Transcript Improvement of Greenland DEM by Using ICESat Satellite

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
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 (>2000 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 > 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 DEM’s
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
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