<html><body><div style="color:#000; background-color:#fff; font-family:arial, helvetica, sans-serif;font-size:10pt">Dear all,<br><br>in the following link I've uploaded an image that gives a bit more context information:<br><br>http://www.flickr.com/photos/hmunstege/9036837366/ <br><br>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).<br>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!)<br><br>Thanks in advance for your attention.<br><div><span><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> Huub Munstege <hmunstege@yahoo.com> <br><b><span style="font-weight: bold;">Cc :</span></b> "grass-user@lists.osgeo.org" <grass-user@lists.osgeo.org> <br> <b><span style="font-weight: bold;">Envoyé le :</span></b>
Mercredi 12 juin 2013 21h58<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>Huub Munstege wrote:<br><br>> Hello Nikos,<br><br>Hello Huub!<br><br>> thx for the swift reply. I'll check out the options you mentioned but at<br>> first sight I noticed that 'i.vi' tool is not available for me ( I'am on<br>> 6.4.3-rc, from the AUR package in Archlinux). I.vi is not a command in the<br>> 'standard' Grass trunk. Neither is it available as an add-on.<br><br>Right! Apologies from my side. I have a setup giving access to all grass <br>modules outside of a grass session [see link to GRASS-Wiki below] which, if <br>not properly handled, as described in the wiki ("strip paths"), it even allows <br>access to all grass70 modules from inside a grass64 session.<br><br>> Some more explanation as you asked: previous Landsat 7 images
we analyzed<br>> with a simple raster calculation with the following formula:<br>> float(Band-4 - Band-3) / (Band-4 + Band-3).<br><br>I guess using grass64 means sticking to the formula above for NDVI.<br><br>> But as you already noticed the bands and ranges have changed under Landsat<br>> 8. Various combinations of bands (4,5 and 8) give a result that is at best<br>> not so clear cut as the analysis done with L-7.<br><br>I didn't test any L8 so far, though I have downloaded some scenes. Strange, <br>in a way -- I would rather think that their improvements would improve S-N-R <br>and, thus, derive "better" vegetation indices... :-?<br><br>> The "bluntly subtraction with 0.12" is based on on a quick scan of the<br>> obtained result. Areas without vegetation in our project area should give<br>> values in the range between -0.05 - 0.<br><br>as per L7 data I guess...<br><br>> The result of the combination of the 5 and 4
bands in the above formula <br>> gives values that are aprroximately 0.12 higher.<br><br>I see. <br><br>> Therefore the blunt and in-elegant subtraction which is definitely wrong.<br>> But it gives us for the time being a better deistinction between cultivated<br>> irrigation schemes and their surroundings. Maybe I am simply too impatient<br>> and too eager to work with the new fresh data from L-8.<br><br>Sorry for asking again: did you correct the data in some way or did you <br>simply feed the formula with DNs?<br><br>> Undoubtedly soon, Grass and the other software will incorporate specific<br>> modules that will be tailored to the L-8 sensors.<br>> Cheers and keep up the good work,<br><br>Thank you for all of the details regarding your work.<br><br>Nikos<br>---<br><br><br><<a href="http://grasswiki.osgeo.org/wiki/Working_with_GRASS_without_starting_it_explicitly#Bash_examples_.28GNU.2FLinux.29"
target="_blank">http://grasswiki.osgeo.org/wiki/Working_with_GRASS_without_starting_it_explicitly#Bash_examples_.28GNU.2FLinux.29</a>><br><br></div> </div> </div> </blockquote></div> </div></body></html>