When will SC and S2AC apply?

I got a "L2A"data on a site( Copernicus Open Access Hub).

Is this already SC and S2AC applied?

Or do SC and S2AC apply when opening with SNAP?

please tell me.

When you download Sentinel-2 L2A data you get already bottom of atmosphere (BOA) reflectance values. So atmospheric correction is already applied. But what do you mean by SC?

The data products are described on the ESA page: Sentinel-2 - Data Products - Sentinel Handbook (esa.int)

I’m sorry, I didn’t understand SC (scene classification) well.

When I open an image with SNAP, only the QUANTIFICATION_VALUE is calculated for the stored value in jp2, isn’t it?

The QUANTIFICATION_VALUE is not computed. It is stored in the product and just applied to the values in the jp2 files.

The scene classification is directly available when you open the product in SNAP.

I am investigating the cause of the change in reflectance that could not be solved by this question.
About reflectance of sentinel-2 image

Therefore, I am investigating what kind of calculation is applied when opening an image with SNAP.

However, there is no information that the calculation is being done so far.

Can you guess what caused it?

I think the issue is in Python.
Because when looking at the values in the jp2 files with QGIS is see the same values as in SNAP. Except the applied quantification value.


Let me ask you one more question.

jp2 is lossless compression.

Is there a process to recompress when opening an image in SNAP?

When the image is opened it needs to be uncompressed. Afterwards it can be exported to another format which supports compression. For example, NetCDF4 or BigGeotiff (compression is enabled in SNAP8 by default) or even jp2000. But data needs to be resampled before to a common resolution.

There is also a new export feature. You can install the snap-zarr plugin (Tools / Plugins). Then you export the compressed data without resampling, and you can use Zarr — zarr 2.5.0 documentation to read it in Python.
But keep in mind that this plugin is still in beta phase.

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Thank you.

I’ll try.