Despite the loss of CryoSat, ESAs first Earthopportunity mission, during its launch sequence in Oct2005 ESA have been fortunate enough to have acquired,processed to Level 1b and analysed a significant amountof campaign data from ESAs demonstration AirborneSAR/Interferometric Radar Altimeter System (ASIRAS)designed to have similar functionality to CryoSatsSynthetic Interferometric Radar Altimeter (SIRAL).This data acquisition took place for the original purposeof validating CryoSat retrievals.Our initial analyses of the level 1b data have revealedsome very interesting results both over land and sea icetest sites from respective campaigns conducted in theArctic during the land-ice spring/autumn campaigns of2004 and for sea-ice in the Bay of Bothnia duringMarch 2005. Since a further ASIRAS campaign in theArctic is guaranteed for April/May 2006 we look at howthis data can be exploited in view of future ESA Earthobservation radar altimeter missions. Verification of theASIRAS data with coincident laser altimeter and in-situdata collected at test sites is also presented.The paper also provides a review of key space and airborne radar altimeters dating from 1957 including thoseusing the synthetic aperture radar (SAR) technique asapplied to radar altimeters leading to the development ofCryoSat.