Hello,
since a couple of years I’m using S2 Band 10 to map Cirrus and cloud with an algorithm similar to Scene Classification.
I have found anomalous values for only this band since 2022 as started. I can’t say when exactly this problem has started.
In particoular i can say that reflectance values are too high for all the surface compared to before.
Anyone can tell me what changed in this data? Any information about it?
Thank you so much!
Regards
Alessandro
Hello @ander
You’d need to be more specific, I’m afraid. There was a major upgrade to S2 L1C and L2A products back in late January (detailed in this News post from September 2021 Open Access Hub).
Cheers
Jan
OPT MPC S2 Technical Manager
Hello @Jan
Well, you are right.
As it is reported in technical docs of Scene Classification, the clear sky threshold is 0.012 and thick cloud is 0.035. I found these two threshold very reliable.
In fact L1C data for clear sky never in band 10 has values between 1 and 35, cirrus around 100-300 while thick clouds over 1000.
I’m checking 29/12/2021 R22 T32TQP and I see similar range of values.
While if i check more recent data, even in clear sky condition, i find reflectance values around 1000, that means 0.1 reflectance and obviusly my cirrus/cloud mask is fully saturated, as it is compleatly cloudy even if it is not.
I’ve just checked R22 T32_TPQ 04/03/2022.
Hope this example could help you to understand what i’m meaning.
Regards
Alessandro
Hello @ander Allesandro
Thanks for your response. A further question…
The products now include an offset (RADIO_ADD_OFFSET) that will affect the computation of the reflectance:
Reflectance (float) = DC DN + RADIO_ADD_OFFSET / (QUANTIFICATION_VALUE)
(Page 444 of the Product Specification Document (PSD) )
The value of RADIO_ADD_OFFSET for L1C is -1000. This can be found in the Datastrip metadata in the <Radiometric_Offset_List>.
Has this Offset been taken into account?
Cheers
Jan
Hello @Jan
When has this offset been added exactly?
That could be the problem solution.
Regards
Alessandro
Hello @ander Allesandro
The RADIO_ADD_OFFSET was introduced in the PB 04.00 on the 25th of January (see Processing Baseline - Sentinel Online)
Cheers
Jan
Thank you so much!
This could be the issue, for the other bands it is less visible and that’s why I find it out so late.
Your help was fundamental.
Best regards
Alessandro
Hi Ander,
There is an option (Tools> Options> S2TBX >Sentinel-2 Reader> add negative radio offset)to apply the offset with the sentinel product version PB04.00. By default the offset should be actived.
Please, could you check the offset options?
Best regards,
Florian
Hello Florian,
I’m sorry but i’m running a automatic Python procedure to download and preprocess S2 data, that why the offset was not included.
Regards
Alessandro
Hi, my SNAP ver. 8 doesn’t show the ‘Add negative radiometric offset’ checkbox in S2TBX Options dialog. It shows only:
‘Load detector footprints mask’
‘Load radiometric quality masks’
‘Load technical quality masks’
‘Load cloud masks’
All other checkboxes aren’t displayed.
System: Win10
Hello @geomujo Sascha
You need to upgrade to SNAP 9.0 SNAP 9.0 released – STEP
Cheers
Jan
Jan Jackson
OPT-MPC S2 Technical Manager
