shaded-relief-image: A georeferenced TIFF image of Okmok Volcano, Umnak Island, Alaska
Schaefer, J.R., 2005, 30-meter shaded relief image of Okmok Volcano, Umnak Island, Alaska: Raw Data File RDF 2005-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.Online Links:
This is a raster data set.
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 World Geodetic System of 1984.
The ellipsoid used is WGS 84.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257223563.
Shuttle Radar Topography Mission (SRTM) DEM data is available for download courtesy of NASA. AirSAR data was provided by NASA JPL via Rick Guritz at the Alaska SAR Facility (ASF)
(907)451-5020 (voice)
dggsgis@alaska.gov
This georeferenced TIFF was created to be used as a base layer for other geographic information system (GIS) projects that display geographic or geologic data pertaining to Okmok Volcano and eastern Umnak Island. This shaded relief image displays topographic features for all of Okmok Volcano, and a small area to the east, across Umnak pass, on Unalaska Island.
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.
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.
Data sources used in this process:
Data sources used in this process:
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, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.Online Links:
Schaefer, J.R., 2005, 30-meter shaded relief image of Okmok Volcano, Umnak Island, Alaska: Raw Data File RDF 2005-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.Online Links:
Schaefer, J.R., Larsen, J.F., and Unema, J.A., 2012, Digital elevation model (DEM) and shaded relief image of Okmok Caldera, 2010: Raw Data File RDF 2011-6, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.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 accuracey 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 dataset. An accuracy of less than 60 meters, or 2 cell sizes, is observed for all visually recognizable data points that can be used to compare the IKONOS imagery to the DEM-derived contour data.
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 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, air-photos, and IKONOS.
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.
(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov
RDF 2005-1
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.
DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media by mail, phone, fax, or email from the DGGS Fairbanks office. 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. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for the exact shipping amount.
| Data format: | GeoTIFF |
|---|---|
| Network links: |
<http://dx.doi.org/10.14509/7041> |
(907)451-5020 (voice)