Abstract：Retrieval of ground reflectance spectrum from satellite sensor digital count requires knowledge of the atmospheric conditions. Images of spectral radiance from ground-atmosphere system recorded by the multi-spectral imager ETM which boarded Landsat-7 sensor can retrieve the ground reflectivity spectrum. The uncertainty of reflectance spectrum retrieval is no more than 17% at the band 1 of ETM, and less than 10% at the band 2 and 3 of ETM. It is superior to those arithmetics widely used at present. Retrieval of ground radiance spectrum from ground-atmosphere system can be used to synthesize the sRGB true color image, but the definition is not excellent. And it was proved that the color of the images can not reflect the actual nature of earth objects before being adjusted. And the accuracy of interpretation based on true color synthesized images is superior to those based on the source images. So the precision of such reflectance spectrum retrieval is not as good as expected if applied to the true color photography on the ground.
Key words：ETM image;Reflectance spectrum retrieval;True color synthesis
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