[GRASS-user] NDVI analyses with Landsat 8

[Huub Munstege]

Hello Nikos,

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. 
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).

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

Huub

 

________________________________
Huub Munstege
BPE 2836
Bamako, Rep. du Mali
Tel:      +223 20226397
Port:     +223 78370695 
________________________________



>________________________________
> De : Nikos Alexandris <nik at nikosalexandris.net>
>À : grass-user at lists.osgeo.org; Huub Munstege <hmunstege at yahoo.com> 
>Envoyé le : Mercredi 12 juin 2013 11h23
>Objet : Re: [GRASS-user] NDVI analyses with Landsat 8
> 
>
>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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