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

ICESat Data to Improve Greenland DEMs2 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 m 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.

ICESat Data to Improve Greenland DEMs3 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 (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

ICESat Data to Improve Greenland DEMs4 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.

ICESat Data to Improve Greenland DEMs5 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)

ICESat Data to Improve Greenland DEMs6 Distribution of Data Points ICESat (red) and ATM (blue)

ICESat Data to Improve Greenland DEMs7 ‘Available DEM’ (Upper Panel) + Interpolated ICESat Residual (Lower) = Merged DEM using ICESat Data and Available DEM

ICESat Data to Improve Greenland DEMs8 Available DEM Improved DEM Close Up Comparison of DEM’s

ICESat Data to Improve Greenland DEMs9 ATM elevations - photoclinometry DEM Dh= m +/ m ATM elevations – new DEM Dh= m +/ m Error Assessment: ATM – DEM Elevations Error Assessment: ATM – DEM Elevations

ICESat Data to Improve Greenland DEMs10 Thank you NEW “AND IMPROVED” SHADED RELIEF MAP