Lidar-derived surface elevation data for Dickason Highlands, Southcentral Alaska, collected August 14, 2024

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Frequently anticipated questions:


What does this data set describe?

Title:
Lidar-derived surface elevation data for Dickason Highlands, Southcentral Alaska, collected August 14, 2024
Abstract:
Lidar-derived surface elevation data for Dickason Highlands, Southcentral Alaska, collected August 14, 2024, Raw Data File 2025-12, releases classified point cloud, digital terrain model (DTM), and an intensity model of of Dickason Highlands, Southcentral Alaska, during leaf-on conditions. The survey provides surface elevations for detailed bedrock and surficial geologic mapping and for potentially active fault investigations. Ground control data were collected July 20, 2024, and aerial lidar data were collected August 14, 2024, and subsequently merged and processed using a suite of geospatial processing software. This data collection is 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/10.14509/31536).
Supplemental_Information:
boundaries:    A boundary, also known as an Area of Interest (AOI) or border, that defines the area covered by the data. Also includes footprints for tiled data.	
classified_points:    Classified point cloud data are provided in LAZ format. Data are classified following ASPRS 2019 guidelines and contain return and intensity information. For classified ground points, the average point density is 0.788 pts/m2, and the average spacing is 112.6 cm.	
dsm:    The DSM represents surface elevations, including heights of vegetation. The DSM is a single-band, 32-bit GeoTIFF file of 1-m resolution. No Data value is set to -3.40282306074e+38 (32-bit, floating-point minimum).	
dtm:    The DTM represents bare earth or snow surface elevations, excluding vegetation. The DTM is a single-band, 32-bit GeoTIFF file of 1-m resolution. No Data value is set to -3.40282306074e+38.	
lidar_intensity:    The lidar intensity image describes the relative amplitude of reflected signals contributing to the point cloud. Lidar intensity is (1) primarily a function of scanned object reflectance in relation to the signal frequency, (2) dependent on ambient conditions, and (3) not necessarily consistent between separate scans. The intensity image is a single-band, 32-bit GeoTIFF file of 1-m resolution. No Data value is set to -3.40282306074e+38.
  1. How might this data set be cited?
    Zechmann, J.M., and Salisbury, J.B., 2025, Lidar-derived surface elevation data for Dickason Highlands, Southcentral Alaska, collected August 14, 2024: Raw Data File RDF 2025-12, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 10 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -151.910323
    East_Bounding_Coordinate: -151.597528
    North_Bounding_Coordinate: 61.923941
    South_Bounding_Coordinate: 61.708764
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 20-Jul-2024
    Ending_Date: 14-Aug-2024
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a raster data set.
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 5
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -153
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.000000
      False_Northing: 0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest .00000001
      Ordinates (y-coordinates) are specified to the nearest .00000001
      Planar coordinates are specified in Meters
      The horizontal datum used is NAD83 (2011).
      The ellipsoid used is GRS 80.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257222101.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: NAVD88, GEOID12B
      Altitude_Resolution: 0.500000
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:
      Explicit elevation coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    boundaries
    A boundary, also known as an Area of Interest (AOI) or border, that defines the area covered by the data. Also includes footprints for tiled data. (Source: DGGS)
    classified_points
    Classified point cloud data are provided in LAZ format. Data are classified following ASPRS 2019 guidelines and contain return and intensity information. For classified ground points, the average point density is 0.788 pts/m2, and the average spacing is 112.6 cm. (Source: DGGS)
    dsm
    The DSM represents surface elevations, including heights of vegetation. The DSM is a single-band, 32-bit GeoTIFF file of 1-m resolution. No Data value is set to -3.40282306074e+38 (32-bit, floating-point minimum). (Source: DGGS)
    dtm
    The DTM represents bare earth or snow surface elevations, excluding vegetation. The DTM is a single-band, 32-bit GeoTIFF file of 1-m resolution. No Data value is set to -3.40282306074e+38. (Source: DGGS)
    lidar_intensity
    The lidar intensity image describes the relative amplitude of reflected signals contributing to the point cloud. Lidar intensity is (1) primarily a function of scanned object reflectance in relation to the signal frequency, (2) dependent on ambient conditions, and (3) not necessarily consistent between separate scans. The intensity image is a single-band, 32-bit GeoTIFF file of 1-m resolution. No Data value is set to -3.40282306074e+38. (Source: DGGS)

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    This work was funded by State of Alaska grant number G23AC00584-00. We thank Clearwater Air for their expertise and contribution to these data products and Melanie Werdon for her review.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.

Why was the data set created?

The survey provides surface elevations for detailed bedrock and surficial geologic mapping and for potentially active fault investigations.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 20-Jul-2024 (process 1 of 3)
    Ground survey - Ground control points were collected on July 20, 2024. We deployed a Trimble R10-2 GNSS base receiver on a ridgetop southeast of Dickason Mountain, with coordinates of 61 degrees 49 minutes 51.0962 seconds N and 151 degrees 47 minutes 21.35069 seconds W, at 1,049.01 m elevation, and surveyed points with a rover Trimble R10-2 GNSS receiver/Mesa controller within the survey area. We collected 81 ground control points and checkpoints in low scrub, medium, tall, and bare earth vegetation. For a GNSS base station occupation to later correct lidar survey flightlines, we set up a Trimble R10-2 at the Skwentna Airstrip. The base station collected points at a rate of 5 Hz from 10:35 am to 7:50 pm (AKT) on August 14, 2024.
    Date: 14-Aug-2024 (process 2 of 3)
    Aerial survey - DGGS used a Riegl VUX1-LR22 laser scanner with a global navigation satellite system (GNSS) and Northrop Grumman LN-200C inertial measurement unit (IMU) integrated by Phoenix LiDAR Systems. The sensor can collect a maximum of 1,500,000 points per second at a range of 230 m or a minimum of 50,000 points per second at 1,000 m (ranges assume greater than 20 percent natural reflectance). The scanner operated with a pulse refresh rate of 400,000 pulses per second at a scan rate of 100 revolutions per second over heavily vegetated areas or a pulse refresh rate of 50,000-200,000 pulses per second at a scan rate of 25-50 revolutions per second over alpine areas. We used a Cessna 180 Skywagon fixed-wing platform to survey from an elevation of approximately 100-300 m above ground level, at a ground speed of approximately 40 m/s, and with a scan angle set from 80 to 280 degrees. The total survey area covers approximately 189.4 km2. The survey area was accessed by air from Skwentna Airstrip.
    Date: 2024 (process 3 of 3)
    Dataset processing - We processed point data in Spatial Explorer for initial filtering and multiple-time-around (MTA) disambiguation. MTA errors, corrected in this process, result from ambiguous interpretations of received pulse time intervals and occur more frequently with higher pulse refresh rates. IMU and GNSS data were processed in Inertial Explorer, and flightline information was integrated with the point cloud in Spatial Explorer. We calibrated the point data at an incrementally precise sensor movement and behavior scale, incorporating sensor velocity, roll, pitch, and yaw fluctuations throughout the survey. For the lidar data collection, the average pulse density is 11.3 pulses/m2, and the average pulse spacing is 29.8 cm. We created a macro (an ordered list of point classification commands tailored to this dataset) in Terrasolid software and classified points in accordance with the American Society for Photogrammetry & Remote Sensing (ASPRS) 2019 guidelines (ASPRS, 2019). Once classified, we applied a geometric transformation and converted the points from ellipsoidal heights to GEOID12B (Alaska) orthometric heights. Raster products were derived from the point cloud in ArcGIS Pro. A 1-m DSM was interpolated from ground and vegetation classes using a binning method and maximum values. A 1-m DTM was interpolated from all ground-class returns with a binning method and minimum values. We also produced a 1-m intensity image using average ArcGIS Pro binning with no normalizations or corrections.
  3. What similar or related data should the user be aware of?
    Salisbury, J.B., 2019, Earthquakes in Alaska: Information Circular IC 73, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 p
    Salisbury, J.B., 2019, Living with earthquakes in Alaska: Information Circular IC 77, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 p

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    Not applicable
  2. How accurate are the geographic locations?
    Horizontal accuracy was not measured for this collection.
  3. How accurate are the heights or depths?
    We measured a mean elevation offset of +57.9 cm between 24 control points and the point cloud. This offset was reduced to -0.8 cm in nonvegetated areas and -0.8 cm in vegetated areas by applying a constant vertical correction to the lidar point data. We used 22 checkpoints to determine the nonvegetated vertical accuracy and 35 checkpoints to determine the vegetated vertical accuracy of the point cloud ground class, using a Triangulated Irregular Network (TIN) approach. The project nonvegetated vertical accuracy has a root mean square error (RMSE) of 12.4 cm and the vegetated vertical accuracy has an RMSE of 17.6 cm. We evaluated the relative accuracy for this dataset as the interswath overlap consistency and measured it at 8.1 cm RMSE.
  4. Where are the gaps in the data? What is missing?
    This is a full-release dataset.
  5. How consistent are the relationships among the observations, including topology?
    DGGS visually inspected the data for errors such as shifts, seamline mismatches, and water noise overlapping land. Data quality is consistent throughout the survey, save for gaps over areas of snow or in very thick vegetation between flightlines. There was no over-collect.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express 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.
  1. Who distributes the data set? (Distributor 1 of 1)
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set? RDF 2025-12
  3. What legal disclaimers am I supposed to read?
    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.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 25-Jun-2025
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK
USA

(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov
Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.50 on Wed Jun 25 17:41:29 2025