Lidar-derived elevation data for Wrangell Island, Southeast Alaska, collected November 28-29, 2023

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Frequently anticipated questions:


What does this data set describe?

Title:
Lidar-derived elevation data for Wrangell Island, Southeast Alaska, collected November 28-29, 2023
Abstract:
Lidar-derived elevation data for Wrangell Island, Southeast Alaska, collected November 28-29, 2023, Raw Data File 2024-1, provides an aerial lidar derived classified point cloud, digital surface model (DSM), digital terrain model (DTM), and intensity model of slopes above the Zimovia Highway on Wrangell Island, Southeast Alaska, during leaf-off conditions (cover figure). The survey provides snow-free surface elevations for use in landslide hazard assessment following a November 20, 2023, debris flow that occurred near Milepost 11 of the Zimovia Highway and tragically claimed the lives of six people. Ground control data were collected June 26-30, 2023 (Zechmann and others, 2023), and aerial lidar data were collected November 28-29, 2023, 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/10.14509/31106).
Supplemental_Information:
boundaries:    A boundary, also known as an Area of Interest (AOI) or border, that defines the area covered by the 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 all ground points, the average point spacing is 49.0 cm, and the average density is 4.16 pts/m2. 	
dsm:    The DSM represents surface elevations, including heights of vegetation, buildings, powerlines, bridge decks, etc. The DSM is a single-band, 32-bit GeoTIFF file of 50 cm resolution. No Data value is set to -3.40282306074e+38 (32-bit, floating-point minimum).	
dtm:    The DTM represents bare earth elevations, excluding vegetation, bridge decks, buildings, etc. The DTM is a single-band, 32-bit GeoTIFF file of 50 cm 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, 16-bit unsigned GeoTIFF file of 50-cm resolution. No Data value is set to 0.
  1. How might this data set be cited?
    Zechmann, J.M., Wikstrom Jones, K.M., and Wolken, G.J., 2024, Lidar-derived elevation data for Wrangell Island, Southeast Alaska, collected November 28-29, 2023: Raw Data File RDF 2024-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 9 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -132.396768
    East_Bounding_Coordinate: -132.258750
    North_Bounding_Coordinate: 56.479434
    South_Bounding_Coordinate: 56.303098
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 29-Nov-2023
    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: 8
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -135
      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: 0.001
      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. (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 all ground points, the average point spacing is 49.0 cm, and the average density is 4.16 pts/m2. (Source: DGGS)
    dsm
    The DSM represents surface elevations, including heights of vegetation, buildings, powerlines, bridge decks, etc. The DSM is a single-band, 32-bit GeoTIFF file of 50 cm resolution. No Data value is set to -3.40282306074e+38 (32-bit, floating-point minimum). (Source: DGGS)
    dtm
    The DTM represents bare earth elevations, excluding vegetation, bridge decks, buildings, etc. The DTM is a single-band, 32-bit GeoTIFF file of 50 cm 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, 16-bit unsigned GeoTIFF file of 50-cm resolution. No Data value is set to 0. (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 survey area is on the traditional homelands of the Stikine Tlingit people. This work was funded by the Disaster Relief Fund under the Governor's declared disaster order on November 21, 2023. Funding was made available to DGGS by the Alaska Department of Military and Veterans Affairs' Division of Homeland Security and Emergency Management. We thank Coastal Helicopters for their aviation expertise and contribution to these data products, Joe Delabrue of the U.S. Forest Service for logistical help, and David Ciampa and Amy Helkenn of the Alaska Division of Mining, Land and Water for providing ground control points. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
  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 snow-free surface elevations for use in landslide hazard assessment following a November 20, 2023, debris flow that occurred near Milepost 11 of the Zimovia Highway

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: 30-Jun-2023 (process 1 of 3)
    Ground survey - Ground control points were collected June 26-30, 2023, by the Alaska Division of Mining, Land and Water (DMLW), supporting an earlier, island-wide lidar survey performed in July of the same year. They deployed a Trimble R12 GNSS receiver to provide a base station occupation and real-time kinematic (RTK) corrections to points they surveyed with a rover Trimble R12i GNSS receiver/TSC5 controller. Benchmark HH-2 (PID BBDX58), located on the Heritage Harbor breakwater in Wrangell, served as the base station location. DMLW collected 257 ground control points and checkpoints to use for calibration and to assess the vertical accuracy of the point cloud, 59 of which overlapped with the November 2023 survey area. Checkpoints were collected in forest, shrubland, grassland, sphagnum bog, bare earth, and paved surfaces.
    Date: 29-Nov-2023 (process 2 of 3)
    Aerial survey - DGGS used a Riegl VUX1-LR22 laser scanner integrated with a global navigation satellite system (GNSS) and Northrop Grumman LN-200C inertial measurement unit (IMU) designed by Phoenix LiDAR Systems. The sensor can collect a maximum of 1,500,000 points per second at a range of 150 m or a minimum of 50,000 points per second at a range of 640 m. The scanner operated with a pulse refresh rate of 800,000 pulses per second over forested terrain and 200,000 pulses per second over alpine terrain, with a scan rate between 50 and 200 lines per second. We used a Bell 206 helicopter to survey from an elevation of approximately 180-360 m above ground level, at a ground speed of approximately 30 m/s, and with a scan angle set from 80 to 280 degrees. The total survey area covers approximately 40.1 km2. The survey area was accessed by air from Juneau International Airport and Wrangell Airport.
    Date: Dec-2023 (process 3 of 3)
    Lidar 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 scale of sensor movement and behavior, incorporating sensor velocity, roll, pitch, and yaw fluctuations throughout the survey. We created macros 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 50 cm DSM was interpolated from maximum return values from ground, vegetation, bridge deck, and building classes using a binning method and maximum values. A 50 cm DTM was interpolated from all ground class returns using a binning method and minimum values. We also produced an intensity image for the entire area using average binning in ArcGIS Pro, with no normalization or corrections applied.
  3. What similar or related data should the user be aware of?
    Stevens, D.S.P., Wolken, G.J., Hubbard, T.D., and Hendricks, K.A., 2018, Landslides in Alaska: Information Circular IC 65, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 p
    Zechmann, J.M., Wikstrom Jones, K.M., and Wolken, G.J., 2023, Lidar-derived elevation data for Wrangell Island, Southeast Alaska, collected July 2023: Raw Data File RDF 2023-28, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 14 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?
    We did not measure horizontal accuracy for this collection.
  3. How accurate are the heights or depths?
    We measured a mean offset of +62.1 cm between 19 control points and the point cloud. This offset was reduced to -0.9 cm in non-vegetated areas and +8.2 cm in vegetated areas by applying a rubber-sheet vertical correction to the lidar point data. We used 40 checkpoints to determine the vertical accuracy of the point cloud ground class using a Triangulated Irregular Network (TIN) approach. The project vertical accuracy has a root mean square error (RMSE) of 5.5 cm in non-vegetated areas and 10.6 cm in vegetated areas. We evaluated the relative accuracy for this dataset as the interswath overlap consistency and measured it at 8.2 cm RMSE.
  4. Where are the gaps in the data? What is missing?
    This data relaease is complete.
  5. How consistent are the relationships among the observations, including topology?
    This is a full-release dataset. The data quality is consistent throughout the survey.

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 2024-1
  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: 31-Jan-2024
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 Jan 31 20:54:29 2024