Plant health using Multispectral cameras and the Vegetation index
What is plant health?
Otherwise known as vegetation index, you can use vegetation indices to investigate several features about a plant, including the stage of its growth cycle, stress levels, or even nutrient deficiencies.
Vegetation indices are calculated according to the reflectance properties of vegetation. It’s done with multispectral imaging.
The light we can see around us is just part of a wider spectrum, where there are different wavelengths that we cannot perceive with a naked eye. How objects around us interact with that light affects how we see them. Plants reflect green light, making them green to us.
If you can look at this signature and analyze changes or deviances from the norm, you could find out about the health of a crop before your eyes even see anything on the plant.
Image 1, shows an RGB image alongside the same image using a multispectral camera. With green showing healthy (high in chlorophyll) and red highlighting issues, you can clearly see the fairway is dry and damaged.
But more interestingly the green is speckled with red, this was due to a Fusarium outbreak.
Some of the vegetation indices we use
Visible Atmospherically Resistant Index (VARI) - VARI works with RGB imagery rather than infrared alternatives. Simply, it detects how much greenery is present and can help
detect plant stress.
Triangular Greenness Index (TGI) - The TGI looks at chlorophyll sensitivity to provide insights into nitrogen levels in leaves, which helps inform how farmers apply fertilizers.
Normalized Difference Vegetation Index (NDVI) - this is the most common vegetation index. It uses the red band of light and the near-infrared light to calculate reflectance values. The index results in providing an estimation of the amount of chlorophyll in plants. The deterioration of chlorophyll is symptomatic of a plant’s declining health, so the NDVI is critical to identifying problems early.
Green Normalized Difference Vegetation Index (GNDVI) - NDVI index without the red bands for areas sensitive to chlorophyll content.
Normalised Difference Red Edge Index (NDRE) - Sensitive to chlorophyll content in leaves with a soil background.