Photogrammetry-derived digital surface model and orthoimagery of land areas near Resurrection Bay, Alaska

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Frequently anticipated questions:

What does this data set describe?

Title:
Photogrammetry-derived digital surface model and orthoimagery of land areas near Resurrection Bay, Alaska
Abstract:
The State of Alaska Division of Geological & Geophysical Surveys (DGGS) produced a digital surface model (DSM) and an orthorectified aerial optical image mosaic (orthoimagery) of the Resurrection Bay watershed, surrounding the city of Seward in south-central Alaska. Aerial photographs and Global Navigation Satellite System (GNSS) data were collected on August 13, 2015, and were processed using Structure-from-Motion (SfM) photogrammetric techniques to create the DSM and orthoimagery. All data are projected in UTM Zone 6 North (meters) using the NAD83 (2011; EPSG 26906) horizontal datum and NAVD88 (Geoid12A; EPOCH 2010.00) vertical datum. The project was part of an ongoing investigation of the impact of flooding, slope instability, and cryosphere hazards on infrastructure and public safety. For the purpose of enabling open access to geospatial datasets in Alaska, this collection is being released as a Raw Data File with an open end-user license. All files can be downloaded free of charge from the DGGS website (<http://doi.org/10.14509/29824>). The orthoimage is a three-band, 8-bit unsigned GeoTIFF file using LZW compression. The orthoimage has a GSD of 0.2 m per pixel, and the No Data value is set to 0. Variable lighting in the orthoimages may result from variable sky conditions during the time of data acquisition.
Supplemental_Information: 
orthoimage: The orthoimage is a three-band, 8-bit unsigned GeoTIFF file using LZW compression. The orthoimage has a GSD of 0.2 m per pixel, and the No Data value is set to 0. Variable lighting in the orthoimages may result from variable sky conditions during the time of data acquisition.
  1. How should this data set be cited?

    Balazs, M.S., Wolken, G.J., and Wikstrom Jones, Katreen, 2018, Photogrammetry-derived digital surface model and orthoimagery of land areas near Resurrection Bay, Alaska: Raw Data File RDF 2018-2, 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: -149.598135
    East_Bounding_Coordinate: -149.184355
    North_Bounding_Coordinate: 60.234358
    South_Bounding_Coordinate: 59.970362

  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: orthoimage

  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: 6
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -147
      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.

  7. How does the data set describe geographic features?

    orthoimage
    The orthoimage is a three-band, 8-bit unsigned GeoTIFF file using LZW compression. The orthoimage has a GSD of 0.2 m per pixel, and the No Data value is set to 0. Variable lighting in the orthoimages may result from variable sky conditions during the time of data acquisition. File format: GeoTIFF. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS) and Fairbanks Airborne Remote Sensing)

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 project is funded by Seward Bear Creek Flood Service Area, Kenai Peninsula Borough, DGGS through a State of Alaska Capital Improvement Project, and the University of Alaska Fairbanks, Geophysical Institute.

  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 orthoimage is a three-band, 8-bit unsigned GeoTIFF file using LZW compression. The orthoimage has a GSD of 0.2 m per pixel, and the No Data value is set to 0. Variable lighting in the orthoimages may result from variable sky conditions during the time of data acquisition. This file was created for ongoing investigation of the impact of flooding, slope instability, and cryosphere hazards on infrastructure and public safety in the the Resurrection Bay watershed. Data were collected on August 13, 2015.

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 - The State of Alaska Division of Geological &amp; Geophysical Surveys contracted the collection of digital aerial photographic data on August 13, 2015. The aerial photography survey used a fixed-wing airborne platform and was planned so flight lines and photograph frequency provided 60 percent side lap and 80 percent end lap coverage, with an average above-sea-level flying height of 1260 m. The aerial photography survey covered 383 km2, resulting in 4021 photos with 0.2 m ground sample distance (GSD). A Nikon D800 camera with AF-Nikkor 28mm f/2.8D lens was used to collect 36.2-megapixel JPEG photographs (7360 x 4912 pixels per image) which were compressed for optimal quality. During the aerial survey, the photograph coordinates were determined using an OxTS GPS-IMU system and a Cirrus Digital Systems intervalometer that linked the camera shutter release to the GPS-IMU. The camera was mounted inside the aircraft with the GPS antenna positioned over the camera. The GPS antenna offset (X=0.3, Y=0.0, Z=0.94) was corrected during GPS post-processing to solve for the camera coordinates. A Trimble 5700 GPS receiver with a Trimble Zephyr 4-point feed antenna was deployed approximately 160 meters north of the northeast corner of the Seward Airport and was used as the GPS base station for horizontal and vertical control during the aerial survey. Nineteen photo-identifiable checkpoints were collected by University of Alaska Fairbanks, Geophysical Institute personnel in September 2015 using two Trimble R8s GPS receivers (fig. 2). The base station was located on National Geodetic Survey benchmark X-74 (PID: TT0396), located west of the Seward Airport.

    Date: 2015 (process 2 of 3)
    GNSS data processing - Aerial survey GPS data were processed using GrafNav GNSS Post-Processing Software, Version 8.40.5121 using post-processing kinematic (PPK) methods. The Trimble Zephyr base station position was corrected using the National Geodetic Survey OPUS with the IGS08 (EPOCH:2015.6162) solution. Both aerial and base GPS data were collected and processed in WGS84 (G1674) using the WGS84 ellipsoid. Standard deviations for the GPS event marker horizontal and vertical positions were less than 0.06 m. After post-processing, GPS event marker coordinates needed to be converted to the datum most frequently used by DGGS stakeholders. We used the National Oceanic and Atmospheric Administration's VDatum tool to transform the GPS event marker coordinates to the North American Datum 1983 (NAD83; 2011) European Petroleum Survey Group Well Known Identification Number (EPSG) 6337 and the North American Vertical Datum of 1988 (NAVD88; Geoid12A; EPOCH 2010.00). The coordinates are projected in UTM Zone 6 North and are in meters. GPS event marker coordinates were manually correlated to image filenames to create a camera exterior orientation file for import into the SfM software, Agisoft Photoscan Professional. The exterior orientation file provides the X, Y, Z positions and Yaw, pitch, and roll for each photograph taken during the survey.

    Date: 2015 (process 3 of 3)
    Photogrammetry - Aerial stereo-photographs were imported into the commercially available Agisoft Photoscan Professional software (Version 1.2.3 build 2331). Photos were processed in Photoscan on a Windows PC to align aerial photos, edit the sparse point cloud, optimize the bundle block adjustment, construct the dense point cloud and triangulated irregular network geometry, and export the natural color (RGB) orthoimagery GeoTIFF.

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

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

  1. How well have the observations been checked?

    The DSM a ground sample distance (GSD) of 0.41 m, and the No Data value is set to -32767. The orthoimage has a GSD of 0.2 m per pixel, and the No Data value is set to 0. The DSM and orthoimagery have been visually inspected for data errors such as pits, border artifacts, and shifting. Pits and peaks are present over water bodies such as lakes. The end-user should be aware that DSM data were not hydro-flattened. Some small areas along the boundary and northern region of the survey area have NO DATA values, which is due to insufficient overlap (gaps) in the aerial photographic survey in areas of extreme topographic relief. The end user is advised that such areas may have a less accurate geographic position than reported for the rest of the scene.

  2. How accurate are the geographic locations?

    Horizontal accuracies of the orthoimagery and DSM were assessed using 19 photo-identifiable checkpoints along the road systems in and near Seward, Alaska. Lower horizontal accuracy is possible in areas of extreme terrain, dense vegetation, and heavy shadow. The X-coordinates have a root-mean-square error (RMSE) of 0.32m and a mean absolute error (MAE) of 0.28 m. The Y Coordinates have an RMSE of 0.47 m and a MAE of 0.42 m. The horizontal linear RMSE in the radial direction (RMSEr) is 0.57 m. See accompanying report for additional detail.

  3. How accurate are the heights or depths?

  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?

    The aerial photography survey used a fixed-wing airborne platform and was planned so flight lines and photograph frequency provided 60 percent side lap and 80 percent end lap coverage, with an average above-sea-level flying height of 1260 m. The aerial photography survey covered 383 km2, resulting in 4021 photos with 0.2 m ground sample distance (GSD). Nineteen photo-identifiable checkpoints were collected by University of Alaska Fairbanks, Geophysical Institute personnel in September 2015 using two Trimble R8s GPS receivers. Checkpoint locations and offsets are provided in the accompanying report.

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 2018-2

  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: 12-Jan-2018
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 Fri Jan 12 11:29:49 2018