Photogrammetry-derived digital surface model and orthoimagery of Valdez Glacier ice-dammed lake, Valdez, Alaska, October 15, 2014

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Frequently anticipated questions:


What does this data set describe?

Title:
Photogrammetry-derived digital surface model and orthoimagery of Valdez Glacier ice-dammed lake, Valdez, Alaska, October 15, 2014
Abstract:
The State of Alaska Division of Geological & Geophysical Surveys (DGGS) produced a digital surface model (DSM) and an orthorectified aerial image over an ice-dammed lake formed by Valdez Glacier. Aerial photographs and Global Navigation Satellite System (GNSS) data were collected on October 15, 2014, and were processed using Structure-from-Motion (SfM) photogrammetric techniques to create a DSM and orthoimagery. 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/10.14509/30181>).
Supplemental_Information:
digital surface model: DSMs  represent  surface  elevations  of  all  surfaces,  including  vegetation,  vegetation-free  land, bridges, buildings, etc. The DSM is a single-band, 32-bit float GeoTIFF file, with a ground sample distance (GSD) of 0.19 m. No Data value is set to -32767.
  1. How should this data set be cited?

    Wikstrom Jones, Katreen, Wolken, G.J., Whorton, E.N., and Hendricks, M.D., 2019, Photogrammetry-derived digital surface model and orthoimagery of Valdez Glacier ice-dammed lake, Valdez, Alaska, October 15, 2014: Raw Data File RDF 2019-2, 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: -146.172
    East_Bounding_Coordinate: -145.986
    North_Bounding_Coordinate: 61.245
    South_Bounding_Coordinate: 61.197

  3. What does it look like?

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

    Calendar_Date: 2014
    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: 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?

    digital surface model
    DSMs represent surface elevations of all surfaces, including vegetation, vegetation-free land, bridges, buildings, etc. The DSM is a single-band, 32-bit float GeoTIFF file, with a ground sample distance (GSD) of 0.19 m. No Data value is set to -32767 (Source: Alaska Division of Geological & Geophysical Surveys (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 City of Valdez and Alaska Department of Natural Resources, Division of Geological & Geophysical Surveys. We thank Alpine 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 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?

This data release is one of a series of Alaska Division of Geological & Geophysical Surveys (DGGS) publications to present elevation data collected prior to and after the annually recurring glacial lake outburst floods (GLOFs) at Valdez Glacier. The goal is to provide information for the City of Valdez to better understand the complex nature of these phenomena.


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: 2014 (process 1 of 3)
    Data acquisition - The State of Alaska Division of Geological & Geophysical Surveys collected digital aerial photographic data on October 15, 2014, using a rotary-wing (Robinson 44) airborne platform. The aerial photographic survey resulted in approximately 60 percent side lap and 80 percent end lap coverage, with an above ground-level flying height of 1100-2000 m, which resulted in 818 photos with 0.096 m per pixel ground resolution. The total area surveyed was approximately 11 km2. A Nikon D800 with an AF-Nikkor 28mm f/5D lens was used to collect 36.2-megapixel JPEG photographs (7360 x 4912 pixels per image) which were compressed for optimal quality. The aerial photographic survey was controlled with a custom intervalometer that linked the camera shutter release with Global Positioning System (GPS) event markers. GPS event markers were created by an onboard Topcon Net G3 receiver and a dual-band Topcon PG-A1 antenna mounted approximately 0.02 m above the camera, with a background sampling frequency of 5 Hz. A GPS base station with a Topcon Hyper-II receiver sampling at 1 Hz was placed approximately 10 km from the survey area and was used to differentially correct the aerial survey GPS data using post-processing kinematic (PPK) methods. Ground control points were not collected at the time of acquisition.

    Date: 2014 (process 2 of 3)
    GNSS data processing - Aerial survey GNSS data (camera coordinates and trajectory data) were processed by DGGS using kinematic (PPK) methods in Topcon Positioning Systems, Inc. Magnet Office Tools commercial GNSS software. Nearby CORS stations were used as the vertical and horizontal control. GNSS data were collected and processed in WGS84 (G1674) using WGS84 ellipsoid. The base station position was corrected using the NGS Online Positioning User Service (OPUS) with the IGS08 (EPOCH 2015.6162). Camera coordinates were converted to the North American Datum 1983 (NAD83; 2011) European Petroleum Survey Group Well Known Identification Number (EPSG) 6335 and the North American Vertical Datum of 1988 (NAVD88; Geoid12A; EPOCH 2010.00) using the National Geodetic Survey (NGS) VDatum tool (version 3.3). The coordinates are projected in UTM Zone 6 North and are in meters. The converted camera coordinates were manually correlated to image filenames to create a camera exterior orientation file for import into the photogrammetric software, Agisoft Photoscan Professional. The exterior orientation file provides the X, Y, and Z position for each photograph taken during the survey. Yaw, pitch, and roll information were not recorded during the flight.

    Date: 2014 (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 and orthoimagery have been visually inspected for data errors such as pits, border artifacts, and shifting. The end-user should be aware that pits and peaks are present in areas of some small water bodies, such as lakes and ponds, and that DSM data have not been hydro-flattened in these areas.

  2. How accurate are the geographic locations?

    All data are projected in UTM Zone 6 North (meters) using the NAD83 (2011; EPSG 6335) horizontal datum. The average camera location error was 0.12 m in the X direction (0.12 m in the Y direction), 0.14 m in the Z, combined XY error of 0.17 m. and resulting total error of 0.22 m. No ground control points, check points, or other reference datasets were available to assess the horizontal accuracy of the resulting digital surface model and orthoimagery.

  3. How accurate are the heights or depths?

    All data utilize the NAVD88 (Geoid12A; EPOCH 2010.00) vertical datum. No ground control points, check points, or other reference datasets were available to assess the vertical accuracy of the resulting digital surface model and orthoimagery.

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

    The State of Alaska Division of Geological & Geophysical Surveys collected digital aerial photographic data on October 15, 2014, using a rotary-wing (Robinson 44) airborne platform. The aerial photographic survey resulted in approximately 60 percent side lap and 80 percent end lap coverage, with an above ground-level flying height of 1100-2000 m, which resulted in 818 photos with 0.096 m per pixel ground resolution. The total area surveyed was approximately 11 km2. This data release is complete.

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

    Ground control points were not collected at the time of acquisition.


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 2019-2

  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: 18-Jun-2019
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 Tue Jun 18 17:42:55 2019