[vegetation monitoring] really bright parcels in VV polarization

[falahfakhri]

I think this what you’re looking for,

Creating Radar Vegetation Index

It will not completely replace NDVI because it is based on surface characteristics (mainly the ratio between cross-polarization and co-polarization) instead of the chlorophyll concentration. But similar to the NDVI higher values indicate higher vegetation presence. It is quite a relative measure with no distinct minimum or maximum.

And this

Creating Radar Vegetation Index

I’d say there is no right or wrong. If you technically derived the index according to the published equation (make sure to set paranetheses around the numerator and denominator), the index is correct. While for some vegetation it might match the variation of the NDVI, it coudl be different for others. It is important to understand that all information derived from SAR backscatter originates from roughness, size and orientation of the objects or surfaces within a pixel.