On which stage of their creation do Sentinel-2A products undergo atmospheric correction?

As part of my thesis I need to reference the way in which the images I used were atmospherically corrected, but since I worked using L2A products, I never needed to apply atmospheric correction myself.

I am aware that L1C products can be corrected using Sen2Cor, among other methods, but I can’t seem to find about how and when L2A products undergo atmospheric correction ? Does the Sentinel-2 system itself apply such a correction when creating the image ? Is it done as the image is saved in the database ? The atmospheric correction method used is the same as Sen2Cor’s ?

Thank you in advance !

I have a similar doubt. I am analyzing some 2017-2018 images. If I take 1C and 2A images from same date and process the second one with sen2cor i have different values.
So, what is the treatment that use in scihub?

the differences have already widely been discussed, e.g. here: Sentinel-2 L2A from Sen2Cor does not match values of downloaded S2 L2A - #5 by ABraun

Can you give me an opinion?

I am working with 2017-2018 images using sen2cor 2.5.5. Some are older than this plugin and are in 2Ap level.

I read yours links, and I discovered that i can assume little diferrences. But these olders images show big differences.

This are a November-2017 image´s values.(L2Ap older than sen2core 255)

And this are a May-2018 image´s values.(L2A newest tan sen2core 255)

I need to process some Sentinel 2B images that not have a L2A version on scihub and I want use it toghether.

L2Ap images have problems, the proble are sen2cor 255 or I had made some mistakes?
You recommend to me reprocess these images?


I found your opinion on this thread Sen2cor: Level-2A meteadata error,
I’m starting to think the problem is L2Ap

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Sentinel-2 Level-2A (L2A) products do undergo atmospheric correction, but this correction is applied by the European Space Agency (ESA) as part of the processing chain before the products are made available to users. The atmospheric correction applied to Sentinel-2 L2A products is indeed similar to Sen2Cor, which is a widely used atmospheric correction tool specifically designed for Sentinel-2 data.

Here’s how the atmospheric correction process for Sentinel-2 L2A products typically works:

  1. Data Acquisition: Sentinel-2 satellites capture data, including information in multiple spectral bands, during their orbits.
  2. Initial Processing (Level-1C): The raw data from the satellites are processed to create Level-1C (L1C) products. L1C products include radiometrically corrected data, geometrically corrected data, and information on the satellite and sun angles.
  3. Atmospheric Correction (Level-2A): After the generation of L1C products, the data undergo further processing to create L2A products. This processing step includes the atmospheric correction. Sen2Cor is one of the tools used for this purpose, and it applies a correction to remove the effects of the Earth’s atmosphere from the imagery. This correction is essential for accurately quantifying surface reflectance values.
  4. Generation of L2A Products: Once the atmospheric correction is applied, the data are organized into L2A products, which include surface reflectance values for various spectral bands. These products are then made available to users through data distribution channels like the Copernicus Open Access Hub.
  5. User Access: Researchers and users can access the L2A products, which already contain atmospherically corrected data suitable for various remote sensing applications, including land cover classification, environmental monitoring, and more.