Strange values for index based built-up index (IBI)

Question

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. To get the IBI, first I calculated NDVI with NIR and SWIR1 bands as

SAVI with NIR and Red bands as

and MNDWI with Green and SWIR1 bands as

Than I use the NDBI, SAVI and MNDWI to calculate IBI as ("NDBI" - ("SAVI" + "MNDWI")/2)/("NDBI" + ("SAVI" + "MNDWI")/2)

My result values for IBI range from -3.10538e+07 to 2.53846e+07, which is rather strange.

I followed the methods of this article to get all to IBI https://link.springer.com/article/10.1007%2Fs10708-020-10148-w

I have also tried to calculate it straight from the bands as done in couple of papers I have seen, where the NDVI is used instead of SAVI but the results did not get any better.

Where is the mistake?

Answer 1

I was also struggling with IBI values going beyond [-1,1]. Check this: Index‐Based Built‐up Index (IBI) no in the specified range

The reference paper of IBI by Xu et.al exerts to rescale the NDVI, SAVI and MNWDI to [0,255] before computing IBI using these input indices.

You can use the formula 255(X - 1)/2 to rescale input indices (X being NDVI,SAVI or MNDWI) ...figured this from here Rescaling NDVI values 0-255 to [-1;1] using ArcGIS Raster Calculator?