Preliminary volcano-hazard assessment for Okmok Volcano, Umnak Island, Alaska

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Frequently-anticipated questions:


What does this data set describe?

Title:
Preliminary volcano-hazard assessment for Okmok Volcano, Umnak Island, Alaska
Abstract:
This shaded relief image of Okmok Volcano serves as the basemap for sheet 1 of the "Preliminary volcano-hazard assessment for Okmok Volcano, Umnak Island, Alaska" (DGGS RI 2004-3). The map area is centered around Okmok Volcano, on eastern Umnak Island. SRTM and AirSAR DEM datasets were combined in ArcGIS to produce a georeferenced shaded relief TIFF image of Okmok Volcano.
Supplemental_Information:
This basemap is a modified version of Schaefer, Janet R., 2005, 30-meter shaded relief image of Okmok Volcano, Umnak Island, Alaska: Alaska Division of Geological & Geophysical Surveys Raw Data File RDF 2005-1, 1 CD. The bulk of the image is based on the SRTM data, but many data holes or shadows in the original SRTM data have been filled in with the AirSAR data to create a better display. Missing data appear as black pixels, especially in steep terrain. The SRTM data was collected during an 11-day mission in February 2000, and the AirSAR data was collected on October 17, 2000. Attribute information for the following layers (entities) is included in this metadata file under the "Entity_and_Attribute_Information" section. Each layer is listed and described in detail under its own heading starting "Entity_Type_Label." Layers include:
OKhazbase    basemap, modified from Schaefer, 2005, 30-meter shaded relief image of Okmok Volcano, Umnak Island, Alaska
  1. How should this data set be cited?

    Beget, J.E., Larsen, J.F., Neal, C.A., Nye, C.J., and Schaefer, J.R., 2005, Preliminary volcano-hazard assessment for Okmok Volcano, Umnak Island, Alaska: Report of Investigation RI 2004-3, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, AK.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:150,000

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -168.7576
    East_Bounding_Coordinate: -167.5153
    North_Bounding_Coordinate: 53.7312
    South_Bounding_Coordinate: 53.1099

  3. What does it look like?

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

    Calendar_Date: 12-Feb-2000
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: raster digital 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. It contains the following raster data types:

      • Dimensions 2200 x 2667 x 1, type Pixel

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 2
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -171.0000
      Latitude_of_Projection_Origin: 0.0000
      False_Easting: 500000.0000
      False_Northing: 0.0000

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 30.003283
      Ordinates (y-coordinates) are specified to the nearest 30.003283
      Planar coordinates are specified in meters

      The horizontal datum used is WGS 1984.
      The ellipsoid used is WGS 1984.
      The semi-major axis of the ellipsoid used is 6378137.0000.
      The flattening of the ellipsoid used is 1/298.257224.

  7. How does the data set describe geographic features?

    OKhazbase.tif
    Object type is raster, describing a basemap, modified from Schaefer, 2005, 30-meter shaded relief image of Okmok Volcano, Umnak Island, Alaska (Source: Alaska Division of Geological & Geophysical Surveys)

    File Type
    The file format of the image (Source: Alaska Division of Geological & Geophysical Surveys)

    TIFF, 24-bit RGB color mode

    File Size
    The file size of the video (Source: Alaska Division of Geological & Geophysical Surveys)

    16.7 Mb

    Line (row)
    The number of lines or rows in the image (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:1
    Maximum:2200
    Units:pixels

    Sample (column)
    The number of samples or columns in the image (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:1
    Maximum:2667
    Units:pixels


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 dataset was compiled by the authors with funds from the Alaska Volcano Observatory, a joint program of the U.S. Geological Survey, the University of Alaska Fairbanks-Geophysical Institute, and the Alaska Division of Geological & Geophysical Surveys.

  3. To whom should users address questions about the data?

    State of Alaska, Division of Geological & Geophysical Surveys
    Alaska Volcano Observatory Geologist III
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907) 451-5010 (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 address all comments or questions to the e-mail address above whenever possible.


Why was the data set created?

This shaded relief image was created to illustrate, at a scale of 1:150,000, the approximate location of volcanic hazard zones around Okmok Volcano.


How was the data set created?

  1. From what previous works were the data drawn?

    NASA SRTM DEM, 2003 (source 1 of 2)
    NASA Jet Propulsion Laboratory (JPL) and the National Geospatial-Intelligence Agency, 2003, Shuttle Radar Topography Mission (SRTM) DEM data, files N53W168.hdr and N53W169.hdr: Initial release 2003, U.S. Geological Survey, unknown.

    Online Links:

    Other_Citation_Details: 2 digital files
    Type_of_Source_Media: on-line
    Source_Contribution: 1-arc second DEM data

    AirSAR DEM, 2001 (source 2 of 2)
    NASA Jet Propulsion Laboratory (JPL) and the Alaska SAR Facility (ASF), 2001, AirSAR DEM data for Okmok Volcano: Initial release September 2001, Alaska SAR Facility, Fairbanks, AK.

    Online Links:

    • NONE

    Other_Citation_Details: 1 CD
    Type_of_Source_Media: CD
    Source_Contribution: 5-meter DEM data

  2. How were the data generated, processed, and modified?

    Date: 2004 (process 1 of 3)
    Process Step 1 - Convert SRTM DEM data to ArcGRID Two SRTM DEM data sets were downloaded in May 2003 from the ftp site <ftp://edcsgs9.cr.usgs.gov/pub/data/srtm/United_States_1arcsec/1arcsec/> Files N53W168.hdr.zip and N53W169.hdr.zip
    1. Unzip SRTM DEM data file unzip FILENAME.hgt.zip
    2. Rename using lower case letters mv FILENAME.hgt filename.bil
    3. Make a hdr text file with the same name as the filename.bil, but call it filename.hdr for example, below is a header file called n53w167.hdr
    BYTEORDER M LAYOUT BIL NROWS 3601 NCOLS 3601 NBANDS 1 NBITS 16 BANDROWBYTES 7202 TOTALROWBYTES 7202 BANDGAPBYTES 0 NODATA -32768 ULXMAP -167.0 ULYMAP 54.0 XDIM 0.000277777777777 YDIM 0.000277777777777
    Note that the SRTM naming convention specifies the lower left corner coordinates, while the hdr file needs the upper left coordinates (ULXMAP, ULYMAP). The variables ULXMAP and ULYMAP are the only two variables that will change with each new hdr file.
    4. Create a grid using the arc command imagegrid Arc - imagegrid filename.bil filename
    IMAGEGRID does not support conversion of signed image data, therefore the negative 16-bit DEM values will not be interpreted correctly. After running IMAGEGRID, an easy fix can be accomplished using the following formula in Grid:
    out_grid = con(in_grid >= 32768, in_grid - 65536, in_grid)
    The converted grid will then have the negative values properly represented, and the statistics of the grid should match those listed in the .ANN file.
    5. Repeat steps 1 through 4 for both SRTM DEM data files.
    6. Merge the two data files in Arc Grid Grid - out_grid = merge(grid1, grid2)
    7. Using Project wizard in ArcToolbox, reproject the merged grid from GCS WGS84 to Transverse Mercator, Zone 2, choosing a cell size of 30 meters.

    Person who carried out this activity:

    Janet R. Schaefer
    State of Alaska, Division of Geological & Geophysical Surveys
    Alaska Volcano Observatory Geologist III
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907) 451-5010 (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 address all comments or questions to the e-mail address above whenever possible.
    Data sources used in this process:
    • NASA SRTM DEM, 2003

    Date: 2004 (process 2 of 3)
    Process Step 2 - Convert AirSAR DEM to Arc Grid. (1) AirSAR data were delivered to DGGS from the Alaska SAR Facility (ASF) in September 2001 in a geoTIFF format. (2) GeoTIFF was converted to an Arc grid using IMAGEGRID function in Arc. (3) Created a 10m contour map of the Arc grid and overlayed contour lines onto IKONOS imagery to determine horizontal accuracy (see Horizontal_Positional_Accuracy_Report). (4) Determined new values for xmin and ymin based on results discussed in Horizontal_Positional_Accuracy_Report. Applied shift to AirSAR DEM Arc Grid using the following command in Arc Grid newgrid = shift(oldgrid, newxmin, newymin).

    Person who carried out this activity:

    Janet R. Schaefer
    State of Alaska, Division of Geological & Geophysical Surveys
    Alaska Volcano Observatory Geologist III
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907) 451-5010 (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 address all comments or questions to the e-mail address above whenever possible.
    Data sources used in this process:
    • AirSAR DEM, 2001

    Date: 2004 (process 3 of 3)
    Process Step 3 - Merge the AirSAR and SRTM DEMs and create a georeferenced shaded relief TIFF. (1) Merge the horizontally corrected AirSAR Arc grid with the SRTM DEM Arc Grid in Arc Grid by replacing all SRTM DEM values less than zero with the AirSAR DEM value. Grid: newgrid = con(srtmdemgrid < 0, airsardem, srtmdemgrid). (2)In ArcMap 8.2, create a hillshade with 2x vertical exaggeration using 3D-Analyst extension. (3) Clip the grid using GRIDCLIP command to encompass an area suitable for displaying hazard zones around Okmok Volcano (see bounding coordinate information). (4)Convert the resulting hillshaded grid into a TIFF using the Arc command GRIDIMAGE. Grid: GRIDIMAGE in_grid NONE out_image TIFF. (5)In ArcMap 8.2, georeference the image to UTM Zone 2, WGS 84, by adding corner control points. RMS error = 0. Update georeferencing, then rectify using bilinear interpretation. (5) Modify the tiff in Corel Photopaint to a 24-bit RGB image and change the color of the ocean (outer black pixels) to blue.

    Person who carried out this activity:

    Janet R. Schaefer
    State of Alaska, Division of Geological & Geophysical Surveys
    Alaska Volcano Observatory Geologist III
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907) 451-5010 (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 address all comments or questions to the e-mail address above whenever possible.
  3. What similar or related data should the user be aware of?

    Schaefer, Janet R., 2005, 30-meter shaded relief image of Okmok Volcano, Umnak Island, Alaska: Raw Data File RDF 2005-1, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, AK.

    Online Links:

    Other_Citation_Details: 1 CD


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

  1. How well have the observations been checked?

    RGB values of the hillshade were computed from the DEM data using ESRI software Arc 8.2 3-D analyst extension.

  2. How accurate are the geographic locations?

    Sub-meter horizontal/vertical accuracy GPS points that were acquired during the summer field season 2000 and 2001 were used to assess the geospatial accuracy of IKONOS remotely sensed imagery. The GPS data collection points were chosen so that they would be visible and distinguishable on the imagery. In a GIS, the GPS points were overlain on the georeferenced IKONOS imagery. The horizontal geospatial accuracy of the remotely sensed imagery was determined to be less than 15 meters. This imagery was then used as the geospatially accurate reference to determine the precision of the DEM data. A 10-meter contour map was made of each DEM dataset. The contour map based on the SRTM DEM data was overlain on the sub-15-meter accurate IKONOS imagery. Visual inspections at a zoom scale of 1:3,000 determined that the horizontal accuracy was correct and no adjustments were made to the SRTM DEM data. The contour map based on the AirSAR DEM data, however, appeared to be inaccurate (creeks did not line up with V-contours, high points did not line up with high-point closed contours, etc.). At a zoom scale of 1:3,000, ten visually distinguishable points were chosen to determine an X-shift and Y-shift needed to align the AirSAR DEM-derived contour data to the imagery. Results (average and standard deviation reported): X = 41 +/- 9 meters, Y = 198 +/- 19 meters. A shift of X = -41 and Y = 198 was applied to the AirSAR DEM data set.

  3. How accurate are the heights or depths?

    Although the vertical data cannot be directly derived from this TIFF data, this vertical positional accuracy report was written to qualify the resulting shade effect that has been derived from a conversion between vertical value and RGB hillshade value. After an assessment of the horizontal accuracy was complete, it was then possible to assess the vertical accuracy (see Horizontal_Positional_Accuracy_Report). Thirty-five sub-meter horizontal/vertical accuracy GPS points that were acquired during the summer field season 2000 and 2001 were used to assess the vertical accuracy. A calculation of the known GPS vertical value minus the SRTM DEM vertical value for the same horizontal position showed that the SRTM vertical data was under-estimating the elevation by 19.3 +/- 4.3 meters (mean and standard deviation of the 35 points reported). Twenty-nine GPS points were used in the same way to assess the vertical accuracy of the AirSAR DEM data. The results of the GPS minus AirSAR vertical values for the same horizontal point (after the X-Y shift was applied) are -0.3 +/- 5.44 (mean and standard deviation reported for 29 points). In conclusion, the vertical values for the SRTM DEM dataset overestimate the true vertical value by about 19 meters, and the AirSAR DEM data vertical values are accurate to about 5 meters. Prior to creating the shaded relief image, these two datasets were combined by filling in any holes of the SRTM data with the AirSAR data. The bulk of the data used to derive the shaded relief image came from the SRTM data, and therefore the vertical accuracy for the values used to create the shaded relief image are taken to be about 19 meters. This agrees well with the NASA reported error for the dataset, which is 20 meters.

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

    This shaded relief image displays topographic features for all of Okmok Volcano, and only a very small area to the east, across Umnak pass, on Unalaska Island. It was originally intended as a base layer for the display of geographic, geologic, and volcano-hazard features of Okmok Volcano, at a scale of 1:150,000.

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

    Shaded relief image was checked for accurate display of topographic features with on-the-ground inspection (geologic fieldwork), helicopter overflights, and imagery sets such as Landsat7, airphotos, and IKONOS.


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 are 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. 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.

  1. Who distributes the data set? (Distributor 1 of 1)

    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
    Natural Resource Technician
    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
    Contact_Instructions:
    Please view our web site (<http://www.dggs.dnr.state.ak.us>) 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?

    Report of Investigation 2004-3

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services 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, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requester or anyone else exceed the fee paid for the electronic service or product.

  4. How can I download or order the data?

  5. What hardware or software do I need in order to use the data set?

    Geospatial software is required to view and manipulate this shaded relief image, such as ENVI <http://www.ittvis.com/envi/>, ER Mapper <http://www.ermapper.com/> or ESRI ArcGIS <http://www.esri.com/software/arcgis/index.html>. Free versions of the software listed may be available to simply view the data.


Who wrote the metadata?

Dates:
Last modified: 06-May-2008
Last Reviewed: 06-May-2008
To be reviewed: 03-Oct-2009
Metadata author:
State of Alaska, Division of Geological & Geophysical Surveys
c/o Janet R. Schaefer
Alaska Volcano Observatory Geologist III
3354 College Road
Fairbanks, AK 99709-3707
USA

(907) 451-5010 (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 contact us through the e-mail address above whenever possible.
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)


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