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NDVI and NRG

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 [![5396083342_3b253ef5ca_o.png](/i/25062)](/i/25062) 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) **** ## 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: <iframe width="560" height="315" src="https://www.youtube.com/embed/Lkn8CbNDPN0?t=2m" frameborder="0" allowfullscreen></iframe> *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) ...

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Image Sequencer /wiki/image-sequencer 11 months ago by liz 8 2,596 4
ImageSequencerBookmarklet /wiki/imagesequencerbookmarklet about 2 years ago by warren 18 414 2
Idea:80%COMPLETED-SAP project (Smart Agriculture Payload) /wiki/idea-80-completed-sap-project-smart-agriculture-payload over 5 years ago by Mohamed 3 484 1
Public Lab Lesson 4: Environmental Monitoring /wiki/public-lab-lesson-4-environmental-monitoring over 5 years ago by gretchengehrke 8 293 0
Public Lab Lesson 3: Photography in a New Light /wiki/public-lab-lesson-3-photography-in-a-new-light over 5 years ago by gretchengehrke 15 1,073 5
Infragram Sandbox /wiki/infragram-sandbox over 5 years ago by liz 6 2,550 0
GoPro /wiki/gopro-cameras over 7 years ago by gonzoearth 10 1,065 6
Photo Monitoring Plugin /wiki/photo-monitoring-plugin over 6 years ago by cfastie 12 2,922 8
Infrablue Kickstarter Update 3 /wiki/infrablue-kickstarter-update-3 over 2 years ago by cfastie 14 144 0
ndvi-gradients /wiki/ndvi-gradients over 6 years ago by cfastie 5 779 3
iFarm 2013 /wiki/ifarm-2013 almost 8 years ago by cfastie 23 222 1
Near Infrared Camera history /wiki/near-infrared-camera-history over 7 years ago by warren 3 964 0
Near infrared imaging /wiki/near-infrared-imaging almost 8 years ago by liz 11 3,439 1
Infragram /wiki/infragram 10 months ago by liz 116 16,286 17
Infragram Media /wiki/infragram-media 4 months ago by liz 52 1,321 1
Interpreting infrared images /wiki/interpreting-infrared-images over 6 years ago by aguchosolano 4 296 0
NDVI from the PLOTS near infrared camera /wiki/ndvi-plots-ir-kit about 5 years ago by cfastie 35 5,119 4
Posters /wiki/posters over 6 years ago by sara 31 277 16
NDVI and NRG /wiki/ndvi over 1 year ago by stevie 27 12,822 13
NDVI Calculation /wiki/ndvi-calculation about 10 years ago by warren 5 848 5