Re: [GRASS-user] NDVI analyses with Landsat 8
Huub Munstege wrote: [...] > 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. Dear Huub, did you eventually progress regarding the VI from L8 images? Any findings you could share? Thanks, Nikos ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] NDVI analyses with Landsat 8
Dear all,
in the following link I've uploaded an image that gives a bit more context
information:
http://www.flickr.com/photos/hmunstege/9036837366/
The problem boils down to the different wavelength range of the the NIR band of
Landsat 8. It's much narrower and applying the ndvi tools from Landsat 7
doesn't give a clear image (see the image).
I am not a remote sensing expert, but we use frequently the ndvi index to
monitor the exploitation of rice schemes along the Niger river in Mali. We
would love to incorporate the Landsat 8 images in our analyses (without the
'nodata scratches' of Landsat 7!)
Thanks in advance for your attention.
Huub Munstege
BPE 2836
Bamako, Rep. du Mali
Tel: +223 20226397
Port: +223 78370695
>
> De : Nikos Alexandris
>À : Huub Munstege
>Cc : "grass-user@lists.osgeo.org"
>Envoyé le : Mercredi 12 juin 2013 21h58
>Objet : Re: [GRASS-user] NDVI analyses with Landsat 8
>
>
>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
>---
>
>
><http://grasswiki.osgeo.org/wiki/Working_with_GRASS_without_starting_it_explicitly#Bash_examples_.28GNU.2FLinux.29>
>
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Re: [GRASS-user] NDVI analyses with Landsat 8
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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Re: [GRASS-user] NDVI analyses with Landsat 8
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 >À : grass-user@lists.osgeo.org; Huub Munstege >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 > > >___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
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 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] NDVI analyses with Landsat 8
Hi there all! Greetings from a happy Grass-root GISser on an Archlinux box... Is there already a way to analyze the new Landsat 8 images (they are already available!)? We are in particularly interested in the Normalized Standardized Vegetation Index (NDVI). We noticed a shift in wavelength range that is best depicted here: http://www.gisagmaps.com/landsat-8-about-refinements/ 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. Without doubr there must be more elegant and correct solutions. Any ideas are very welcome Cheers, Huub Munstege BPE 2836 Bamako, Rep. du Mali Tel: +223 20226397 Port: +223 78370695 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
