Improvement of Digital Elevation Improvement of Digital Elevation Model of Greenland Ice Sheet by Model of Greenland Ice Sheet by

Using ICESat Satellite Laser Altimetry Using ICESat Satellite Laser Altimetry DataData

Bea Csatho, Taehun Yoon and Yushin AhnByrd Polar Research Center, OSU

ICESat Data to Improve Greenland DEMs 2

Current Status and ObjectivesCurrent 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 DataInput 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) + Available DEM’ (Upper Panel) + Interpolated ICESat Residual (Lower)Interpolated ICESat Residual (Lower)= Merged DEM using

ICESat Data and Available DEM

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Available DEM Improved DEM

Close Up Comparison of DEM’s

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ATM elevations - photoclinometry DEM

Dh= -4.63 m +/- 45.06 m

ATM elevations – new DEM

Dh= -0.12 m +/- 31.84 m

Error Assessment: ATM – DEM ElevationsError Assessment: ATM – DEM Elevations

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Thank you

NEW “AND IMPROVED”SHADED RELIEF MAP