<html><body><div style="color:#000; background-color:#fff; font-family:arial, helvetica, sans-serif;font-size:10pt">Hello Nikos,<br><br>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. <br>Some more explanation as you asked: previous Landsat 7 images we analyzed with a simple raster calculation with the following formula:<br><br><div style="margin-left: 40px;">float(Band-4 - Band-3) / (Band-4 + Band-3).<br><br></div>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. <br>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. <br><div><br></div><div><span>Cheers and keep up the good work,</span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><br><span></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color:
transparent; font-style: normal;"><span>Huub<br></span></div><div> </div><div><hr style="width:100%;height:2px;"><font class="Apple-style-span" face="arial, helvetica, sans-serif" size="2">Huub Munstege<br>BPE 2836<br><span style="font-weight:bold;">Bamako</span><span style="font-weight:bold;">, Rep. du Mali</span><br>Tel: +223 20226397<br>Port: +223 78370695 </font><br><hr style="width:100%;height:2px;"><br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; margin-top: 5px; padding-left: 5px;"> <div style="font-family: arial, helvetica, sans-serif; font-size: 10pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div dir="ltr"> <hr size="1"> <font face="Arial" size="2"> <b><span style="font-weight:bold;">De :</span></b> Nikos Alexandris <nik@nikosalexandris.net><br> <b><span style="font-weight: bold;">À :</span></b> grass-user@lists.osgeo.org; Huub
Munstege <hmunstege@yahoo.com> <br> <b><span style="font-weight: bold;">Envoyé le :</span></b> Mercredi 12 juin 2013 11h23<br> <b><span style="font-weight: bold;">Objet :</span></b> Re: [GRASS-user] NDVI analyses with Landsat 8<br> </font> </div> <div class="y_msg_container"><br>On Wednesday 12 of June 2013 02:05:48 Huub Munstege wrote:<br>> Hi there all! Greetings from a happy Grass-root GISser on an Archlinux<br>> box...<br><br>Hi!<br><br>> Is there already a way to analyze the new Landsat 8 images (they are already<br>> available!)?<br><br>In grass64 you would want to use i.landsat.toar first (with one of the <br>correction methods) which supports the new Landsat_8 OLI/TIRS sensor(s).<br><br>> We are in particularly interested in the Normalized<br>> Standardized Vegetation Index (NDVI).<br><br>Having (top-of-canopy) reflectances is, if I am not wrong, a *must* in order <br>to get the desired ration that reflects the
status of the vegetation. You are, <br>I guess, probably interested in the "i.vi" module (with "viname=ndvi").<br><br>> We noticed a shift in wavelength<br>> range that is best depicted here:<br>> <a href="http://www.gisagmaps.com/landsat-8-about-refinements/" target="_blank">http://www.gisagmaps.com/landsat-8-about-refinements/</a><br><br>Interesting, they "narrowed" the band. They probably know what they are doing. <br>New stuff to explore :D<br><br>> Doing the well-known raster map calculation with the bands 5 (NIR) and 4 (R)<br>> of L-8 doesn't give a satisfying result. Very bluntly we subtracted 0.12<br>> from the 'ndvi' raster derived from L-8.<br><br>Why subtract? Precisely, if I may ask, did you "threshold" it? Cut-off <br>anything below?<br><br>> Without doubr there must be more<br>> elegant and correct solutions. Any ideas are very welcome<br><br>Would you mind to elaborate a bit more?<br><br>Thanks,
Nikos<br><br><br></div> </div> </div> </blockquote></div> </div></body></html>