First Results from Taklamagan Desert Campaign for Smos Cal/val

Chinese academy of sciences) SMOS is a satellite dedicated to measuring soil moisture(SM) and sea surface salinity (SSS) continuously at a resolution around 50km from space for the first time in the history. It is also the first spaceborne mission that carries a synthetic aperture radiometer at L band. CAL/VAL is a big challenge to this kind of mission considering its frequency, resolution scale and imaging characteristics. Taklamagan desert has been selected as a key site for SMOS CAL/VAL purpose. The original idea is proposed by the author as a response to ESA SMOS AO-1 (Announcement of opportunity, 2005). Then after simulation, discussion, historical data review, field experiment and site visiting, high confidence has been set up to take this place as a potential site that can monitor SMOS' behavior, i.e., its accuracy, stability and sensitivity etc. The rationales behind it are area, homogeneity, radiometric stability and easy to access of the site. Taklamagan desert is the 2nd largest desert in the world. It covers an area almost 1000 km length and 600 km width. This makes it rather useful since SMOS has a comparative scale of snapshot. 85% of the land surface is covered with sand dunes. Other places are mixed with sand and shrubs, mainly distributed in the brim of the desert. Dielectric behavior benefit from its extremely arid climate: annual precipitation is only 25~45mm and concentrated on May-Aug according to statistics of historical meteorology record. Most of the precipitation is tiny rain (0.0~2.0mm) while annual evaporation is about 2100~3400mm. Low frequency (6-37GHz) microwave brightness temperature from center of the Taklamagan desert shows a triangle function relationship with time as an overall trend while fluctuates to some significant extent at the day-today temporal scale. A high level road had been built across the sand desert by the government which makes it possible to accommodate a relatively intensive campaign to