Hello, I was just thinking of starting theme with the same request. I’m not sure what I’m doing with all parameters set with default values. I guess I have read something about them, but no official info from the developers of SNAP. The help section of the software is not very useful.
So I fully support the above request for more details on all those params.
You set 10 m to get 10 m resolution outputs and this takes the longest as not all S2 bands are the same pixel size. There is"AUTO" option dropdown for some parameters (aerosol, mid lat); most atmospheric correction tools decide them from the image metadata and I’m not sure how Sen2Cor does it. I’m also ensure the effect of manually setting “AUTO”. Dem is downloaded automatically for the image area; although it seems you can create and point to your own DEM file for the area (but you’ll need to do some pre-processing work to ensure it matches the auto-downloaded DEM).
Thank you for your help! After I processed the imagery to level 2A, the image quality is not so clear as the level 1 (just my feeling) and the why band 8 disapper (I selected 10m scence). Thank you again!
the values are now representing Bottom of Atmosphere reflectance which might have less contrasts than before but now show the real values of the surfaces. You might just use the color manipulation tool to get better visual contrats.
@Jan When I open the L2A product in SNAP I see as unit/dimension dl. I’m not sure if after atmospheric correction what is the unit of the reflectance from the surface e.g. W⋅sr−1⋅m−2. It is my understanding that L1C (TOA) is the radiation reflected from the surface registered by the sensor.
I am using the Sen2Cor 280 plugin with SNAP 8.0 for Atmospheric correction of Sentinel-2 Level-1C products and I have already executed it several times (with different options, for example for the parameter aerosol type: RURAL and MARITIME and AUTO) and I do not see significant differences in the results of the atmospheric correction of S2B Level-1C TOA to S2 Level-2A BOA (for Vietnam area). Just slight change in the histogram values (images below). From what I read in other posts on this forum the main question is related to the definition of the processing parameters (as the user “Maria” 1 had already requested help in this post).
Therefore, some users of this forum in other posts referred to use an xml configuration file for the atmospheric correction (“Ground Image Processing Parameters (GIPP)”) of an S2 L2A image of the study area. And apply this same configuration in the plugin, and I don’t need to define the parameters such as “Nb Threads”, “Median filter”, “Ozone” (image below).
By the way, where I can find a clear description and explanation of these parameters and mainly of the available classes, as we can see in the image below for the parameter “Ozone”.
I would also like to know what the options “Scene only”, “Cr Only” represents, because I don’t see any difference in the results.
So, I don’t have any S2 L2A reference image for that area of Vietnam… so I have to look for the parameterization of aerosol Optical Thickness, Water Vapor Retrieval, Cirrus Correction, Surface Reflectance Retrieval (as described in the Sen2Cor Configuration and User Manual, url: Sen2Cor Configuration and User Manual. The problem is how to define the thresholds. That’s where I want to find answers. I don’t think this has to be through the Trial & Error method.