SMOS-Next: High Resolution Observations of Soil Moisture and Ocean Salinity.
Cabot, Francois1; Kerr, Yann1; Rouge, Bernard1; Soldo, Yan1; Lesthievent, Guy2; Anterrieu, Eric3

Since shortly after its launch on November 2nd, 2009, SMOS has been acquiring global maps of brightness temperature at L-band, in full polarization mode, for a variety of incidence angles. The nominal ground resolution granted by the two dimensional interferometric radiometer is about 43km at boresight. These maps are used to retrieve soil moisture over land and surface salinity over oceans. The achieved accuracy, after 3 years on orbit, is slightly above the required 4% for soil moisture, with expected improvements at various levels of the processing and instrument characterization. Although these achievements seem well in line with climate and NWP needs, they are still short of satisfying to more stringent requirements, like water resource managements, fine coastal analysis of fresh water flow, and crisis management. These applications clearly need a dramatic increase in the spatial resolution of the final products. And despite some promising works related to resolution enhancement based on data fusion that have been successfully applied to SMOS data, the original brightness temperature maps are definitely too coarse to address these issues. This paper will present the instrumental concept for a new satellite based mission aimed at fulfilling these needs. This concept relies on time-shifted interferometry, as an extension to SMOS capabilities. Preliminary basic design will be presented and assessment of expected system performances based on ground based experimentation and numerical simulation will be demonstrated. At last a status of the project development will be given. The proposed mission concept relies on the same basic principles as SMOS 2 dimensional radiometric interferometer. But in order to use larger baselines, thus giving access to finer ground resolution will also make use of the satellite motion to artificially extend the synthetic aperture of the radiometer. Of course, since the observed radiation is not coherent light, the analysis has to be conducted within very narrow bands to guarantee a coherence length consistent with the required baseline length. On the other hand, accumulation of these fine bands afterwards can bring back radiometric accuracy within acceptable range. These basic principles have been used to build the concept of an interferometer operating on both simultaneous acquired baselines and delayed ones. Real time correlations are measured along a direction perpendicular to the direction of flight whereas time delayed correlations are accumulated along the direction of flight.