Photogrammetry-derived orthoimagery and elevation for Napakiak, Alaska, collected June 30, 2021

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Frequently anticipated questions:

What does this data set describe?

Title:
Photogrammetry-derived orthoimagery and elevation for Napakiak, Alaska, collected June 30, 2021
Abstract:
The Alaska Division of Geological & Geophysical Surveys (DGGS) collected low-altitude aerial images from an unmanned aerial vehicle (UAV) on June 30, 2021 and used Structure-from-Motion (SfM) photogrammetry to produce a digital surface model (DSM) and orthoimage of Napakiak. The orthoimage and elevation data are for assessing coastal hazards and changes. We used Trimble Business Center to process the Global Navigation Satellite System (GNSS) data used for positional control. We used Agisoft Metashape to process the photogrammetry data. These products are 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/10.14509/30793).
Supplemental_Information: 
digital surface model:    The DSM represents surface elevations such as the height of vegetation and buildings. Water bodies can introduce noise. We manually delineated the river boundaries to restrict the DSM to the land. We selectively removed areas where inland water bodies introduced great noise. The DSM is a single-band, 32-bit floating point GeoTIFF file with a GSD of 0.066 m; the "No Data" value is set to -3.4028231 x 10^38.	
orthoimagery:    The orthoimage is a three-band (red, green, blue), 8-bit unsigned GeoTIFF file with a GSD of 0.033 m per pixel; the "No Data" value is set to 0.
  1. How might this data set be cited?
    Buzard, R.M., Christian, J.E., and Overbeck, J.R., 2021, Photogrammetry-derived orthoimagery and elevation for Napakiak, Alaska, collected June 30, 2021: Raw Data File RDF 2021-20, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 4 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -161.993743
    East_Bounding_Coordinate: -161.967944
    North_Bounding_Coordinate: 60.699068
    South_Bounding_Coordinate: 60.683104
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 30-Jun-2021
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: GeoTIFF
  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: 4
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -159
      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 1/298.257222101000025.
      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?
    digital surface model
    The DSM represents surface elevations such as the height of vegetation and buildings. Water bodies can introduce noise. We manually delineated the river boundaries to restrict the DSM to the land. We selectively removed areas where inland water bodies introduced great noise. The DSM is a single-band, 32-bit floating point GeoTIFF file with a GSD of 0.066 m; the "No Data" value is set to -3.4028231 x 10^38. (Source: DGGS)
    orthoimagery
    The orthoimage is a three-band (red, green, blue), 8-bit unsigned GeoTIFF file with a GSD of 0.033 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 and City of Napakiak for funding and supporting the creation of 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?

The orthoimage and elevation data are for assessing coastal hazards and changes near the community of Napakiak.

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-2021 (process 1 of 3)
    Airborne survey - DGGS used a DJI Phantom 4 RTK UAV with a FC6310R camera model (8.8 mm lens) to collect 20-megapixel JPEG photographs (5472 x 3648 pixels per image). We flew the aerial survey with 70 percent sidelap and 80 percent frontlap, 120 m above the ground at 7.9 m/s, with nadir camera orientation stabilized by a 3-axis gimbal. The resulting images cover 1.35 km2 with ground sampling distance (GSD) of approximately 0.03 m. DGGS conducted flights on June 30, 2021, from 8:00 to 10:00 PM AKDT. The operator returned the UAV five times to change batteries. The weather was favorable with high overcast clouds, no rain, and light wind. No abnormalities were observed during the flights.
    Date: 30-Jun-2021 (process 2 of 3)
    Ground survey - DGGS set up a GNSS base station using a Trimble R10 receiver sampling at 5 Hz. The base was installed over a temporary benchmark of unknown position. This provided real-time kinematic (RTK) corrections to the UAV and Trimble R8s GNSS receiver. DGGS measured 16 photo-identifiable points with the R8s. We derived the corrected base position using the Online Positioning User Service (found at www.ngs.noaa.gov/OPUS/) and post-processed the R8s positions in Trimble Business Center.
    Date: 2021 (process 3 of 3)
    Photogrammetric dataset processing - The UAV maintained RTK connection throughout the survey. The RTK system automatically applies the lever arm correction when writing camera GNSS coordinates (WGS84 ellipsoid) to the image metadata. Yaw, pitch, and roll information were not written to the image metadata. We update UAV positions using a X, Y, and Z shift from the initial to the corrected base position. DGGS processed images in Agisoft Metashape Professional software (Version 1.6.3 build 10732). We masked image corners where shadows and image warping were disruptive. Processing steps included aligning images, identifying ground control points (GCPs), manually cleaning the sparse point cloud, optimizing the bundle block adjustment (refining camera positions and lens distortion parameters), constructing the dense point cloud, building the DSM, and creating the orthomosaic image. We used six GCPs to create the model, leaving ten survey check points.
  3. What similar or related data should the user be aware of?
    Buzard, R.M., Overbeck, J.R., and Maio, C.V., 2019, Community-based methods for monitoring coastal erosion: Information Circular IC 84, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 35 p
    Buzard, R.M., Turner, M.M., Miller, K.Y., Antrobus, D.C., and Overbeck, J.R., 2021, Erosion exposure assessment of infrastructure in Alaska coastal communities: Report of Investigation RI 2021-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 29 p
    Buzard, R.M., Overbeck, J.R., Miller, K.Y., and Christian, J.E., 2021, Coastal flood impact assessments for Alaska communities: Napakiak: Report of Investigation RI 2021-1B, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 45 p
    Overbeck, J.R., Buzard, R.M., Turner, M.M., Miller, K.Y., and Glenn, R.J., 2020, Shoreline change at Alaska coastal communities: Report of Investigation RI 2020-10, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 29 p., 47 sheets
    Overbeck, J.R., 2018, Coastal flooding & erosion in Alaska: Information Circular IC 68, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 p
    Overbeck, J.R., 2018, Alaska coastal mapping gaps & priorities: Information Circular IC 72, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 34 p
    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 quantify the horizontal accuracy of the DSM and orthoimage by comparing the known locations of 10 photo-identifiable check points measured with GNSS against their modeled locations in the photogrammetric products. X and Y errors are calculated as the root-mean-square (RMS) error of offsets. The total horizontal error is the root-sum-square error of X and Y RMS errors, 0.081 m. See accompanying report for a table of check point coordinates and offsets from orthoimage and DSM.
  3. How accurate are the heights or depths?
    We assess the vertical accuracy of the DSM using the same check points. The RMS error of Z offsets is 0.073 m (table 1 of the accompanying report). The total error of the DSM (X, Y, and Z) is 0.109 m.
  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?
    DGGS visually inspected the orthoimage for data errors such as shifts, seamline mismatches, and water noise overlapping land. There were no significantly erroneous areas that required repair. Visual errors common to these SfM photogrammetry products include discontinuous powerlines, blurriness near high-angle features like buildings, and distortion at water boundaries. Bright objects like metal roofs and white paint can cause overexposure, leading to spurious elevation points.

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 2021-20
  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: 09-Dec-2021
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 Dec 08 15:48:46 2021