[GRASS-user] NDVI analyses with Landsat 8

Nikos Alexandris nik at nikosalexandris.net
Wed Jun 12 04:23:05 PDT 2013


On Wednesday 12 of June 2013 02:05:48 Huub Munstege wrote:
> Hi there all! Greetings from a happy Grass-root GISser on an Archlinux
> box...

Hi!

> Is there already a way to analyze the new Landsat 8 images (they are already
> available!)?

In grass64 you would want to use i.landsat.toar first (with one of the 
correction methods) which supports the new Landsat_8 OLI/TIRS sensor(s).

> We are in particularly interested in the Normalized
> Standardized Vegetation Index (NDVI).

Having (top-of-canopy) reflectances is, if I am not wrong, a *must* in order 
to get the desired ration that reflects the status of the vegetation. You are, 
I guess, probably interested in the "i.vi" module (with "viname=ndvi").

> We noticed a shift in wavelength
> range that is best depicted here:
> http://www.gisagmaps.com/landsat-8-about-refinements/

Interesting, they "narrowed" the band. They probably know what they are doing. 
New stuff to explore :D

> Doing the well-known raster map calculation with the bands 5 (NIR) and 4 (R)
> of L-8 doesn't give a satisfying result. Very bluntly we subtracted 0.12
> from the 'ndvi' raster derived from L-8.

Why subtract?  Precisely, if I may ask, did you "threshold" it?  Cut-off 
anything below?

> Without doubr there must be more
> elegant and correct solutions. Any ideas are very welcome

Would you mind to elaborate a bit more?

Thanks, Nikos


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