NDVI (Normalised Difference Vegetation Index) is a way of visualising crop health by measuring how well the crop reflects the light it doesn’t need for normal growth. It’s one of many vegetation index models but the most commonly-used model for accurate aerial crop health imaging.
As plants grow, they absorb light and use it to produce chlorophyll in a process called photosynthesis (you know this, right, but stay with me). They absorb blue light, green light, red light and infrared light, but they really only use the blue and red light to produce the chlorophyll. If the plant is healthy, it reflects most of the green light and all of the infrared light back to the atmosphere. This is why healthy plants look green to our eyes. Although we can’t see the infrared light, it’s reflected back in much higher amounts by the healthy plants, and that’s what we measure with near-infrared (NIR) imaging.
Generally speaking the more infrared light a plant or leaf reflects, the healthier it is. And the less infrared light it’s reflecting, the more likely it is that there’s something causing stress to the plant.
This is nothing new. Farmers have been acquiring this data using satellites since the ’70s. What is new is the ability to image NIR and create NDVI at very high resolutions. Where satellites often capture images at 50 metres per pixel, aerial surveys capture images at a minimum 20 centimetres per pixel – 250 times more precise than some satellite imagery. For smaller surveys, we can create imaging at 10 cm, 5 cm or even 2 cm per pixel. It’s the difference between seeing a field and seeing a plant.
Why is drone-sourced NDVI so much better than satellite NDVI? Well we’re shooting our images at 200-400 feet above the ground, not 400 miles above the ground. It’s that simple.
We also provide imagery on demand, when you need it most (which is often just when you’re getting ready to irrigate a crop, apply fertiliser or pesticides, harvest the crop or see what can be salvaged after a storm or pest invasion).
It’s usually not convenient to wait 4-6 weeks for the next satellite pass, and even then you might not get imaging if it’s cloudy when the satellite passes over your farm. We can usually image your crop within 24-48 hours.
What results can you expect from NDVI imaging?
NDVI imaging has lots of different uses. If there’s stress or damage in a crop or field, NDVI will detect it long before you see it with the naked eye (often weeks before, and while you still have a good chance of doing something about it).
The colours in the NDVI imaging will indicate how severely the crop is stressed. In the above image you are seeing a wheat field that has been impacted by an aphid attack. If this field had been imaged two weeks earlier, most of the crop could have been saved. But even at this late stage we are able to show which parts of the crop can still be saved and harvested.