This data set is part of the ESA Greenland Ice sheet CCI project. The data set provides surface elevation changes (SEC) for the Greenland Ice sheet derived from satellite (ERSâ1, ERSâ2, Envisat and Cryosat) radar altimetry. The ice mask is based on the GEUS/GST land/ice/ocean mask provided as part of national mapping projects, and based on 1980âs aerial photography. The data from ERS and Envisat are based on a 5âyear running average, using combined algorithms of repeatâtrack (RT), alongâtrack (AT) or crossâover (XO) algorithms, and include propagated error estimates. It is important to note that different processing algorithms were applied to the ERSâ1, ERSâ2, Envisat and CryoSat data; for details see the Product User Guide (PUG), available on the CCI website and in the documentation section here. For ERSâ1, the radar data were processed using a crossâover algorithm (XO) only. For ERSâ2 data and Envisat data in repeat mode, a combination of RT and XO algorithms was applied, followed by filtering. For acrossâmission (i.e. ERSâ2âEnvisat) combinations, and for Envisat operating in a drifting orbit, an AT and XO combination was applied (the difference between RT and AT algorithms is that AT use reference tracks and searches for data in the vicinity of this track). For CryoSat data a binning/gridding and plane fit method has been applied, following by weak filtering (0.05 degree resolution).