[GRASS-user] NDVI analyses with Landsat 8

[Nikos Alexandris]

Huub Munstege wrote:

> Hello Nikos,

Hello Huub!

> thx for the swift reply. I'll check out the options you mentioned but at
> first sight I noticed that 'i.vi' tool is not available for me ( I'am on
> 6.4.3-rc, from the AUR package in Archlinux). I.vi is not a command in the
> 'standard' Grass trunk. Neither is it available as an add-on.

Right!  Apologies from my side.  I have a setup giving access to all grass 
modules outside of a grass session [see link to GRASS-Wiki below] which, if 
not properly handled, as described in the wiki ("strip paths"), it even allows 
access to all grass70 modules from inside a grass64 session.

> Some more explanation as you asked: previous Landsat 7 images we analyzed
> with a simple raster calculation with the following formula:
> float(Band-4 - Band-3) / (Band-4 + Band-3).

I guess using grass64 means sticking to the formula above for NDVI.

> But as you already noticed the bands and ranges have changed under Landsat
> 8. Various combinations of bands (4,5 and 8) give a result that is at best
> not so clear cut as the analysis done with L-7.

I didn't test any L8 so far, though I have downloaded some scenes.  Strange, 
in a way -- I would rather think that their improvements would improve S-N-R 
and, thus, derive "better" vegetation indices... :-?

> The "bluntly subtraction with 0.12" is based on on a quick scan of the
> obtained result. Areas without vegetation in our project area should give
> values in the range between -0.05 - 0.

as per L7 data I guess...

> The result of the combination of the 5 and 4 bands in the above formula 
> gives values that are aprroximately 0.12 higher.

I see.  

> Therefore the blunt and in-elegant subtraction which is definitely wrong.
> But it gives us for the time being a better deistinction between cultivated
> irrigation schemes and their surroundings. Maybe I am simply too impatient
> and too eager to work with the new fresh data from L-8.

Sorry for asking again:  did you correct the data in some way or did you 
simply feed the formula with DNs?

> Undoubtedly soon, Grass and the other software will incorporate specific
> modules that will be tailored to the L-8 sensors.
> Cheers and keep up the good work,

Thank you for all of the details regarding your work.

Nikos
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<http://grasswiki.osgeo.org/wiki/Working_with_GRASS_without_starting_it_explicitly#Bash_examples_.28GNU.2FLinux.29>
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