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In Brazil, the increase of the application of quantitative approaches in the natural resources studies using remote sensing technology has required knowledge about the radiometric conditions of remote sensors as the Thematic Mapper (TM) and the Enhanced TM Plus, for instance, The establishment of a correlation between radiometric data and biophysical and geophysical ones has become a frequent need in the Brazilian remote sensing community, and it has increased the demand of calibration coefficients in order to transform digital numbers to physical values like radiance and reflectance. Since the China-Brazil Environmental Remote Sensing Satellite became a reality, the necessity to perform calibration campaigns increased significantly. Following Price and other researcher's suggestions, an in-flight absolute calibration of the Landsat-5 data was carried out in the Salar de Uyuni, Bolivia. It was only possible to determine calibration coefficients for bands TM2, TM3, and TM4 due to the saturation of band TM! and surface moisture conditions that impacted the TM5 and TM7. The methodology applied here seemed to be sufficient to determine valid calibration coefficients for orbital sensors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]