Ross Ice Shelf Transantarctic outlet glacier surface elevations from 1960-1964

Description

Historical digital elevation models (DEMs) of Darwin/Hatherton, Byrd, Nimrod, Beardmore, Shackleton, Amundsen, and Scott glaciers have been generated for portions of their grounded ice using oblique trimetrogon aerial (TMA) photography with modern-day ground control in structure-from-motion photogrammetric (SfM) software. The TMA photos were collected over 1960-1964 by the U.S. Navy at high-oblique (>30º) angles at altitudes ranging from 6,100 to 7,600 m. The 9x9 in (23x23 cm) film negatives were digitized decades later by the U.S. Geological Survey at a resolution of 25 μm and freely available for download. A total of 65 oblique photographs were used in sets of three or five (2-3 sets per glacier) in SfM photogrammetric software with ground control of stable terrain that was manually extracted from the Regional Elevation Model of Antarctica (REMA; https://www.pgc.umn.edu/data/rema/) 2 m DEM strips from 2012-2017. 22-30 ground control points were used for each set of processed photos. The final raster products have a gridded resolution of 250 m, are horizontally transformed to WGS84 Antarctic Polar Stereographic (EGSP: 3031), and are vertically projected to WGS84. The mean residual from the camera calibration for all 17 sets of TMA photos is less than 1 pixel and the average error for the ground control points from the bundle adjustment is 2.58 pixels or 2.77 m, -6.38 m, and 0.65 m in the X, Y, and Z in the directions, respectively. The resulting DEMs were co-registered to the REMA datasets over stable terrain (static elevations with slopes <20º) and then differenced to determine the amount of geodetic mass change the outlet glaciers have undergone for ~60 years. To assess the error of the historical DEMs, elevation differences over stable terrain for values within the 95% confidence value were analyzed. The mean difference in elevation values was -3.311 m. The median is -1.895 m and the normalized median absolute deviation is 1.806 m. The total amount of elevation uplift due to isostatic adjustment for the region is ~3 mm/yr. Since it is well within the margin of error for the historical DEMs, it was omitted. Differencing the historical elevations from the present-day DEM reveals little change has occurred in the mass of these seven glaciers. The total mean elevation change for 1960-2017 is 0.331 m with Nimrod Glacier gaining the most in elevation with 6.68 m and Amundsen Glacier undergoing the most amount of thinning at 3.10 m. The results show that for these seven Transantarctic outlet glaciers south of 79º, the minor elevation changes they have experienced shows that they are in relatively stable condition. To date, this is the oldest elevation dataset of the Transantarctic Mountains.

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