OKhazbase basemap, modified from Schaefer, 2005, 30-meter shaded relief image of Okmok Volcano, Umnak Island, Alaska
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:
This is a Raster data set. It contains the following raster data types:
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.
TIFF, 24-bit RGB color mode
16.7 Mb
| Range of values | |
|---|---|
| Minimum: | 1 |
| Maximum: | 2200 |
| Units: | pixels |
| Range of values | |
|---|---|
| Minimum: | 1 |
| Maximum: | 2667 |
| Units: | pixels |
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.
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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.
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:
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
Person who carried out this activity:
(907) 451-5010 (voice)
(907) 451-5050 (FAX)
dggspubs@alaska.gov
Person who carried out this activity:
(907) 451-5010 (voice)
(907) 451-5050 (FAX)
dggspubs@alaska.gov
Person who carried out this activity:
(907) 451-5010 (voice)
(907) 451-5050 (FAX)
dggspubs@alaska.gov
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:
RGB values of the hillshade were computed from the DEM data using ESRI software Arc 8.2 3-D analyst extension.
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.
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.
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.
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.
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.
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Report of Investigation 2004-3
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Current publication is available on paper. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard.
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| Data format: | TIFF |
|---|---|
| Network links: |
<http://dx.doi.org/10.14509/7042> |
| Media you can order: |
CD-ROM
(format Joliet)
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Digital files on CD-ROM are available for $10.00 (contact information below). No fees charged for downloaded files.
Order by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). The DGGS web site (<http://www.dggs.alaska.gov/>) has a list of electronic data available and an order form that can be printed. Payment accepted: Cash, check, money order, VISA, or MasterCard.
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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.
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