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Field work was carried out on June 8 and 9, 1999 to evaluate the use of the Salar de Uyuni as a test site for in-orbit satellite calibration. A dataset of ten Thematic Mapper (TM) images, from 1988-1997, was used to select three test points based on the analysis of the temporal stability of the reflectance of Salar's surface. Bidirectional reflectance factor (BRF) values of Salar's surface within the precision suitable for vicarious calibration procedures were obtained using a CE313-2/CIMEL radiometer. In spite of seeming visually homogeneous, the BRF values of one test point have presented significative statistical differences with the two others. Atmospheric characterization was possible with a sunphotometer CE317/CIMEL showing the low importance of the atmospheric effects in the image acquisition. The results confirm that the Salar de Uyuni has the characteristics pointed out by many authors as suitable for a vicarious calibration site, specially from April to November because of the reduced rainfall occurrence. The main disadvantages are the difficult access and the critical period for data collecting in the rainy season from November to March. An angular reflectance variation study is recommended in order to evaluate its Lambertian properties.