[GRASS-dev] Unexpected EVI range from "i.vi"

Markus Metz markus.metz.giswork at gmail.com
Thu Jun 20 10:03:08 PDT 2013

On Thu, Jun 20, 2013 at 6:24 PM, Nikos Alexandris
<nik at nikosalexandris.net> wrote:
> Markus Metz wrote:
>> I think I figured it out:
>> The EVI formula in i.vi is for MODIS.
> That's precise, EVI is MODIS specific.  We should clearly describe this in the
> manual (I will try to alter the respective text).

>From the literature, I gor the impression that EVI can be calculated
from other sensors as well, as long as you get the coefficients right.
>> The generic formula is
>> G * ( nir - red)  / (nir + C1 * red - C2 * blue + L)
>> where G is a gain factor, C1, C2 are coefficients to correct for
>> aerosol influences in the red band using the blue band and L is the
>> canopy background adjustment that addresses non-linear, differential
>> NIR and red radiant transfer through a canopy.

Assuming that the input to i.vi should be properly preprocessed bands
with a theoretically maximum range of [0, 1], you could set L to
0.0001 and would get reasonable EVI values, sensor-independent.

Markus M

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