Can enhanced vegetation index have values greater than 1? I am using the ENVI software to calculate enhanced vegetation index (EVI) of a hyperspectral image and my EVI value range was from 0 to 1.9. Is it wrong?
[GIS] Enhanced Vegetation Index Value
enviremote sensing
Related Solutions
The BYTSCL rescales your output from -1 to 1 -> 0 to 255. Remove that last bit, and you don't have your problem. BYTSCL is usually used for minimizing storage and bandwidth requirements associated with displaying data online.
If you want to make sure that you do not have values below -1 and above 1, you can use this function:
(float(b1) lt -1)*(-1)+(float(b1) gt -1)*(float(b1) lt 1)*float(b1)+(float(b1) gt 1)
You are right: the range of the NDVI is limited to values between -1 and 1 due to its' normalization properties.
The negative limit of -1 will be reached if you encounter maximal reflectance (1) in the red wavelength region and zero reflectance in the NIR. The positive limit will be reached by maximal reflectance in the NIR region and zero reflectance in the read wavelength region.
The EVI:
uses coefficients to correct for canopy background () and aerosol influences (
,
) (see e.g. Huete et al. (2002) for details.
Especially for artificial surfaces you can encounter values out of the range between -1 and 1. For example, blue rooftops, which show high reflectance (e.g. above 0.6) in the blue wavelength region will generate EVI values outside the "typical" range. This is caused by the use of the blue band to correct for aerosol influences in the red band.
Consequently, you can encounter values greater 1 or below -1 for the EVI but for the NDVI the values will always range between -1 and 1. Regarding your second question: you should try different vegetation indices and analysis techniques according to your problem at hand. If you want to estimate vegetation abundance in urban areas you could for example use spectral mixture analysis.
Best Answer
Based on documentation from ENVI software the values should be between -1 and 1, see here
The Enhanced Vegetation Index (EVI) is an algebraic equation of:
Where NIR is the value of the near infrared band, RED is the value of the red band, BLUE is the value of the blue band, (all three bands are atmospherically-corrected), L is the canopy background adjustment. Additionally G is the gain factor, C1 and C2 are the coefficients of the aerosol resistance term. In ENVI software G = 2.5, C1 = 6, C2 = 7.5, and L = 1.
For more background information on EVI go to the Wikipedia page here or for a thread on how to implement the equation manually go here.