iCOR -S2 - understanding the pixel values

snap iCOR
#1

Hello all,

I have used iCOR for Sentinel-2 in SNAP. I did the following steps

  1. Download S2 MSIL1C image
  2. Go to iCOR - S2 in SNAP, give the MTD_MSIL1C.xml as source product
  3. Under the parameter settings - leave everything to default and run

The _10m, _20m and _60m output images are generated. The pixel values of these bands are very different from that of the original - the value range is between Min = -0.005, Max = 1.057 for the Blue band in the processed _10m image. The original blue band has Min = 869, Max = 1872.

Why is there this difference between the values before and after running iCOR on the image?

Thank you!

#2

the original values seem to be in DN, i.e. reflectance expressed as unsigned integers. For getting reflectances, divide them by the QUANTIFICATION_VALUE, usually 10000.
iCor output is directly in reflectances. they will be different from the original reflectances as iCor output is bottom-of-atmosphere reflectances, original values are top-of-atmosphere reflectances.

1 Like
#3

Thats perfect! Thanks very much!