Photogrammetric digital surface models and orthoimagery for the continuous coastline, Wales to Platinum, Alaska, segment C: Nome to Elim

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Frequently anticipated questions:


What does this data set describe?

Title:
Photogrammetric digital surface models and orthoimagery for the continuous coastline, Wales to Platinum, Alaska, segment C: Nome to Elim
Abstract:
Aerial photographs of the coastline from Nome to Elim were collected on August 23, 2015. The photographs were processed using Structure-from-Motion (SfM) photogrammetric techniques. Global Positioning System (GPS) checkpoints were collected via a Global Navigation Satellite System (GNSS) survey conducted between August 15 and September 14, 2015. For the purposes of open access to elevation and orthoimagery datasets in coastal regions of Alaska, this collection is being released as a Raw Data File with an open end-user license. This file is a single-band, 32-bit float DSM (digital surface model) which represents surface elevations of buildings, vegetation, and uncovered ground surfaces in meters with 20 cm GSD. The No Data value is set to -32767. The file employs LZW compression.
  1. How should this data set be cited?

    Overbeck, J.R., Hendricks, M.D., and Kinsman, N.E.M., 2017, Photogrammetric digital surface models and orthoimagery for the continuous coastline, Wales to Platinum, Alaska, segment C: Nome to Elim: Raw Data File RDF 2017-8C, 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: -165.617886
    East_Bounding_Coordinate: -161.895030
    North_Bounding_Coordinate: 64.752796
    South_Bounding_Coordinate: 64.296216

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 2015
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: digital surface model

  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 North American Datum of 1983.
      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; Geoid12A; EPOCH 2010.00
      Altitude_Resolution: 20
      Altitude_Distance_Units: centimeters
      Altitude_Encoding_Method: Implicit coordinate

  7. How does the data set describe geographic features?

    digital surface model
    This file is a single-band, 32-bit float DSM (digital surface model) which represents surface elevations of buildings, vegetation, and uncovered ground surfaces in meters with 20 cm GSD. The No Data value is set to -32767. The file employs LZW compression. File format: GeoTIFF. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS) and Fairbanks Fodar.)


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 publication is funded with qualified outer continental shelf oil and gas revenues by the Coastal Impact Assistance Program, U.S. Fish and Wildlife Service, U.S. Department of the Interior. 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 U.S. Government. Mention of trade names or commercial products does not constitute their endorsement by 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 99709-3707
    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


Why was the data set created?

The State of Alaska Division of Geological & Geophysical Surveys contracted with Fairbanks Fodar to acquire photogrammetric digital surface models (DSMs) and co-registered orthorectified aerial images (orthoimages) for the west coast of Alaska in support of coastal vulnerability mapping. Users can access the data, as well as additional metadata, from the DGGS website: <http://doi.org/10.14509/29772>.


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: 2015 (process 1 of 3)
    Data acquisition - Fairbanks Fodar collected aerial photographs between July 31 and May 7, 2016, using a small aircraft (Cessna 170B) platform. The aerial survey was planned so flight lines and photograph frequency provided 60 percent side lap and 80 percent end lap photo coverage along with flying heights between 800 and 2,700 feet (244-823 m), resulting in 20 cm ground sample distance (GSD) of the aerial photos. A Nikon D800E with a 24 mm Nikkor f/1.4 lens was used to collect 36 megapixel photographs (7,360 × 4,912 pixels per image), in Joint Photographic Experts Group (JPEG) or Nikon Electronic Format (NEF), depending on location. Photos were collected at 1- to 3-second intervals. On-board global positioning system (GPS) data were acquired by a Trimble 5700 with roof-mounted antenna approximately 1 m above the camera, collecting at 5 Hertz. Each camera shutter trip placed an event marker onto the GPS datastream for precise timing and location.

    Date: 2015 (process 2 of 3)
    Data processing - Aerial survey GNSS data were processed using Waypoint's Grafnav commercial GNSS software using GPS constellation. Each project was processed using either post-processing kinematic (PPK) or precise point positioning (PPP) methods, depending on the quality of the solution, which was primarily dependent on the distance from Continually Operating Reference Stations (CORS), such that all flights resulted in data with better than 10 cm separation in forward and reverse trajectory solutions. GPS data were processed to the North American Datum 1983 (NAD83; 2011) European Petroleum Survey Group Well Known Identification Number (EPSG) 6318, and the North American Vertical Datum of 1988 (NAVD88; Geoid12A; EPOCH 2010.00). Photos were individually processed for optimum contrast and exposure using Adobe Camera Raw. To accommodate the large data acquisition volumes, most photos were shot and processed to JPEG format. Aerial survey GPS data (event marker coordinates) were manually correlated to image filenames using the image timestamp to create a camera external orientation file for import into Agisoft Photoscan Professional (Photoscan) software. The external orientation file provides the X, Y, Z position of the camera for each photograph taken during the survey.

    Date: 2015 (process 3 of 3)
    Photogrammetry - Aerial stereophotographs were imported into the photogrammetric software, which uses a SfM algorithm to create a three-dimensional terrain model from the stereo-imagery. The terrain model was then used to orthometrically correct the photos and produce the final orthoimage mosaic in Photoscan. Within the Photoscan software application, standard workflow steps were followed: photo-alignment, alignment optimization, dense point cloud building, mesh creation, DSM and orthoimage creation, and exporting the results.

  3. What similar or related data should the user be aware of?

    Overbeck, J.R., Hendricks, M.D., and Kinsman, N.E.M., 2016, Photogrammetric digital surface models and orthoimagery for 26 coastal communities of western Alaska: Raw Data File RDF 2016-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p
    Overbeck, J.R., Hendricks, M.D., and Kinsman, N.E.M., 2017, Photogrammetric digital surface models and orthoimagery for the continuous coastline, Wales to Platinum, Alaska: Raw Data File RDF 2017-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 21 p


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    Data are in their raw format; for community-level data where vertical controls have been rigorously applied, are higher resolution, and have fewer gaps, see Overbeck and others (2016; <http://doi.org/10.14509/29548>). General data collection, processing, and accuracy assessment procedures in this release are described in a data release overview (Overbeck and others, 2017; <http://doi.org/10.14509/29744>). Horizontal and vertical accuracies of the orthoimagery and DSMs are evaluated using photo-identifiable checkpoints and elevation checkpoints collected by RECON, LLC (Overbeck and others, 2016). Accuracy assessment values reported for each alongshore segment are the mean residual between non-vegetated ground control and checkpoints and the DSM. Known, uncorrected anomalies over water bodies and cloud or snow covered areas exist throughout the project area. See accompanying report for comprehensive metadata, including discussion of the number of ground control checkpoints, accuracy statistics, and known anomalies.

  2. How accurate are the geographic locations?

    Positional (horizontal) accuracy has been determined by identifying ground control points visually and comparing their location to the GPS-collected ground control, quantified as the horizontal radial root mean square error (RMSE; ASPRS, 2015). The positional accuracy at 95% confidence level was also computed according to ASPRS (2015). Horizontal accuracy statistics are available in table format in the accompanying report.

  3. How accurate are the heights or depths?

    Elevation data have not been vertically shifted to best fit checkpoint elevations. Instead, GPS points have been used to assess the data quality only. The approach will allow the user to make informed decisions about how to vertically adjust the DSMs to best align with local vertical datums and/or meet project accuracy requirements. Vertical accuracy was determined at the 95% confidence level according to ASPRS (2015), using checkpoints for non-vegetated and vegetated locations separately. Vertical accuracy values relative to the reported altitude datum are available in table format in the accompanying report. The accompanying report provides a table of vertical accuracy values relative to the reported altitude datum.

  4. Where are the gaps in the data? What is missing?

    This data release provides continuous coastline data are in their raw format. Known issues are addressed in the accompanying reports. It is a supplement to Overbeck and others 2016; <http://dggs.alaska.gov/pubs/id/29548>, which provides high resolution for each coastal community.

  5. How consistent are the relationships among the observations, including topology?

    Data quality have been assessed relative to checkpoints collected simultaneously with the aerial survey described in the community scale data release (Overbeck and others, 2016). Since no ground control points were used to control these data, all points are considered checkpoints. Although checkpoints are focused at community locations and at large alongshore intervals, they have been used to assess the accuracy of these data at a regional scale. Photo-identifiable points were used to determine the horizontal accuracy of these data, while all points were used to determine the vertical accuracy unless the ground cover was irregular and non-vegetated (e.g. boulder piles). Data within this alongshore segment may overlap with data in an adjacent segment, and data segments may not overlap seamlessly.


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 99709-3707
    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
  2. What's the catalog number I need to order this data set?

    RDF 2017-8C

  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: 15-Nov-2017
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
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 2.9.21 on Wed Nov 15 16:48:44 2017