Ndsi calculation rate is wrong

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1

I downloaded sentinel2 data from google earth engine.
I changed L1C to L2A using sen2cor280.
I calculated NDSI(b3-b11/b3+b11) after resampled data.
but ndsi rate is -3.8~ -1.86.
What more do I need to do?

2

What is the value range of B3 and B11 before the calculation? You can check with the Statistics tool

3

I solved this problem. when I calculated ndsi, I didn’t put ()() parentheses.
(b3-b11)/(b3+b11) and b3-b11/b3+b11 are different result.