Using near IR to look for photosynthesis and plant health with NDVI

The NoIR Raspberry Pi camera comes with a blue filter to do near infrared photography – the blue filter ices the visible red but passes near IR which records as red, apparently.

NDVI image of something in the polytunnels
NDVI image of something in the polytunnels. Should have made a not of what this plant is 😉 Anyway, more red and going to magenta white overload=more photosynthesis

NDVI (Normalized Difference Vegetation Index) is the near IR plus red divided by near IR minus red. Take a look at this image for the meaning of the colours – red, magenta and white is more photosynthesis, cool colours and black are less. Chlorophyll uses red but doesn’t use near IR which it reflects, hence the difference carries useful information.Lots more at Public Lab.

So I thought I might use this to look for plant health at The Oak Tree. My NoIR Rpi camera was out in the field so I was looking for a different way to do this using a regular camera to take two images. The blue filter starts off bad by throwing out the red channel, but in some of the older Public Lab stuff there is a way of integrating two photos-  one a bog-standard RGB pic and the other a picture taken through an IR filter. I have a B&W IR filter that looks almost black so I shot pictures with the filter and without filter, both using a tripod, then used Ned Horning’s photo monitoring plugin for Fiji image processing to do the grunt work of matching the two images up.

The NRG image has its own charm and is reminiscent of IR film days – I think the IR is added to the red but I am not sure

The NRG image has its own aestetic.
The NRG image has its own aesthetic.

The normal colour image is this

The r5eal colour image
The real colour image.

Exposure times through the IR filter are shockingly long, presumably because the camera IR stop filter is fighting what residual gets through. There is a case to be made for using a raspberry Pi or perhaps two to take simultaneous pictures, one with the NoIR and the IR filter and the other with the regular Pi camera.

from a different angle, NDVI
from a different angle, NDVI
The flowers are doing quite well
The flowers are doing quite well
Flowers, NDVU (red is more photosynthesis)

2 thoughts on “Using near IR to look for photosynthesis and plant health with NDVI”

  1. Hi! Great work! Congrats 🙂 I have a small doubt. all those images with yellowish and pinkish images. Are they taken using the same raspberry pi camera? If you could reply ASAP it would be reaaaalllly great. Thanks 🙂

    1. > Are they taken using the same raspberry pi camera

      No, I used an Olympus E20 on a tripod, first to take a regular photo, then with the B&W IR only filter mentioned. I did have the idea of mounting two Pi cameras side by side, on normal, one noIR, and putting the B&W over the NoIR, but the parallax canned that idea. At the focal length of the Pi camera, you’d be too close to the plants to be able to register the pictures.

      A Pi NoIR camera on a tripod would work better, but I’d need a separate IR cut filter for the front of the camera, and that B&W IR filter for the second IR only shot

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