MWR and DORIS - Supporting Envisat's radar altimetry mission

Following on from the great success of its ERS-1 and ERS-2 satellite missio ns, which have contributed to a much better understanding of the role that oceans and ice play in determining the global climate, ESA is currently pre paring to launch Envisat, the largest European satellite to be built to dat e. The Envisat altimetric mission objectives are addressed by the Radar Altime ter instrument (RA-2), complemented by the Microwave Radiometer (MWR), used to correct the error introduced by the Earth's troposphere, and by the Dop pler Orbitography and Radio-positioning Integrated by Satellite (DORIS) ins trument. DORIS has been developed by ONES, and is already operational on se veral satellites. It will measure Envisat's orbit to an unprecedented accur acy, thereby serving as a major source of the improved performance that the RA-2 system will be able to achieve.