elevations of ground surfaces, excluding vegetation, bridges, buildings, etc. The DTM is a single-band, 1 meter, 32-bit float GeoTIFF file, with a ground sample distance (GSD) of 15 cm on the ground and 60 cm below dense vegetation. No Data value is set to -3.40282306074e+038.

>dsm: A 2-meter DSM raster was created from the first returns of the laser point cloud. The No Data value is set to -3.40282306074e+038.

>intensity_image: A grayscale image that displays 0-255 grayscale values according to relative reflectivity. The laser intensity image is provided as a 1-meter raster.

The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data 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 or any failure thereof or otherwise. 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 evaluated for this project.

The Root Mean Square Error of the final data layers for the bare earth elevation between the checkpoints and lidar ground points is 8.5 centimeters.

The total area surveyed was approximately 224 km2. This data release is complete and there is no over-collect, except for the aircraft turns that were eliminated from the dataset. There are a few areas where data coverage is limited due to the slow response of the fixed wing aircraft the fast elevation changes along the flight path, e.g., canyons. Void areas for lakes and ponds, which were hydroflattened in the elevation models, were delineated as null data in the intensity rasters.

To evaluate data consistency, ground checkpoints were collected (November 15, 2018) as RTK-GNSS points with a Trimble R8 GNSS receiver. A Trimble R7 GNSS receiver with Zephyr-2 antenna was deployed near the center of the study area and was used as horizontal and vertical control for checkpoint baseline corrections. The checkpoints were compared with the DTM. The comparison showed a 7.1 cm average magnitude difference between the checkpoints and the DTM. The checkpoint differences had a Root Mean Square Error of 8.5 cm and a standard deviation of 8.6 cm.