I have been trying to calculate the NDVI for a scene using Sentinel 2 bands 4(red) & 8(NIR). I first did it in ArcMap and then QGIS. In both softwares, I used the raster calculator and included the basic NDVI formula = (NIR-Red)/(NIR+Red).
ArcMap gave me a range of 0-9221 (this varies with the stretch applied) while QGIS gave me more plausible values from 0.0258-0.5255.
I have read briefly that Sentinel 2 is TOA reflectance and has a scaling factor of 10000, which apparently can be found in the xml file that gets downloaded with the images. I never found this scaling factor mentioned in the xml file I downloaded.
Why is there this difference? How is the calculation being done on QGIS?