rdf2011-6-okmok-dem-21-jan2010 DEM dataset provides elevation data of the Okmok Caldera, georeferenced TIFF format (.tif and .tfw files) rdf2011-6-okmok-shaded-relief shaded relief image of the Okmok Caldera, georeferenced TIFF format (.tif and .tfw files)
Schaefer, J.R., Larsen, J.F., and Unema, J.A., 2011, Digital elevation model (DEM) and shaded relief image of Okmok Caldera, 2010: Raw Data File RDF 2011-6, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, AK, USA.
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 2
Ordinates (y-coordinates) are specified to the nearest 2
Planar coordinates are specified in meters
The ellipsoid used is World Geodetic System of 1984.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257223563.
The original DEM was created by 'i-cubed:information integration & imaging LLC'; the initial Worldview images were provided by Rick Wessels, U.S. Geological Survey, Alaska Volcano Observatory.
The DEM dataset provides high-resolution elevation data for Okmok Caldera. The georeferenced shaded relief map of Okmok Caldera provides a basemap for visualization of new geographic features following the 2008 eruption
Attributes for the DEM are the elevation values for the individual pixels and the encoded values for easting and northing coordinates. Attributes for the shaded relief image are the elevation values for the individual pixels and the encoded values for easting and northing coordinates. See horizontal and vertical positional accuracy sections of this metadata file to learn more about the accuracy of this data.
Based on several years of fieldwork and thus familiarity with the geographic features around Okmok volcano, in addition to known locations of GPS survey sites, there are several point locations that can be accurately identified on the new DEM surface.A comparison of horizontal position was made by plotting these known locations along with the new DEM in a GIS.See Horizontal Positional Accuracy Explanation for more details.
Assessment of the DEM vertical accuracy is complicated by the high rate of erosion and changing surface hydrology that occurred between the image acquisition date of January 21, 2010 and the RTK GPS survey seven months later in August of 2010.The most significant vertical changes due to erosion occurred within the caldera in areas with the most ash fall.As a first step to assessing the vertical accuracy of the DEM, only sites outside the caldera that experienced less than 2 cm of ash fall were used to compare the surveyed point values to the DEM cell values. See Vertical Positional Accuracy Explanation for more details.
The DEM coverage area is limited to the size of the original Worldview-1 image stereo pair and thus does not encompass the entire volcano and is mostly centered about the caldera.
Several campaign GPS sites and RTK surveyed GPS sites were plotted in a GIS along with the DEM to ensure that both horizontal placement and vertical Z values were reasonably accurate.
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