i apply 6S atmospheric correction on Landsat 8 imagery. My study area is in the ocean. After applying 6S atmospheric correction, there is a negative value in my result instead of being between 0 to 1.

Is this result is good or do I need to retry the correction?

2 Answers 2


We just has a similar discussion in the GRASS bugtracker. It seems that a negative result may originate from visibility is assumed too low (optical thickness too high). See here for the reference:



Yes it is rather commonplace to obtain some negative reflectances after atmospheric correction over dark surfaces.

As said by Markus, this may result :

  • from a too high aerosol optical thickness in the parameters used for the atmospheric correction,

  • from not taking into account the altitude of the pixels (as the molecular and aerosol optical thickness decrease with altitude). Then, it's a bug in your correction

  • there might also be some negative values in the cloud or terrain shadows, which do not receive as much irradiance as a standard dark surface.

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