The Altika altimetry mission: science objectives and system definition

During the OCEANOBS99 Conference, scientists argued that a multi-satellite altimetric system should be maintained beyond 2005. In 1999, proposals were formulated to complement the Jason series of high accuracy ocean altimetry missions. In that frame, J. Verron et al. (1999) produced the "Altika" proposal which is presented in this paper. As a complement to the Jason series, the present authors analyze the possibilities of flying the Altika mission on a microsatellite to answer the main orbits science requirements. In terms of altimetric system, preliminary accommodation studies proved that embarking a combined Ka-band altimeter and a two frequency (23.8 and 37.5 GHz) radiometer together with a laser retroreflector and DORIS is feasible on micro-satellite platforms. Choosing the Ka-band for the altimeter results in low ionospheric effects whereas tropospheric effects and attenuation by rain are larger than for Ku-band altimeters. However, the availability of simultaneous passive and active measurements at Ka-band allows a better quantification of the corresponding altimeter perturbations. The joint use of both types of measurements may also help improving our knowledge of statistics of rain, and interpreting better measurements over ice surfaces.