1) I first made atmospheric and radiometric corrections for Landsat - 8 and then calculated NDVI and get such values 2) then I made only radiometric correction and calculated NDVI and got such values. why did you get such values? which one is correct?
Hi,
I suggest to use the NDVI function in the Image Analysis Window in ArcGIS. You can properly calculate NDVI with the scientific output of [-1,1]. You can find info here: https://desktop.arcgis.com/en/arcmap/10.3/manage-data/raster-and-images/using-the-ndvi-button.htm
Good luck!
Liliya Yusupova Apart from the answer provided by Alin Plesoianu you can use the Raster Calculator tool in ArcGIS to get the ideal -1 to 1 range for NDVI output image. Optionally, you can also download NDVI Image directly from USGS in addition to Level 2 Atmospherically Corrected 'Surface Reflectance' bands for the landsat scene and follow the Landsat Product guide rescaling.
As I realized, aside from what pair of reflectances you are using, you should always get a range of values between -1 and 1 (no matter DN values, calibrated radiance, reflectance), since it is normalized. However as I see, neither of your scenes seem to be correct. Please try to calculate it again (even raw bands should result between -1 and 1). I suggest using ArcGis, raster calculator. Nevertheless, you can use band math in Envi5.3 as well
Liliya Yusupova - regardless of the software you use to calculate NDVI, I would highly encourage you to take a close look at an area on the ground that you know well. View the R and NIR values of a given pixel and calculate NDVI longhand. Do this for a few different areas. This will give you confidence that you calculated NDVI correctly across your area of interest correctly - AND - it will serve as a check. As others have said, values should always be between -1 and 1, regardless of the input bands used (DN, reflectance, scaled reflectance, etc.)
Good luck!
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