Mission Objectives and Scientific Requirements of the Soil Moisture and Ocean Salinity (SMOS)

The main scientific objectives of the Soil Moisture and Ocean Salinity (SMOS) mission are to observe two crucial variables: soil moisture over land surface and sea surface salinity over oceans. The mission should also provide information on root zone soil moisture and vegetation and contribute to significant research in the field of the cryosphere SMOS is a demonstrator with broad and ambitious scientific objectives, as the lack of global observations of salinity and soil moisture are retarding progress in many research fields. The need for these data has been highlighted for a long time in major international scientific initiatives. The mission will give Europe a clear lead in this area. The SMOS concept may also pave the way for more ambitious concepts providing higher spatial resolution. The baseline instrument of SMOS is a L-band (1.4GHz) 2D interferometric radiometer, Y shaped, with three arms each about 4.5m long. The instrument will be accommodated on a PROTEUS platform. The folded satellite i s compatible with most launchers. The technological solution is feasible as proven by several pre-developments (see Microwave Imaging Radiometer using Aperture Synthesis (MIRAS)). However, significant challenges are still to be addressed for the sea surface salinity retrieval over oceans, and in terms of accounting for mixed pixels and variable footprints for soil moisture retrieval over land. These issues will be studied further during Phase A studies supported by dedicated campaign activities planned to be conducted in the near future.