Markus Metz wrote: > >> I think I figured it out: > >> The EVI formula in i.vi is for MODIS.
Nikos A: > > That's precise, EVI is MODIS specific. We should clearly describe this in > > the manual (I will try to alter the respective text). MM: > 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. Yes, but this is not an easy job, is it? This is (also) why, I think, they (MODIS science team) developed the EVI2, which is cross-sensor. > >> 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. This reminds, if I am not wrong (didn't check) the scale factor for MOD09 surface reflectance products. Makes sense. Thank you Markus for the time you invested for this. Nikos _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
