Multispectral analysis plays a key role in determining what treatments are required. With Variable Rate Applications, plant indexes are used to create unique prescription maps for the spray drone to follow.
So which plant index is used? and at what time?
The Normalised Difference Vegitation index or NDVI, is the most commonly known and for good reason. By utilizing the Red and Near Infra-red light spectrums, things like Chlorophyll and biomass can be detected, which are incredibly important for plant health.
However the Red light spectrum has the tendency to over-expose or overpower Near Infra-red when used on mature crops, with broad leaf such as Canola. This issue makes it difficult for the Multispectral sensor to record reflectance detail further down the stem.
NDVI is mainly used with VRA in early intervention treatments, because the earlier the treatment, the higher the yield potential. This is because the plants have a healthier start and throughout thier growth cycle, giving them a boost.
NDRE uses the RED-EDGE light spectrum with Near Infra-Red, and has less reflectance, making it less likely to overpower the Near Infra-red light spectrum. Because Red-Edge is on the limit of Red, it is used to detect similar issues, but on mature plants.
The NDRE Index will create a more accurate and defined Prescription map for VRA on mature crops. This is because more detail is collected further down the plants stem, which helps detect issues in the lower part of the canopy.
So why not use NDRE for both early and mature?
Because NDRE has less reflectance, smaller (younger) plants cannot produce enough detail for NDRE to be effective for analysis. This is where NDVI has a better ability for distinguishing plant health in younger plants.
