Buzz in Agriculture

The Technology Work
Drones in agriculture are simply a low-cost aerial camera platform, equipped with an autopilot using GPS and sensors for collecting relevant data, like a regular point-and-shoot camera for visible images. While a regular camera can provide some information about plant growth, coverage and other things, a multi-spectral sensor expands the utility of the technique and unleashes its full potential. It allows you to see things which you cannot see in the visible spectrum, such as moisture content in the soil, plant health, stress levels and fruits.

In the 1970s, a NASA scientist named Compton Tucker used reflected light from plants to quickly and easily identify vegetated areas and their overall conditions in satellite imagery using a method called normalised difference vegetation index (NDVI).

The basic principle of NDVI relies on leaves reflecting a lot of light in the near-infrared, in stark contrast to most non-plant objects. Leaves are green in colour due to the presence of a pigment called chlorophyll, which strongly absorbs almost all non-green light from the visible spectrum of sunlight and reflects mostly green light back to our eyes. Live green plants absorb solar radiation in the photosynthetically active region (PAR) and leaf cells re-emit the solar radiation in the near-infrared spectral region. Thus, a healthy plant appears dark in PAR and bright in near infrared.

On the other hand, in an unhealthy or stressed plant, the leaves reflect less near-infrared light even if its emissions in the visible spectrum remain unchanged. Tucker found that combining these two signals can help differentiate plants from non-plants and a healthy plant from a sickly plant. This work gave rise to indices like the NDVI, which is now used to assess plant health.
 

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