Calibration and validation of SMOS brightness emperature over the Salar de Uyuni

Abstract

International audienceThe Salar de Uyuni is the largest salt flat in the world. It is located in the Bolivian altiplane at a height of about 3700 m between latitudes 19o45' S and 20o40' S and between longitudes 68o17'W and 66o45'W. Its surface is about 9 600 km2 (several tenths the SMOS footprint). It is located in a rather uninhabited area where no RFI is to be expected. Potosi is the closest village. Salar's climate is cold and dry, being characterized by low temperatures, low relative humidity levels and low precipitation. The rainfall is very low and concentrated from December to March. During the austral summer (from December to March), the surface can be covered by a thin water layer. This water layer disappears in the dry season, from April to November, leaving the Salar surface extremely flat and smooth. Analysis of AMSR-E data at 6.9, 10 and 18 GHz shows that microwave emissivity over the Salar is spatially homogeneous. Temporal analysis of brightness temperature shows that at vertical polarization is basically dependent on soil temperature and that emissivity remains high and constant during the dry period (emissivity 0.93-0.94). Furthermore brightness temperature at vertical polarization was shown to be very similar at 6.9 and 10.7 GHz, indicating a very low penetration depth, similar behavior is to be expected for emissivity at 1.4 GHz. Vertically polarised brightness temperature at 6.9GHz was simulated with annual rmse of 1.1K. Further study is needed to characterize H-pol. A piece of the Salar has been taken for its dielectric constant characterisation (scheduled November 2009). The salar de Uyuni is therefore an excellent site for the calibration and validation of the SMOS brightness temperature. In this presentation, SMOS brightness temperatures measured over the Salar will be shown and compared to those of models and also compared to AMSR-E data