2019 AK DGGS Lidar DEM: Speel Arm, Alaska

This metadata record describes the Speel Arm, Alaska digital elevation model hosted on the Digital Coast by NOAA OCM. This data was retrieved from the Alaska Elevation portal, and the following information accompanied the dataset and is left for greater context.

The Alaska Division of Geological & Geophysical Surveys (DGGS) used aerial lidar to produce a classified point cloud, digital surface model (DSM), digital terrain model (DTM), and intensity model of a mountain slope adjacent to Speel Arm near Port Snettisham, Southeast Alaska, during near snow-free ground conditions on September 7, 2019. The survey provides snow-free surface elevations for deriving snow depth distribution models with repeat surveys during snow-covered conditions. Aerial lidar and ground control data were collected on September 7, 2019, and subsequently processed in a suite of geospatial processing software. These products are released as a Raw Data File with an open end-user license. All files can be downloaded from the Alaska Division of Geological & Geophysical Surveys website (http://doi.org/10.14509/30730).

The survey provides snow-free surface elevations for deriving snow depth distribution models with repeat surveys during snow-covered conditions. The goal of this project and related works is to improve understanding of the complex interaction between the changing cryosphere, snow avalanches, natural resources, and people in their natural and built environments.

The following products may be available through the Alaska Elevation Portal. NOAA OCM has not downloaded or reviewed any product other than the digital surface model this metadata record represent. The following information is left for contextual information regarding the construction of this dataset.

>classified point cloud data: Classified point cloud data are provided in compressed LAZ format. Data are classified in accordance with ASPRS 2014 guidelines and contain return and intensity information. The average pulse spacing is 3 cm and the average density is 48.5 pts/m2.

>digital surface model: The DSM represents surface elevations including heights of vegetation, buildings, powerlines, etc. The DSM is a single band, 32-bit GeoTIFF file of 50-centimeter resolution. No Data value is set to -3.40282306074e+38 (32-bit, floating-point minimum).

>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 of 50-centimeter resolution. No Data value is set to -3.40282306074e+38.

>lidar intensity image: The lidar intensity image describes the relative amplitude of reflected signals contributing to the point cloud. 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 of 50-centimeter resolution. No Data value is set to -3.40282306074e+38.

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 or 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.

We did not measure horizontal accuracy for this collection.

We measured a mean offset of -21.3 cm between 39 control points and the point cloud (appendix 1). We reduced this offset to -0.3 cm by performing a vertical transformation of the lidar point data. We used 12 check points to determine the non-vegetated vertical accuracy (NVA) of the point cloud ground class using a Triangulated Irregular Network (TIN) approach. We calculated the project NVA to have a root mean square error (RMSE) of 18.6 cm (appendix 2). We evaluated the relative accuracy for this dataset as the interswath overlap consistency and measured it at a 1.8 cm RMSE.

This data release is complete.

This data release is complete, and there was no over collect except for aircraft turns that were eliminated from the dataset. The data quality is consistent throughout the survey, apart from a sliver-shaped area in the center of the survey area where lack of overlap between the flightlines resulted in a gap in the lidar coverage. When we built the DSM and DTM in ArcGIS, we interpolated this area using Natural Neighbor void filling.