How can I calibrate Sentinel-2 products, to extract the reflectance?
I've downloaded few Sentinel-2 products from https://scihub.copernicus.eu/s2/#/home, and opened them with SNAP but its radiometric calibration is dedicated only to SAR products.
On ENVI, the Radiometric calibration tool is seemingly only capable of extracting the radiance. What is the difference between the radiance and the reflectance? Is the estimation of the radiance counted as a radiometric calibration of a product?
Answer
Sentinel-2 Level 1C data are expressed in reflectance with a scaling factor, not in radiance. You have to divide by 10000 to get the reflectance. In the preliminary products shown this autumn, you had to divide by 1000.
The scaling factor is given in the xml file at the root of the product directory.
10000 There is no offset and the no_data value is 0.
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