In order to ensure long-term climate records, ESA has launched the Climate Change Initiative (ESA CCI), which puts focus on 13 different Essential Climate Variables, one of them being Ice Sheets. In this program, four selected key parameters will be determined for the Greenland Ice Sheet: Surface elevation changes (SEC), surface velocities, calving front locations, and grounding line locations. This work focuses on SEC, and the goal is to develop the best routine for estimating this by means of radar altimetry. In order to find the most optimal approach we have completed a Round Robin experiment (RR) in which researchers from various European and US institutions have provided SEC estimates derived from either Envisat radar or ICESat laser altimeter data. The test area was Jakobshavn Isbræ drainage basin, and by analyzing, inter-comparing and validating the results, we have found that a combination of repeat-track and cross-over analyses will result in SEC estimates with a high spatial resolution and low error estimates.