Dear Jorge, thank you very much for the help. i have used the same landsat package but did not convert on the ground reflection but the on sensor reflectance. For MODIS and AVHRR, i need better spatial resolution that is the reason i am using landsat and I was not getting negative values even places where there is no vegetation instead getting higher values like 0.2-0.4 which is quite high for non vegetated area. Now i am trying to get NDVI from surface reflectance.
Regards, Vikram. On 1/18/2012 2:26 PM, Jorge Cabrera wrote: > Dear Vikram, > I do not know which procedure you used for transforming the values > from DN to reflectivity. But anyway I would like to recommend to use > the landsat package or take a look on it. > www.jstatsoft.org/v43/i04/paper > The values of NDVI should be negative where there is no vegetation. > Also for getting a better idea of the phenological cycle you can use > MODIS data to sample ndvi changes within a longer period with more > temporal resolution. > > I hope this help. > > Best, > > Jorge > > > ------------------------------------------------------------------------ > *From:* Vikram Ranga <babuaw...@gmail.com> > *To:* r-sig-geo@r-project.org > *Sent:* Wednesday, January 18, 2012 10:49 AM > *Subject:* [R-sig-Geo] problem with ndvi > > Hello list, > I am working with landsat images and would like to create a > phenological cycle with NDVI. > I am using R for that but NDVI values changes if i use on sensor > reflectance instead of DN values i.e. giving different result in every > case. > I tried to compare histograms seems to have changed and I am not > getting negative values where there is no vegetation but if i use DN > values it gives negative values to such locations. Do anybody have any > idea what went wrong?? > > Thanks in advance and would be much appreciated. > > Vikram > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@r-project.org <mailto:R-sig-Geo@r-project.org> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > > [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo
