Weird results of index based built-up index (IBI)

Question

Hi,

I am trying to calculate index based built-up index (IBI) in ArcMap using raster calculator and getting strange values. I downloaded Landsat 8 data and using green, red, NIR and SWIR1 bands for the equation:

IBI = (NDBI - (SAVI + MNDWI) / 2) / (NDBI + (SAVI + MNDWI) / 2)

I followed the equations in this article to get all the indexes needed for IBI https://link.springer.com/article/10.1007%2Fs10708-020-10148-w

My result values for IBI range from -3.10538e+07 to 2.53846e+07, which is rather strange. My NDBI values range from -0.64 to  0.66, SAVI from -0.33 to 1.47, MNDWI from -0.98 to 0.47. All these 3 rasters seem to correct. I can't really get my head around where the mistake is.

Any suggestion? I would be really grateful for any help.

HarmonRayPagar · Answer

You must add 1 to the NDBI, SAVI, and MNDWI to have the results of IBI.

Hornbydd · Answer

Well I tried setting your variables to their lowest values:

ndbi = -0.64
savi = -0.33
mndwi = -0.98

Then pumped them into your equation and it generate:

ibi = (ndbi - (savi + mndwi)/2)/(ndbi+(savi+mndwi)/2)

ibi = -0.011583011583011595

Which is nothing like your erroneous values, so unless you show us how you ran the tools no one is going to be able to help you.