Long Term Survey of Antarctica with Altimetry: ERS1/2, EnviSat, SARAL, the Key Importance of Continuous Observations
Remy, Frederique1; Flament, Thomas2; Michel, Aurelie2; Verron, Jacques3

For almost 20 years, ERS-1/2, EnviSat and SARAL/AltiKa satellite altimeters surveyed Greenland and Antarctica ice sheets on a 35-day repeat orbit, providing a unique data set for ice sheets mass balance studies. In particular from September 2002 to October 2010, EnviSat provides up to 85 repeat cycles that may be along-track reprocessed in order to retrieve height variability and trend with a good space resolution for the objectives of ice sheet survey. It also allows to capture acceleration of losses or gains and some short scale events such as emptying and refilling subglacial lakes. The space and time variability of the height but also of the backscatter and waveform shape parameters will be shown over Antarctica with the help of this high resolution along-track observations from ERS1/2 and EnviSat. It is shown that at least 50 repeat cycles are needed to reach the required accuracy on the elevation trend so it strengthens the need of continuous observations along the same repeat orbit.
At the time of writing the abstract, a joint CNES/ISRO mission, SARAL, with the AltiKa payload on board, is planned to be launched in February exactly on the same orbit (more or less 1 km in the across-track direction). This will allow an extension of previous ESA missions. Moreover, AltiKa operates in Ka-band (35.75 GHz), a higher frequency than the classical Ku-band (13.6 GHz), leading to important modifications and potential improvements in the penetration of the radar wave within the snow pack.