Photogrammetry-derived orthoimagery and elevation data in Tuntutuliak, Alaska, collected June 8, 2023

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Frequently anticipated questions:


What does this data set describe?

Title:
Photogrammetry-derived orthoimagery and elevation data in Tuntutuliak, Alaska, collected June 8, 2023
Abstract:
Photogrammetry-derived orthoimagery and elevation data in Tuntutuliak, Alaska, collected June 8, 2023, Raw Data File 2024-24, provides low-altitude aerial images from an unmanned aerial vehicle (UAV) in the community of Tuntutuliak, Alaska, on June 8, 2023. We used Structure-from-Motion (SfM) photogrammetry to produce a digital surface model (DSM) and orthorectified imagery. The orthoimage and elevation data are useful for assessing riverine hazards and changes over time. All files can be downloaded from the Alaska Division of Geological & Geophysical Surveys website (http://doi.org/10.14509/31292).
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.	
dsm:    The DSM represents surface elevations including the height of vegetation, buildings, and other man-made features derived from the dense point cloud. The DSM is a single-band, 32-bit floating point GeoTIFF file with a GSD of 0.049 m; the No Data value is set to -3.4028235e+38.	
ortho_rgb:    The orthoimage is a three-band (red, green, blue), eight-bit unsigned GeoTIFF file derived from a color-adjusted mosaic of 1,983 aerial photographs with a GSD of 0.025 m per pixel; the No Data value is set to 0.
  1. How might this data set be cited?
    Horen, K.C., Nieminski, N.M., Poisson, A.C., and Siemsen, Z.J., 2024, Photogrammetry-derived orthoimagery and elevation data in Tuntutuliak, Alaska, collected June 8, 2023: Raw Data File RDF 2024-24, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 6 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -162.695670
    East_Bounding_Coordinate: -162.643877
    North_Bounding_Coordinate: 60.358582
    South_Bounding_Coordinate: 60.334326
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 08-Jul-2022
    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: 3
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -165
      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)
    dsm
    The DSM represents surface elevations including the height of vegetation, buildings, and other man-made features derived from the dense point cloud. The DSM is a single-band, 32-bit floating point GeoTIFF file with a GSD of 0.049 m; the No Data value is set to -3.4028235e+38. (Source: DGGS)
    ortho_rgb
    The orthoimage is a three-band (red, green, blue), eight-bit unsigned GeoTIFF file derived from a color-adjusted mosaic of 1,983 aerial photographs with a GSD of 0.025 m per pixel; the 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?
    We thank the Native Village of Tuntutuliak for supporting the creation of these data products, made possible with National Fish and Wildlife Foundation's National Coastal Resilience Funding through our partners at the Alaska Native Tribal Health Consortium. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the Alaska Division of Geological & Geophysical Surveys, the U.S. Government, or the National Fish and Wildlife Foundation and its funding sources. Mention of trade names or commercial products does not constitute their endorsement by the Alaska Division of Geological & Geophysical Surveys, the U.S. Government, or the National Fish and Wildlife Foundation and its funding sources.
  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 orthoimage and elevation data are useful for assessing riverine hazards and changes over time.

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: 08-Jul-2022 (process 1 of 3)
    Ground survey - On June 8, 2023, DGGS temporarily installed a Trimble R10 receiver sampling at 5 Hz as a Global Navigation Satellite System (GNSS) base station over a temporary benchmark. This provided real-time kinematic (RTK) corrections to the ground rover, a Trimble R8s GNSS receiver. DGGS measured the location of 38 photo-identifiable ground control points (GCPs) with the ground rover.
    Date: 08-Jul-2022 (process 2 of 3)
    Aerial survey - DGGS conducted flights on June 8, 2023, from approximately 2:00 PM to 4:45 PM AKDT using a DJI Phantom 4 RTK UAV with a FC6310R camera model (8.8 mm lens) to collect 1,993 20-megapixel JPEG photographs (5,472 x 3,648 pixels per image). The operator returned the UAV eight times to change batteries. DGGS flew the aerial survey with 75 percent sidelap and 75 percent frontlap, 120 m above ground-level at 9.5 m/s, with nadir orientation stabilized using a three-axis gimbal. This resulted in images covering 3.357 km2 with a ground sampling distance (GSD) of 0.025 m. The weather throughout the survey was mostly cloudy with light wind. No abnormalities were observed during the flights.
    Date: 2023 (process 3 of 3)
    Dataset processing - Base positions were corrected using Online Positioning User Service (OPUS) solutions, which were used to update the UAV and ground rover positions with post-processed kinematic (PPK) adjustments. UAV positions were updated in RTKLIB (Version 2.4.3) software with the following settings applied: L1+L2 frequencies forward and backward filtered; a 10-degree elevation mask; receiver dynamics disabled; broadcast ionosphere and Saastamoinen troposphere corrections; a minimum fixed-ambiguity ratio of three; and L1/L2 code/carrier-phase error ratios of 100/100. During post-processing, DGGS applied International GNSS Service (IGS) precise orbits and final clock solutions retrieved from the Crustal Dynamics Data Information System (CDDIS) found at urs.earthdata.nasa.gov. Final corrected data were exported as time-stamped position files in WGS84 horizontal coordinate system with ellipsoidal heights and paired to corresponding photographs using an Aerotas P4RTK PPK Adjustments (Version 1) macro-enabled Microsoft Excel file. Ground rover positions were updated using PPK corrections in Trimble Business Center (Version 5.51) software using default settings. Final corrected data were exported as comma-delimited text files in WGS84 horizontal coordinate system with ellipsoidal heights. DGGS used Agisoft Metashape Professional (Version 1.8.3 build 14331) software for photogrammetric processing following the steps and settings outlined in Over and others (2021). During processing, DGGS used 19 GCPs for photograph alignment and lens distortion parameter optimization, leaving 19 GCPs as horizontal and vertical check points. A confidence filter was applied to the resulting dense point cloud, eliminating all points derived from fewer than three discrete camera positions. Additional noise was removed from the dense point cloud through visual inspection.
  3. What similar or related data should the user be aware of?
    Horen, K.C., Nieminski, N.M., Poisson, A.C., and Siemsen, Z.J., 2024, Single-beam bathymetric data near Tuntutuliak, Alaska, collected June 8, 2023: Raw Data File RDF 2024-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 8 p
    Zechmann, J.M., Herbst, A.M., and Buzard, R.M., 2023, Lidar-derived elevation data for Tuntutuliak, southwest Alaska, collected August 18, 2021: Raw Data File RDF 2023-17, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 7 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?
    DGGS quantified the horizontal accuracy of the GNSS position data using the latitudinal and longitudinal peak-to-peak errors provided by OPUS. Consistent with OPUS shared solution requirements (NOAA, 2022), DGGS considers high-quality GNSS solutions to have latitudinal and longitudinal errors less than or equal to 0.04 m. We quantified the horizontal accuracy of the DSM and orthoimage by comparing the known locations of 19 photo-identifiable check points measured with GNSS against their modeled locations in the photogrammetric products. These are independent checkpoints not used during processing. X and Y errors are calculated as the root-mean-square (RMS) error of offsets, 0.027 m and 0.030 m, respectively. The total horizontal error is the root-sum-square error of X and Y RMS errors, 0.040 m.
  3. How accurate are the heights or depths?
    DGGS quantified the vertical accuracy of the GNSS position data using the combined ellipsoidal height peak-to-peak errors provided by OPUS and orthometric height RMS error provided by NOAA's Vertical Datum Transformation software (NOAA, 2016; table 1). Consistent with OPUS shared solution requirements (NOAA, 2022), DGGS considers high-quality GNSS solutions to have vertical errors less than or equal to 0.08 m. We quantified the vertical accuracy of the DSM using the same 19 check points used to quantify the horizontal accuracy. The RMS error of Z offsets is 0.031 m. The total RMS error of the DSM (X, Y, and Z) is 0.050 m.
  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 orthoimage for data errors such as shifts, seamline mismatches, and water noise overlapping land. Visual errors common to these SfM photogrammetry products include discontinuous powerlines and distortion near high-angle features like buildings, as well as water boundaries. Highly reflective objects such as water bodies, metal roofs, and white paint may cause overexposure, leading to spurious elevation points. There were no significantly erroneous areas that required repair.

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 2024-24
  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: 08-Aug-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 Thu Aug 08 15:45:44 2024