Improvement of Digital Elevation Model of Greenland Ice Sheet by Using ICESat Satellite Laser Altimetry Data

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Improvement of Digital Elevation Model of
Greenland Ice Sheet by Using ICESat Satellite
Laser Altimetry Data

• Bea Csatho, Taehun Yoon and Yushin Ahn
• Byrd Polar Research Center, OSU

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Current Status and Objectives
Available DEMs of the Greenland Ice Sheet are
based on satellite radar altimetry data (e.g.,
Bamber and Ekholm, 2001), or on the combination
of radar altimetry data with AVHRR imagery by
using photoclinometry techniques to fill the
regions between radar orbits (Scambos and
Harran). Here out referred to as available
DEM Elevation errors of these DEMs range from a
few meters at the middle of the ice sheet (gt2000
m) to 50-100m in marginal regions. Our objective
is to improve the accuracy of these Available
DEMs by using ICESat data. The following
example is shown for the boxed region, however a
whole ice sheet DEM is currently being
developed.
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Input Data

• 3/20/03- 6/23/05 ICESat satellite laser altimetry
  observations (L1, L2a-c, L3a-c) (L3d and L3e
  should be added)
• Airborne Topographic Mapper (ATM) laser altimetry
  data from 1999-2003 (Krabill, NASA WFF)
• Available DEMs from Bamber et al. (2001) and
  Scambos and Harran
• Landcover map of Greenland from KMS
• Categories ice sheet, local ice caps, land and
  ocean

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Processing Steps

• Step 1 Detection and removal of outliers from
  the ICESat and ATM data sets.
• Only points on ice sheet and local ice caps are
  used
• ICESat outliers elevations are compared with
  median elevation of 2 X 2 km grid cells. Points
  with elevation difference gt 40 m from the median
  are removed.
• ATM outliers are removed by using the same
  technique. In addition, all observations in
  cells with less than 2 data points are removed.
• Step 2 Residuals between the ICESat data and the
  Available DEM' are computed at each ICESat point
  over the ice sheet and local ice caps. Residuals
  are set zero at grid posts over land and ocean
• Step 3 Residuals are interpolated into a regular
  grid by using minimum curvature interpolation.

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Processing Steps cont.

• Step 4 Improved DEM Available DEM
  interpolated residual
• Step 5 The accuracy of the improved DEM is
  assessed by using the ICESS data set (compressed
  ATM airborne laser scanning data derived by plane
  fitting to original laser point swaths)

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Distribution of Data Points ICESat (red) and ATM
(blue)
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Available DEM (Upper Panel) Interpolated
ICESat Residual (Lower)
Merged DEM using ICESat Data and
Available DEM
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Close Up Comparison of DEMs
Available DEM Improved DEM
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Error Assessment ATM DEM Elevations
ATM elevations - photoclinometry DEM Dh -4.63
m /- 45.06 m
ATM elevations new DEM Dh -0.12 m /- 31.84 m
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NEW AND IMPROVED SHADED RELIEF MAP
Thank you