Lidar-derived elevation data for Sitka, Southeast Alaska, collected April 27-29, 2018, and September 27-28, 2019

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Frequently anticipated questions:


What does this data set describe?

Title:
Lidar-derived elevation data for Sitka, Southeast Alaska, collected April 27-29, 2018, and September 27-28, 2019
Abstract:
Lidar-derived elevation data for Sitka, Southeast Alaska, collected April 27-29, 2018, and September 27-28, 2019, Raw Data File 2026-19, provides aerial lidar derived classified point cloud, digital surface model (DSM), digital terrain model (DTM), and intensity model of Sitka, Southeast Alaska, during leaf-on ground conditions. The survey provides snow-free surface elevations for studying landslide hazards. Ground control data were collected April 27-30, 2018, and aerial lidar data were collected April 27-29, 2018 and September 27-18, 2019, and subsequently processed using a suite of geospatial processing software. These data and accompanying documentation are released as a Raw Data File and are available from the DGGS website at http://doi.org/10.14509/32132.
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 2025 guidelines and contain return and intensity information.  Point cloud elevation information was recorded, processed, and published rounded to the nearest centimeter. For classified ground points, the average density is 6.17 pts/m2, and the average point spacing is 40.3 cm. 	
dsm:    The DSM represents surface elevations, including heights of vegetation, buildings, bridge decks, etc. The DSM is a single-band, 32-bit GeoTIFF file with a 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 float GeoTIFF file with a 50-cm resolution. No Data value is set to -3.40282306074e+38.	
footprints:    Footprints for tiled data.	
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 50-cm resolution. No Data value is set to -3.40282306074e+38.
  1. How might this data set be cited?
    Zechmann, J.M., Wolken, G.J., Daanen, R.P., Wikstrom Jones, K.M., and Herbst, A.M., 2026, Lidar-derived elevation data for Sitka, Southeast Alaska, collected April 27-29, 2018, and September 27-28, 2019: Raw Data File RDF 2026-19, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 14 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -135.424959
    East_Bounding_Coordinate: -135.082872
    North_Bounding_Coordinate: 57.209405
    South_Bounding_Coordinate: 56.980135
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 27-Apr-2018
    Ending_Date: 27-Sep-2019
    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: 0.500000
      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. (Source: DGGS)
    classified_points
    Classified point cloud data are provided in LAZ format. Data are classified following ASPRS 2025 guidelines and contain return and intensity information. Point cloud elevation information was recorded, processed, and published rounded to the nearest centimeter. For classified ground points, the average density is 6.17 pts/m2, and the average point spacing is 40.3 cm. (Source: DGGS)
    dsm
    The DSM represents surface elevations, including heights of vegetation, buildings, bridge decks, etc. The DSM is a single-band, 32-bit GeoTIFF file with a 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 float GeoTIFF file with a 50-cm resolution. No Data value is set to -3.40282306074e+38. (Source: DGGS)
    footprints
    Footprints for tiled data. (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 50-cm 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?
    The area of this survey lies within the traditional homelands of the Tlingit peoples. These data products were funded by the State of Alaska and by National Park Service awards #P17AC00903 and #P15AC01879 and collected and processed by DGGS. We thank Coastal Helicopters and Clearwater Air for their aviation expertise and contribution to these data products. 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 studying landslide hazards. This information is essential for assessing hazards, informing risk-mitigation efforts, and supporting decision-making for communities and infrastructure.

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: 27-Sep-2019 (process 1 of 3)
    Ground survey - Ground control points were collected April 27-30, 2018 (Daanen and others, 2020). We deployed a base Trimble R7 GNSS receiver to provide base station occupation and real-time kinematic (RTK) corrections to points. We surveyed with a rover Trimble R8 GNSS receiver/Trimble Juno 5 Series controller. We collected 234 ground control points and check points, not all of which overlapped with the April 27-29, 2018, and September 27-28, 2019, point cloud. Daanen and others (2020) reported Easting values to 1 decimal place and Northing values to the nearest whole number. Of the 234 ground control points and check points collected in 2018, 195 could be used for calibration and vertical accuracy assessment of the 2018 and 2019 point cloud. Ground control points and check points were collected on bare earth.
    Date: 30-Apr-2019 (process 2 of 3)
    Lidar survey - DGGS used a Riegl VUX1-LR laser scanner integrated with a global navigation satellite system (GNSS) and a Northrop Grumman LN-200C inertial measurement unit (IMU) integrated by Phoenix LiDAR Systems. The sensor can collect a maximum of 820,000 points per second at a range of 215 m, or a minimum of 50,000 points per second at a range of 820 m (ranges assume greater than or equal to 20 percent natural reflectance). The scanner operated with a pulse refresh rate of 100,000-200,000 pulses per second in alpine areas and 400,000-820,000 pulses per second over forested areas, at a scan rate between 20 and 200 revolutions per second. We used a Cessna 180 Skywagon fixed-wing platform and a Bell 206 JetRanger to survey from elevations of 60-400 m above ground level, at a ground speed of ~40 m/s (Cessna 180 Skywagon) or ~30 m/s (Bell 206 JetRanger), and with a scan angle set from 55 to 305 degrees (2018) or 90 to 270 degrees (2019). The total survey area covers ~168 km2. The survey area was accessed by air from Sitka Rocky Gutierrez Airport.
    Date: 2025 (process 3 of 3)
    Dataset processing - We processed point data using SDCimport software 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. For the lidar data collection, the average pulse density is 48.6 pulses/m2, and the average pulse spacing is 14.4 cm. Macros (ordered lists of point classification commands tailored to this dataset) were created in Terrasolid software and used to classify points in accordance with the American Society for Photogrammetry & Remote Sensing (ASPRS) 2025 guidelines. Once classified, we applied a geometric transformation and converted the points from ellipsoidal heights to GEOID12B (Alaska) orthometric heights. We used ArcGIS Pro to derive raster products from the point cloud. A 50-cm DSM was interpolated from maximum return values from ground, vegetation, bridge deck, and building classes using a binning method. A 50-cm DTM was interpolated from all ground class returns using a binning method and minimum values. We also produced a 1-meter 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?
    Daanen, R.P., Wolken, G.J., and Herbst, A.M., 2020, Lidar-derived elevation data for Sitka, Alaska: Raw Data File RDF 2020-13, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 11 p
    Hubbard, T.D., Daanen, R.P., and Stevens, D.S.P., 2025, Debris flow hazard evaluations for multi-hazard risk mapping in Sitka, Alaska: Report of Investigation RI 2024-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 14 p., 6 sheets, scale 1:20,000

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 offset of -79 cm between 156 control points and the point cloud. This offset was reduced to -9 cm by applying a rubber-sheet vertical correction to the lidar point data. We used 39 check points to assess the non-vegetated vertical accuracy of the point cloud ground class using a Triangulated Irregular Network (TIN) approach. The project's vertical accuracy has a root mean square error (RMSE) of 14 cm. We evaluated the relative accuracy for this dataset as the interswath overlap consistency and measured it at 9 cm RMSE.
  4. Where are the gaps in the data? What is missing?
    There was no over-collect except for aircraft turns that were eliminated from the dataset.
  5. How consistent are the relationships among the observations, including topology?
    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 2026-19
  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: 06-Aug-2026
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 Thu Aug 06 16:52:00 2026