Improved weather forecast and climate monitoring relly on a better quantification of soil moisture (SM) and sea surface salinity (SSS). The most accurate way to measure them from remote sensors is by usign radiometers at L band, where the sensitivity of the brightness temperature is maximum and the atmosphere is almost transparent. In order to provide a global coverage of these basic parameters within a revisit time of 3 days and 30-50 Km spatial resolution, the SMOS mission was recently selected by ESA in the frame of the Earth Exploer Opportunity Missions. The sensor being considered for this mission (called MIRAS) uses the concept of 2D interferometric radiometry~(1,2,3), and is scheduled to be launched in 2005. A demonstrator consisting of a number of receivers is now under development by CASA (E) by contract with ESA. This work presents the block diagram of a single receiver chain in the SMOS instrument and its main requirements in terms of mission tradeoffs.
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