2018 AK DGGS Lidar DEM: Turnagain Pass, AK

The State of Alaska Division of Geological & Geophysical Surveys (DGGS) used lidar to produce a digital terrain model (DTM) and digital surface model (DSM) of Turnagain Pass, southcentral Alaska, during snow-free ground conditions. This dataset includes point cloud data, a 32-bit digital terrain model and digital surface model, and an intensity image covering Turnagain Pass located southeast of Anchorage within the Chugach National Forest on the Kenai Peninsula in southcentral Alaska. The lidar and Global Navigation Satellite System (GNSS) data were collected on September 2, 2018, and processed using Terrasolid. 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/10.14509/30567).

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

https://elevation.alaska.gov/

These 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.

The goal of the survey is to provide snow-free surface elevations for deriving snow depth distribution models with repeat surveys during snow-covered surface conditions. This data release is one of a series of DGGS publications to present elevation data.

>classified point cloud data: The ground-classified point cloud has an average point spacing of 43 cm (43 cm on the ground in open alpine areas and 32 cm below dense vegetation in the valley) and an average point density of 2.3 points per square meter.

>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 50 cm. No Data value is set to -3.40282306074e+038.

>digital terrain model: The DTM represents 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 50 cm. No Data value is set to -3.40282306074e+038.

>lidar intensity image: The intensity image represents the return strengths of the first return laser pulses. The intensity image is a single band, 32-bit GeoTIFF file, with a ground sample distance of 50 centimeter and normalized to the 0-255 range. No Data value is set to -3.40282306074e+038.

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 measured for this collection.

The elevation values of 62 ground control points were compared with the elevation values of the lidar points classified as ground points. The average vertical offset was corrected with a z-transformation. Fifteen check points were used to determine the final accuracy of the z-transformed lidar point cloud. The lidar point cloud had a vertical offset of +2.2 cm (root mean squared error [RMSE] 3.6 cm) compared to ground control, therefore a vertical transformation of -2.2 cm was applied to the lidar point cloud. Relative accuracy for this dataset was evaluated as the interswath overlap consistency and was measured at 1.2 cm RMSE.

The final accuracy assessment showed a mean vertical offset of -0.3 cm and RMSE of 3.3 cm.

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 laser range exceedance, which is related to the slow response of the fixed wing aircraft to the fast elevation change along the flight path. All low points and air points were eliminated from the dataset.

Relative accuracy for this dataset was evaluated as the interswath overlap consistency and was measured at 1.2 cm RMSE.

Data is backed up to tape and to cloud storage.

The data were collected for the Alaska Division of Geological and Geophysical Surveys (DGGS) and made available on the AK DGGS Elevation Portal (https://elevation.alaska.gov/). The NOAA Office for Coastal Management (OCM) downloaded the data from this site to make the data available for custom downloads from the NOAA Digital Coast Data Access Viewer and for bulk downloads from https.