| Abstract |
ASIRAS is an airborne SAR-altimeter instrument of ESA in preparation for CryoSat validations campaigns. The objectives are to increase the confidence level in the expected instrument performance and to validate the measurement/processing concepts prior to the CryoSat implementation and launch - and to use the instrument after the spaceborne mission launch in underflights during the commissioning phase of the CryoSat mission for calibration validation analysis.
The SIRAL (SAR/Interferometric Radar Altimeter) instrument of CryoSat, built by Alcatel Alenia Space, happens to be a new technology development with rather demanding observation requirements in accuracy; namely to observe ice sheet interiors and the ice sheet margins for sea ice and other topography. SIRAL is a nadir-looking radar instrument operating in Ku-band. In along-track direction, the lateral resolution is enhanced by means of Doppler filtering, while in the across-track direction, interferometric techniquesare applied. While this concept had been verified by simulations, no dedicated experimental validation had been performed.
ASIRAS was built by Radar Systemtechnik (RST) of Rorschacherberg, Switzerland with the support of the Alfred Wegener Institute (AWI) and Optimare for the implementation and operation on an aircraft. The instrument design is very similar to the D2P (Delay-Doppler Phase-monopulse Radar) system, an airborne system of JHU/APL, which demonstrated the new technology in varies test flights over Greenland in the spring and summer of 2000. - However, with the D2Ps range resolution of ~40 cm, it became clear that if one could improve on this value, then it would be possible to provide a better opportunity to understand radar pulse penetration within the first few meters of snow pack and therefore provide a better tool for validating the CryoSat retrievals.
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