NDVI stands for "Normalized Difference Vegetation Index". NRG stands for "Near-infrared / Red / Green". NDVI and NRG are both ways to visualize the amounts of infrared and other wavelengths of light reflected from vegetation. Because both these methods compare ratios of blue and red light absorbed versus green and IR light reflected, they can be used to evaluate the health of vegetation. It's a snapshot of how much photosynthesis is happening. This is helpful in assessing vegetative health or stress. (Read more here: https://www.agronomy.org/publications/jeq/articles/36/3/832) ## Do-It-Yourself These techniques for vegetation analysis were developed for satellite imagery, but at Public Lab, we've been working a lot on capturing infrared imagery using our DIY [near-infrared camera](/wiki/near-infrared-camera) setup, and combining it with visible bands to produce NDVI images such as the one above. ## What these images mean What exactly are these images we're trying to make? What do they tell us about vegetation, and why? These diagrams should help to understand what it is we're doing and why these are good ways to analyze plant life. ## The NDVI equation [![NDVI_is_eq.jpg](/i/44723)](/i/44723) **NDVI = (Near Infrared - Red)/(Near Infrared + Red)** NDVI is a ratio which tries to emphasize photosynthesis while filtering out sun glare. The above equation is run for every pixel, using source data from an infrared photo and a visible light photo, like this pair: [![5390895115_c9d4d38fec_o.jpg](https://publiclab.org/system/images/photos/000/021/771/large/5390895115_c9d4d38fec_o.jpg)](https://publiclab.org/system/images/photos/000/021/771/original/5390895115_c9d4d38fec_o.jpg) The result can be false-colored to make the high-photosynthesis areas more clear, and used to examine where plants are and how healthy they are. [![PetVISNDVIcomp.png](https://publiclab.org/system/images/photos/000/021/770/large/PetVISNDVIcomp.png)](https://publiclab.org/system/images/photos/000/021/770/original/PetVISNDVIcomp.png) _Figure above: Normal color photo (right) and normalized difference vegetation index (NDVI) image (left). NDVI image was derived from two color channels in a single photo taken with a camera modified with a special infrared filter. Note that tree trunks, brown grass, and rocks have very low NDVI values because they are not photosynthetic. Healthy plants typically have NDVI values between 0.1 and 0.9. -- @cfastie_ ### Activities Here are a range of activities you can do to produce and interpret your own NDVI imagery, whether downloaded from a satellite imagery provider or [collected yourself using a DIY technique](/wiki/multispectral-imaging) [activities:ndvi] **** ![IMG_0511-split.png](https://i.publiclab.org/system/images/photos/000/000/279/medium/IMG_0511-split.png) ![infrared-combination.png](https://i.publiclab.org/system/images/photos/000/000/278/medium/infrared-combination.png) Most DIY converted cameras today (those from Public Lab) use RGN instead of NRG, so the blue channel represents infrared instead of the red channel. That looks like this: [![rgn-split.png](/i/45468)](/i/45468?s=o) **** ## NRG imagery Some people are also interested in producing NRG imagery (like the below image), where `Near-Infrared, Red, and Green` are used to compose a picture instead of the usual `Red, Green, and Blue`. [![5415783775_502f79ac8c_o.png](/i/25064)](/i/25064) This diagram explains the swapping, which allows us to 'see' infrared as if it were a normal color: [![5396083368_40528d3da2_o.png](/i/25063)](/i/25063) **In NRG images, the deeper and clearer the red color, the denser and healthier the vegetation (more or less).** ### Questions [questions:ndvi] ### Other examples of DIY NDVI imaging From around the internet: Begin watching at 2 minutes to see the resulting imagery: *This topic is part of the [Grassroots Mapping Curriculum](/wiki/mapping-curriculum) series.* **** [![5416397210_5e3be40cf5_o.png](/i/25066)](/i/25066) [![5412520298_93873f36d0_o.png](/i/25065)](/i/25065) ...
Author | Comment | Last activity | Moderation | ||
---|---|---|---|---|---|
eustatic | "Excellent note. remind me to post estimated weights of each component. " | Read more » | about 10 years ago | |||
cschweik | "I've purchased a titan from Chris Fastie as well, and have to agree that his product and service is terrific! Thanks Chris for your great support! " | Read more » | about 10 years ago | |||
cfastie | "Yikes. I didn't know the stakes were so high. Whew. " | Read more » | about 10 years ago | |||
gpenzo | "Hello Check my notes for daul cam system maybe they can help http://publiclab.org/notes/gpenzo/02-16-2014/ndvi-720nm-850nm-filter-two-camera-setup-..." | Read more » | about 10 years ago | |||
patcoyle | "Nice imagery and great work on the KAP rigs. We're just finishing up a New England holiday. No KAP though. " | Read more » | about 10 years ago | |||
airfix4 | "Thank you. " | Read more » | about 10 years ago | |||
nedhorning | "At this time it is not possible to use geo-reference data. If there is sufficient interest in that functionality I could try to add it but it's not..." | Read more » | about 10 years ago | |||
btbonval | "I think part of the problem is that infrared light and visible light (and each subdivision thereof) are reflected differently at the interface of a..." | Read more » | about 10 years ago | |||
airfix4 | "Hello, I'm new to the organization...and NIR technology in general. I have played some with the Photo-monitoring plug in. Great too by the way! Is ..." | Read more » | about 10 years ago | |||
zamudio | "Ned, I have been working in the spectrometry field for many years and have been involved in calibrating various hyperspectral sensors. I plan on us..." | Read more » | about 10 years ago | |||
aldehyde | "Hi jtuhtan. You can get a MATLAB script? Thanks! " | Read more » | about 10 years ago | |||
aldehyde | "Hello. how to calculate the chlorophyll content in terms of NDVI? " | Read more » | about 10 years ago | |||
aldehyde | "how to calculate the chlorophyll content in terms of NDVI? " | Read more » | about 10 years ago | |||
geraldmc | "Thanks Chris, I got your lookup table working now, sweet! " | Read more » | about 10 years ago | |||
cfastie | "I have updated this note to include a link to the new colormap, which is also here: NDVI_VGYRM.lut This should be copied to the C:\Program Files..." | Read more » | over 10 years ago | |||
cfastie | "Glad it's working. Here is the look up table (lut) I have been using recently. . A legend for the new colormap. . After another few weeks of tria..." | Read more » | over 10 years ago | |||
silvanhi | "Thank you! now it works! :) " | Read more » | over 10 years ago | |||
geraldmc | "/Applications/Fiji.app/luts " | Read more » | over 10 years ago | |||
silvanhi | "Thanks for your response.. I did manage it to work it like you describe. my only problem is that I want to use the "NDVIblue2red.lut" which is in t..." | Read more » | over 10 years ago | |||
geraldmc | "Good question. There are some luts in a separate directory on Github that I didn't grab. Once you install the plugins you'll see an added option 'P..." | Read more » | over 10 years ago | |||
silvanhi | "But the .lut files aren't included in your approach, are they? " | Read more » | over 10 years ago | |||
geraldmc | "I created a directory in my root and put everything there, then opened Fiji and registered the plugins manually: Plugins -> Install Plugin ->..." | Read more » | over 10 years ago | |||
cfastie | "I have not previously seen NDVI images quite like these, so the first thing to check is that the expression you include above: I've measured NDVI ..." | Read more » | over 10 years ago | |||
cfastie | "Public Lab promoted dual-camera IR systems more than three years ago before they found that the one camera systems worked well enough to get people..." | Read more » | over 10 years ago |