Lidar-derived elevation data for Penguin Ridge, Southcentral Alaska, collected September 22, 2021

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Frequently anticipated questions:


What does this data set describe?

Title:
Lidar-derived elevation data for Penguin Ridge, Southcentral Alaska, collected September 22, 2021
Abstract:
Lidar-derived elevation data for Penguin Ridge, Southcentral Alaska, collected September 22, 2021, Raw Data File 2024-5, classified point cloud, digital surface model (DSM), digital terrain model (DTM), and intensity model of Penguin Ridge, Southcentral Alaska, during near snow-free ground conditions on September 22, 2021. The survey provides snow-free surface elevations for deriving snow depth distribution models with repeat surveys during snow-covered conditions. Aerial lidar data were collected on September 22, 2021, and ground control data were collected on September 27, 2021, and subsequently processed in a suite of geospatial processing software. All files can be downloaded from the Alaska Division of Geological & Geophysical Surveys website (http://doi.org/10.14509/31158).
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 compressed LAZ format. Data are classified in accordance with ASPRS 2019 guidelines and contain return and intensity information. Class 14 (Wire [conductor]) comprises both transmission lines and towers. For classified ground points, the average point density is 3.24 pts/m2 	
dsm:    The DSM represents surface elevations, including heights of vegetation, buildings, powerlines, etc. The DSM is a single-band, 32-bit float GeoTIFF file of 50-centimeter resolution. No Data value is set to -3.40282306074e+38.	
dtm:    The DTM represents bare earth elevations, excluding vegetation, bridges, buildings, etc. The DTM is a single-band, 32-bit float GeoTIFF file of 0.20-meter 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 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 1-meter resolution. No Data value is set to -3.40282306074e+38.
  1. How might this data set be cited?
    Wikstrom Jones, K.M., and Wolken, G.J., 2024, Lidar-derived elevation data for Penguin Ridge, Southcentral Alaska, collected September 22, 2021: Raw Data File RDF 2024-5, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 11 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -149.436745
    East_Bounding_Coordinate: -149.154860
    North_Bounding_Coordinate: 60.976461
    South_Bounding_Coordinate: 60.922553
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 22-Sep-2021
    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. Also includes footprints for tiled data. (Source: DGGS)
    classified_points
    Classified point cloud data are provided in compressed LAZ format. Data are classified in accordance with ASPRS 2019 guidelines and contain return and intensity information. Class 14 (Wire [conductor]) comprises both transmission lines and towers. For classified ground points, the average point density is 3.24 pts/m2 (Source: DGGS)
    dsm
    The DSM represents surface elevations, including heights of vegetation, buildings, powerlines, etc. The DSM is a single-band, 32-bit float GeoTIFF file of 50-centimeter resolution. No Data value is set to -3.40282306074e+38. (Source: DGGS)
    dtm
    The DTM represents bare earth elevations, excluding vegetation, bridges, buildings, etc. The DTM is a single-band, 32-bit float GeoTIFF file of 0.20-meter 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 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 1-meter 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?
    These data products were funded by Alaska Department of Transportation & Public Facilities and the State of Alaska, and they were collected and processed by DGGS. We thank Clearwater Air for their aviation expertise and contribution to these data products.
  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?

These data provide snow-free surface elevations for deriving snow depth distribution models with repeat surveys during snow-covered conditions.

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: 21-Sep-2021 (process 1 of 3)
    Ground survey - We collected ground control and check points on September 27, 2021. We deployed a Trimble R10-2 GNSS receiver (internal antenna) at Bird Point, located in the center of the survey area. It provided a base station occupation and real-time kinematic (RTK) corrections to points that we surveyed with a rover Trimble R10-2 GNSS receiver (internal antenna). We collected a total of 170 ground control points and check points to use for calibration and to assess the vertical accuracy of the point cloud. All points were collected on paved surfaces.
    Date: 02-Sep-2021 (process 2 of 3)
    Aerial survey - DGGS used a Riegl VUX1-LR laser scanner integrated with a global navigation satellite system (GNSS) and Northrop Grumman LN-200C inertial measurement unit (IMU). The lidar integration system was designed by Phoenix LiDAR Systems. The sensor can collect up to 820,000 points per second at a range of up to 150 m. The scanner operated with a pulse refresh rate of 200,000 pulses per second in the alpine areas and 400,000 pulses per second over forested areas at a scan rate of 160 lines per second. We used a Cessna 180 fixed-wing aircraft to survey from an elevation of approximately 200 m above ground level, at a ground speed of approximately 37 m/s, and with a scan angle set from 80 to 280 degrees. The total survey area covered approximately 14.5 km2. We flew the aerial survey on September 22, 2021, with departure at 11:50 am from Merrill Field Airport, Anchorage, Alaska, and landed back at the airport at 2:45 pm. The weather throughout the survey was clear with no wind. There was a dusting of snow in the alpine areas on Penguin Ridge prior to the survey.
    Date: 2023 (process 3 of 3)
    Lidar dataset processing - We processed point data in SDCimport software for initial filtering and multiple-time-around (MTA) disambiguation. MTA errors, corrected in this process, are the result of ambiguous interpretations of received pulse time intervals and occur more frequently with higher pulse refresh rates. Inertial Measurement Unit (IMU) and Global Navigation Satellite System (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 nominal pulse density is 17.1 pts/m2 and the average nominal pulse spacing is 24.2 cm. We created macros in Terrasolid software and classified points in accordance with American Society for Photogrammetry and Remote Sensing (ASPRS) 2019 guidelines. 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. The DSM was interpolated from maximum return values from the ground, vegetation, wire, and vehicle classes using a Triangulated Irregular Network (TIN) method. The DTM was interpolated from all ground class returns also using a TIN method and minimum values. In ArcMap we produced an intensity image using closest-to-mean binning.
  3. What similar or related data should the user be aware of?
    Wolken, G.J., Hendricks, K.A., Daanen, R.P., Overbeck, J.R., Stevens, D.S.P., and Masterman, S.S., 2017, Alaska & climate change: Information Circular IC 64, 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?
    We did not measure horizontal accuracy for this collection.
  3. How accurate are the heights or depths?
    We measured a mean offset of +42.1 cm between 132 control points and the point cloud. We reduced this offset to +0.3 cm by performing a vertical transformation of the lidar point data. We used 35 check points to determine the non-vegetated vertical accuracy (NVA) of the point cloud ground class using a TIN approach. We calculated the project NVA to have a root mean square error (RMSE) of 3.3 cm. We evaluated the relative accuracy for this dataset as the interswath overlap consistency and measured it at 0.7 cm RMSE. See accompanying report for a table of checkpoints and further discussion of factors impacting the vertical accuracy.
  4. Where are the gaps in the data? What is missing?
    This data release is complete.
  5. How consistent are the relationships among the observations, including topology?
    This publication is a complete release dataset. There was no over-collect except for aircraft turns that were eliminated from the 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 2024-5
  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: 13-Mar-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 Mar 13 15:28:36 2024