Satellite Altimetry in Glaciology : SARAL/AltiKa Benefits for Ice Sheets Survey, Focus on Antarctica
Michel, Aurélie1; Ollivier, Annabelle2; Flament, Thomas1; Remy, Frédérique1
1LEGOS, FRANCE; 2CLS, FRANCE
AltiKa/SARAL, launched in February 2013 on exactly the same orbit than the previous ESA altimetric mission ERS1-2 and Envisat, is a very promising mission for ice sheets survey. It will extend the current observations and provide new informations due to its innovative characteristics. First, it will reduce one of the greatest errors in the retrieved height on ice sheets. Indeed, the comparison with Icesat suggested a penetration error of -0.45m for a slope less than 2 m/km and increases up to -1m for slopes higher than 10m/km. The variability of the error induces surface fluctuations of 0.5m to 3m depending on the slope, jeopardizing the retrieved surface height precision. AltiKa operate in Ka band (35Ghz, 500 MHz), so that the penetration depth into the snowpack is nearly 50 times lower than in Ku-band, with a 5cm value approximatively. The waveform consists thus in the surface, near-surface scattering, allowing a better characterization in the penetration error. Moreover, the footprint is narrower, the waveform is less distorted by km-scale topography. Because of this and a weaker penetration, the waveform will be more easily retrackable. Moreover, the better sampling of the waveform is achieved thanks to the larger bandwidth and a better vertical resolution, it will improve the retracking technique. We plus have twice as much along-track measurements, thanks to the higher PRF (Pulse Repetition Frequency). Finally, it is also the first time the surfaces are surveyed simultaneously by an active and passive sensor at the same frequency, allowing more reliability in the electromagnetic models to retrieve the snowpack parameters. AltiKa is an unprecedented enhancement in altimetry and we show in this poster preliminary results of the improvements it will provide in glaciology using the first data brought by the mission.