ESA's Ice Sheets CCI: validation and inter-comparison of surface elevation changes derived from laser and radar altimetry over Jakobshavn Isbræ, Greenland – Round Robin results
J. F. Levinsen1, K. Khvorostovsky2, F. Ticconi3,4, A. Shepherd3, R. Forsberg1, L. S. Sørensen1, A. Muir5, N. Pie6, D. Felikson6, T. Flament7, R. Hurkmans8, G. Moholdt9, B. Gunter10,11, R. C. Lindenbergh10, and M. Kleinherenbrink101DTU Space, National Space Institute, Technical University of Denmark, Elektrovej, Building 327 + 328, 2800 Kongens Lyngby, Denmark 2Nansen Environmental and Remote Sensing Center, Thormøhlens gate 47, 5006 Bergen, Norway 3School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK 4EUMETSAT, Remote Sensing and Product Unit, Eumetsat Allee 1, 64295 Darmstadt, Germany 5University College London, Gower Street, London, WC1E 6BT, UK 6University of Texas, Center for Space Research, 3925 West Braker Lane, Suite 200, Austin, Texas 78759-5321, USA 7Laboratoire d'Études en Géophysique et Océanographie Spatiales (LEGOS), 14 avenue Edouard Belin, 31400 Toulouse, France 8Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, University Road, Bristol, BS8 1SS, UK 9Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, 92093-0225, USA 10Department of Geoscience & Remote Sensing, Delft University of Technology, 2600 GA Delft, the Netherlands 11School of Aerospace Engineering, Georgia Institute of Technology, 270 Ferst Drive, Atlanta, GA 30332-0150, USA
Received: 17 Oct 2013 – Accepted for review: 04 Nov 2013 – Discussion started: 15 Nov 2013
Abstract. In order to increase the understanding of the changing climate, the European Space Agency has launched the Climate Change Initiative (ESA CCI), a program which joins scientists and space agencies into 13 projects either affecting or affected by the concurrent changes. This work is part of the Ice Sheets CCI and four parameters are to be determined for the Greenland Ice Sheet (GrIS), each resulting in a dataset made available to the public: Surface Elevation Changes (SEC), surface velocities, grounding line locations, and calving front locations. All CCI projects have completed a so-called Round Robin exercise in which the scientific community was asked to provide their best estimate of the sought parameters as well as a feedback sheet describing their work. By inter-comparing and validating the results, obtained from research institutions world-wide, it is possible to develop the most optimal method for determining each parameter. This work describes the SEC Round Robin and the subsequent conclusions leading to the creation of a method for determining GrIS SEC values. The participants used either Envisat radar or ICESat laser altimetry over Jakobshavn Isbræ drainage basin, and the submissions led to inter-comparisons of radar vs. altimetry as well as cross-over vs. repeat-track analyses. Due to the high accuracy of the former and the high spatial resolution of the latter, a method, which combines the two techniques will provide the most accurate SEC estimates. The data supporting the final GrIS analysis stem from the radar altimeters on-board Envisat, ERS-1 and ERS-2. The accuracy of laser data exceeds that of radar altimetry; the Round Robin analysis has, however, proven the latter equally capable of dealing with surface topography thereby making such data applicable in SEC analyses extending all the way from the interior ice sheet to margin regions. This shows good potential for a~future inclusion of ESA CryoSat-2 and Sentinel-3 radar data in the analysis, and thus for obtaining reliable SEC estimates throughout the entire GrIS.
Levinsen, J. F., Khvorostovsky, K., Ticconi, F., Shepherd, A., Forsberg, R., Sørensen, L. S., Muir, A., Pie, N., Felikson, D., Flament, T., Hurkmans, R., Moholdt, G., Gunter, B., Lindenbergh, R. C., and Kleinherenbrink, M.: ESA's Ice Sheets CCI: validation and inter-comparison of surface elevation changes derived from laser and radar altimetry over Jakobshavn Isbræ, Greenland – Round Robin results, The Cryosphere Discuss., 7, 5433-5460, doi:10.5194/tcd-7-5433-2013, 2013.