Reflectance values and units

Optical Toolbox sen2cor
#1

Hi all,

I know there are already various topics about this subject, but I am still confused, so I hope someone is able to help me with this.

I downloaded Sentinel 2 images acquired in 2017 from SciHub. Then I used Sen2cor to process the images to L2A. If I understood correct, 2A gives the BOA reflectances as a DC (digital count). When I want to obtain the reflectance, I divide the 2A by 10000 to obtain the reflection between 0 and 1. However, the values are then very small and do not overtop the 30% reflectance. Is this possible?

Also, is it correct to state that L2A values are unitless? So is a Digital Count unitless? Because it is also a measure of reflectance and reflectance is unitless because it represents a relation (thus a relative number and not an absolute number)? So if I decided to present my data in DCs instead of reflectance, can I then say that DC is unitless reflectance?

Once again, apologies for asking about this subject again, but as I said, any help is really appreciated!

Thanks!

#2

Hi all, is there anyone that can provide some explanation on this? Any help is really appreciated!

#3

Have you validated this on multiple scenes? Maybe it can happen on certain images. I have seen already higher values. It also depends on which band you are looking at.
However, 10000 is the right value to use for the conversion.

On Wikipedia you can see typical reflectance values in a graph


There you also see that the value is actually given in percentage. The unit is cancelled in the calculation.