Soil moisture and sea surface salinity are directly linked to the global water cycle that governs the exchange of water between land, oceans and the atmosphere. High and low sea surface salinity patches can be directly linked to evaporation and precipitation respectively and with knowledge of the soil moisture it is possible to gain a deeper insight into the water cycle budget. Furthermore ocean salinity is a key variable in ocean circulation by effecting water density and thus density driven currents.
The European Space Agency (ESA) has launched the soil moisture and ocean salinity (SMOS) remote sensing satellite in November 2009 to measure these two parameters. SMOS is part of the Earth Explorer Opportunities as part of ESA Living Planet programme and as a requisite for opportunity missions and carries a new sensor technology previously not used in space. The payload is a 2-dimensional interferometric passive microwave sensor measuring the incoming blackbody radiation at L-band frequency of 1.4 GHz which at this frequency is correlated to soil moisture and salinity that affect the dielectric constant of the radiating material and thus the radiation. Interferometry to simulate a synthetic aperture has been used extensively on active sensors but the simulation of a synthetic aperture for a passive radiometer is a novel approach in space.
An international consortium of scientists in cooperation with ESA is in charge to calibrate and validate the data that SMOS is measuring against simultaneous measurements on the ground. SMOS has gone through a 6 months commissioning phase during which the sensor was calibrated to deliver the data with the accuracy that has been aimed for.
The remote sensing group at the Institute of Oceanography in Hamburg is part of that international Calibration and Validation team and has set up national SMOS Cal Val activities.
The following link will take you directly to the SMOS Salinity project website.