What is NDVI Imagery and How is it Used?

The use of satellite imagery has greatly advanced what is possible with farming and forestry in the 21st-century.

What is NDVI imagery? NDVI stands for Normalized Difference Vegetation Index, and it is a simple formula designed to measure the approximate amount of photosynthesis plants are undergoing in a location. Satellite images are used to find the levels of red light and near infrared light emitting from a location, and the difference is the NDVI.

This post will quickly go over the NDVI and how it works, and then cover some examples of how it is used in our modern times.

A Simple Breakdown of How NDVI Works

Without going too deep into the weeds on the scientific side of things, keep reading for a quick overview of how the NDVI works, as well as why it works.

NDVI is all About Measuring What Plants Do Best

The light plants receive from the sun is comprised of lights from different parts of spectrum, two of which are the following:

  • Near Infrared Light (NIR)
  • Red Light

The reality is that photosynthesis is limited to a certain part of light spectrum, and most of the light that plants use in creating energy comes from the red and blue parts of the light spectrum.

What Plants Do With Near Infrared (NIR) Light:

The process of photosynthesis has very little use for near infrared light. As such, plants actually re-emit a lot of the near infrared light back into the atmosphere.

What Plants Do With Red Light:

On the other hand, the process of photosynthesis allows for plants to take in red light and convert it into chemical energy. As plants are so efficient at converting red light into energy, very little of the red light is re-emitted into the atmosphere.

So What is the Normalized Difference Vegetative Index Trying to Actually Measure?

As the NDVI is a calculation based around the colors present in an image captured by a satellite, that image is only capturing the light that was re-emitted from the Earth back into the atmosphere.

Like I mentioned above, plants actively undergoing photosynthesis re-emit much light in the near infrared part of the spectrum, and they re-emit very little light in the red part of the spectrum.

As the Normalized Difference Vegetative Index is attempting to measure how much photosynthesis is taking place at a certain location, it merely calculates the difference in the levels of red light and near infrared light.

What Different NDVI Values Mean

Alright, so NDVI values are attempting to calculate the amount of photosynthesis occurring in a satellite image.

What do the numerical results of the NDVI calculation actually mean when it comes down to plants? First things first, the outcome of a NDVI calculation allows for any number in the following range: from -1 to 1.

Positive numbers indicate some level of photosynthesis.

The closer the number is to 1, the more photosynthesis is happening at that location.

A Few Examples of How NDVI is Used in Real Life

Now that we’ve got the theory and calculations out of the way, let’s check out how people are using such a valuable tool.

Real-Time Measurements of Crop Performance

Many farmers with large operations have benefited greatly from NDVI, as it allows for more efficient monitoring of large amounts of crops. For example, a farmer could use NDVI values to search for sections of a field that are under-performing when compared to the expectations at the time for that crop.

Measurements of How Much NDVI Changes Over Time

More than useful for just crops and farming, the NDVI is a major part of detecting natural disasters and other changes that occur in our forests and fields.

screenshot of the ndvi 10 year change layer in the forwarn ii application
This screenshot shows the impact of a windstorm on the Nicolet National Forest. The areas in red are showing a severe drop in vegetative productivity when compared to past production.

Think about it this way: any time there is an event like a tornado that kills a large amount of well-established plants like trees, NDVI is going to be able to measure a drastic change when compared to the performance the past years.

Concluding Thoughts

While a bit technical, I hope you got value out of this article and came away with a new appreciation for the capabilities of satellite imagery. I know I’ve been blown away by the possibilities that are created by this functionality.

If you’d like to learn more about how this technology is applied in the realy world, then check these articles out:

By Drew Meulemans

I've long admired forests and devote much energy to learning about them and exploring. I enjoy sharing what I learn and wish to inspire others to do the same.