About scaling factor and exporting product etc

[Shellyin]

Hi,
I am using sentinel 2 image to do atmospheric correction and confused about following questions:

1. I didn’t find any Explanation about what unit dl means, and its value usually between 0.0-0.35(can be seen in Spectrum View) in shallow water region. Is it similar to DN values?

2. Another question is about Scaling factor. Should I use the previous dl value to divide by the scaling factor(10000)before Sen2cor operation?? Does this affect the last results?

3. After the Sen2cor operation, when I using EXPORT PRODUCT to ENVI format and displaying it in ENVI software, I found the spectral value is above 2000. I really don’t know why or how it is tranformed.

4. The last question, due to the large amount of data, I should subset the image first before Sen2cor. And essentially it needs a resampled operation, and I found this operation has an influence on dl value, and I want to know whether this could affect the last atmospheric correction result. Because I need this result to do quantitative studies. The following 2 figures are before and after resampling operation, repectively.
   

   
   
   upper: before sampling down: after sampling

THANKS ahead!

[marpet]

1. dl means dimensionless. This means value has no unit. DN stands for Digital Number. Also often called as raw data. Often a scaling factor and/or scaling offset needs to be applied before you have geophysical values.
2. You don’t need to prepare the data for sen2cor. It can handle that data on its own.
3. This has already been answered in an other post of you. The ENVI data is exported as raw data. In Envi you need to apply these values manually. Or you can create a copy of each band by using the Band Maths. As expression use simply the band name. When you export the copies you have also the geophysical values in ENVI. But the file size will be a lot higher.
4. I think both images show the same graph. It is just that the range of the y-axis is different. You can press SHIFT while moving the mouse to let the range adjust automatically.