Traditional NDVI is an indicator of healthy green vegetation and usually is used to measure biomass or density. You can use this index to measure crop population and weed density. Also, NDVI helps evaluate the long-term effects of stress due to declining biomass affected by the stress.

NDVI measures the difference between visible and near-infrared (NIR) light reflectance from vegetation to create a snapshot of photosynthetic vigor. Vegetation in a vigorous canopy absorbs visible light and reflects most NIR light. On the contrary, a sparse canopy reflects more visible light and less NIR light. The imagery represents these differences in light reflectance using a color classification ranging from red to green, with red indicating the least vigorous crop.

There are several shortages of NDVI:

  • It may be saturated in dense vegetation

  • NDVI is not a very dynamic index 

  • Also, this vegetation index is quite sensitive to soil brightness and atmospheric effects.

  • when vegetation cover is too scarce, its spectral reflectance is too low

  • Sometimes, there is no difference between crop and weed

The next type of indices - Chlorophyll - calculates the total amount of chlorophyll in plants. As Chlorophyll is a pigment that converts sun energy into chemical energy via a process called photosynthesis. Thus, chlorophyll is a good indicator of a plant’s health.

The chlorophyll Index assesses canopy quality—offering an accurate representation of plant health throughout the season. It’s a powerful resource for nutrient management, both for in-season adjustments and season-to-season planning.

Sometimes NDVI index does not show stress in a short period. The illustration below compares the NDVI index and Chlorophyll Red for the month. It is also known that a strong wind struck the culture in the first days of July, which led to lodging.

As you see in the picture above, the NDVI index does not react to stress about 01 July, but the Chlorophyll Red index shows a local minimum at the time of disaster. 

NDVI imagery is most potent and cost-effective when used with the Chlorophyll Index, which provides a complementary view of the crop canopy's quality rather than the density. Together, the two types of imagery tell a holistic story of plant health and nutrient availability, helping growers pinpoint insect and disease pressures and areas of poor soil fertility in each field.