I am using Landsat 8 C2L2 and I would like to compose Bands 1-6. If I don't apply the scale factor at all, what would be the problem? Also, when I am trying to find, for instance, NDVI value after I have applied a scaling factor to bands 4, 5, my new band'5 value is shown bellow like NDVI range. On the other hand, when I calculate NDVI without using the scaling factor I get the expected results. Why is this happening?
Scaled NDVI Histogram:
Unscaled NDVI Histogram:
USGS Website:
Best Answer
Generally, we always want to scale our units to the correct units of measurement. Scaling is often for data compression purposes but it isn't well suited for scientific purposes. Surface reflectance is a scientific unit and should be treated as such. You cannot substitute them for scaled values.
However, it is possible to have NDVI values outside of your expected range of -1 to 1. This can occur where you have very noisy or anomalous pixels, so the expected relationship between RED and NIR does not hold true. You may want to look at whether the pixel values in various places in your image image look right, rather than just relying on the stretch (min and max). for example does vegetation have a value of 0.4 and above? Is water around the 0 value? Is bare ground also a low value? These are general values that we would expected to see for known land covers.