ground truth for NDVI maps

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Jose F Moreno April 10, 2016 at 10:23am

I suppose it will be different in each case, depending on coverage, type of crop, crop stage, etc. What is important is to first clarify the final goal of doing such thing as going to the field with tools, otherwise you would´t know which tools to use or how.

Bottomline is that trying to ground truth aerial/satellite images in extensive agriculture makes sense if you can then find the way to make valuable decisions, and that´s a big if.
- DAVE BEHR > Jose F Moreno April 16, 2016 at 9:54pm
  
  Which Sattellite images do you use for NDVI or crop yield ? Do you compare it to Drone images ?
Antonio Vigoni April 10, 2016 at 3:43am

Agree with Alexander, usually we do correlation with biomass
- Andrii Seleznov > Antonio Vigoni April 10, 2016 at 7:27am
  
  Thanks for this discussion but I would like to clarify: what do you do exactly coming to the field?
  
  I mean: do you go to the field and look by eyes or make photos?
  
  Do you use any tools like mobile apps, leaf area scanners or any other device?
- Cala > Andrii Seleznov April 10, 2016 at 10:32am
  
  Andrii: What is the way of your question? are you thinking in something for add to petiole with aerial images?
  
  or work with them?
  
  , perhaps we can oriented better if you clarify your idea.
- Andrii Seleznov > Cala April 10, 2016 at 1:32pm
  
  Cala, you are a mind-reader :)
  
  In my project - Petiole, we have a successful work with agriscientists in measuring leaf surface area and level of chlorophyll using Petiole. In simple words, it is an Android-based app to measure these parameters with a mobile phone + cloud app, which makes an analysis of this data.
  
  In one discussion, a person who is doing aerial imagery for agriculture told that he would like to use our Petiole for ground truth and calibration of the NDVI maps.
  
  Hence, I decided to ask experts (I mean this Community) about this option and does it have any sense from a practical point of view...
  
  Petiole - leaf area meter & chlorophyll content measurement in a smartphone
  
  You don't need ImageJ leaf area measurement with Petiole mobile app
- Cala > Andrii Seleznov April 10, 2016 at 1:58pm
  
  Andrii: I'm only give a quick view to your app and imagine ;) ; yes It can be usefull if, for ex your app can measure cover-uncover areas from an aerial photo, that's is an usefull info for agronomist for ex you have a problem like insect attact and you need to decide re seeding or not, with an aerial photo and a measure app you can have a better desicion, that it's possible to do with complex expensive softwares but UAVs are becoming massive and no everyone have access to that softwares.
  
  Looks if it is your idea (sorry my horrible english or, perhaps any misunderstand)
  
  Here you can see that plants are missing and it's going to affect yield but .how much is the damaged area?
  
  here the procesed photo
  
  but not always NDVI is the more usefull index, perhaps software need to allow specialist to choose the image type that He needs.
- Andrii Seleznov > Cala April 17, 2016 at 3:56am
  
  Cala, thank you so much for a great idea!
  
  I have a little bit different thought how Petiole app can help with NDVI.
  
  So let's imagine a field. It is the same on every image or NDVI map.
  
  But, actually - it is different because there are many factors with impact on aerial imagery: the time of a day, cloud amount, solar weather, shades. So every time we need to have some constant to compare field on today's image and yesterday's image. In other words, it is important to equalize conditions and adjust to a common basis. But it is very difficult and sometimes impossible.
  
  So I suggest that leaf surface area & chlorophyll might be such parameters and serve as a common basis to show changes. You just measure the leaves every time you fly and after comparing NDVIs also compare leaf area and chlorophyll measurements and, consequently, monitor plant changes.
  
  Does it make any sense?
  
  There are too many factors which influence on aerial imagery: the time of a day, cloud amount, solar weather, shades, etc
- Fernando de Saracho > Andrii Seleznov April 17, 2016 at 6:52am
  
  what kind of readings would protected agriculture have?
  
  I am referring to protected agriculture by glass, plastic or mesh.
  
  These are tomatoes being grown in Mesh HH, the mesh would vary by zone and it could be darker, lighter or shinier.
  
  how accurate would readings be over mesh?
  
  could there be a calibration for such?
- DAVE BEHR > Cala April 16, 2016 at 9:52pm
  
  Hi Cala, How did you produce the NDVI ? Which drone/camera did you use for the field image ? Thx.

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Agricultural UAVs

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