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The Dunhuang test site is situated close to the northwestern border of the Gobi desert near the city of Dunhuang. The calibration area is 40 m X 400 m and situated in the center of an homogeneous and perfectly flat zone of 30 km x 40 km.

During August to September, 2000, China. Center for Resources Satellite Data and Application (CRESDA) has conducted a field measurement campaign for determine the characteristics of the ground reflectance and of the atmosphere. The results show that the test site has a very good homogeneity with a variation coefficient of the reflectance in any channel lower than 3%. The ground reflectance increases progressively from 0.18 at 485 nm to 0.26 at 830 nm. Atmospheric measurements have shown that, at 0.55 mu m the total atmospheric optical depth (about 0.34) and the aerosol optical depth (about 0. 26) are relatively low and the effect of atmospheric water vapor content is also relatively small. These preliminary results show that the selected test site is well adapted for absolute radiometric calibration of in-flight satellite sensors such as CBERS - 1 CCD.